Antibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks

Antibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Antibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks Abdulwaris Tijani, Gbenga Ayodele This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9372898/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 4 You are reading this latest preprint version Abstract The increasing use of antibiotics and heavy metals in livestock production has resulted in their widespread presence in farm animal wastewater, posing serious environmental and public health risks. This review examines the sources, occurrence, and environmental behavior of these contaminants, with emphasis on their interactions and contribution to antimicrobial resistance (AMR). These pollutants enter the environment through manure application, wastewater discharge, and agricultural runoff, where they undergo processes such as degradation, adsorption, and transport in soil and aquatic systems. Their co-occurrence enhances persistence and bioavailability, promoting co-selection mechanisms including cross-resistance, co-resistance, and horizontal gene transfer of antimicrobial resistance genes (ARGs). Consequently, ecosystems become contaminated, affecting soil microbial communities, aquatic organisms, and biodiversity. Human exposure through food chains, water, and environmental contact further increases AMR risks. The review also highlights analytical methods for detection and discusses mitigation strategies such as wastewater treatment, phytoremediation, and sustainable livestock practices. Despite these advances, gaps remain in understanding multi-pollutant interactions and integrated risk assessment. Addressing these challenges requires a multidisciplinary “ One Health ” approach to protect environmental and human health. Antibiotics Heavy metals Farm animal wastewater Antimicrobial resistance Co-selection Environmental contamination Ecotoxicology Figures Figure 1 Figure 2 Introduction Livestock production has expanded rapidly over the past few decades in response to the growing global demand for animal protein, resulting in more intensive farming practices and increased generation of animal waste and wastewater (Steinfeld et al., 2006 ; FAO, 2019 ). These production systems, while essential for food security, are increasingly recognized as significant sources of environmental contamination due to the release of chemical residues and biologically active compounds into surrounding ecosystems (Tilman et al., 2002 ; O’Neill, 2016 ). Among the most concerning contaminants associated with animal agriculture are antibiotics and heavy metals, both of which are widely used in livestock production and frequently detected in farm-derived waste streams (Sarmah et al., 2006 ; Kümmerer, 2009 ). Antibiotics are commonly administered to food-producing animals for therapeutic and preventive purposes, and in some cases to promote growth, although such practices are now being restricted in many regions (Landers et al., 2012 ; Van Boeckel et al., 2015 ; Luo et al., 2014 ). A substantial fraction of these compounds is not fully metabolized by animals and is excreted in active or partially transformed forms through urine and feces, thereby entering manure and wastewater systems (Kemper, 2008 ; Boxall et al., 2004 ; Sarmah et al., 2006 ; Gao et al., 2012 ). Livestock wastewater often contains a mixture of antibiotic residues that can persist in the environment and retain their biological activity (Kümmerer, 2009 ). This persistence increases the likelihood of environmental exposure and contributes to the selective pressure on microbial communities (Martínez, 2009 ). Heavy metals such as copper, zinc, cadmium, lead, and arsenic are routinely introduced into animal production systems through feed additives, mineral supplements, and environmental inputs (Nicholson et al., 2003 ; Alloway, 2013 ). These metals are not biodegradable and tend to accumulate in animal tissues and excreta, leading to their continuous release into manure and wastewater (Wuana and Okieimen, 2011 ; Tchounwou et al., 2012 ; Qiao et al., 2018 ; Zhang et al., 2015 ). Over time, repeated application of contaminated manure to agricultural land can result in the gradual buildup of heavy metals in soils and their eventual transfer to water bodies through runoff and leaching processes (Nicholson et al., 2003 ). The simultaneous presence of antibiotics and heavy metals in farm animal wastewater has drawn increasing attention due to their potential interactions and combined environmental effects (Seiler and Berendonk, 2012 ; Pal et al., 2015 ). These contaminants do not exist in isolation; rather, they coexist in complex environmental matrices where they can influence each other’s behavior, including their mobility, persistence, and bioavailability (Kümmerer, 2009 ). More importantly, their co-occurrence has been linked to the development and spread of antimicrobial resistance (AMR), a global health challenge that threatens the effectiveness of modern medicine (O’Neill, 2016 ). Heavy metals play an important role in this context because they can exert selective pressure on microbial communities even in the absence of antibiotics, thereby promoting the maintenance of antibiotic resistance genes (ARGs) (Baker-Austin et al. , 2006). This process, known as co-selection, occurs when resistance to different stressors is genetically linked, often through mobile genetic elements such as plasmids, integrons, and transposons (Pal et al., 2015 ; Seiler and Berendonk, 2012 ). As a result, environments contaminated with heavy metals can act as reservoirs of antibiotic resistance, facilitating its persistence and spread even when antibiotic use is reduced (Martínez, 2009 ). Farm animal wastewater represents an important interface where antibiotics, heavy metals, and microorganisms converge, creating favorable conditions for the exchange of genetic material and the proliferation of resistant strains (Heuer et al., 2011 ). Through environmental pathways such as runoff, irrigation, and leaching, these contaminants can be transported from farms to surrounding soils, surface waters, and groundwater systems (Boxall et al., 2004 ). This environmental dissemination not only affects ecosystem health but also increases the risk of human exposure through contaminated water, crops, and animal products (O’Neill, 2016 ). The presence of antibiotic and heavy metal residues in the environment can disrupt microbial community structure and interfere with essential ecosystem processes such as nutrient cycling and organic matter decomposition (Cycoń et al., 2019 ). In aquatic systems, these contaminants have been shown to exert toxic effects on a wide range of organisms, including algae, invertebrates, and fish, with potential consequences for biodiversity and ecosystem stability (Kim and Aga, 2007 ). The combined effects of antibiotics and heavy metals may be additive or synergistic, further complicating the assessment of their environmental risks (Yang et al., 2021 ). Sources and Pathways of Contaminants in Farm Animal Wastewater The occurrence of antibiotics and heavy metals in farm animal wastewater is closely linked to the structure and management of modern livestock production systems, where multiple inputs and processes contribute to the introduction and dissemination of these contaminants (Steinfeld et al., 2006 ; Sarmah et al., 2006 ). In intensive animal farming, the routine use of veterinary pharmaceuticals, feed additives, and mineral supplements creates a continuous influx of chemical substances into the production cycle, many of which are ultimately released into the environment through waste streams (Kümmerer, 2009 ; Van Boeckel et al., 2015 ). Antibiotics represent one of the primary contaminant groups in livestock systems, largely due to their widespread application for disease treatment, prevention, and productivity enhancement (Landers et al., 2012 ; Van Boeckel et al., 2015 ). After administration, a significant proportion of these compounds is not fully metabolized by animals and is excreted via urine and feces in active or partially transformed forms (Kemper, 2008 ; Boxall et al., 2004 ). This excreted fraction accumulates in manure, slurry, and farm wastewater, especially in intensive systems where large numbers of animals are confined in relatively small areas (Sarmah et al., 2006 ). The persistence of these residues in waste matrices allows them to retain biological activity, thereby increasing their potential to interact with environmental microorganisms (Kümmerer, 2009 ). Heavy metals are introduced into livestock production systems through several pathways, most notably through feed supplementation (Nicholson et al., 2003 ; Alloway, 2013 ). Elements such as copper and zinc are commonly added to animal feed to promote growth and improve feed efficiency, while others such as cadmium, lead, and arsenic may be present as contaminants in feed ingredients, water sources, or the surrounding environment (Wuana and Okieimen, 2011 ; Tchounwou et al., 2012 ). Unlike antibiotics, heavy metals are not subject to degradation and therefore persist in animal tissues and excreta, leading to their continuous release into manure and wastewater systems (Alloway, 2013 ). Over time, repeated input of these metals can result in their accumulation in soils and sediments, particularly in areas where manure is applied as fertilizer (Nicholson et al., 2003 ). Farm animal wastewater is generated through a combination of biological and operational processes, including animal excretion, cleaning of housing facilities, feedlot runoff, and effluents from slaughterhouses and processing units (FAO, 2019 ). In intensive production systems, large volumes of water are used for washing and waste management, which facilitates the transport of both dissolved and particulate contaminants into wastewater streams (Steinfeld et al., 2006 ). These wastewater streams are often stored in lagoons, applied to agricultural land, or discharged into nearby water bodies, depending on farm management practices and regulatory frameworks (Boxall et al., 2004 ). Once released into the environment, antibiotics and heavy metals are transported through multiple pathways that determine their distribution and impact (Martínez, 2009 ). Surface runoff during rainfall events can carry contaminants from manure-amended soils into rivers, lakes, and other surface water, while leaching processes enable their movement into groundwater systems (Sarmah et al., 2006 ). The use of contaminated wastewater for irrigation further contributes to the spread of these substances into agricultural soils and crops, thereby extending their reach into the food chain (Boxall et al., 2004 ). The behavior and transport of these contaminants in the environment are strongly influenced by physicochemical and biological factors such as pH, temperature, soil composition, and microbial activity (Thiele-Bruhn, 2003). Antibiotics may undergo degradation through microbial metabolism, hydrolysis, or photolysis, although some compounds exhibit considerable persistence depending on environmental conditions (Kümmerer, 2009 ). Heavy metals tend to bind to soil particles and organic matter, where they can remain for extended periods and may be remobilized under changing environmental conditions (Alloway, 2013 ). These differences in behavior highlight the complexity of contaminant dynamics in agricultural environments. In many regions, particularly in developing countries, inadequate waste management practices and limited access to effective wastewater treatment systems exacerbate the release of these contaminants into the environment (Van Boeckel et al., 2015 ). Untreated or poorly managed animal waste is often discharged directly into surrounding ecosystems, increasing the risk of contamination of water resources and agricultural land (FAO, 2019 ). This situation explained the importance of identifying critical control points within livestock production systems where interventions can reduce the entry and spread of antibiotics and heavy metals. The sources and pathways of antibiotics and heavy metals in farm animal wastewater are interconnected and influenced by both management practices and environmental conditions. A proper understanding of these processes provides the foundation for assessing environmental risks, designing effective mitigation strategies, and addressing the broader challenges associated with antimicrobial resistance and ecological contamination. Occurrence and Distribution of Antibiotic Residues Antibiotic residues have been widely detected in farm animal wastewater across different regions of the world, reflecting their extensive use in livestock production systems and their persistence in environmental matrices (Sarmah et al., 2006 ; Kümmerer, 2009 ). These residues originate primarily from the excretion of unmetabolized antibiotics and their active metabolites, which are subsequently released into manure, slurry, and wastewater during routine farm operations (Kemper, 2008 ; Landers et al., 2012 ). The continuous input of these compounds into the environment has led to their widespread occurrence in both developed and developing countries, raising concerns about their ecological and public health implications (Boxall et al., 2004 ; Martínez, 2009 ). Several classes of antibiotics are commonly reported in livestock wastewater, with tetracyclines, sulfonamides, fluoroquinolones, and macrolides being among the most frequently detected (Kümmerer, 2009 ; Sarmah et al., 2006 ). Tetracyclines are particularly prevalent due to their extensive use in poultry and swine production, as well as their strong affinity for binding to organic matter, which enhances their persistence in manure and wastewater systems (Chopra and Roberts, 2001 ; Thiele-Bruhn, 2003). Sulfonamides and fluoroquinolones, are more mobile in the environment and are often detected in surface and groundwater systems due to their relatively higher solubility (Hamscher et al., 2002 ; Hirsch et al., 1999 ). The concentration of antibiotic residues in farm animal wastewater varies widely depending on factors such as animal species, dosage, management practices, and environmental conditions (Sarmah et al., 2006 ; Kemper, 2008 ). Reported concentrations typically range from a few micrograms per liter to several hundred micrograms per liter in wastewater, and even higher levels in manure and slurry (Boxall et al., 2004 ; Kümmerer, 2009 ). These variations are also influenced by the physicochemical properties of the antibiotics, including their solubility, stability, and adsorption potential (Thiele-Bruhn, 2003). In developing regions, including parts of Africa and Asia, the occurrence of antibiotic residues in farm wastewater is often exacerbated by inadequate regulation, lack of wastewater treatment infrastructure, and unregulated use of veterinary drugs (Landers et al., 2012 ; Van Boeckel et al., 2015 ). In such settings, untreated or poorly managed animal waste is frequently discharged into the environment, increasing the likelihood of contamination of surrounding soils and water bodies (Martínez, 2009 ). This highlights the importance of understanding regional patterns of contamination in order to develop targeted mitigation strategies. Several studies have documented the occurrence of antibiotic residues in farm animal wastewater across different countries and production systems, as summarized in (Table I). These findings demonstrate not only the global nature of the problem but also the variability in contamination levels depending on local practices and environmental conditions. Table I Antibiotic Residues in Farm Animal Wastewater Across Region Country/Region Farm Type Antibiotic Class Concentration Range Sample Type Reference China Swine Tetracyclines 50–500 µg/L Wastewater Zhang et al., 2015 USA Cattle Sulfonamides 10–200 µg/L Lagoon water Campagnolo et al. , 2002 Germany Pig Fluoroquinolones 5–100 µg/L Slurry Hamscher et al., 2002 Nigeria Poultry Tetracyclines 20–150 µg/L Wastewater Adesokan et al. , 2015 India Mixed livestock Macrolides 15–250 µg/L Farm effluent Kumar et al. , 2014 Occurrence and Distribution of Heavy Metals Heavy metals are among the most persistent contaminants in farm animal wastewater due to their widespread use in livestock production and resistance to environmental degradation (Nicholson et al., 2003 ; Alloway, 2013 ). Common metals detected include copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As), which primarily enter wastewater through feed additives, mineral supplements, and environmental contamination of water and soil (Wuana and Okieimen, 2011 ; Tchounwou et al., 2012 ). Copper and zinc are frequently added to poultry and swine feeds to enhance growth and feed efficiency, contributing to elevated concentrations in manure and wastewater (Sarmah et al., 2006 ; Nicholson et al., 2003 ). Trace metals such as cadmium and lead may also accumulate due to contaminated feed, water, or soil, even when not intentionally introduced (Wuana and Okieimen, 2011 ). The concentration of heavy metals in farm wastewater varies depending on animal species, feeding practices, farm management systems, and regional environmental conditions (Alloway, 2013 ; Sarmah et al., 2006 ). Intensive livestock operations often show higher Cu and Zn levels, whereas Cd and Pb concentrations are more influenced by local environmental exposure (Wuana and Okieimen, 2011 ; Nicholson et al., 2003 ). Unlike antibiotics, metals do not degrade and therefore persist in wastewater, manure, and sludge, with the potential to accumulate in soils over repeated manure applications (Tchounwou et al., 2012 ; Alloway, 2013 ). Their mobility and bioavailability are further influenced by factors such as pH, organic matter content, and redox conditions, which can either immobilize or remobilize metals into more bioavailable forms (Sarmah et al., 2006 ; Wuana and Okieimen, 2011 ). Spatial and temporal studies show that heavy metal concentrations differ between countries and farm types, reflecting variations in livestock production intensity and waste management practices (Nicholson et al., 2003 ; Zhang et al., 2015 ). Intensive poultry farms in Asia and Europe often report higher Cu and Zn concentrations compared to cattle farms in North America (Sarmah et al., 2006 ; Zhang et al., 2015 ). Repeated application of manure can further lead to accumulation of metals in soils, which may eventually leach into surface and groundwater systems (Alloway, 2013 ; Wuana and Okieimen, 2011 ). This persistence increases the risk of long-term environmental contamination and potential entry into the food chain (Tchounwou et al., 2012 ; Nicholson et al., 2003 ). The persistence of heavy metals in wastewater and manure, combined with their potential for accumulation in soil and aquatic systems, underscores the importance of monitoring and management (Alloway, 2013 ; Tchounwou et al., 2012 ). Their co-occurrence with antibiotics further complicates environmental dynamics, as both contaminants can exert selective pressure on microbial communities and contribute to antimicrobial resistance (Seiler and Berendonk, 2012 ; Pal et al., 2015 ). The regional patterns of heavy metal contamination, as shown in Table II, is important for designing effective mitigation strategies and assessing ecological risk (Wuana and Okieimen, 2011 ; Nicholson et al., 2003 ). Table II Heavy Metal Residues in Farm Animal Wastewater Across Regions Country/Region Farm Type Heavy Metal Concentration Range (mg/L) Sample Type Reference China Swine Cu 10–250 Wastewater Zhang et al., 2015 USA Cattle Zn 5–120 Lagoon water Campagnolo et al. , 2002 | Germany Pig Pb 0.01–5 Slurry Hamscher et al., 2002 Nigeria Poultry Cu 8–200 Wastewater Adesokan et al. , 2015 India Mixed livestock Cd 0.02–3 Farm effluent Kumar et al. , 2014 Interaction Between Antibiotics and Heavy Metals In farm environments, antibiotics and heavy metals frequently co-occur due to their simultaneous use in livestock production systems (Seiler and Berendonk, 2012 ; Pal et al., 2015 ; Kümmerer, 2009 ; Chen et al., 2016 ). Wastewater, manure, and slurry from intensive farms often contain residues of both contaminants, reflecting routine veterinary practices and the inclusion of metal-based feed additives (Sarmah et al., 2006 ; Nicholson et al., 2003 ). The co-occurrence of these substances in wastewater creates complex environmental matrices where both antibiotics and metals interact with each other and with microbial communities, influencing their ecological fate (Kümmerer, 2009 ; Heuer et al., 2011 ). Chemical interactions between antibiotics and heavy metals can significantly affect their behavior in the environment (Wuana and Okieimen, 2011 ; Song et al., 2017 ). Metals can bind to antibiotic molecules through complexation or adsorption to particulates, altering their solubility and bioavailability (Sarmah et al., 2006 ; Kümmerer, 2009 ). Such interactions may stabilize certain antibiotics in wastewater, reducing their biodegradation and increasing their persistence, or conversely, may lead to precipitation and reduced mobility depending on pH, ionic strength, and the presence of organic matter (Thiele-Bruhn, 2003; Grenni et al., 2018 ). These chemical associations also influence the transport of contaminants, potentially facilitating their accumulation in soils, sediments, and aquatic systems (Boxall et al., 2004 ; Wuana and Okieimen, 2011 ). The co-occurrence and chemical interactions of antibiotics and heavy metals directly impact their mobility, persistence, and bioavailability (Alloway, 2013 ; Song et al., 2017 ). Antibiotics complexed with metals may remain biologically active for longer periods, enhancing their potential to exert selective pressure on microbial communities (Martínez, 2009 ; Pal et al., 2015 ). Metals bound to organic particles can also affect the adsorption and desorption of antibiotics, influencing their environmental distribution and availability to microorganisms (Kümmerer, 2009 ; Cycoń et al., 2019 ). As a result, wastewater environments act as hotspots for co-selection of resistance genes, since microbes are simultaneously exposed to multiple stressors over extended periods (Heuer et al., 2011 ; Baker-Austin et al. , 2006). The interaction between antibiotics and heavy metals in farm environments amplifies their environmental risks. These interactions influence not only the persistence and transport of contaminants but also their ecological impact and the potential for antimicrobial resistance to develop and spread (Seiler and Berendonk, 2012 ; Pal et al., 2015 ). Understanding these dynamics is essential for effective monitoring and management of farm wastewater, and it provides the foundation for exploring mechanisms of co-selection and resistance in subsequent sections. Co-selection Mechanisms and Antimicrobial Resistance Co-selection is a major mechanism driving antimicrobial resistance in environmental systems (Seiler and Berendonk, 2012 ; Berendonk et al., 2015 ). Farm animal wastewater frequently contains a complex mixture of antibiotics and heavy metals, which together create conditions that favor the persistence and spread of antimicrobial resistance genes (ARGs) (Seiler and Berendonk, 2012 ; Pal et al., 2015 ). Co-selection occurs when exposure to one stressor, such as heavy metals, promotes the maintenance of resistance to another, such as antibiotics, due to genetic or environmental linkage (Baker-Austin et al. , 2006; Martínez, 2009 ) (Table III). This phenomenon is particularly relevant in livestock wastewater, where both types of contaminants coexist at concentrations sufficient to exert selective pressure on microbial communities (Heuer et al., 2011 ). Mechanisms of co-selection include cross-resistance, where a single resistance determinant such as an efflux pump confers protection against both metals and antibiotics, allowing microorganisms to survive in environments contaminated with either stressor (Baker-Austin et al. , 2006; Pal et al., 2015 ; Heuer et al., 2011 ; Smalla et al., 2018 ). Co-resistance is another mechanism, in which separate resistance genes are physically linked on mobile genetic elements like plasmids, integrons, or transposons. Selection pressure on one gene, for instance from heavy metals, indirectly maintains resistance to antibiotics encoded on the same element (Heuer et al., 2011 ; Seiler and Berendonk, 2012 ). These mobile elements are abundant in farm wastewater, facilitating horizontal gene transfer (HGT) and the spread of resistance among diverse microbial populations (Li et al., 2020 ; Martínez, 2009 ). Heavy metals such as copper, zinc, cadmium, and lead are important in promoting ARGs (Martínez, 2009 ; Zhu et al., 2013 ). Even at low environmental concentrations, these metals select for microbial strains carrying resistance genes, many of which are co-located with metal-resistance determinants (Baker-Austin et al. , 2006; Pal et al., 2015 ). This process ensures the persistence of ARGs in soils, water, and sediments impacted by farm wastewater, creating environmental reservoirs that can reintroduce resistance into agricultural or clinical systems (Martínez, 2009 ; Heuer et al., 2011 ). Horizontal gene transfer is an important pathway for ARG dissemination in these environments. Wastewater provides ideal conditions for HGT due to high microbial density, presence of selective agents, and the prevalence of mobile genetic elements (Martínez, 2009 ; Heuer et al., 2011 ). Through HGT, resistance traits can spread not only among environmental bacteria but also to potentially pathogenic species, increasing risks for animal and human health (O’Neill, 2016 ; Van Boeckel et al., 2015 ). Knowing co-selection and HGT in wastewater environments is therefore essential for designing strategies to mitigate the environmental and public health impacts of antibiotics and heavy metals (Li et al., 2020 ; Pal et al., 2015 ). Table III Co-selection Mechanisms and Antimicrobial Resistance in Farm Wastewater Mechanism Description Example Role in ARG Persistence Reference Cross-resistance Single resistance determinant protects against multiple stressors Efflux pumps in E. coli extruding tetracycline and copper ions Allows bacteria to survive in environments with both metals and antibiotics, maintaining ARGs Baker-Austin et al. , 2006; Pal et al., 2015 Co-resistance Separate resistance genes are physically linked on mobile genetic elements (plasmids, integrons, transposons) Plasmid carrying zinc resistance gene along with sulfonamide resistance gene Metal selection indirectly preserves antibiotic resistance Heuer et al., 2011 ; Seiler and Berendonk, 2012 Selection by heavy metals Metals exert selective pressure on bacteria carrying both metal and antibiotic-resistance genes Copper, zinc, cadmium in poultry wastewater selecting for tetracycline-resistant strains Maintains ARGs even without direct antibiotic exposure Baker-Austin et al. , 2006; Pal et al., 2015 Horizontal gene transfer (HGT) Movement of genetic material between bacteria via plasmids or integrons Transfer of ARGs from environmental Enterococcus to pathogens Enables ARG spread across microbial communities and ecosystems Heuer et al., 2011 ; Martínez, 2009 Chemical interactions Antibiotics and metals form complexes or bind to particulates Copper-tetracycline complex in wastewater Stabilizes contaminants, prolongs selective pressure, enhances ARG persistence Kümmerer, 2009 ; Grenni et al., 2018 Environmental Fate and Transport The environmental fate and transport of antibiotics and heavy metals in farm animal wastewater are governed by a range of physicochemical and biological processes that determine their distribution, transformation, and long-term impact on ecosystems (Sarmah et al., 2006 ; Kümmerer, 2009 ). Once released into the environment through manure application, wastewater discharge, or runoff, these contaminants undergo various degradation and transport processes that influence their persistence and mobility (Boxall et al., 2004 ; Martínez, 2009 ). Understanding these processes is essential for evaluating the environmental risks associated with livestock production systems and waste management practices (Cycoń et al., 2019 ). Antibiotics may undergo both biotic and abiotic degradation in environmental matrices, including microbial degradation, hydrolysis, and photodegradation, depending on factors such as temperature, pH, and sunlight exposure (Kümmerer, 2009 ; Thiele-Bruhn, 2003; Halling-Sørensen et al. , 1998). Microbial activity plays a particularly important role in transforming antibiotic compounds into less active forms, although some compounds exhibit resistance to degradation and persist for extended periods (Grenni et al., 2018 ; Sarmah et al., 2006 ; Jechalke et al., 2014 ). Heavy metals are non-biodegradable and cannot be broken down through biological or chemical processes, leading to their persistence once introduced into soils and aquatic systems (Alloway, 2013 ; Tchounwou et al., 2012 ). Adsorption and desorption processes also influence the environmental behavior of these contaminants by regulating their mobility and bioavailability in soil and sediment systems (Thiele-Bruhn, 2003; Wuana and Okieimen, 2011 ). Antibiotics, particularly tetracyclines, tend to bind strongly to soil particles and organic matter, which may reduce their immediate mobility but increase their persistence in the environment (Kümmerer, 2009 ; Sarmah et al., 2006 ). Also, heavy metals can form stable associations with clay minerals and organic matter, leading to their accumulation in soils and sediments over time (Alloway, 2013 ). However, changes in environmental conditions such as pH, redox potential, and ionic strength can trigger desorption, releasing these contaminants back into the soil solution and increasing their availability for transport and biological uptake (Wuana and Okieimen, 2011 ; Cycoń et al., 2019 ). Leaching and surface runoff represent major pathways through which antibiotics and heavy metals are transported from agricultural lands into surrounding aquatic systems (Boxall et al., 2004 ; Sarmah et al., 2006 ). During rainfall, contaminants present in manure-amended soils can be mobilized and carried into rivers, lakes, and drainage networks, contributing to the contamination of surface waters (Martínez, 2009 ; Zhang et al., 2015 ). Leaching processes also enable soluble compounds, including certain antibiotics and metal ions, to migrate through soil profiles and reach groundwater systems (Kümmerer, 2009 ). The use of contaminated wastewater for irrigation can further facilitate the spread of these pollutants across agricultural landscapes, increasing their environmental footprint (Van Boeckel et al., 2015 ). The persistence and long-term accumulation of antibiotics and heavy metals pose significant ecological concerns, particularly in regions with continuous livestock production and repeated manure application (Kümmerer, 2009 ; Alloway, 2013 ). While some antibiotics degrade over time, continuous inputs can maintain their presence at biologically active concentrations in soils and water bodies (Grenni et al., 2018 ; Sarmah et al., 2006 ). Heavy metals, due to their non-degradable nature, accumulate progressively in soils, sediments, and biota, leading to chronic exposure of organisms and potential bioaccumulation in food chains (Tchounwou et al., 2012 ; Wuana and Okieimen, 2011 ). Over time, these persistent contaminants can act as long-term sources of environmental stress, contributing to ecosystem degradation and supporting the maintenance of antimicrobial resistance in environmental microbial communities (Martínez, 2009 ; Cycoń et al., 2019 ). Ecotoxicological Implications The presence of antibiotics and heavy metals in farm animal wastewater shows significant ecotoxicological risks to both terrestrial and aquatic ecosystems by disrupting biological processes and altering species composition (Kim and Aga, 2007 ; Cycoń et al., 2019 ). In soil environments these contaminants can adversely affect microorganisms that help in nutrient cycling, organic matter decomposition, and soil fertility (Grenni et al., 2018 ; Thiele-Bruhn, 2003; Giller et al., 2009 ). Antibiotics, even at low concentrations, can inhibit sensitive microbial populations while promoting resistant strains, thereby reducing microbial diversity and altering community structure (Martínez, 2009 ; Heuer et al., 2011 ; Danner et al., 2019 ). Heavy metals also exacerbate these effects by inducing toxicity through oxidative stress, enzyme inhibition, and disruption of cellular processes in soil microbes (Tchounwou et al., 2012 ; Wuana and Okieimen, 2011 ). Aquatic organisms are also highly vulnerable to contamination from antibiotics and heavy metals transported via runoff and wastewater discharge (Boxall et al., 2004 ; Rizzo et al., 2013 ). Exposure to antibiotic residues has been associated with growth inhibition, reproductive impairment, and behavioral changes in fish, algae, and invertebrates (Kim and Aga, 2007 ; Cycoń et al., 2019 ). Heavy metals such as cadmium, mercury, and lead can accumulate in aquatic organisms, leading to physiological stress, impaired development, and increased mortality rates (Alloway, 2013 ; Li et al., 2020 ). These toxic effects can disrupt aquatic food webs and reduce biodiversity, particularly in ecosystems receiving continuous pollutant inputs (Wuana and Okieimen, 2011 ; Zhang et al., 2015 ). One of the major concerns associated with these contaminants is their ability to bioaccumulate and biomagnify within food chains, posing risks to higher trophic levels, including humans (Tchounwou et al., 2012 ; Alloway, 2013 ). Heavy metals, due to their persistence, are especially prone to accumulation in the tissues of organisms, where they can reach toxic concentrations over time (Wuana and Okieimen, 2011 ). Although antibiotics are generally less prone to biomagnification, their continuous input into the environment can lead to sustained exposure and accumulation in certain organisms (Kümmerer, 2009 ; Grenni et al., 2018 ). This accumulation increases the likelihood of chronic toxicity and long-term ecological impacts (Cycoń et al., 2019 ). Toxicity associated with antibiotics and heavy metals can manifest through both acute and chronic effects, depending on exposure concentration and duration (Kim and Aga, 2007 ; Yang et al., 2021 ). Acute toxicity typically results in immediate effects such as mortality or severe physiological disruption, while chronic exposure may lead to sub-lethal effects including reduced growth, reproductive failure, and genetic damage (Tchounwou et al., 2012 ; Cycoń et al., 2019 ). These sub-lethal effects are particularly concerning because they can accumulate over time and impact population dynamics and ecosystem stability (Grenni et al., 2018 ). The combined presence of antibiotics and heavy metals in the environment can result in additive or synergistic toxic effects, further complicating ecological risk assessments (Yang et al., 2021 ; Pal et al., 2015 ). Interactions between these contaminants may enhance their bioavailability and toxicity, for example through metal-antibiotic complex formation or increased oxidative stress in exposed organisms (Kümmerer, 2009 ; Grenni et al., 2018 ). Such combined exposures better reflect real-world conditions in agricultural environments, where multiple contaminants coexist and interact (Rizzo et al., 2013 ). These interactions not only intensify ecological damage but also contribute to the persistence and spread of antimicrobial resistance within environmental microbial communities (Heuer et al., 2011 ; Martínez, 2009 ). Implications on Public Health The presence of antibiotics and heavy metals in farm animal wastewater poses serious public health concerns, primarily due to their role in the emergence and spread of antimicrobial resistance (AMR) and their potential for human exposure through multiple environmental pathways (O’Neill, 2016 ; Van Boeckel et al., 2015 ; Laxminarayan et al., 2013 ). One of the major routes of concern is the transmission of antibiotic resistance through the food chain, where resistant bacteria originating from livestock environments can be transferred to humans via contaminated meat, milk, vegetables, and other agricultural products (Marshall and Levy, 2011 a; Levy and Marshall, 2004 b; Heuer et al., 2011 ). The application of manure and wastewater to farmlands facilitates the introduction of antibiotic residues, heavy metals, and resistance genes into soil systems, from where they can be taken up by crops or persist in food-producing environments (Boxall et al., 2004 ; Martínez, 2009 ). This continuous cycling of contaminants between animals, the environment, and humans increases the likelihood of resistance dissemination across different ecological compartments (Pal et al., 2015 ; Grenni et al., 2018 ). Contamination of drinking water sources is another critical pathway through which these pollutants pose risks to human health (Kümmerer, 2009 ; Rizzo et al., 2013 ). Antibiotics and heavy metals can enter surface water and groundwater systems through leaching, runoff, and direct discharge of untreated or poorly treated farm wastewater (Sarmah et al., 2006 ; Zhang et al., 2015 ). In many regions, especially where wastewater treatment infrastructure is limited, these contaminants may persist in water supplies used for domestic purposes, including drinking, cooking, and sanitation (Van Boeckel et al., 2015 ; Cycoń et al., 2019 ). Conventional water treatment systems are not always fully effective in removing antibiotic residues or resistance genes, thereby increasing the risk of chronic low-level exposure in human populations (Rizzo et al., 2013 ; Grenni et al., 2018 ). Human exposure to antibiotics and heavy metals from farm wastewater occurs through several interconnected routes, including ingestion of contaminated food and water, dermal contact with polluted soils or water, and inhalation of dust or aerosols containing contaminants (Boxall et al., 2004 ; Wuana and Okieimen, 2011 ). Occupational exposure is particularly relevant for farmers, farm workers, and individuals living near livestock production facilities, who may come into direct contact with contaminated materials on a regular basis (Heuer et al., 2011 ; Martínez, 2009 ). These exposure pathways not only increase the risk of direct toxic effects but also contribute to the transfer of resistant microorganisms to humans, thereby complicating the treatment of infectious diseases (Pal et al., 2015 ; O’Neill, 2016 ). The global health burden associated with antimicrobial resistance continues to rise, with environmental reservoirs such as farm wastewater playing a significant role in its persistence and spread (O’Neill, 2016 ; Van Boeckel et al., 2015 ). The presence of both antibiotics and heavy metals in the environment enhances selective pressure on microbial communities, promoting the maintenance and dissemination of resistance genes even in the absence of direct antibiotic use (Seiler and Berendonk, 2012 ; Baker-Austin et al. , 2006). This situation shows major challenge to public health systems, as infections caused by resistant pathogens are more difficult and costly to treat, often resulting in increased morbidity, mortality, and healthcare expenditure (O’Neill, 2016 ). Addressing these risks requires integrated strategies that consider environmental, agricultural, and public health perspectives to reduce contaminant release and limit the spread of resistance across human and ecological systems (Van Boeckel et al., 2015 ; Rizzo et al., 2013 ). Methods for Detection and Analysis Accurate detection and analysis of antibiotics, heavy metals, and antimicrobial resistance genes (ARGs) in farm animal wastewater are important for assessing environmental contamination and associated risks (Kümmerer, 2009 ; Cycoń et al., 2019 ). The reliability of analytical results begins with appropriate sampling strategies, which must account for spatial and temporal variability in wastewater, manure, and sludge systems (Sarmah et al., 2006 ; Boxall et al., 2004 ). Samples are typically collected from multiple points, including animal housing effluents, storage lagoons, and discharge outlets, to ensure representative characterization of contaminant distribution (Zhang et al., 2015 ; Van Boeckel et al., 2015 ). Proper sample preservation, including cooling, acidification, or filtration, is critical to prevent degradation or transformation of analytes prior to laboratory analysis (Kümmerer, 2009 ; Grenni et al., 2018 ). The analysis of antibiotic residues in environmental samples commonly relies on advanced chromatographic techniques such as high-performance liquid chromatography (HPLC) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) due to their high sensitivity and specificity (Hirsch et al., 1999 ; Kümmerer, 2009 ; Hamscher et al., 2002 ). These methods enable the detection of trace concentrations of antibiotics in complex matrices such as wastewater and sludge, even at microgram or nanogram levels (Sarmah et al., 2006 ; Boxall et al., 2004 ). Sample preparation techniques, including solid-phase extraction (SPE) (Fig. I), are often employed to concentrate and purify analytes prior to analysis, improving detection accuracy and reproducibility (Thiele-Bruhn, 2003; Grenni et al., 2018 ). The use of LC-MS/MS has become particularly important in environmental monitoring due to its ability to simultaneously quantify multiple antibiotic compounds with high precision (Zhang et al., 2015 ; Kümmerer, 2009 ). Detection of heavy metals in farm wastewater is typically carried out using techniques such as atomic absorption spectroscopy (AAS) (Fig. II) and inductively coupled plasma mass spectrometry (ICP-MS), which offer high sensitivity and accuracy for metal quantification (Alloway, 2013 ; Wuana and Okieimen, 2011 ). AAS is widely used for routine analysis due to its cost-effectiveness and reliability, while ICP-MS provides multi-element detection with lower detection limits, making it suitable for trace-level analysis (Tchounwou et al., 2012 ; Alloway, 2013 ). Prior to analysis, samples often undergo digestion using strong acids to convert metals into measurable forms, ensuring accurate quantification (Wuana and Okieimen, 2011 ). These analytical techniques are essential for monitoring the accumulation and distribution of heavy metals in environmental samples (Tchounwou et al., 2012 ). Molecular techniques helps in detecting and quantifying antimicrobial resistance genes in wastewater environments (Heuer et al., 2011 ; Martínez, 2009 ; Pruden et al., 2013 ). Polymerase chain reaction (PCR) and quantitative PCR (qPCR) are commonly used to identify and quantify specific ARGs, providing insights into their abundance and distribution (Pal et al., 2015 ; Grenni et al., 2018 ). More advanced approaches such as metagenomic sequencing allow for comprehensive analysis of microbial communities and the full spectrum of resistance genes present in environmental samples (Cycoń et al., 2019 ; Zhang et al., 2015 ). These molecular tools are essential for understanding the dynamics of resistance dissemination and the impact of environmental contaminants on microbial ecosystems (Heuer et al., 2011 ; Martínez, 2009 ). The integration of robust sampling strategies with advanced analytical and molecular techniques provides a comprehensive framework for assessing the occurrence, fate, and impact of antibiotics, heavy metals, and ARGs in farm animal wastewater (Kümmerer, 2009 ; Cycoń et al., 2019 ). Such approaches are critical for generating reliable data that can inform environmental monitoring, risk assessment, and the development of effective mitigation strategies (Van Boeckel et al., 2015 ; Rizzo et al., 2013 ). Mitigation and Remediation Strategies Addressing the environmental and public health risks associated with antibiotics and heavy metals in farm animal wastewater requires integrated mitigation and remediation strategies that combine technological, biological, and policy-based approaches (Kümmerer, 2009 ; Cycoń et al., 2019 ). Wastewater treatment technologies play a central role in reducing contaminant loads before environmental discharge, with biological, chemical, and physical methods widely applied depending on the nature of the pollutants (Rizzo et al., 2013 ; Van Boeckel et al., 2015 ; Daghrir and Drogui, 2013 ). Biological treatments, such as activated sludge systems and anaerobic digestion, utilize microbial processes to degrade organic contaminants, including certain antibiotics, although their efficiency may vary depending on compound structure and operational conditions (Kümmerer, 2009 ; Cycoń et al., 2019 ). Chemical treatments, including advanced oxidation processes, can effectively degrade persistent antibiotic residues, while physical methods such as filtration, sedimentation, and adsorption using activated carbon help remove both antibiotics and heavy metals from wastewater (Rizzo et al., 2013 ; Zhang et al., 2015 ). Phytoremediation has emerged as a sustainable and cost-effective approach for mitigating contamination in agricultural environments, particularly in developing regions where advanced treatment systems may be limited (Wuana and Okieimen, 2011 ; Ali et al., 2013 ; Carvalho et al., 2014 ). This approach involves the use of plants to uptake, stabilize, or transform contaminants, with certain species capable of accumulating heavy metals from soils and wastewater (Ali et al., 2013 ; Alloway, 2013 ). In addition to metal removal, some plants can enhance microbial activity in the rhizosphere, thereby promoting the degradation of antibiotic residues (Cycoń et al., 2019 ; Grenni et al., 2018 ). Phytoremediation strategies are particularly relevant for treating runoff and contaminated soils associated with livestock production systems (Wuana and Okieimen, 2011 ; Cycoń et al., 2019 ; Kuppusamy et al., 2018 ). The use of phytogenic feed additives represents another promising strategy for reducing antibiotic use in livestock production, thereby minimizing the release of antibiotic residues into the environment (Windisch et al., 2008 ; Greathead, 2003 ). These plant-derived compounds, including essential oils and herbal extracts, can improve animal health and productivity while serving as alternatives to conventional antibiotics (Windisch et al., 2008 ; Yang et al., 2015 ). By reducing reliance on antibiotics, phytogenic additives help lower the selective pressure for antimicrobial resistance and decrease the concentration of antibiotic residues in manure and wastewater (Pal et al., 2015 ; Van Boeckel et al., 2015 ). This approach aligns with global efforts to promote sustainable livestock production and reduce environmental contamination. Effective manure management practices are also essential for mitigating the release of antibiotics and heavy metals into the environment (Sarmah et al., 2006 ; Nicholson et al., 2003 ). Techniques such as composting, controlled storage, and proper timing of manure application can significantly reduce contaminant levels and limit their transport to soil and water systems (Boxall et al., 2004 ; Cycoń et al., 2019 ). Composting, for example, can enhance microbial degradation of antibiotics and stabilize heavy metals, reducing their bioavailability (Grenni et al., 2018 ; Wuana and Okieimen, 2011 ). Implementing buffer zones and controlled irrigation practices can minimize runoff and leaching of contaminants into surrounding ecosystems (Sarmah et al., 2006 ). Policy and regulatory frameworks also helps in controlling the use of antibiotics and managing environmental contamination from livestock production (O’Neill, 2016 ; Van Boeckel et al., 2015 ). Regulations that restrict the non-therapeutic use of antibiotics, monitor residue levels in animal products, and enforce wastewater treatment standards are essential for reducing environmental and public health risks (Marshall and Levy, 2011 ; Rizzo et al., 2013 ). International and national initiatives aimed at combating antimicrobial resistance emphasize the need for a One Health approach that integrates human, animal, and environmental health considerations (O’Neill, 2016 ; Pal et al., 2015 ). Research Gap and Future Perspectives Despite the growing body of research on antibiotics and heavy metals in farm animal wastewater, several limitations remain that constrain a comprehensive understanding of their environmental and public health impacts (Cycoń et al., 2019 ; Grenni et al., 2018 ). Many existing studies are limited by short-term experimental designs, small sample sizes, and a focus on single contaminants rather than complex mixtures, which reduces their applicability to real-world conditions (Kümmerer, 2009 ; Sarmah et al., 2006 ; Grenni et al., 2018 ; Kraemer et al., 2019 ). Furthermore, there is often a lack of standardized methodologies for sampling, analysis, and reporting, making it difficult to compare results across studies and regions (Rizzo et al., 2013 ; Zhang et al., 2015 ). These gaps explain the need for more robust, long-term, and large-scale investigations that reflect the variability and complexity of livestock production systems (Van Boeckel et al., 2015 ). A major research need lies in the development of integrated risk assessment frameworks that consider the combined effects of antibiotics, heavy metals, and antimicrobial resistance genes (ARGs) across environmental compartments (Pal et al., 2015 ; Seiler and Berendonk, 2012 ). Current risk assessments often evaluate contaminants in isolation, neglecting the synergistic or antagonistic interactions that may significantly influence ecological and human health outcomes (Yang et al., 2021 ; Cycoń et al., 2019 ). There is also a need to incorporate both chemical and microbiological indicators, including ARG abundance and horizontal gene transfer potential, into risk assessment models (Heuer et al., 2011 ; Martínez, 2009 ). Such integrated approaches would provide a more realistic evaluation of environmental risks and support evidence-based decision-making (Rizzo et al., 2013 ). Emerging contaminants and multi-pollutant interactions represent another critical area requiring further investigation (Grenni et al., 2018 ; Gothwal and Shashidhar, 2015 ; Yang et al., 2021 ). In addition to conventional antibiotics and heavy metals, livestock wastewater may contain other pollutants such as microplastics, disinfectants, hormones, and nanoparticles, which can interact with existing contaminants and influence their fate and toxicity (Cycoń et al., 2019 ; Kümmerer, 2009 ). These interactions can alter contaminant behavior, enhance toxicity, and further promote antimicrobial resistance, yet they remain poorly understood due to limited research in this area (Pal et al., 2015 ; Seiler and Berendonk, 2012 ). Addressing these knowledge gaps requires multidisciplinary studies that integrate environmental chemistry, microbiology, and toxicology (Martínez, 2009 ; Grenni et al., 2018 ). Future research should focus on developing sustainable and cost-effective mitigation strategies that are adaptable to different agricultural contexts, particularly in low- and middle-income countries where wastewater management infrastructure may be limited (Van Boeckel et al., 2015 ; Wuana and Okieimen, 2011 ). There is also a need for innovation in analytical techniques to improve detection sensitivity, especially for trace-level contaminants and emerging resistance genes (Kümmerer, 2009 ; Zhang et al., 2015 ). Furthermore, studies should explore the long-term ecological and health impacts of chronic exposure to low concentrations of contaminants, as these conditions better reflect real environmental scenarios (Cycoń et al., 2019 ; Grenni et al., 2018 ). Strengthening interdisciplinary collaboration and aligning research efforts with policy development will be essential for effectively addressing the challenges associated with antibiotics and heavy metals in farm animal wastewater (O’Neill, 2016 ; Rizzo et al., 2013 ). Conclusion The widespread occurrence of antibiotics and heavy metals in farm animal wastewater represents a significant environmental and public health challenge due to their persistence, mobility, and capacity to promote antimicrobial resistance (AMR). Their continuous release from livestock production systems leads to contamination of soil and aquatic environments, where they interact, accumulate, and exert toxic effects on microorganisms, plants, and aquatic organisms. These contaminants not only disrupt ecological processes but also contribute to the co-selection and dissemination of antibiotic resistance genes (ARGs), increasing the risk of resistant infections in humans and animals. The complexity of their environmental fate, coupled with multiple exposure pathways such as food chains and water systems, highlights the urgent need for integrated and sustainable management strategies. Recommendations Implement integrated biological, chemical, and physical treatment systems to enhance removal efficiency of both antibiotics and heavy metals before environmental discharge. Promote alternatives such as phytogenic feed additives and improved animal husbandry practices to minimize reliance on antibiotics and reduce residue release. Encourage composting, controlled application, and proper storage of manure to limit contaminant leaching and runoff into surrounding ecosystems. Enforce stricter regulations on antibiotic use and environmental discharge standards while promoting monitoring and surveillance systems for contaminants and resistance genes. Foster collaboration between environmental scientists, veterinarians, and public health professionals to address AMR from a holistic perspective. Declarations Acknowledgment: Not applicable Funding : The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Competing Interests: The authors declare no competing interests Author contributions: Abdulwaris Tijani: writing—review and editing, writ- ing—original draft, validation, resources, methodology, investigation, formal analysis, data curation, conceptualization. Gbenga Ayodele: writing—review and editing, writing—original draft, validation, con- ceptualization. Data Statement No new data were generated or analyzed in this study. All information presented in this review was obtained from previously published articles cited in the reference list. Ethical approval: Not applicable Consent to participate: Not applicable Consent for publication All authors agree with publishing. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9372898","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":631586517,"identity":"debf300b-28b9-4f85-a135-7c4bb06a9bda","order_by":0,"name":"Abdulwaris Tijani","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEklEQVRIiWNgGAWjYDACZoYEBgYDIHGAuQHIlWDgB4kmFODWwYPQwgjRIgmiEgzwaIHSMC1A7QfAJG4t9uwMDz8XFNjl8d1IbJP4ucfC3vj86sQPDwwY5PnFDuByWLL0DIPkYkmgFsmeZxKJ22683SwBdJjhzNkJOP0izWPAnLgBqOUGzwGJBLMbZzeAtCQY3MapJfk3j0E9WMvNPwck7I1nnN38g4CWNKAth8FabgNtYdzA37sNvy2HGdKseQyOF0ueedj+W+aAROKMG7zbLBIMJHD6hb3/TPJtnj/VeXzHkw8bvjlQZ8/ff3bzzR8VNvL80ti1AO1Bl5AAC0jgUA625wCaAD+6wCgYBaNgFIx0AAAqWGIPNpcaXQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0009-0005-8073-6679","institution":"Department of Animal Production and Health, Federal University of Technology Akure, Akure, Nigeria","correspondingAuthor":true,"prefix":"","firstName":"Abdulwaris","middleName":"","lastName":"Tijani","suffix":""},{"id":631586518,"identity":"324800d3-ea53-4927-994d-3e79f040e7b1","order_by":1,"name":"Gbenga Ayodele","email":"","orcid":"","institution":"Department of Animal Production and Health, Federal University of Technology Akure, Akure, Nigeria","correspondingAuthor":false,"prefix":"","firstName":"Gbenga","middleName":"","lastName":"Ayodele","suffix":""}],"badges":[],"createdAt":"2026-04-09 23:45:59","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9372898/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9372898/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108703593,"identity":"407f5290-4e58-4c65-9314-50c8a5ced4fd","added_by":"auto","created_at":"2026-05-07 12:58:37","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":479017,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSolid Phase Extractor\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9372898/v1/09f541b5dc1c258b6c10e42e.png"},{"id":108703592,"identity":"1a13020c-2092-4969-815f-a3fe4e6fc5f2","added_by":"auto","created_at":"2026-05-07 12:58:36","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":604183,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAtomic Absorption Spectrometer (AAS)\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-9372898/v1/0661bbd90f2061c12bd41d46.png"},{"id":108807567,"identity":"93c92a42-d6af-4fa9-aa00-b53a04c7e261","added_by":"auto","created_at":"2026-05-08 15:30:40","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1617499,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9372898/v1/0323e818-f3a4-4326-a7c6-2c14b8deeaa8.pdf"}],"financialInterests":"","formattedTitle":"\u003cp\u003eAntibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eLivestock production has expanded rapidly over the past few decades in response to the growing global demand for animal protein, resulting in more intensive farming practices and increased generation of animal waste and wastewater (Steinfeld et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; FAO, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These production systems, while essential for food security, are increasingly recognized as significant sources of environmental contamination due to the release of chemical residues and biologically active compounds into surrounding ecosystems (Tilman et al., \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Among the most concerning contaminants associated with animal agriculture are antibiotics and heavy metals, both of which are widely used in livestock production and frequently detected in farm-derived waste streams (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAntibiotics are commonly administered to food-producing animals for therapeutic and preventive purposes, and in some cases to promote growth, although such practices are now being restricted in many regions (Landers et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Luo et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2014\u003c/span\u003e ). A substantial fraction of these compounds is not fully metabolized by animals and is excreted in active or partially transformed forms through urine and feces, thereby entering manure and wastewater systems (Kemper, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Gao et al., \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Livestock wastewater often contains a mixture of antibiotic residues that can persist in the environment and retain their biological activity (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This persistence increases the likelihood of environmental exposure and contributes to the selective pressure on microbial communities (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHeavy metals such as copper, zinc, cadmium, lead, and arsenic are routinely introduced into animal production systems through feed additives, mineral supplements, and environmental inputs (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). These metals are not biodegradable and tend to accumulate in animal tissues and excreta, leading to their continuous release into manure and wastewater (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Qiao et al., \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Over time, repeated application of contaminated manure to agricultural land can result in the gradual buildup of heavy metals in soils and their eventual transfer to water bodies through runoff and leaching processes (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe simultaneous presence of antibiotics and heavy metals in farm animal wastewater has drawn increasing attention due to their potential interactions and combined environmental effects (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These contaminants do not exist in isolation; rather, they coexist in complex environmental matrices where they can influence each other\u0026rsquo;s behavior, including their mobility, persistence, and bioavailability (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). More importantly, their co-occurrence has been linked to the development and spread of antimicrobial resistance (AMR), a global health challenge that threatens the effectiveness of modern medicine (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHeavy metals play an important role in this context because they can exert selective pressure on microbial communities even in the absence of antibiotics, thereby promoting the maintenance of antibiotic resistance genes (ARGs) (Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006). This process, known as co-selection, occurs when resistance to different stressors is genetically linked, often through mobile genetic elements such as plasmids, integrons, and transposons (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). As a result, environments contaminated with heavy metals can act as reservoirs of antibiotic resistance, facilitating its persistence and spread even when antibiotic use is reduced (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFarm animal wastewater represents an important interface where antibiotics, heavy metals, and microorganisms converge, creating favorable conditions for the exchange of genetic material and the proliferation of resistant strains (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Through environmental pathways such as runoff, irrigation, and leaching, these contaminants can be transported from farms to surrounding soils, surface waters, and groundwater systems (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). This environmental dissemination not only affects ecosystem health but also increases the risk of human exposure through contaminated water, crops, and animal products (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe presence of antibiotic and heavy metal residues in the environment can disrupt microbial community structure and interfere with essential ecosystem processes such as nutrient cycling and organic matter decomposition (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In aquatic systems, these contaminants have been shown to exert toxic effects on a wide range of organisms, including algae, invertebrates, and fish, with potential consequences for biodiversity and ecosystem stability (Kim and Aga, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). The combined effects of antibiotics and heavy metals may be additive or synergistic, further complicating the assessment of their environmental risks (Yang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eSources and Pathways of Contaminants in Farm Animal Wastewater\u003c/h3\u003e\n\u003cp\u003eThe occurrence of antibiotics and heavy metals in farm animal wastewater is closely linked to the structure and management of modern livestock production systems, where multiple inputs and processes contribute to the introduction and dissemination of these contaminants (Steinfeld et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). In intensive animal farming, the routine use of veterinary pharmaceuticals, feed additives, and mineral supplements creates a continuous influx of chemical substances into the production cycle, many of which are ultimately released into the environment through waste streams (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAntibiotics represent one of the primary contaminant groups in livestock systems, largely due to their widespread application for disease treatment, prevention, and productivity enhancement (Landers et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). After administration, a significant proportion of these compounds is not fully metabolized by animals and is excreted via urine and feces in active or partially transformed forms (Kemper, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). This excreted fraction accumulates in manure, slurry, and farm wastewater, especially in intensive systems where large numbers of animals are confined in relatively small areas (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The persistence of these residues in waste matrices allows them to retain biological activity, thereby increasing their potential to interact with environmental microorganisms (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHeavy metals are introduced into livestock production systems through several pathways, most notably through feed supplementation (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Elements such as copper and zinc are commonly added to animal feed to promote growth and improve feed efficiency, while others such as cadmium, lead, and arsenic may be present as contaminants in feed ingredients, water sources, or the surrounding environment (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Unlike antibiotics, heavy metals are not subject to degradation and therefore persist in animal tissues and excreta, leading to their continuous release into manure and wastewater systems (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Over time, repeated input of these metals can result in their accumulation in soils and sediments, particularly in areas where manure is applied as fertilizer (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFarm animal wastewater is generated through a combination of biological and operational processes, including animal excretion, cleaning of housing facilities, feedlot runoff, and effluents from slaughterhouses and processing units (FAO, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In intensive production systems, large volumes of water are used for washing and waste management, which facilitates the transport of both dissolved and particulate contaminants into wastewater streams (Steinfeld et al., \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). These wastewater streams are often stored in lagoons, applied to agricultural land, or discharged into nearby water bodies, depending on farm management practices and regulatory frameworks (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOnce released into the environment, antibiotics and heavy metals are transported through multiple pathways that determine their distribution and impact (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Surface runoff during rainfall events can carry contaminants from manure-amended soils into rivers, lakes, and other surface water, while leaching processes enable their movement into groundwater systems (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). The use of contaminated wastewater for irrigation further contributes to the spread of these substances into agricultural soils and crops, thereby extending their reach into the food chain (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe behavior and transport of these contaminants in the environment are strongly influenced by physicochemical and biological factors such as pH, temperature, soil composition, and microbial activity (Thiele-Bruhn, 2003). Antibiotics may undergo degradation through microbial metabolism, hydrolysis, or photolysis, although some compounds exhibit considerable persistence depending on environmental conditions (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Heavy metals tend to bind to soil particles and organic matter, where they can remain for extended periods and may be remobilized under changing environmental conditions (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). These differences in behavior highlight the complexity of contaminant dynamics in agricultural environments.\u003c/p\u003e \u003cp\u003eIn many regions, particularly in developing countries, inadequate waste management practices and limited access to effective wastewater treatment systems exacerbate the release of these contaminants into the environment (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Untreated or poorly managed animal waste is often discharged directly into surrounding ecosystems, increasing the risk of contamination of water resources and agricultural land (FAO, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). This situation explained the importance of identifying critical control points within livestock production systems where interventions can reduce the entry and spread of antibiotics and heavy metals.\u003c/p\u003e \u003cp\u003eThe sources and pathways of antibiotics and heavy metals in farm animal wastewater are interconnected and influenced by both management practices and environmental conditions. A proper understanding of these processes provides the foundation for assessing environmental risks, designing effective mitigation strategies, and addressing the broader challenges associated with antimicrobial resistance and ecological contamination.\u003c/p\u003e \u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eOccurrence and Distribution of Antibiotic Residues\u003c/h2\u003e \u003cp\u003eAntibiotic residues have been widely detected in farm animal wastewater across different regions of the world, reflecting their extensive use in livestock production systems and their persistence in environmental matrices (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These residues originate primarily from the excretion of unmetabolized antibiotics and their active metabolites, which are subsequently released into manure, slurry, and wastewater during routine farm operations (Kemper, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Landers et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). The continuous input of these compounds into the environment has led to their widespread occurrence in both developed and developing countries, raising concerns about their ecological and public health implications (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSeveral classes of antibiotics are commonly reported in livestock wastewater, with tetracyclines, sulfonamides, fluoroquinolones, and macrolides being among the most frequently detected (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Tetracyclines are particularly prevalent due to their extensive use in poultry and swine production, as well as their strong affinity for binding to organic matter, which enhances their persistence in manure and wastewater systems (Chopra and Roberts, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Thiele-Bruhn, 2003). Sulfonamides and fluoroquinolones, are more mobile in the environment and are often detected in surface and groundwater systems due to their relatively higher solubility (Hamscher et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2002\u003c/span\u003e; Hirsch et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1999\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe concentration of antibiotic residues in farm animal wastewater varies widely depending on factors such as animal species, dosage, management practices, and environmental conditions (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Kemper, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Reported concentrations typically range from a few micrograms per liter to several hundred micrograms per liter in wastewater, and even higher levels in manure and slurry (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These variations are also influenced by the physicochemical properties of the antibiotics, including their solubility, stability, and adsorption potential (Thiele-Bruhn, 2003).\u003c/p\u003e \u003cp\u003eIn developing regions, including parts of Africa and Asia, the occurrence of antibiotic residues in farm wastewater is often exacerbated by inadequate regulation, lack of wastewater treatment infrastructure, and unregulated use of veterinary drugs (Landers et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In such settings, untreated or poorly managed animal waste is frequently discharged into the environment, increasing the likelihood of contamination of surrounding soils and water bodies (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This highlights the importance of understanding regional patterns of contamination in order to develop targeted mitigation strategies.\u003c/p\u003e \u003cp\u003eSeveral studies have documented the occurrence of antibiotic residues in farm animal wastewater across different countries and production systems, as summarized in (Table I). These findings demonstrate not only the global nature of the problem but also the variability in contamination levels depending on local practices and environmental conditions.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTable I\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAntibiotic Residues in Farm Animal Wastewater Across Region\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCountry/Region\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFarm Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAntibiotic Class\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eConcentration Range\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSample Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChina\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSwine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTetracyclines\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50\u0026ndash;500 \u0026micro;g/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWastewater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUSA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCattle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSulfonamides\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u0026ndash;200 \u0026micro;g/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLagoon water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCampagnolo \u003cem\u003eet al.\u003c/em\u003e, 2002\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGermany\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePig\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFluoroquinolones\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;100 \u0026micro;g/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSlurry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHamscher et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2002\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNigeria\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePoultry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTetracyclines\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20\u0026ndash;150 \u0026micro;g/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWastewater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAdesokan \u003cem\u003eet al.\u003c/em\u003e, 2015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMixed livestock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMacrolides\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15\u0026ndash;250 \u0026micro;g/L\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFarm effluent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eKumar \u003cem\u003eet al.\u003c/em\u003e, 2014\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eOccurrence and Distribution of Heavy Metals\u003c/h3\u003e\n\u003cp\u003eHeavy metals are among the most persistent contaminants in farm animal wastewater due to their widespread use in livestock production and resistance to environmental degradation (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Common metals detected include copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), mercury (Hg), and arsenic (As), which primarily enter wastewater through feed additives, mineral supplements, and environmental contamination of water and soil (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Copper and zinc are frequently added to poultry and swine feeds to enhance growth and feed efficiency, contributing to elevated concentrations in manure and wastewater (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Trace metals such as cadmium and lead may also accumulate due to contaminated feed, water, or soil, even when not intentionally introduced (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe concentration of heavy metals in farm wastewater varies depending on animal species, feeding practices, farm management systems, and regional environmental conditions (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Intensive livestock operations often show higher Cu and Zn levels, whereas Cd and Pb concentrations are more influenced by local environmental exposure (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Unlike antibiotics, metals do not degrade and therefore persist in wastewater, manure, and sludge, with the potential to accumulate in soils over repeated manure applications (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Their mobility and bioavailability are further influenced by factors such as pH, organic matter content, and redox conditions, which can either immobilize or remobilize metals into more bioavailable forms (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSpatial and temporal studies show that heavy metal concentrations differ between countries and farm types, reflecting variations in livestock production intensity and waste management practices (Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Intensive poultry farms in Asia and Europe often report higher Cu and Zn concentrations compared to cattle farms in North America (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Repeated application of manure can further lead to accumulation of metals in soils, which may eventually leach into surface and groundwater systems (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). This persistence increases the risk of long-term environmental contamination and potential entry into the food chain (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe persistence of heavy metals in wastewater and manure, combined with their potential for accumulation in soil and aquatic systems, underscores the importance of monitoring and management (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Their co-occurrence with antibiotics further complicates environmental dynamics, as both contaminants can exert selective pressure on microbial communities and contribute to antimicrobial resistance (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The regional patterns of heavy metal contamination, as shown in Table II, is important for designing effective mitigation strategies and assessing ecological risk (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cb\u003eTable II\u003c/b\u003e \u003c/p\u003e \u003cp\u003eHeavy Metal Residues in Farm Animal Wastewater Across Regions\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCountry/Region\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFarm Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHeavy Metal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eConcentration Range (mg/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSample Type\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChina\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSwine\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10\u0026ndash;250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWastewater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eZhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUSA\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCattle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eZn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u0026ndash;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLagoon water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCampagnolo \u003cem\u003eet al.\u003c/em\u003e, 2002 |\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGermany\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePig\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.01\u0026ndash;5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSlurry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eHamscher et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2002\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNigeria\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePoultry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCu\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8\u0026ndash;200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWastewater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eAdesokan \u003cem\u003eet al.\u003c/em\u003e, 2015\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIndia\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMixed livestock\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCd\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.02\u0026ndash;3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eFarm effluent\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eKumar \u003cem\u003eet al.\u003c/em\u003e, 2014\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eInteraction Between Antibiotics and Heavy Metals\u003c/h3\u003e\n\u003cp\u003eIn farm environments, antibiotics and heavy metals frequently co-occur due to their simultaneous use in livestock production systems (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Chen et al., \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Wastewater, manure, and slurry from intensive farms often contain residues of both contaminants, reflecting routine veterinary practices and the inclusion of metal-based feed additives (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). The co-occurrence of these substances in wastewater creates complex environmental matrices where both antibiotics and metals interact with each other and with microbial communities, influencing their ecological fate (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eChemical interactions between antibiotics and heavy metals can significantly affect their behavior in the environment (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Song et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Metals can bind to antibiotic molecules through complexation or adsorption to particulates, altering their solubility and bioavailability (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Such interactions may stabilize certain antibiotics in wastewater, reducing their biodegradation and increasing their persistence, or conversely, may lead to precipitation and reduced mobility depending on pH, ionic strength, and the presence of organic matter (Thiele-Bruhn, 2003; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). These chemical associations also influence the transport of contaminants, potentially facilitating their accumulation in soils, sediments, and aquatic systems (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe co-occurrence and chemical interactions of antibiotics and heavy metals directly impact their mobility, persistence, and bioavailability (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Song et al., \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Antibiotics complexed with metals may remain biologically active for longer periods, enhancing their potential to exert selective pressure on microbial communities (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Metals bound to organic particles can also affect the adsorption and desorption of antibiotics, influencing their environmental distribution and availability to microorganisms (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). As a result, wastewater environments act as hotspots for co-selection of resistance genes, since microbes are simultaneously exposed to multiple stressors over extended periods (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006).\u003c/p\u003e \u003cp\u003eThe interaction between antibiotics and heavy metals in farm environments amplifies their environmental risks. These interactions influence not only the persistence and transport of contaminants but also their ecological impact and the potential for antimicrobial resistance to develop and spread (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Understanding these dynamics is essential for effective monitoring and management of farm wastewater, and it provides the foundation for exploring mechanisms of co-selection and resistance in subsequent sections.\u003c/p\u003e\n\u003ch3\u003eCo-selection Mechanisms and Antimicrobial Resistance\u003c/h3\u003e\n\u003cp\u003eCo-selection is a major mechanism driving antimicrobial resistance in environmental systems (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Berendonk et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Farm animal wastewater frequently contains a complex mixture of antibiotics and heavy metals, which together create conditions that favor the persistence and spread of antimicrobial resistance genes (ARGs) (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Co-selection occurs when exposure to one stressor, such as heavy metals, promotes the maintenance of resistance to another, such as antibiotics, due to genetic or environmental linkage (Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e) (Table III). This phenomenon is particularly relevant in livestock wastewater, where both types of contaminants coexist at concentrations sufficient to exert selective pressure on microbial communities (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMechanisms of co-selection include cross-resistance, where a single resistance determinant such as an efflux pump confers protection against both metals and antibiotics, allowing microorganisms to survive in environments contaminated with either stressor (Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Smalla et al., \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Co-resistance is another mechanism, in which separate resistance genes are physically linked on mobile genetic elements like plasmids, integrons, or transposons. Selection pressure on one gene, for instance from heavy metals, indirectly maintains resistance to antibiotics encoded on the same element (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). These mobile elements are abundant in farm wastewater, facilitating horizontal gene transfer (HGT) and the spread of resistance among diverse microbial populations (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHeavy metals such as copper, zinc, cadmium, and lead are important in promoting ARGs (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zhu et al., \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Even at low environmental concentrations, these metals select for microbial strains carrying resistance genes, many of which are co-located with metal-resistance determinants (Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This process ensures the persistence of ARGs in soils, water, and sediments impacted by farm wastewater, creating environmental reservoirs that can reintroduce resistance into agricultural or clinical systems (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHorizontal gene transfer is an important pathway for ARG dissemination in these environments. Wastewater provides ideal conditions for HGT due to high microbial density, presence of selective agents, and the prevalence of mobile genetic elements (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Through HGT, resistance traits can spread not only among environmental bacteria but also to potentially pathogenic species, increasing risks for animal and human health (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Knowing co-selection and HGT in wastewater environments is therefore essential for designing strategies to mitigate the environmental and public health impacts of antibiotics and heavy metals (Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cb\u003eTable III\u003c/b\u003e \u003c/p\u003e \u003cp\u003eCo-selection Mechanisms and Antimicrobial Resistance in Farm Wastewater\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabc\" border=\"1\"\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eMechanism\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDescription\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExample\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRole in ARG Persistence\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCross-resistance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSingle resistance determinant protects against multiple stressors\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEfflux pumps in \u003cem\u003eE. coli\u003c/em\u003e extruding tetracycline and copper ions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eAllows bacteria to survive in environments with both metals and antibiotics, maintaining ARGs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBaker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCo-resistance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSeparate resistance genes are physically linked on mobile genetic elements (plasmids, integrons, transposons)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePlasmid carrying zinc resistance gene along with sulfonamide resistance gene\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMetal selection indirectly preserves antibiotic resistance\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHeuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSelection by heavy metals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMetals exert selective pressure on bacteria carrying both metal and antibiotic-resistance genes\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCopper, zinc, cadmium in poultry wastewater selecting for tetracycline-resistant strains\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMaintains ARGs even without direct antibiotic exposure\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBaker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHorizontal gene transfer (HGT)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMovement of genetic material between bacteria via plasmids or integrons\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTransfer of ARGs from environmental \u003cem\u003eEnterococcus\u003c/em\u003e to pathogens\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eEnables ARG spread across microbial communities and ecosystems\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eHeuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChemical interactions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAntibiotics and metals form complexes or bind to particulates\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCopper-tetracycline complex in wastewater\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStabilizes contaminants, prolongs selective pressure, enhances ARG persistence\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eK\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e\n\u003ch3\u003eEnvironmental Fate and Transport\u003c/h3\u003e\n\u003cp\u003eThe environmental fate and transport of antibiotics and heavy metals in farm animal wastewater are governed by a range of physicochemical and biological processes that determine their distribution, transformation, and long-term impact on ecosystems (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Once released into the environment through manure application, wastewater discharge, or runoff, these contaminants undergo various degradation and transport processes that influence their persistence and mobility (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Understanding these processes is essential for evaluating the environmental risks associated with livestock production systems and waste management practices (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAntibiotics may undergo both biotic and abiotic degradation in environmental matrices, including microbial degradation, hydrolysis, and photodegradation, depending on factors such as temperature, pH, and sunlight exposure (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Thiele-Bruhn, 2003; Halling-S\u0026oslash;rensen \u003cem\u003eet al.\u003c/em\u003e, 1998). Microbial activity plays a particularly important role in transforming antibiotic compounds into less active forms, although some compounds exhibit resistance to degradation and persist for extended periods (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Jechalke et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Heavy metals are non-biodegradable and cannot be broken down through biological or chemical processes, leading to their persistence once introduced into soils and aquatic systems (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAdsorption and desorption processes also influence the environmental behavior of these contaminants by regulating their mobility and bioavailability in soil and sediment systems (Thiele-Bruhn, 2003; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Antibiotics, particularly tetracyclines, tend to bind strongly to soil particles and organic matter, which may reduce their immediate mobility but increase their persistence in the environment (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Also, heavy metals can form stable associations with clay minerals and organic matter, leading to their accumulation in soils and sediments over time (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). However, changes in environmental conditions such as pH, redox potential, and ionic strength can trigger desorption, releasing these contaminants back into the soil solution and increasing their availability for transport and biological uptake (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eLeaching and surface runoff represent major pathways through which antibiotics and heavy metals are transported from agricultural lands into surrounding aquatic systems (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). During rainfall, contaminants present in manure-amended soils can be mobilized and carried into rivers, lakes, and drainage networks, contributing to the contamination of surface waters (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Leaching processes also enable soluble compounds, including certain antibiotics and metal ions, to migrate through soil profiles and reach groundwater systems (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). The use of contaminated wastewater for irrigation can further facilitate the spread of these pollutants across agricultural landscapes, increasing their environmental footprint (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe persistence and long-term accumulation of antibiotics and heavy metals pose significant ecological concerns, particularly in regions with continuous livestock production and repeated manure application (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). While some antibiotics degrade over time, continuous inputs can maintain their presence at biologically active concentrations in soils and water bodies (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Heavy metals, due to their non-degradable nature, accumulate progressively in soils, sediments, and biota, leading to chronic exposure of organisms and potential bioaccumulation in food chains (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Over time, these persistent contaminants can act as long-term sources of environmental stress, contributing to ecosystem degradation and supporting the maintenance of antimicrobial resistance in environmental microbial communities (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eEcotoxicological Implications\u003c/h2\u003e \u003cp\u003eThe presence of antibiotics and heavy metals in farm animal wastewater shows significant ecotoxicological risks to both terrestrial and aquatic ecosystems by disrupting biological processes and altering species composition (Kim and Aga, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In soil environments these contaminants can adversely affect microorganisms that help in nutrient cycling, organic matter decomposition, and soil fertility (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Thiele-Bruhn, 2003; Giller et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Antibiotics, even at low concentrations, can inhibit sensitive microbial populations while promoting resistant strains, thereby reducing microbial diversity and altering community structure (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Danner et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Heavy metals also exacerbate these effects by inducing toxicity through oxidative stress, enzyme inhibition, and disruption of cellular processes in soil microbes (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAquatic organisms are also highly vulnerable to contamination from antibiotics and heavy metals transported via runoff and wastewater discharge (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Exposure to antibiotic residues has been associated with growth inhibition, reproductive impairment, and behavioral changes in fish, algae, and invertebrates (Kim and Aga, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Heavy metals such as cadmium, mercury, and lead can accumulate in aquatic organisms, leading to physiological stress, impaired development, and increased mortality rates (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Li et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These toxic effects can disrupt aquatic food webs and reduce biodiversity, particularly in ecosystems receiving continuous pollutant inputs (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eOne of the major concerns associated with these contaminants is their ability to bioaccumulate and biomagnify within food chains, posing risks to higher trophic levels, including humans (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Heavy metals, due to their persistence, are especially prone to accumulation in the tissues of organisms, where they can reach toxic concentrations over time (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Although antibiotics are generally less prone to biomagnification, their continuous input into the environment can lead to sustained exposure and accumulation in certain organisms (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). This accumulation increases the likelihood of chronic toxicity and long-term ecological impacts (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eToxicity associated with antibiotics and heavy metals can manifest through both acute and chronic effects, depending on exposure concentration and duration (Kim and Aga, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2007\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Acute toxicity typically results in immediate effects such as mortality or severe physiological disruption, while chronic exposure may lead to sub-lethal effects including reduced growth, reproductive failure, and genetic damage (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). These sub-lethal effects are particularly concerning because they can accumulate over time and impact population dynamics and ecosystem stability (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe combined presence of antibiotics and heavy metals in the environment can result in additive or synergistic toxic effects, further complicating ecological risk assessments (Yang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Interactions between these contaminants may enhance their bioavailability and toxicity, for example through metal-antibiotic complex formation or increased oxidative stress in exposed organisms (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Such combined exposures better reflect real-world conditions in agricultural environments, where multiple contaminants coexist and interact (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). These interactions not only intensify ecological damage but also contribute to the persistence and spread of antimicrobial resistance within environmental microbial communities (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eImplications on Public Health\u003c/h3\u003e\n\u003cp\u003eThe presence of antibiotics and heavy metals in farm animal wastewater poses serious public health concerns, primarily due to their role in the emergence and spread of antimicrobial resistance (AMR) and their potential for human exposure through multiple environmental pathways (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Laxminarayan et al., \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). One of the major routes of concern is the transmission of antibiotic resistance through the food chain, where resistant bacteria originating from livestock environments can be transferred to humans via contaminated meat, milk, vegetables, and other agricultural products (Marshall and Levy, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2011\u003c/span\u003ea; Levy and Marshall, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2004\u003c/span\u003eb; Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The application of manure and wastewater to farmlands facilitates the introduction of antibiotic residues, heavy metals, and resistance genes into soil systems, from where they can be taken up by crops or persist in food-producing environments (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). This continuous cycling of contaminants between animals, the environment, and humans increases the likelihood of resistance dissemination across different ecological compartments (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eContamination of drinking water sources is another critical pathway through which these pollutants pose risks to human health (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Antibiotics and heavy metals can enter surface water and groundwater systems through leaching, runoff, and direct discharge of untreated or poorly treated farm wastewater (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). In many regions, especially where wastewater treatment infrastructure is limited, these contaminants may persist in water supplies used for domestic purposes, including drinking, cooking, and sanitation (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Conventional water treatment systems are not always fully effective in removing antibiotic residues or resistance genes, thereby increasing the risk of chronic low-level exposure in human populations (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHuman exposure to antibiotics and heavy metals from farm wastewater occurs through several interconnected routes, including ingestion of contaminated food and water, dermal contact with polluted soils or water, and inhalation of dust or aerosols containing contaminants (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Occupational exposure is particularly relevant for farmers, farm workers, and individuals living near livestock production facilities, who may come into direct contact with contaminated materials on a regular basis (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These exposure pathways not only increase the risk of direct toxic effects but also contribute to the transfer of resistant microorganisms to humans, thereby complicating the treatment of infectious diseases (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe global health burden associated with antimicrobial resistance continues to rise, with environmental reservoirs such as farm wastewater playing a significant role in its persistence and spread (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). The presence of both antibiotics and heavy metals in the environment enhances selective pressure on microbial communities, promoting the maintenance and dissemination of resistance genes even in the absence of direct antibiotic use (Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Baker-Austin \u003cem\u003eet al.\u003c/em\u003e, 2006). This situation shows major challenge to public health systems, as infections caused by resistant pathogens are more difficult and costly to treat, often resulting in increased morbidity, mortality, and healthcare expenditure (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Addressing these risks requires integrated strategies that consider environmental, agricultural, and public health perspectives to reduce contaminant release and limit the spread of resistance across human and ecological systems (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e"},{"header":"Methods for Detection and Analysis","content":"\u003cp\u003eAccurate detection and analysis of antibiotics, heavy metals, and antimicrobial resistance genes (ARGs) in farm animal wastewater are important for assessing environmental contamination and associated risks (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). The reliability of analytical results begins with appropriate sampling strategies, which must account for spatial and temporal variability in wastewater, manure, and sludge systems (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Samples are typically collected from multiple points, including animal housing effluents, storage lagoons, and discharge outlets, to ensure representative characterization of contaminant distribution (Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Proper sample preservation, including cooling, acidification, or filtration, is critical to prevent degradation or transformation of analytes prior to laboratory analysis (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe analysis of antibiotic residues in environmental samples commonly relies on advanced chromatographic techniques such as high-performance liquid chromatography (HPLC) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) due to their high sensitivity and specificity (Hirsch et al., \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e1999\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Hamscher et al., \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2002\u003c/span\u003e). These methods enable the detection of trace concentrations of antibiotics in complex matrices such as wastewater and sludge, even at microgram or nanogram levels (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e). Sample preparation techniques, including solid-phase extraction (SPE) (Fig. I), are often employed to concentrate and purify analytes prior to analysis, improving detection accuracy and reproducibility (Thiele-Bruhn, 2003; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). The use of LC-MS/MS has become particularly important in environmental monitoring due to its ability to simultaneously quantify multiple antibiotic compounds with high precision (Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eDetection of heavy metals in farm wastewater is typically carried out using techniques such as atomic absorption spectroscopy (AAS) (Fig. II) and inductively coupled plasma mass spectrometry (ICP-MS), which offer high sensitivity and accuracy for metal quantification (Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). AAS is widely used for routine analysis due to its cost-effectiveness and reliability, while ICP-MS provides multi-element detection with lower detection limits, making it suitable for trace-level analysis (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Prior to analysis, samples often undergo digestion using strong acids to convert metals into measurable forms, ensuring accurate quantification (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). These analytical techniques are essential for monitoring the accumulation and distribution of heavy metals in environmental samples (Tchounwou et al., \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2012\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eMolecular techniques helps in detecting and quantifying antimicrobial resistance genes in wastewater environments (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Pruden et al., \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Polymerase chain reaction (PCR) and quantitative PCR (qPCR) are commonly used to identify and quantify specific ARGs, providing insights into their abundance and distribution (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). More advanced approaches such as metagenomic sequencing allow for comprehensive analysis of microbial communities and the full spectrum of resistance genes present in environmental samples (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These molecular tools are essential for understanding the dynamics of resistance dissemination and the impact of environmental contaminants on microbial ecosystems (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe integration of robust sampling strategies with advanced analytical and molecular techniques provides a comprehensive framework for assessing the occurrence, fate, and impact of antibiotics, heavy metals, and ARGs in farm animal wastewater (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Such approaches are critical for generating reliable data that can inform environmental monitoring, risk assessment, and the development of effective mitigation strategies (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eMitigation and Remediation Strategies\u003c/h2\u003e \u003cp\u003eAddressing the environmental and public health risks associated with antibiotics and heavy metals in farm animal wastewater requires integrated mitigation and remediation strategies that combine technological, biological, and policy-based approaches (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Wastewater treatment technologies play a central role in reducing contaminant loads before environmental discharge, with biological, chemical, and physical methods widely applied depending on the nature of the pollutants (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Daghrir and Drogui, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Biological treatments, such as activated sludge systems and anaerobic digestion, utilize microbial processes to degrade organic contaminants, including certain antibiotics, although their efficiency may vary depending on compound structure and operational conditions (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Chemical treatments, including advanced oxidation processes, can effectively degrade persistent antibiotic residues, while physical methods such as filtration, sedimentation, and adsorption using activated carbon help remove both antibiotics and heavy metals from wastewater (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePhytoremediation has emerged as a sustainable and cost-effective approach for mitigating contamination in agricultural environments, particularly in developing regions where advanced treatment systems may be limited (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Ali et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Carvalho et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). This approach involves the use of plants to uptake, stabilize, or transform contaminants, with certain species capable of accumulating heavy metals from soils and wastewater (Ali et al., \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Alloway, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). In addition to metal removal, some plants can enhance microbial activity in the rhizosphere, thereby promoting the degradation of antibiotic residues (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Phytoremediation strategies are particularly relevant for treating runoff and contaminated soils associated with livestock production systems (Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Kuppusamy et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe use of phytogenic feed additives represents another promising strategy for reducing antibiotic use in livestock production, thereby minimizing the release of antibiotic residues into the environment (Windisch et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Greathead, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). These plant-derived compounds, including essential oils and herbal extracts, can improve animal health and productivity while serving as alternatives to conventional antibiotics (Windisch et al., \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2008\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). By reducing reliance on antibiotics, phytogenic additives help lower the selective pressure for antimicrobial resistance and decrease the concentration of antibiotic residues in manure and wastewater (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). This approach aligns with global efforts to promote sustainable livestock production and reduce environmental contamination.\u003c/p\u003e \u003cp\u003eEffective manure management practices are also essential for mitigating the release of antibiotics and heavy metals into the environment (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Nicholson et al., \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Techniques such as composting, controlled storage, and proper timing of manure application can significantly reduce contaminant levels and limit their transport to soil and water systems (Boxall et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2004\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Composting, for example, can enhance microbial degradation of antibiotics and stabilize heavy metals, reducing their bioavailability (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). Implementing buffer zones and controlled irrigation practices can minimize runoff and leaching of contaminants into surrounding ecosystems (Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e).\u003c/p\u003e \u003cp\u003ePolicy and regulatory frameworks also helps in controlling the use of antibiotics and managing environmental contamination from livestock production (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Regulations that restrict the non-therapeutic use of antibiotics, monitor residue levels in animal products, and enforce wastewater treatment standards are essential for reducing environmental and public health risks (Marshall and Levy, \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). International and national initiatives aimed at combating antimicrobial resistance emphasize the need for a One Health approach that integrates human, animal, and environmental health considerations (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eResearch Gap and Future Perspectives\u003c/h2\u003e \u003cp\u003eDespite the growing body of research on antibiotics and heavy metals in farm animal wastewater, several limitations remain that constrain a comprehensive understanding of their environmental and public health impacts (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Many existing studies are limited by short-term experimental designs, small sample sizes, and a focus on single contaminants rather than complex mixtures, which reduces their applicability to real-world conditions (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Sarmah et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2006\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Kraemer et al., \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Furthermore, there is often a lack of standardized methodologies for sampling, analysis, and reporting, making it difficult to compare results across studies and regions (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). These gaps explain the need for more robust, long-term, and large-scale investigations that reflect the variability and complexity of livestock production systems (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eA major research need lies in the development of integrated risk assessment frameworks that consider the combined effects of antibiotics, heavy metals, and antimicrobial resistance genes (ARGs) across environmental compartments (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Current risk assessments often evaluate contaminants in isolation, neglecting the synergistic or antagonistic interactions that may significantly influence ecological and human health outcomes (Yang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). There is also a need to incorporate both chemical and microbiological indicators, including ARG abundance and horizontal gene transfer potential, into risk assessment models (Heuer et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Such integrated approaches would provide a more realistic evaluation of environmental risks and support evidence-based decision-making (Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eEmerging contaminants and multi-pollutant interactions represent another critical area requiring further investigation (Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Gothwal and Shashidhar, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Yang et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In addition to conventional antibiotics and heavy metals, livestock wastewater may contain other pollutants such as microplastics, disinfectants, hormones, and nanoparticles, which can interact with existing contaminants and influence their fate and toxicity (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). These interactions can alter contaminant behavior, enhance toxicity, and further promote antimicrobial resistance, yet they remain poorly understood due to limited research in this area (Pal et al., \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Seiler and Berendonk, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Addressing these knowledge gaps requires multidisciplinary studies that integrate environmental chemistry, microbiology, and toxicology (Mart\u0026iacute;nez, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eFuture research should focus on developing sustainable and cost-effective mitigation strategies that are adaptable to different agricultural contexts, particularly in low- and middle-income countries where wastewater management infrastructure may be limited (Van Boeckel et al., \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Wuana and Okieimen, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). There is also a need for innovation in analytical techniques to improve detection sensitivity, especially for trace-level contaminants and emerging resistance genes (K\u0026uuml;mmerer, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Zhang et al., \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Furthermore, studies should explore the long-term ecological and health impacts of chronic exposure to low concentrations of contaminants, as these conditions better reflect real environmental scenarios (Cycoń et al., \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Grenni et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Strengthening interdisciplinary collaboration and aligning research efforts with policy development will be essential for effectively addressing the challenges associated with antibiotics and heavy metals in farm animal wastewater (O\u0026rsquo;Neill, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Rizzo et al., \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2013\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThe widespread occurrence of antibiotics and heavy metals in farm animal wastewater represents a significant environmental and public health challenge due to their persistence, mobility, and capacity to promote antimicrobial resistance (AMR). Their continuous release from livestock production systems leads to contamination of soil and aquatic environments, where they interact, accumulate, and exert toxic effects on microorganisms, plants, and aquatic organisms. These contaminants not only disrupt ecological processes but also contribute to the co-selection and dissemination of antibiotic resistance genes (ARGs), increasing the risk of resistant infections in humans and animals. The complexity of their environmental fate, coupled with multiple exposure pathways such as food chains and water systems, highlights the urgent need for integrated and sustainable management strategies.\u003c/p\u003e \u003cp\u003e \u003cb\u003eRecommendations\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eImplement integrated biological, chemical, and physical treatment systems to enhance removal efficiency of both antibiotics and heavy metals before environmental discharge.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePromote alternatives such as phytogenic feed additives and improved animal husbandry practices to minimize reliance on antibiotics and reduce residue release.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eEncourage composting, controlled application, and proper storage of manure to limit contaminant leaching and runoff into surrounding ecosystems.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eEnforce stricter regulations on antibiotic use and environmental discharge standards while promoting monitoring and surveillance systems for contaminants and resistance genes.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFoster collaboration between environmental scientists, veterinarians, and public health professionals to address AMR from a holistic perspective.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment:\u0026nbsp;\u003c/strong\u003eNot applicable\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e: \u003cem\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests:\u003c/strong\u003e The authors declare no competing interests\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u0026nbsp;\u003c/strong\u003eAbdulwaris Tijani: writing\u0026mdash;review and editing, writ- ing\u0026mdash;original draft, validation, resources, methodology, investigation, formal analysis, data curation, conceptualization. Gbenga Ayodele: writing\u0026mdash;review and editing, writing\u0026mdash;original draft, validation, con- ceptualization.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNo new data were generated or analyzed in this study. All information presented in this review was obtained from previously published articles cited in the reference list.\u003c/p\u003e\n\u003cp\u003eEthical approval: Not applicable\u003c/p\u003e\n\u003cp\u003eConsent to participate: Not applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication All authors agree with publishing.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eClinical trial number: Not applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAli H, Khan E, Sajad MA (2013) Phytoremediation of heavy metals\u0026mdash;Concepts and applications. 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PNAS 110:3435\u0026ndash;3440. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1073/pnas.1222743110\u003c/span\u003e\u003cspan address=\"10.1073/pnas.1222743110\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Antibiotics, Heavy metals, Farm animal wastewater, Antimicrobial resistance, Co-selection, Environmental contamination, Ecotoxicology","lastPublishedDoi":"10.21203/rs.3.rs-9372898/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9372898/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe increasing use of antibiotics and heavy metals in livestock production has resulted in their widespread presence in farm animal wastewater, posing serious environmental and public health risks. This review examines the sources, occurrence, and environmental behavior of these contaminants, with emphasis on their interactions and contribution to antimicrobial resistance (AMR). These pollutants enter the environment through manure application, wastewater discharge, and agricultural runoff, where they undergo processes such as degradation, adsorption, and transport in soil and aquatic systems. Their co-occurrence enhances persistence and bioavailability, promoting co-selection mechanisms including cross-resistance, co-resistance, and horizontal gene transfer of antimicrobial resistance genes (ARGs). Consequently, ecosystems become contaminated, affecting soil microbial communities, aquatic organisms, and biodiversity. Human exposure through food chains, water, and environmental contact further increases AMR risks. The review also highlights analytical methods for detection and discusses mitigation strategies such as wastewater treatment, phytoremediation, and sustainable livestock practices. Despite these advances, gaps remain in understanding multi-pollutant interactions and integrated risk assessment. Addressing these challenges requires a multidisciplinary \u0026ldquo;\u003cem\u003eOne Health\u003c/em\u003e\u0026rdquo; approach to protect environmental and human health.\u003c/p\u003e","manuscriptTitle":"Antibiotics and Heavy Metals Residues in Farm Animal Wastewater: Environmental Contamination, Co-selection Mechanisms, and Ecotoxicological Risks","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-05-07 12:58:29","doi":"10.21203/rs.3.rs-9372898/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewersInvited","content":"","date":"2026-04-29T08:07:29+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2026-04-28T14:14:06+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-16T05:33:44+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2026-04-14T02:55:52+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8f59a1b6-f067-480b-a1bc-e27d30a470f6","owner":[],"postedDate":"May 7th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewersInvited","content":"","date":"2026-04-29T08:07:29+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-05-07T12:58:30+00:00","versionOfRecord":[],"versionCreatedAt":"2026-05-07 12:58:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9372898","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9372898","identity":"rs-9372898","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}