Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges

Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges | 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 Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges Lukas Plaß, Felix Heid, Ute Windisch This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3832560/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract The entry of heavy metals into rivers affects both the water quality and the biocoenosis of the water bodies. Heavy metals that are discharged with wastewater are distributed with the current and can be stored downstream in the sediment of the watercourse and absorbed by aquatic organisms. The aim of the study is to examine how heavy metals entering water bodies are found in samples of water, sediment, and freshwater amphipods (Gammarus spp.). Several smaller rivers in Hesse and Bavaria are being investigated, establishing a connection to existing wastewater discharge points. For the examined rivers, it is determined that the concentration of heavy metals in sediment is about 10,000 times higher than in a scoop sample of water from the same section of the water body. In the species Gammarus fossarum , G. pulex and G. roeselii , heavy metal concentrations are about 1,000 times higher than those found in the investigated river water. A comparison of heavy metal contents in gammarids and in sediment shows no linear relationship. Gammarids inhabit the bottom of water bodies and the bank area, accumulating heavy metals with their food throughout their lifetime. Due to their high abundance, they serve as accumulation indicators in most smaller rivers. However, the sampling process is labor-intensive, requiring sufficient sample weight and the removal of other macrozoobenthos species. Sampling sediment in water bodies with gravel or fine sediment requires less effort. Water samples can be obtained quickly from any water body. The investigations of the Kössein and Röslau rivers in Bavaria, known for their mercury contamination, show a decrease in heavy metal concentrations over a period of about ten years. Due to the low flow velocity at the Wölsauerhammer weir, elevated levels can still be observed in the settled sediment. Dredging the riverbed and securing the banks of previously heavily contaminated sections lead to an overall decrease in concentrations throughout the river system. Sediment analyses from several sampling sites along the Wieseck river near Trohe, where untreated sewage was discharged for a week, indicate that an increase in heavy metal contamination due to the event can still be detected about a year later. The example of Rosbach in the Taunus region illustrates the suitability of combining different types of samples. Water analysis shows an increase in heavy metal concentrations (including zinc) downstream of a wastewater treatment plant's discharge point, which can be found in the sediment further along the watercourse. The examination of water samples is mainly suitable for short-term monitoring of known contamination events. Conversely, environmental media such as sediment and Gammarus spp. can be used to assess past wastewater discharges. The increase in heavy metal contamination in water bodies due to wastewater discharges is confirmed for both sediment and gammarids. heavy metals copper mercury zinc anthropogenic discharges untreated sewage small streams sediment water Gammarus pulex Gammarus fossarum Gammarus roeselii bioindicator accumulation benthic invertebrates Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Background Watercourses are essential components of the Earth's ecosystem. They serve as habitats for plants and animals within and around these water bodies. For humans, water bodies are used for irrigation in agriculture, for cooling industrial processes, for drinking water production and as recreational areas. However, human interventions also pose a threat to the natural balance of these water bodies. The input of various pollutants endangers both the water quality and the living conditions of aquatic flora and fauna. The impacts of pollutant contamination are evident in local examples in Germany, such as the mercury legacy of the Chemical Factory in Marktredwitz (1788–1985) (Nováková et al. 2022 ), wastewater discharge into the Wieseck River in 2020 (Bothe 2020 ) or fish mortality in the Oder River in 2022 (Free et al. 2023 ). The pollutant contamination in rivers and watercourses can originate from natural sources (such as geogenic background pollution in soils) or anthropogenic sources (including atmospheric deposition and wastewater discharges). The influence of diffuse pollutant inputs is difficult to assess and limit. In the case of point sources, the improved purification performance of multi-stage wastewater treatment plants, as well as legislative measures such as the implementation of regulations for indirect dischargers, result in a reduced input of pollutants (Fuchs et al. 2002 ). However, wastewater also contains substances such as heavy metals that cannot be completely removed in wastewater treatment plants. These substances either remain in the sewage sludge or enter receiving waters with the treated wastewater. Aquatic microorganisms are already harmed by traces of lead, cadmium, or copper (Hillenbrand et al. 2005 ). Moreover, heavy metals accumulate in aquatic organisms and can enter the human body through the food chain. This study focuses on the heavy metals lead, cadmium, chromium, copper, nickel, mercury, and zinc, as these are typically found in municipal wastewater. Various target values exist for these metals to protect surface inland waters, for instance, set by the German Working Group of the Federal States on water issues (LAWA) (LAWA 1998a). The Water Framework Directive 2000/60/EC (WFD) mandates the protection and improvement of aquatic ecosystems, aiming for a good ecological and chemical status for all surface water bodies by 2027 (EEA 2000). This requires suitable measures and management practices, monitored through assessment procedures. In Germany, surface waters are monitored and assessed according to the Surface Water Ordinance (OGewV). Environmental quality standards (EQS) for priority and river basin-relevant pollutants are listed in Annexes 6 and 8 of the OGewV (OGewV 2016 ). If the LAWA targets are achieved, significant adverse effects on the aquatic ecosystem can be largely ruled out (LAWA 1998b). The influence of anthropogenic discharges on the heavy metal contents in sediment, water and gammarid samples will be compared. The latter are proposed as alternative monitoring organisms to fish in fish-poor or fish-free smaller watercourses. For this purpose, the species Gammarus fossarum (Fig. 1 ), G. pulex , and G. roeselii were selected, as they represent the three most common species of freshwater amphipods in Central European running waters (Pöckl 1993 ; LANUV 2010). Gammarids inhabit the bottom and bank of water bodies, where they reside among stones, aquatic plants, root weaves and leaf litter (Haeckel et al. 1973 ; Meijering 1982 ; Westheide et al. 1996; Schönborn 1999 ). They can move short distances by swimming or crawling sideways, provided there are enough bottom structures for cover (Meijering 1972 ; Brehm et al. 1996). In small watercourses, Gammarus species are often the most abundant in terms of individuals and biomass. They hold an essential role within the ecosystem of a watercourse (Meijering et al. 1982; Foeckler et al. 1985; Pöckl 1993 ; Pöckl 2014 ). Firstly, they consume organic matter and thereby uptake heavy metals both dissolved in water and bound in sediment as consumers. Secondly, due to their high reproduction rate, they are considered one of the most significant food sources for fish and other predators. Furthermore, Gammarus species are relatively site-specific and have specific habitat requirements (Pöckl 1993 ; Schirling et al. 2005 ). Overall, due to these characteristics, they are suitable as bioindicators. Finally, gammarids reproduce quickly and in large numbers, making the collection of larger samples ecologically unproblematic (Pöckl 1993 ; Pöckl 2014 ). In the context of this study, the hypothesis to be verified is whether localized wastewater discharges or contamination from legacy pollution sites lead to an accumulation of heavy metals in the water body compartments water, sediment, and gammarids. Sampling locations The study area encompasses various small rivers in Hesse and Bavaria. Samples are collected from the respective watercourses, both near discharge points ("contaminated") and at relatively uncontaminated sections, to assess the impact of anthropogenic wastewater discharges on the heavy metal levels in the studied water compartments. The selection of sampling locations focused on the characteristics of known pollution cases in the Wieseck at Buseck/Hesse and the Kössein at Marktredwitz/Bavaria. Additional river sections were chosen for comparison, resembling the studied section of the Wieseck. These comparison sections are expected to be located in silicate-rich low mountain streams and rivers with a range of fine to coarse materials and exhibit good ecological conditions. Additionally, they should be accessible by foot. Their surroundings are predominantly agricultural but not urban. These water bodies should have fine-grained sediments (particle size < 20 µm), hence rivers with a natural bed structure and moderately altered course were chosen. Furthermore, rivers were selected that include sections influenced by combined sewage or wastewater treatment plant discharges as well as sections that are as natural and minimally affected as possible (comparison sections). The mentioned data were sourced from governmental specialized information systems, namely the 'WRRL-Viewer Hessen' (HLNUG 2022a), 'UmweltAtlas Bayern' (LfU 2022a), and 'Gewässerkundlicher Dienst Bayern' (LfU 2022b). In the following table, all sampling locations are numbered in an upstream order, and their proximity to a discharge point is indicated by a specific abbreviation. Table 1 : Sampling locations in Hesse and Bavaria The abbreviation following the sampling location indicates the proximity to discharge points. c: uncontaminated comparison section d: directly (≤ 0,2 km) behind a wastewater discharge point n: near (> 0,2 ≤ 2 km) behind a wastewater discharge point f: far (> 2 ≤ 12,2 km) behind a wastewater discharge point d*/n*: directly/near behind a wastewater treatment plant District Location Watercourse Sampling locations Gießen Buseck-Großen-Buseck Buseck-Trohe Wieseck WG1(d), WG2(d) WT1(n), WT2(d), WT3(n), WT4(n), WT5(n), WT6(d) Gießen Buseck-Beuern Krebsbach KR1(c), KR2(n) Gießen Laubach Laubach-Wetterfeld Wetter WE1(c) WE2(d) Vogelsberg Schotten-Rudingshain Nidda N1(c) Schotten N2(d) Schotten-Rainrod N3(n) Wetterau Nidda-Eichelsdorf N4(d), N5(d) Vogelsberg Wetterau Schotten-Eschenrod -Wingershausen -Eichelsachsen Nidda-Eichelsdorf Eichelbach E1(f) E2(d) E3(d) E4(f) Hochtaunus Wehrheim-Obernhain Erlenbach ER1(c) Wehrheim ER2(n) Köppern ER3(f) Burgholzhausen ER4(n), ER5(d), ER6(n), ER7(d) Bad Homburg-Ober-Erlenbach ER8(d*) Hochtaunus Bad Homburg-Ober-Erlenbach Seulbach S1(n) Hochtaunus Frankfurt a. M. Oberursel-Oberstedten Bad Homburg-Ober-Eschbach Nieder-Eschbach Eschbach ES1(c), ES2(d) ES3(n*) ES4(n) Wetterau Rosbach v. d. H. Fahrenbach F1(c) Rosbach RO1(d*) Wöllstadt RO2(d) Wunsiedel Waldershof Kössein K1(f) (Bavaria) Marktredwitz K2(f), K3(n*) Arzberg K4(n) Schirnding-Fischern Röslau R1(n) Methods At the selected river sections, a total of 30 gammarid, 100 sediment, and 30 water samples were collected in January 2022. At each sampling point, a 50-meter-long representative section upstream was sampled. To prevent contamination, all equipment and containers that came into contact with the samples were made of chemically inert material that does not interact with the heavy metals under investigation. The samples were transported to the laboratory under cooled conditions and stored at temperatures below − 18°C until analysis (DWA-M 517). The water samples were collected in LDPE laboratory bottles directly from the watercourse according to DIN EN ISO 5667-6. A 50 mL aliquot of river water was collected to assess the current contamination level at the time of sampling (DIN EN ISO 5667-1). A significant portion of heavy metals in water samples is adsorbed on particles. Therefore, the water samples were analyzed unfiltered, including suspended particulate matter, to provide an overview of the entire heavy metal load. Additionally, for further preservation, the water samples were acidified with nitric acid to lower the sample's pH to below 2 (DIN EN ISO 5667-3). Sediment sampling was performed using a stainless steel Van Veen grab sampler, aided by spoons made of stainless steel and plastic, along with a plastic funnel. To assess the current contamination situation (deposition from the water), sediment was exclusively taken from the uppermost centimeters of the surface layer using the Van Veen grab sampler (DWA-M 517). During sampling, multiple subsamples were taken in a uniform grid and combined to create a composite sample. Great care was taken to ensure that mainly fine-grained sediments (fraction < 20 µm) were sampled, as heavy metals tend to accumulate predominantly in the fine particle fraction (particle size effect) (LAWA 2002). Two or three composite samples were collected at the investigation sites according to DIN ISO 5667-12, as river sediments are vertically and horizontally heterogeneous (DIN ISO 5667-12). Approximately 100 g of sediment were placed in wide-mouth LDPE bottles for transport to the laboratory under cooled conditions (DIN ISO 5667-15). For gammarid sampling, plastic containers, hand sieves, nets, stainless steel spoons, and spring steel tweezers were used. Gammarids were sampled from various habitats within a sampling site following DIN EN 16150 standards (DIN EN 16150). Typical habitats of gammarids include root weavers, leaf accumulations, and aquatic plants (Pöckl 2014 ). During the 'kick-sampling' method, the riverbed was agitated by kicks, and the stirred-up material was captured using a downstream-held net. Additionally, habitat structures located just below the water surface were shaken by hand, and the gammarids were captured using hand sieves. Individuals of Gammarus fossarum , G. pulex , and G. roeselii were combined into a composite sample (pool sample) for each sampling location after removing other macrozoobenthos species. Approximately 20 g of fresh weight was needed for laboratory analysis. Excess water was decanted from the sample bottles, and the samples were frozen at -18°C until laboratory analysis. The heavy metal contents of the samples were determined qualitatively and quantitatively by the external laboratory 'SGS Analytics' using appropriate standard methods. For the elements lead, cadmium, chromium (total), copper, nickel, and zinc, the inductively coupled plasma mass spectrometry (ICP-MS) method according to DIN EN ISO 17294-2 was employed (DIN EN ISO 17294-2). Due to its specific chemical and physical properties, mercury was determined using the cold vapor atomic absorption spectrometry (CV-AAS) method as per DIN EN ISO 12846 (DIN EN ISO 12846). For water sample analysis, the limit of quantification (LOQ) for the elements lead, chromium, copper, nickel and zinc was 0.001 mg/L, while for cadmium and mercury, it was 0.0001 mg/L. In sediment sample analysis, the LOQ for lead, chromium, copper, nickel and zinc was 3 mg/kg DM, for cadmium, it was 0.3 mg/kg DM, and for mercury, it was 0.05 mg/kg DM. In gammarid sample analysis, the LOQ was set at 0.08 mg/kg for lead, 0.01 mg/kg for cadmium, chromium, copper, nickel and zinc, and 0.005 mg/kg for mercury. For water sample analysis, the acidified water samples were directly used. The sediment samples were homogenized before heavy metal analysis, and the dry matter was determined following DIN EN 15934 (DIN EN 15934). Additionally, the sediment was digested using aqua regia as per DIN EN 13657 to release the bound elements from the substrates (DIN EN 13657). In the case of Gammarid samples, the liquid phase in the sample bottles was initially separated. Subsequently, the sampled gammarids were crushed, homogenized, and subjected to aqua regia digestion (DIN EN 13657). Results, discussion and conclusions In the following segment the results of this study are presented and discussed. Variation among investigated water compartments Significant differences in the average heavy metal concentrations are observed among the water compartments: sediment, gammarids, and water (Fig. 2 ). The analysis of sediment samples reveals average concentrations ranging from 0.4 to 104 mg/kg DM, which are approximately 10,000 times higher compared to the river water. Consequently, this study highlights a pronounced accumulation of heavy metals in river sediments. The adsorption of heavy metals on fine-grained sediment and the sedimentation of suspended matter containing heavy metals has the greatest enrichment potential of all sample types examined (Förstner et al. 1974; Lichtfuß et al. 1981). Hence, sediments are considered as a 'long-term memory' for stream contaminants (Fritsche et al. 2002). In the sedimentation zones of water bodies, substantial proportions of released heavy metals from the surroundings are often stored (Macklin et al. 1997 ; Müller 1986 ). Additionally, the heavy metal content in river sediments affects the aquatic fauna since fine-grained sediment, due to its high biological productivity, serves as a feeding ground for many aquatic organisms (ARGE Elbe 1980). Gammarid samples show average heavy metal concentrations ranging from 0.05 to 10.4 mg/kg. Consequently, the accumulation of heavy metals in gammarids results in concentrations that are, on average, approximately 1,000 times higher than those in water samples. Aquatic organisms accumulate heavy metals both through the surrounding water and contaminated organic food sources. Gammarids accumulate available heavy metals in their habitat over their lifetime due to their relatively site fidelity (Pöckl 1993 , Schirling et al. 2005 ). Aquatic organisms intake heavy metals through the food chain, which could lead to increased heavy metal levels in higher trophic levels. Thus, the heavy metal content in sampled fish would likely be higher, as indicated by the Hessian and Bavarian fish monitoring reports (HLNUG 2022c ; LfU 2022b). In the water samples, average heavy metal concentrations range only from 0.0001 to 0.008 mg/L. This sample type investigates both dissolved and particulate-bound heavy metals in the water, as the water samples were not filtered. However, the unfiltered river water samples do not exhibit significant contamination with heavy metals. The magnitude of the measured values for the investigated heavy metals aligns with the results from the monitoring program of Hessian waters and the River Rhine (IKSR 2022; HLNUG 2022b ). River water as a sample material allows only a snapshot of the current pollution in the water body since present heavy metals are distributed by the flow. Events such as inputs from point sources or precipitation events lead to fluctuations in heavy metal concentrations. Suitability of sample types for assessing heavy metal contamination In this study, similar amounts of heavy metals exceeding the limit of quantification (LOQ) were detected in samples of Gammarus and sediment. Only about 14% (29 out of 210 measurements) of the recorded heavy metal values were below the LOQ in Gammarus samples, and around 19% (136 out of 700 measurements) were below the LOQ in sediment samples. In contrast, despite the low LOQ, a total of 61% (129 out of 210 measurements) of the measured heavy metal levels in river water were below the LOQ. Furthermore, only three out of seven heavy metals showed a sufficient number of measured concentrations above the LOQ. Therefore, individual measurements of river water are not suitable for comparisons. Next, the assessed heavy metal concentrations in Gammarus are evaluated to determine if they correlate with sediment sample measurements. For each heavy metal, a linear regression between the two sample types is calculated and the coefficient of determination (R²) is computed (Table 2 ). The individual values of the 30 sampling points where gammarids were found are compared with the average values of the sediment samples from these water sections. Table 2 Linear correlation between the heavy metal concentration of Gammarus and sediment at 30 sampling points, represented by the coefficient of determination (R 2 ) Heavy metal Lead Cad-mium Chromium Copper Nickel Mercury Zinc R 2 0,014 0,010 0,197 0,020 0,240 0,998 0,001 For the element mercury, a linear relationship is indicated (R² = 0.998). However, this strong correlation for mercury is less meaningful due to the proximity of the measurement values of both sample types to the LOQ. For the other heavy metals, either no or only a slight linear relationship exists. For instance, the coefficient of determination R² is 0.240 for nickel, and for the remaining five heavy metals, it is less than 0.200. Due to the differences among the investigated watercourses and the varying magnitudes of measurement values, a high correlation could not be achieved. This is also due to other environmental influences not examined here, which can influence the heavy metal concentration of the sample types. The coefficients of determination indicate that the trends in heavy metal contamination in gammarids are only minimally similar to those in sediment. Therefore, the examination of heavy metals in sediment cannot be replaced by assessing heavy metals in gammarids. As these organisms are part of the food chain, their consideration is also relevant with regard to compliance with other limit values. It allows an examination of the ecological impact and also reveals increased concentrations along the course of the water body. German and European regulations indicate that the chemical status assessment based on biota investigations (fish, crustaceans, molluscs) is preferred (OGewV 2016 ; Directive 2013/39/EU 2013). In this study, gammarids were investigated as bioindicators because they play a key role in a water body as shredders and decomposers of organic substances and as prey organisms for predators. Thus, the identified heavy metal contamination in gammarids is more relevant to the aquatic ecosystem than sediment contamination. However, the time required for gammarid sampling was significantly higher than that for sediment and water, and gammarids were not present at every sampling site. A study conducted by the University of Bonn demonstrates that heavy metals accumulate significantly in Gammarus fossarum during their relatively short lifespan of approximately 12 to 18 months. This finding is supported by the fact that the levels of heavy metals in the examined Gammarus samples were higher than in the leaf samples (their food source) (Hüsecken et al., 2013 ). Gammarids can also be used for assessing heavy metal pollution in small streams, as they are ubiquitous unlike fish and typically represent the largest number of individuals within the macrozoobenthos community. In summary, for a separate analysis of heavy metal pollution in specific flowing waters and their anthropogenic discharge points, the measurements from water samples are inadequate since a large portion of the determined concentrations is below the limit of quantification (LOQ). The results from the examined Gammarus samples provide a comprehensive view of heavy metal pollution in the water sections, as the measurements, except for mercury, predominantly exceed the LOQ. However, not all sampling sites can be investigated using Gammarus samples due to the absence of freshwater amphipods at certain locations. Furthermore, only one pool sample could be taken from each study section for analysis, as the weight of the organisms found was only sufficient for one analysis sample if the necessary quantity was taken into account. In contrast, during sediment sampling, multiple samples were collected at all locations. This allowed the assurance of the heavy metal content by averaging individual measurements and identifying any potential differences. Additionally, sediment analysis is a standard procedure in heavy metal investigations, providing data on sediment heavy metal contents in previously surveyed water bodies. In flowing waters with known pollution (e.g., Kössein due to mercury contamination) as well as in major rivers (e.g., the Rhine), the heavy metal content of water, suspended solids, and sediment is analyzed (Pedall et al., 2011 ; IKSR 2022; HLNUG 2022b ). Overall, the sediment heavy metal content in this study stands out as the most informative dataset. Hence, in the following sections, the sediment heavy metal contents will be utilized for assessing relevant heavy metal pollution. Temporal trend of mercury levels in the effluents of the hazardous waste site „Chemical Factory Marktredwitz“ In this chapter, the determined mercury levels in the effluents of the hazardous waste site "Chemical Factory Marktredwitz (CFM)" are compared with the measurement data from earlier investigations. The aim is to demonstrate to what extent the effects of remediation measures are reflected in the mercury concentrations in the sediments. Thus, Fig. 3 compares the average mercury levels in the sediments of the Kössein and Röslau rivers in the years 2011 and 2022. The actual flow direction of the water is depicted from left to right by arranging the sampling points. The data from 2011 are derived from the study "Quecksilber im Zulauf zum Stausee Skalka” commissioned by the responsible water authority (Pedall et al. 2011 ). The mercury levels in the surveyed sections of the watercourses decreased in the period from 2011 to 2022. However, despite this reduction, the LAWA target value of 0.8 mg/kg DM (LAWA 1998a) was exceeded at the four survey points both in 2011 and 2022. The mercury contamination at the surveyed sections decreases over time as increased water flow mobilizes sedimented heavy metal particles, carrying them downstream into the Skalka reservoir. The largest quantity of mercury is adsorbed by the finest fraction, which in turn exhibits slow settling rates (Dikau et al., 2019 ). According to Czech authorities, up to 50 kilograms of mercury enter the reservoir annually (Gschwendtner, 2021 ). Therefore, primarily oxbows, reservoirs, and areas with low flow velocities are affected in these two waters. The surveyed section of the Kössein at the former CFM site (K2) exhibits the lowest mercury concentration at 0.9 mg/kg DM, even though a mercury content of 227 mg/kg DM was measured in a regulatory examination in 1977 before the closure of the chemical factory (LfW, 1998). The investigated section underwent artificial restructuring due to decontamination and site remediation, and contaminated river sediment was properly disposed of (Pedall et al., 2011 ; Hošek et al., 2020 ; Haussel, 2009 ). Additionally, increased flow velocities resulted from the construction of the riverbed and the straightening of the river, transporting contaminated sediment downstream. Furthermore, existing heavy metal contents are diluted as uncontaminated fine material from the upper reaches deposits into the watercourse. Similar to 2011, the next surveyed section at the 'Wölsauerhammer' weir (K3) holds the highest concentration of mercury. The sedimentation of heavy metals is favored by the weir structure and the confluence of a drainage ditch (Pedall et al., 2011 ). The confluence point of the Kössein into the Röslau (K4) shows a significant decrease in mercury concentration. In 2021, an upstream stretch of the riverbank was fortified due to heavy soil erosion (Bavarian State Parliament, 2022). The successful remediation of the contaminated section may have resulted in the decrease of mercury concentration approximately one kilometer away at the sampling site. Similarly, at the sampling site of the Röslau before it merges into the Skalka reservoir (R1), the mercury content has decreased. The high flow velocity of the watercourse, particularly following the previous flood event, leads to a relatively low mercury contamination in the river sediment. Effects of sewage discharge into the Wieseck river In November 2020, due to a technical fault in a control valve of a storage canal (combined sewer overflow system), untreated wastewater was discharged into the Wieseck for approximately one week. This led to significant deposits and a fish mortality (Bothe 2020 ). Subsequently, within an observation program, the ecological condition of the affected sections of the watercourse was evaluated based on ecological and physicochemical quality components. The present study supplements this program by investigating the heavy metal contamination before and after the discharge point. The average concentrations of heavy metals in the analyzed sediments from three sections of the watercourse before (WG1, WG2, WT1) and five sections after (WT2 to WT6) the wastewater discharge point were calculated (Fig. 4 ). The analyzed sediment samples show an increase in the concentrations of the heavy metals chromium, copper, nickel, and zinc after the faulty discharge point. Therefore, the uncontrolled wastewater discharge at the faulty control valve has an impact on downstream sections of the watercourse. Normally, the upstream section before the considered discharge point is already affected by six additional combined sewer overflow points with anthropogenic wastewater discharges. The highest percentage increase is observed in the elements zinc and copper, typically originating from municipal wastewater, thus confirming the heavy metal input through the faulty discharge point (Hillenbrand et al. 2005 ). Despite the elevation of some heavy metal concentrations, all environmental quality standards and targets are met. The results demonstrate that even one year after the anthropogenic discharge, heavy metal contamination can still be observed in the analyzed sediments ("long-term memory"). The cause of the high lead concentration before the discharge point could not be determined. Various sources are possible, as lead has been used as chemical compounds in different products, for example, from foundries, the chemical industry, fertilizer production, batteries, or from its past use as a gasoline additive (Förstner et al. 1974). Influence of wastewater discharges on heavy metal concentrations in river sediment using the example of the Rosbach At the Rosbach river, with a sampling point near its source (F1), as well as a site immediately after a municipal wastewater treatment plant (RO1), and several kilometers downstream from it (RO2), the accumulation of heavy metals in river sediment can be demonstrated (Fig. 5 ). Most of the heavy metal concentrations in section RO1, just downstream of the wastewater treatment plant, show only slight increases (lead, copper) or are not significantly elevated, except for zinc, which appears in concentrations about three times higher. In contrast, notably higher levels of heavy metals were measured in section RO2, located downstream of several combined sewer overflow outlets. Chromium and nickel concentrations, in particular, are notably higher in this section. Only trace amounts of mercury and cadmium are detected, with slight increases that are not visible in the diagram. Regarding the parallel water analysis, it can be observed that zinc was found in higher concentration (0.0192 mg/L) only in RO1, directly after the wastewater treatment plant. Both F1 (0.0116 mg/L) and RO2 (0.0111 mg/L) show lower measurements at roughly the same level. Except for copper, which slightly increases from F1 (0.0010 mg/L) to RO1 (0.0011 mg/L) and further to RO2 (0.0013 mg/L), and nickel, which decreases from F1 (0.0022 mg/L) to RO1 (0.0017 mg/L) and increases again to RO2 (0.0020 mg/L), the other heavy metal elements remain at similar concentrations. The discrepancy between sediment and water analyses, except for zinc, can be attributed to the flushing of heavy metals after rain discharge from the treatment plant or through combined sewer overflow outlets. These heavy metals are primarily transported with the river water and eventually settle in the later course of the water body as sediment. Therefore, in the water phase, they can only be detected during the exact period when such rain discharge occurs. Heavy metals discharged into the water during these events subsequently lead to a concentration increase in more distant sections, explaining the previously described trend towards RO2. Zinc emerges from this study as an element commonly found in the water phase downstream of effluents. The already higher concentration of zinc in the water behind the wastewater treatment plant could be the cause of the comparatively higher zinc levels in the sediment at RO1 compared to other elements. Zinc and copper are heavy metal elements, and based on the obtained analysis results, their sediment concentrations frequently increase after the discharge of municipal wastewater. Comparison of zinc and copper concentrations in the sediment of the sampling sites closer to the source with those of the subsequent watercourse sections The hypothesis is put forth that the concentrations of heavy metals in the sediment increase along the watercourse. Various discharge points may be causative factors for this. The values of a sampling site closer to the source (comparison) are presented, which are compared to the measurement results of all examined sampling sites downstream (Fig. 6 ). The values of each subsequent river course are derived from the average of all sampling sites located downstream from the comparison section. In six out of ten watercourses (Krebsbach, Wieseck (Trohe), Nidda, Erlenbach, Eschbach and Rosbach), the concentrations of zinc and copper are higher below the comparison sections closer to the source. Conversely, the concentrations in the comparison sections of Wieseck (Buseck) and Kössein are higher. In the case of Wetter, the zinc concentration in the comparison section is significantly lower, and the copper content is not much higher than that of the subsequent river sections. For Eichelbach, the comparison concentration for zinc is only slightly higher. The comparison of zinc and copper elements shows overall analogies. The comparison sections closer to the source are not all completely uncontaminated, as there may be a geogenic background contamination or diffuse or unknown inputs. In summary, it can be observed that there has been an accumulation of heavy metals in the sediment of the examined watercourses due to wastewater discharges. Conclusions The results presented show that the examined sample types exhibit certain differences. In the water samples, only heavy metal concentrations ranging from 0.0001 to 0.008 mg/L are measured, with a majority falling below the limit of quantification (LOQ). River water provides only a snapshot of the current pollution in the water body and is influenced by dynamic processes. The accumulation of heavy metals in the gammarids leads to metal concentrations that are on average about 1,000 times higher than those found in the water samples and mostly above the LOQ, except for mercury. Water organisms can uptake various heavy metals from the surrounding water and contaminated food. The relatively stationary gammarids accumulate available heavy metals in their habitat over their lifespan. Comparatively, the accumulation of heavy metals in the river sediments is about 10,000 times higher than in the river water. The sedimentation of suspended solids containing heavy metals and their adsorption on fine-grained sediment have the greatest potential for accumulation among the three examined sample types, so that these measurement data have the greatest significance for detecting past wastewater discharges. The comparison of mercury levels in the sediment of the “Chemical Factory Marktredwitz” contamination area's tributaries with earlier survey data indicates a decline in mercury levels at all sampling sites. This decrease is attributed to the increased water flow mobilizing the sedimented heavy metal particles, carrying them downstream into the Skalka reservoir. Consequently, the high flow rate of the studied watercourse after previous flood events leads to a decrease in mercury contamination in the river sediment and the deposition of uncontaminated fine material from the upper reaches. The successful remediation of a problematic erosion area before “Wölsauerhammer” and the reduction in the runoff of contaminated soil were evidenced by a significant decrease in mercury contamination at a sampling site approximately one kilometer away. The heavy metal contamination of the Wieseck river sediment before and after a discharge point at which untreated wastewater was discharged into the river due to a technical error shows an increase in the concentration of the heavy metals chromium, copper, nickel and zinc after the faulty discharge point. The most significant percentage increase is observed in zinc and copper, typically originating from domestic wastewater, suggesting heavy metal input due to the faulty valve. Despite upstream sections being influenced by six combined sewage discharge points, the uncontrolled wastewater outflow has a more pronounced impact on downstream sections of the water body. Even one year after the anthropogenic discharge, there remains evidence of heavy metal contamination in the examined sediments ("long-term memory"). In the Rosbach, as well as in other water bodies, heavy metals such as zinc and copper continuously enter the flowing water through the discharge channel of the municipal wastewater treatment plant, which is confirmed by sediment and water analyses. The remaining examined heavy metals enter the water body only after the discharge of untreated wastewater, typically following heavy rain events, and can only be determined through immediate water sample analysis. Transported by water flow, these heavy metal elements eventually sediment to the bottom of the water body and bind to the sediment present there. Consequently, they are no longer detectable in the water at a later time but can be identified through sediment analysis. To assess an increase in contamination in the water body, an additional examination of a less polluted reference section in the upper part of the water body is necessary. This approach helps reduce the influence of other sources of heavy metals, such as the geogenic background, especially when comparing with other water bodies. In a majority of the examined water bodies, an increase in zinc and copper concentrations in the water course compared to the respective reference sections was observed. This once again indicates a relationship between the discharge of municipal wastewater and the rise in heavy metal concentrations in the sediment. The existing variations, such as higher concentrations in reference sections, indicate that these sections might also be previously contaminated. Therefore, a precise selection of sampling sites, preferably those with minimal contamination, as well as before-and-after comparisons, is recommended. Gammarids, also known as freshwater amphipods, can serve as bioindicators for heavy metal contamination related to anthropogenic inputs, providing a comprehensive view of heavy metal pollution in the sampled sections of water bodies. However, no direct correlation could be established between the measurement values of gammarids and the influence of anthropogenic discharge points. Moreover, the detected levels of heavy metals at a specific section of the water body could not be confirmed by averaging individual measurements as the weight of the collected organisms was only sufficient for a single gammarid sample. Additionally, not all sampling sites could be investigated using gammarid samples due to the absence of these organisms in some sections of the study area. However, these limitations were not encountered in assessing heavy metal contamination using sediment analysis. The standardized analysis of heavy metals in sediment cannot be substituted by the assessment of heavy metals in gammarids, as there is only a low correlation observed between the heavy metal levels in gammarids and the sediment measurement values. Despite these limitations, the observed heavy metal contaminations in gammarids have greater significance for the aquatic ecosystem compared to sediment pollution. Ultimately, the examined gammarids play a key role in water bodies as decomposers of organic substances and prey organisms in the food chain, reaching up to fish. They are commonly found ubiquitously in smaller water bodies with a large number of individuals. Furthermore, both German and European regulations stipulate that results from biota surveys (fish, crustaceans, molluscs) are favored in the chemical status assessment (Directive 2013/39/EU 2013). The results of this study indicate that gammarids can serve as bioindicators for heavy metal pollution in water bodies, provided that the described limitations are taken into account. Further investigations should assess the extent to which they could serve as an alternative to standardized electrofishing methods. Declarations Ethics approval and consent to participate: Not applicable Consent for publication: Not applicable Availability of data and material: "The datasets supporting the conclusions of this article are included within the article Competing interests: All co-authors have seen and agree with the contents of the manuscript and there is no financial interest to report. We certify that the submission is original work and is not under review for any other publication. Funding: Not applicable Authors' contributions: Lukas Plaß, Felix Heid and Ute Windisch performed the data calculations, participated in its coordination and drafted the manuscript. 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(1993): Beitrage zur Ökologie des Bachflohkrebses ( Gammarus fossarum ) und Flussflohkrebses ( Gammarus roeseli ). Natur und Museum 123 Pöckl, M. (2014): Süßwasser-Amphipoden: eine Liebeserklärung? – Selbstreflexionen eines so genannten „Spezialisten“. Denisia 33:369-392. Richtlinie 2013/39/EU (2013): Richtlinie 2013/39/EU des Europäischen Parlaments und des Rates vom 12. August 2013 zur Änderung der Richtlinien 2000/60/EG und 2008/105/EG in Bezug auf prioritäre Stoffe im Bereich der Wasserpolitik. Schirling, M., Jungmann, D., Ladewig, V., Nagel, R., Triebskorn, R., Köhler, H.-R. (2005): Endocrine effects in Gammarus fossarum (Amphipoda): influence of wastewater effluents, temporal variability, and spatial aspects on natural populations. Archives of environmental contamination and toxicology 49:53-61 Schönborn, W. (1999): Fließgewässerbiologie. Jena, Stuttgart: Gustav Fischer Verlag Westheide. W., Rieger, R. (Hrsg.) (1996): Spezielle Zoologie. Erster Teil: Einzeller und Wirbellose Tiere. Jena, Stuttgart, New York: Gustav Fischer Verlag Williams, P. E. V., Macdearmid, A., Innes, G. M., Gauld, S. A. (1984): Ammonia-treated barley straw and rolled barley offered either together, in a mixed ration, or successively to beef steers. Animal Feed Science and Technology 10 (4):247-255 Windisch, U., Springer, F., Stahl, T. (2020): Freshwater amphipods ( Gammarus pulex/fossarum ) and brown trout as bioindicators for PFC contamination with regard to the aquatic ecological status of a small stream. Environmental Sciences Europe 32:108-122 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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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-3832560","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":265720888,"identity":"60fcf37c-57aa-4a36-97ff-660d5d75ba1d","order_by":0,"name":"Lukas Plaß","email":"","orcid":"","institution":"Technische Hochschule Mittelhessen - University of Applied Sciences","correspondingAuthor":false,"prefix":"","firstName":"Lukas","middleName":"","lastName":"Plaß","suffix":""},{"id":265720889,"identity":"9f366778-1c93-40db-b63d-d2d0d05d2aef","order_by":1,"name":"Felix Heid","email":"","orcid":"","institution":"Technische Hochschule 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18:44:15","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3832560/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3832560/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":49299182,"identity":"4557fec2-974e-4be4-b182-12d10576439b","added_by":"auto","created_at":"2024-01-08 09:01:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":265926,"visible":true,"origin":"","legend":"\u003cp\u003eHabitus of \u003cem\u003eGammarus fossarum\u003c/em\u003e (© Frank Eiseler)\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/5a74078e01240fad377ac7d9.png"},{"id":49299187,"identity":"70cd5832-c4a6-470d-b1a2-eb71b8f944b0","added_by":"auto","created_at":"2024-01-08 09:01:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":235030,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of heavy metal concentrations in the sediment [mg/kg DM], in the gammarids [mg/kg] and in the water [mg/L]\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/f52d3b29f51908bc18e1425d.png"},{"id":49299436,"identity":"a7e00aa0-369d-4cb6-92aa-1280321e2217","added_by":"auto","created_at":"2024-01-08 09:09:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":18662,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of mercury levels in the sediments of the Kössein and Röslau rivers in 2011 (Pedall et al. 2011) and 2022\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/9eb169baeb00036f52768ac5.png"},{"id":49299186,"identity":"0ff4cf07-97fc-424e-a2c4-582366f32b82","added_by":"auto","created_at":"2024-01-08 09:01:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":58161,"visible":true,"origin":"","legend":"\u003cp\u003eHeavy metal content in the sediment of the Wieseck river in watercourse sections before and after the wastewater discharge point\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/9058bd8f994393c69657fd97.png"},{"id":49299437,"identity":"d4462daf-4bb9-4726-9914-d8c47a8b0704","added_by":"auto","created_at":"2024-01-08 09:09:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":45803,"visible":true,"origin":"","legend":"\u003cp\u003eHeavy metal contents in the sediment of the Rosbach (zinc on the secondary axis) in the near-source section (F1), downstream of a wastewater treatment plant (RO1) and downstream of several combined water discharge points (RO2)\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/df549aecdc28bd7517eb6897.png"},{"id":49299184,"identity":"a62a745a-c4f1-48f6-bc41-72ccff464abb","added_by":"auto","created_at":"2024-01-08 09:01:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":44083,"visible":true,"origin":"","legend":"\u003cp\u003eZinc and copper concentrations in the sediment of the sections closer to the source (comparison) and in the following river course\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/bed96c5b4f1aaf4d10ef3c6c.png"},{"id":83705662,"identity":"d0c56221-bcab-4a42-b916-39276b5b6507","added_by":"auto","created_at":"2025-05-31 11:31:41","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1565996,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3832560/v1/4c4d0f01-c09e-4fcf-9df7-9c148df7eb6e.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges","fulltext":[{"header":"Background","content":"\u003cp\u003eWatercourses are essential components of the Earth's ecosystem. They serve as habitats for plants and animals within and around these water bodies. For humans, water bodies are used for irrigation in agriculture, for cooling industrial processes, for drinking water production and as recreational areas.\u003c/p\u003e \u003cp\u003eHowever, human interventions also pose a threat to the natural balance of these water bodies. The input of various pollutants endangers both the water quality and the living conditions of aquatic flora and fauna. The impacts of pollutant contamination are evident in local examples in Germany, such as the mercury legacy of the Chemical Factory in Marktredwitz (1788\u0026ndash;1985) (Nov\u0026aacute;kov\u0026aacute; et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), wastewater discharge into the Wieseck River in 2020 (Bothe \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e) or fish mortality in the Oder River in 2022 (Free et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2023\u003c/span\u003e). The pollutant contamination in rivers and watercourses can originate from natural sources (such as geogenic background pollution in soils) or anthropogenic sources (including atmospheric deposition and wastewater discharges). The influence of diffuse pollutant inputs is difficult to assess and limit.\u003c/p\u003e \u003cp\u003eIn the case of point sources, the improved purification performance of multi-stage wastewater treatment plants, as well as legislative measures such as the implementation of regulations for indirect dischargers, result in a reduced input of pollutants (Fuchs et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2002\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHowever, wastewater also contains substances such as heavy metals that cannot be completely removed in wastewater treatment plants. These substances either remain in the sewage sludge or enter receiving waters with the treated wastewater. Aquatic microorganisms are already harmed by traces of lead, cadmium, or copper (Hillenbrand et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Moreover, heavy metals accumulate in aquatic organisms and can enter the human body through the food chain. This study focuses on the heavy metals lead, cadmium, chromium, copper, nickel, mercury, and zinc, as these are typically found in municipal wastewater. Various target values exist for these metals to protect surface inland waters, for instance, set by the German Working Group of the Federal States on water issues (LAWA) (LAWA 1998a).\u003c/p\u003e \u003cp\u003eThe Water Framework Directive 2000/60/EC (WFD) mandates the protection and improvement of aquatic ecosystems, aiming for a good ecological and chemical status for all surface water bodies by 2027 (EEA 2000). This requires suitable measures and management practices, monitored through assessment procedures. In Germany, surface waters are monitored and assessed according to the Surface Water Ordinance (OGewV). Environmental quality standards (EQS) for priority and river basin-relevant pollutants are listed in Annexes 6 and 8 of the OGewV (OGewV \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). If the LAWA targets are achieved, significant adverse effects on the aquatic ecosystem can be largely ruled out (LAWA 1998b). The influence of anthropogenic discharges on the heavy metal contents in sediment, water and gammarid samples will be compared. The latter are proposed as alternative monitoring organisms to fish in fish-poor or fish-free smaller watercourses. For this purpose, the species \u003cem\u003eGammarus fossarum\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), \u003cem\u003eG. pulex\u003c/em\u003e, and \u003cem\u003eG. roeselii\u003c/em\u003e were selected, as they represent the three most common species of freshwater amphipods in Central European running waters (P\u0026ouml;ckl \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; LANUV 2010).\u003c/p\u003e \u003cp\u003eGammarids inhabit the bottom and bank of water bodies, where they reside among stones, aquatic plants, root weaves and leaf litter (Haeckel et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e1973\u003c/span\u003e; Meijering \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Westheide et al. 1996; Sch\u0026ouml;nborn \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1999\u003c/span\u003e). They can move short distances by swimming or crawling sideways, provided there are enough bottom structures for cover (Meijering \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e1972\u003c/span\u003e; Brehm et al. 1996).\u003c/p\u003e \u003cp\u003eIn small watercourses, Gammarus species are often the most abundant in terms of individuals and biomass. They hold an essential role within the ecosystem of a watercourse (Meijering et al. 1982; Foeckler et al. 1985; P\u0026ouml;ckl \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; P\u0026ouml;ckl \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). Firstly, they consume organic matter and thereby uptake heavy metals both dissolved in water and bound in sediment as consumers. Secondly, due to their high reproduction rate, they are considered one of the most significant food sources for fish and other predators.\u003c/p\u003e \u003cp\u003eFurthermore, Gammarus species are relatively site-specific and have specific habitat requirements (P\u0026ouml;ckl \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Schirling et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Overall, due to these characteristics, they are suitable as bioindicators. Finally, gammarids reproduce quickly and in large numbers, making the collection of larger samples ecologically unproblematic (P\u0026ouml;ckl \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; P\u0026ouml;ckl \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the context of this study, the hypothesis to be verified is whether localized wastewater discharges or contamination from legacy pollution sites lead to an accumulation of heavy metals in the water body compartments water, sediment, and gammarids.\u003c/p\u003e \u003cdiv id=\"Sec2\" class=\"Section2\"\u003e \u003ch2\u003eSampling locations\u003c/h2\u003e \u003cp\u003eThe study area encompasses various small rivers in Hesse and Bavaria. Samples are collected from the respective watercourses, both near discharge points (\"contaminated\") and at relatively uncontaminated sections, to assess the impact of anthropogenic wastewater discharges on the heavy metal levels in the studied water compartments. The selection of sampling locations focused on the characteristics of known pollution cases in the Wieseck at Buseck/Hesse and the K\u0026ouml;ssein at Marktredwitz/Bavaria.\u003c/p\u003e \u003cp\u003eAdditional river sections were chosen for comparison, resembling the studied section of the Wieseck. These comparison sections are expected to be located in silicate-rich low mountain streams and rivers with a range of fine to coarse materials and exhibit good ecological conditions. Additionally, they should be accessible by foot. Their surroundings are predominantly agricultural but not urban. These water bodies should have fine-grained sediments (particle size\u0026thinsp;\u0026lt;\u0026thinsp;20 \u0026micro;m), hence rivers with a natural bed structure and moderately altered course were chosen.\u003c/p\u003e \u003cp\u003eFurthermore, rivers were selected that include sections influenced by combined sewage or wastewater treatment plant discharges as well as sections that are as natural and minimally affected as possible (comparison sections). The mentioned data were sourced from governmental specialized information systems, namely the 'WRRL-Viewer Hessen' (HLNUG 2022a), 'UmweltAtlas Bayern' (LfU 2022a), and 'Gew\u0026auml;sserkundlicher Dienst Bayern' (LfU 2022b).\u003c/p\u003e \u003cp\u003eIn the following table, all sampling locations are numbered in an upstream order, and their proximity to a discharge point is indicated by a specific abbreviation.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTable\u0026nbsp;1\u003c/b\u003e: Sampling locations in Hesse and Bavaria\u003c/p\u003e \u003cp\u003eThe abbreviation following the sampling location indicates the proximity to discharge points.\u003c/p\u003e \u003cp\u003ec: uncontaminated comparison section\u003c/p\u003e \u003cp\u003ed: directly (\u0026le;\u0026thinsp;0,2 km) behind a wastewater discharge point\u003c/p\u003e \u003cp\u003en: near (\u0026gt;\u0026thinsp;0,2\u0026thinsp;\u0026le;\u0026thinsp;2 km) behind a wastewater discharge point\u003c/p\u003e \u003cp\u003ef: far (\u0026gt;\u0026thinsp;2\u0026thinsp;\u0026le;\u0026thinsp;12,2 km) behind a wastewater discharge point\u003c/p\u003e \u003cp\u003ed*/n*: directly/near behind a wastewater treatment plant\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"4\"\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 \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDistrict\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWatercourse\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSampling locations\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGie\u0026szlig;en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBuseck-Gro\u0026szlig;en-Buseck\u003c/p\u003e \u003cp\u003eBuseck-Trohe\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWieseck\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWG1(d), WG2(d)\u003c/p\u003e \u003cp\u003eWT1(n), WT2(d), WT3(n), WT4(n), WT5(n), WT6(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGie\u0026szlig;en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBuseck-Beuern\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eKrebsbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKR1(c), KR2(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGie\u0026szlig;en\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLaubach\u003c/p\u003e \u003cp\u003eLaubach-Wetterfeld\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eWetter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWE1(c)\u003c/p\u003e \u003cp\u003eWE2(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVogelsberg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSchotten-Rudingshain\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNidda\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN1(c)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSchotten\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN2(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSchotten-Rainrod\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN3(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWetterau\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNidda-Eichelsdorf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eN4(d), N5(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eVogelsberg\u003c/p\u003e \u003cp\u003eWetterau\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSchotten-Eschenrod\u003c/p\u003e \u003cp\u003e-Wingershausen\u003c/p\u003e \u003cp\u003e-Eichelsachsen\u003c/p\u003e \u003cp\u003eNidda-Eichelsdorf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEichelbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eE1(f)\u003c/p\u003e \u003cp\u003eE2(d)\u003c/p\u003e \u003cp\u003eE3(d)\u003c/p\u003e \u003cp\u003eE4(f)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHochtaunus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWehrheim-Obernhain\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eErlenbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eER1(c)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWehrheim\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eER2(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eK\u0026ouml;ppern\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eER3(f)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBurgholzhausen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eER4(n), ER5(d), ER6(n), ER7(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBad Homburg-Ober-Erlenbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eER8(d*)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHochtaunus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBad Homburg-Ober-Erlenbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSeulbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eS1(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHochtaunus\u003c/p\u003e \u003cp\u003eFrankfurt a. M.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOberursel-Oberstedten\u003c/p\u003e \u003cp\u003eBad Homburg-Ober-Eschbach\u003c/p\u003e \u003cp\u003eNieder-Eschbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eEschbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eES1(c), ES2(d)\u003c/p\u003e \u003cp\u003eES3(n*)\u003c/p\u003e \u003cp\u003eES4(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWetterau\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eRosbach v. d. H.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFahrenbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eF1(c)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eRosbach\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRO1(d*)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eW\u0026ouml;llstadt\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRO2(d)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWunsiedel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eWaldershof\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u0026ouml;ssein\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eK1(f)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(Bavaria)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMarktredwitz\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eK2(f), K3(n*)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eArzberg\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eK4(n)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSchirnding-Fischern\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eR\u0026ouml;slau\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eR1(n)\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"},{"header":"Methods","content":"\u003cp\u003eAt the selected river sections, a total of 30 gammarid, 100 sediment, and 30 water samples were collected in January 2022. At each sampling point, a 50-meter-long representative section upstream was sampled. To prevent contamination, all equipment and containers that came into contact with the samples were made of chemically inert material that does not interact with the heavy metals under investigation. The samples were transported to the laboratory under cooled conditions and stored at temperatures below \u0026minus;\u0026thinsp;18\u0026deg;C until analysis (DWA-M 517).\u003c/p\u003e \u003cp\u003eThe water samples were collected in LDPE laboratory bottles directly from the watercourse according to DIN EN ISO 5667-6. A 50 mL aliquot of river water was collected to assess the current contamination level at the time of sampling (DIN EN ISO 5667-1). A significant portion of heavy metals in water samples is adsorbed on particles. Therefore, the water samples were analyzed unfiltered, including suspended particulate matter, to provide an overview of the entire heavy metal load. Additionally, for further preservation, the water samples were acidified with nitric acid to lower the sample's pH to below 2 (DIN EN ISO 5667-3).\u003c/p\u003e \u003cp\u003eSediment sampling was performed using a stainless steel Van Veen grab sampler, aided by spoons made of stainless steel and plastic, along with a plastic funnel. To assess the current contamination situation (deposition from the water), sediment was exclusively taken from the uppermost centimeters of the surface layer using the Van Veen grab sampler (DWA-M 517). During sampling, multiple subsamples were taken in a uniform grid and combined to create a composite sample. Great care was taken to ensure that mainly fine-grained sediments (fraction\u0026thinsp;\u0026lt;\u0026thinsp;20 \u0026micro;m) were sampled, as heavy metals tend to accumulate predominantly in the fine particle fraction (particle size effect) (LAWA 2002). Two or three composite samples were collected at the investigation sites according to DIN ISO 5667-12, as river sediments are vertically and horizontally heterogeneous (DIN ISO 5667-12). Approximately 100 g of sediment were placed in wide-mouth LDPE bottles for transport to the laboratory under cooled conditions (DIN ISO 5667-15).\u003c/p\u003e \u003cp\u003eFor gammarid sampling, plastic containers, hand sieves, nets, stainless steel spoons, and spring steel tweezers were used. Gammarids were sampled from various habitats within a sampling site following DIN EN 16150 standards (DIN EN 16150). Typical habitats of gammarids include root weavers, leaf accumulations, and aquatic plants (P\u0026ouml;ckl \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). During the 'kick-sampling' method, the riverbed was agitated by kicks, and the stirred-up material was captured using a downstream-held net. Additionally, habitat structures located just below the water surface were shaken by hand, and the gammarids were captured using hand sieves. Individuals of \u003cem\u003eGammarus fossarum\u003c/em\u003e, \u003cem\u003eG. pulex\u003c/em\u003e, and \u003cem\u003eG. roeselii\u003c/em\u003e were combined into a composite sample (pool sample) for each sampling location after removing other macrozoobenthos species. Approximately 20 g of fresh weight was needed for laboratory analysis. Excess water was decanted from the sample bottles, and the samples were frozen at -18\u0026deg;C until laboratory analysis.\u003c/p\u003e \u003cp\u003eThe heavy metal contents of the samples were determined qualitatively and quantitatively by the external laboratory 'SGS Analytics' using appropriate standard methods. For the elements lead, cadmium, chromium (total), copper, nickel, and zinc, the inductively coupled plasma mass spectrometry (ICP-MS) method according to DIN EN ISO 17294-2 was employed (DIN EN ISO 17294-2). Due to its specific chemical and physical properties, mercury was determined using the cold vapor atomic absorption spectrometry (CV-AAS) method as per DIN EN ISO 12846 (DIN EN ISO 12846).\u003c/p\u003e \u003cp\u003eFor water sample analysis, the limit of quantification (LOQ) for the elements lead, chromium, copper, nickel and zinc was 0.001 mg/L, while for cadmium and mercury, it was 0.0001 mg/L. In sediment sample analysis, the LOQ for lead, chromium, copper, nickel and zinc was 3 mg/kg DM, for cadmium, it was 0.3 mg/kg DM, and for mercury, it was 0.05 mg/kg DM. In gammarid sample analysis, the LOQ was set at 0.08 mg/kg for lead, 0.01 mg/kg for cadmium, chromium, copper, nickel and zinc, and 0.005 mg/kg for mercury.\u003c/p\u003e \u003cp\u003eFor water sample analysis, the acidified water samples were directly used. The sediment samples were homogenized before heavy metal analysis, and the dry matter was determined following DIN EN 15934 (DIN EN 15934). Additionally, the sediment was digested using aqua regia as per DIN EN 13657 to release the bound elements from the substrates (DIN EN 13657). In the case of Gammarid samples, the liquid phase in the sample bottles was initially separated. Subsequently, the sampled gammarids were crushed, homogenized, and subjected to aqua regia digestion (DIN EN 13657).\u003c/p\u003e"},{"header":"Results, discussion and conclusions","content":"\u003cp\u003eIn the following segment the results of this study are presented and discussed.\u003c/p\u003e\n\u003ch3\u003eVariation among investigated water compartments\u003c/h3\u003e\n\u003cp\u003eSignificant differences in the average heavy metal concentrations are observed among the water compartments: sediment, gammarids, and water (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe analysis of sediment samples reveals average concentrations ranging from 0.4 to 104 mg/kg DM, which are approximately 10,000 times higher compared to the river water. Consequently, this study highlights a pronounced accumulation of heavy metals in river sediments.\u003c/p\u003e \u003cp\u003eThe adsorption of heavy metals on fine-grained sediment and the sedimentation of suspended matter containing heavy metals has the greatest enrichment potential of all sample types examined (F\u0026ouml;rstner et al. 1974; Lichtfu\u0026szlig; et al. 1981). Hence, sediments are considered as a 'long-term memory' for stream contaminants (Fritsche et al. 2002). In the sedimentation zones of water bodies, substantial proportions of released heavy metals from the surroundings are often stored (Macklin et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; M\u0026uuml;ller \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). Additionally, the heavy metal content in river sediments affects the aquatic fauna since fine-grained sediment, due to its high biological productivity, serves as a feeding ground for many aquatic organisms (ARGE Elbe 1980).\u003c/p\u003e \u003cp\u003eGammarid samples show average heavy metal concentrations ranging from 0.05 to 10.4 mg/kg. Consequently, the accumulation of heavy metals in gammarids results in concentrations that are, on average, approximately 1,000 times higher than those in water samples. Aquatic organisms accumulate heavy metals both through the surrounding water and contaminated organic food sources. Gammarids accumulate available heavy metals in their habitat over their lifetime due to their relatively site fidelity (P\u0026ouml;ckl \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1993\u003c/span\u003e, Schirling et al. \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Aquatic organisms intake heavy metals through the food chain, which could lead to increased heavy metal levels in higher trophic levels. Thus, the heavy metal content in sampled fish would likely be higher, as indicated by the Hessian and Bavarian fish monitoring reports (HLNUG \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2022c\u003c/span\u003e; LfU 2022b).\u003c/p\u003e \u003cp\u003eIn the water samples, average heavy metal concentrations range only from 0.0001 to 0.008 mg/L. This sample type investigates both dissolved and particulate-bound heavy metals in the water, as the water samples were not filtered. However, the unfiltered river water samples do not exhibit significant contamination with heavy metals. The magnitude of the measured values for the investigated heavy metals aligns with the results from the monitoring program of Hessian waters and the River Rhine (IKSR 2022; HLNUG \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e). River water as a sample material allows only a snapshot of the current pollution in the water body since present heavy metals are distributed by the flow. Events such as inputs from point sources or precipitation events lead to fluctuations in heavy metal concentrations.\u003c/p\u003e\n\u003ch3\u003eSuitability of sample types for assessing heavy metal contamination\u003c/h3\u003e\n\u003cp\u003eIn this study, similar amounts of heavy metals exceeding the limit of quantification (LOQ) were detected in samples of Gammarus and sediment. Only about 14% (29 out of 210 measurements) of the recorded heavy metal values were below the LOQ in Gammarus samples, and around 19% (136 out of 700 measurements) were below the LOQ in sediment samples. In contrast, despite the low LOQ, a total of 61% (129 out of 210 measurements) of the measured heavy metal levels in river water were below the LOQ. Furthermore, only three out of seven heavy metals showed a sufficient number of measured concentrations above the LOQ. Therefore, individual measurements of river water are not suitable for comparisons.\u003c/p\u003e \u003cp\u003eNext, the assessed heavy metal concentrations in Gammarus are evaluated to determine if they correlate with sediment sample measurements. For each heavy metal, a linear regression between the two sample types is calculated and the coefficient of determination (R\u0026sup2;) is computed (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The individual values of the 30 sampling points where gammarids were found are compared with the average values of the sediment samples from these water sections.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eLinear correlation between the heavy metal concentration of Gammarus and sediment at 30 sampling points, represented by the coefficient of determination (R\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\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 \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHeavy metal\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLead\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCad-mium\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChromium\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCopper\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNickel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eMercury\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eZinc\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eR\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0,014\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0,010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0,197\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0,020\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0,240\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0,998\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e0,001\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor the element mercury, a linear relationship is indicated (R\u0026sup2; = 0.998). However, this strong correlation for mercury is less meaningful due to the proximity of the measurement values of both sample types to the LOQ. For the other heavy metals, either no or only a slight linear relationship exists. For instance, the coefficient of determination R\u0026sup2; is 0.240 for nickel, and for the remaining five heavy metals, it is less than 0.200.\u003c/p\u003e \u003cp\u003eDue to the differences among the investigated watercourses and the varying magnitudes of measurement values, a high correlation could not be achieved. This is also due to other environmental influences not examined here, which can influence the heavy metal concentration of the sample types.\u003c/p\u003e \u003cp\u003eThe coefficients of determination indicate that the trends in heavy metal contamination in gammarids are only minimally similar to those in sediment. Therefore, the examination of heavy metals in sediment cannot be replaced by assessing heavy metals in gammarids.\u003c/p\u003e \u003cp\u003eAs these organisms are part of the food chain, their consideration is also relevant with regard to compliance with other limit values. It allows an examination of the ecological impact and also reveals increased concentrations along the course of the water body.\u003c/p\u003e \u003cp\u003eGerman and European regulations indicate that the chemical status assessment based on biota investigations (fish, crustaceans, molluscs) is preferred (OGewV \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Directive 2013/39/EU 2013). In this study, gammarids were investigated as bioindicators because they play a key role in a water body as shredders and decomposers of organic substances and as prey organisms for predators. Thus, the identified heavy metal contamination in gammarids is more relevant to the aquatic ecosystem than sediment contamination. However, the time required for gammarid sampling was significantly higher than that for sediment and water, and gammarids were not present at every sampling site.\u003c/p\u003e \u003cp\u003eA study conducted by the University of Bonn demonstrates that heavy metals accumulate significantly in \u003cem\u003eGammarus fossarum\u003c/em\u003e during their relatively short lifespan of approximately 12 to 18 months. This finding is supported by the fact that the levels of heavy metals in the examined Gammarus samples were higher than in the leaf samples (their food source) (H\u0026uuml;secken et al., \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2013\u003c/span\u003e). Gammarids can also be used for assessing heavy metal pollution in small streams, as they are ubiquitous unlike fish and typically represent the largest number of individuals within the macrozoobenthos community.\u003c/p\u003e \u003cp\u003eIn summary, for a separate analysis of heavy metal pollution in specific flowing waters and their anthropogenic discharge points, the measurements from water samples are inadequate since a large portion of the determined concentrations is below the limit of quantification (LOQ). The results from the examined Gammarus samples provide a comprehensive view of heavy metal pollution in the water sections, as the measurements, except for mercury, predominantly exceed the LOQ. However, not all sampling sites can be investigated using Gammarus samples due to the absence of freshwater amphipods at certain locations. Furthermore, only one pool sample could be taken from each study section for analysis, as the weight of the organisms found was only sufficient for one analysis sample if the necessary quantity was taken into account.\u003c/p\u003e \u003cp\u003eIn contrast, during sediment sampling, multiple samples were collected at all locations. This allowed the assurance of the heavy metal content by averaging individual measurements and identifying any potential differences. Additionally, sediment analysis is a standard procedure in heavy metal investigations, providing data on sediment heavy metal contents in previously surveyed water bodies. In flowing waters with known pollution (e.g., K\u0026ouml;ssein due to mercury contamination) as well as in major rivers (e.g., the Rhine), the heavy metal content of water, suspended solids, and sediment is analyzed (Pedall et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; IKSR 2022; HLNUG \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022b\u003c/span\u003e). Overall, the sediment heavy metal content in this study stands out as the most informative dataset. Hence, in the following sections, the sediment heavy metal contents will be utilized for assessing relevant heavy metal pollution.\u003c/p\u003e \u003cp\u003e \u003cb\u003eTemporal trend of mercury levels in the effluents of the hazardous waste site \u0026bdquo;Chemical Factory Marktredwitz\u0026ldquo;\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn this chapter, the determined mercury levels in the effluents of the hazardous waste site \"Chemical Factory Marktredwitz (CFM)\" are compared with the measurement data from earlier investigations. The aim is to demonstrate to what extent the effects of remediation measures are reflected in the mercury concentrations in the sediments. Thus, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e compares the average mercury levels in the sediments of the K\u0026ouml;ssein and R\u0026ouml;slau rivers in the years 2011 and 2022. The actual flow direction of the water is depicted from left to right by arranging the sampling points. The data from 2011 are derived from the study \"Quecksilber im Zulauf zum Stausee Skalka\u0026rdquo; commissioned by the responsible water authority (Pedall et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2011\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe mercury levels in the surveyed sections of the watercourses decreased in the period from 2011 to 2022. However, despite this reduction, the LAWA target value of 0.8 mg/kg DM (LAWA 1998a) was exceeded at the four survey points both in 2011 and 2022. The mercury contamination at the surveyed sections decreases over time as increased water flow mobilizes sedimented heavy metal particles, carrying them downstream into the Skalka reservoir. The largest quantity of mercury is adsorbed by the finest fraction, which in turn exhibits slow settling rates (Dikau et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). According to Czech authorities, up to 50 kilograms of mercury enter the reservoir annually (Gschwendtner, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Therefore, primarily oxbows, reservoirs, and areas with low flow velocities are affected in these two waters.\u003c/p\u003e \u003cp\u003eThe surveyed section of the K\u0026ouml;ssein at the former CFM site (K2) exhibits the lowest mercury concentration at 0.9 mg/kg DM, even though a mercury content of 227 mg/kg DM was measured in a regulatory examination in 1977 before the closure of the chemical factory (LfW, 1998). The investigated section underwent artificial restructuring due to decontamination and site remediation, and contaminated river sediment was properly disposed of (Pedall et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Hošek et al., \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Haussel, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Additionally, increased flow velocities resulted from the construction of the riverbed and the straightening of the river, transporting contaminated sediment downstream. Furthermore, existing heavy metal contents are diluted as uncontaminated fine material from the upper reaches deposits into the watercourse.\u003c/p\u003e \u003cp\u003eSimilar to 2011, the next surveyed section at the 'W\u0026ouml;lsauerhammer' weir (K3) holds the highest concentration of mercury. The sedimentation of heavy metals is favored by the weir structure and the confluence of a drainage ditch (Pedall et al., \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2011\u003c/span\u003e). The confluence point of the K\u0026ouml;ssein into the R\u0026ouml;slau (K4) shows a significant decrease in mercury concentration. In 2021, an upstream stretch of the riverbank was fortified due to heavy soil erosion (Bavarian State Parliament, 2022). The successful remediation of the contaminated section may have resulted in the decrease of mercury concentration approximately one kilometer away at the sampling site. Similarly, at the sampling site of the R\u0026ouml;slau before it merges into the Skalka reservoir (R1), the mercury content has decreased. The high flow velocity of the watercourse, particularly following the previous flood event, leads to a relatively low mercury contamination in the river sediment.\u003c/p\u003e\n\u003ch3\u003eEffects of sewage discharge into the Wieseck river\u003c/h3\u003e\n\u003cp\u003eIn November 2020, due to a technical fault in a control valve of a storage canal (combined sewer overflow system), untreated wastewater was discharged into the Wieseck for approximately one week. This led to significant deposits and a fish mortality (Bothe \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Subsequently, within an observation program, the ecological condition of the affected sections of the watercourse was evaluated based on ecological and physicochemical quality components. The present study supplements this program by investigating the heavy metal contamination before and after the discharge point. The average concentrations of heavy metals in the analyzed sediments from three sections of the watercourse before (WG1, WG2, WT1) and five sections after (WT2 to WT6) the wastewater discharge point were calculated (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe analyzed sediment samples show an increase in the concentrations of the heavy metals chromium, copper, nickel, and zinc after the faulty discharge point. Therefore, the uncontrolled wastewater discharge at the faulty control valve has an impact on downstream sections of the watercourse. Normally, the upstream section before the considered discharge point is already affected by six additional combined sewer overflow points with anthropogenic wastewater discharges. The highest percentage increase is observed in the elements zinc and copper, typically originating from municipal wastewater, thus confirming the heavy metal input through the faulty discharge point (Hillenbrand et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2005\u003c/span\u003e). Despite the elevation of some heavy metal concentrations, all environmental quality standards and targets are met.\u003c/p\u003e \u003cp\u003eThe results demonstrate that even one year after the anthropogenic discharge, heavy metal contamination can still be observed in the analyzed sediments (\"long-term memory\"). The cause of the high lead concentration before the discharge point could not be determined. Various sources are possible, as lead has been used as chemical compounds in different products, for example, from foundries, the chemical industry, fertilizer production, batteries, or from its past use as a gasoline additive (F\u0026ouml;rstner et al. 1974).\u003c/p\u003e \u003cp\u003e \u003cb\u003eInfluence of wastewater discharges on heavy metal concentrations in river sediment using the example of the Rosbach\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAt the Rosbach river, with a sampling point near its source (F1), as well as a site immediately after a municipal wastewater treatment plant (RO1), and several kilometers downstream from it (RO2), the accumulation of heavy metals in river sediment can be demonstrated (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMost of the heavy metal concentrations in section RO1, just downstream of the wastewater treatment plant, show only slight increases (lead, copper) or are not significantly elevated, except for zinc, which appears in concentrations about three times higher. In contrast, notably higher levels of heavy metals were measured in section RO2, located downstream of several combined sewer overflow outlets. Chromium and nickel concentrations, in particular, are notably higher in this section. Only trace amounts of mercury and cadmium are detected, with slight increases that are not visible in the diagram.\u003c/p\u003e \u003cp\u003eRegarding the parallel water analysis, it can be observed that zinc was found in higher concentration (0.0192 mg/L) only in RO1, directly after the wastewater treatment plant. Both F1 (0.0116 mg/L) and RO2 (0.0111 mg/L) show lower measurements at roughly the same level. Except for copper, which slightly increases from F1 (0.0010 mg/L) to RO1 (0.0011 mg/L) and further to RO2 (0.0013 mg/L), and nickel, which decreases from F1 (0.0022 mg/L) to RO1 (0.0017 mg/L) and increases again to RO2 (0.0020 mg/L), the other heavy metal elements remain at similar concentrations.\u003c/p\u003e \u003cp\u003eThe discrepancy between sediment and water analyses, except for zinc, can be attributed to the flushing of heavy metals after rain discharge from the treatment plant or through combined sewer overflow outlets. These heavy metals are primarily transported with the river water and eventually settle in the later course of the water body as sediment. Therefore, in the water phase, they can only be detected during the exact period when such rain discharge occurs. Heavy metals discharged into the water during these events subsequently lead to a concentration increase in more distant sections, explaining the previously described trend towards RO2.\u003c/p\u003e \u003cp\u003eZinc emerges from this study as an element commonly found in the water phase downstream of effluents. The already higher concentration of zinc in the water behind the wastewater treatment plant could be the cause of the comparatively higher zinc levels in the sediment at RO1 compared to other elements. Zinc and copper are heavy metal elements, and based on the obtained analysis results, their sediment concentrations frequently increase after the discharge of municipal wastewater.\u003c/p\u003e \u003cp\u003e \u003cb\u003eComparison of zinc and copper concentrations in the sediment of the sampling sites closer to the source with those of the subsequent watercourse sections\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe hypothesis is put forth that the concentrations of heavy metals in the sediment increase along the watercourse. Various discharge points may be causative factors for this. The values of a sampling site closer to the source (comparison) are presented, which are compared to the measurement results of all examined sampling sites downstream (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe values of each subsequent river course are derived from the average of all sampling sites located downstream from the comparison section.\u003c/p\u003e \u003cp\u003eIn six out of ten watercourses (Krebsbach, Wieseck (Trohe), Nidda, Erlenbach, Eschbach and Rosbach), the concentrations of zinc and copper are higher below the comparison sections closer to the source. Conversely, the concentrations in the comparison sections of Wieseck (Buseck) and K\u0026ouml;ssein are higher. In the case of Wetter, the zinc concentration in the comparison section is significantly lower, and the copper content is not much higher than that of the subsequent river sections. For Eichelbach, the comparison concentration for zinc is only slightly higher. The comparison of zinc and copper elements shows overall analogies.\u003c/p\u003e \u003cp\u003eThe comparison sections closer to the source are not all completely uncontaminated, as there may be a geogenic background contamination or diffuse or unknown inputs.\u003c/p\u003e \u003cp\u003eIn summary, it can be observed that there has been an accumulation of heavy metals in the sediment of the examined watercourses due to wastewater discharges.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe results presented show that the examined sample types exhibit certain differences. In the water samples, only heavy metal concentrations ranging from 0.0001 to 0.008 mg/L are measured, with a majority falling below the limit of quantification (LOQ). River water provides only a snapshot of the current pollution in the water body and is influenced by dynamic processes.\u003c/p\u003e \u003cp\u003eThe accumulation of heavy metals in the gammarids leads to metal concentrations that are on average about 1,000 times higher than those found in the water samples and mostly above the LOQ, except for mercury. Water organisms can uptake various heavy metals from the surrounding water and contaminated food. The relatively stationary gammarids accumulate available heavy metals in their habitat over their lifespan.\u003c/p\u003e \u003cp\u003eComparatively, the accumulation of heavy metals in the river sediments is about 10,000 times higher than in the river water. The sedimentation of suspended solids containing heavy metals and their adsorption on fine-grained sediment have the greatest potential for accumulation among the three examined sample types, so that these measurement data have the greatest significance for detecting past wastewater discharges.\u003c/p\u003e \u003cp\u003eThe comparison of mercury levels in the sediment of the \u0026ldquo;Chemical Factory Marktredwitz\u0026rdquo; contamination area's tributaries with earlier survey data indicates a decline in mercury levels at all sampling sites. This decrease is attributed to the increased water flow mobilizing the sedimented heavy metal particles, carrying them downstream into the Skalka reservoir. Consequently, the high flow rate of the studied watercourse after previous flood events leads to a decrease in mercury contamination in the river sediment and the deposition of uncontaminated fine material from the upper reaches.\u003c/p\u003e \u003cp\u003eThe successful remediation of a problematic erosion area before \u0026ldquo;W\u0026ouml;lsauerhammer\u0026rdquo; and the reduction in the runoff of contaminated soil were evidenced by a significant decrease in mercury contamination at a sampling site approximately one kilometer away.\u003c/p\u003e \u003cp\u003eThe heavy metal contamination of the Wieseck river sediment before and after a discharge point at which untreated wastewater was discharged into the river due to a technical error shows an increase in the concentration of the heavy metals chromium, copper, nickel and zinc after the faulty discharge point.\u003c/p\u003e \u003cp\u003eThe most significant percentage increase is observed in zinc and copper, typically originating from domestic wastewater, suggesting heavy metal input due to the faulty valve. Despite upstream sections being influenced by six combined sewage discharge points, the uncontrolled wastewater outflow has a more pronounced impact on downstream sections of the water body. Even one year after the anthropogenic discharge, there remains evidence of heavy metal contamination in the examined sediments (\"long-term memory\").\u003c/p\u003e \u003cp\u003eIn the Rosbach, as well as in other water bodies, heavy metals such as zinc and copper continuously enter the flowing water through the discharge channel of the municipal wastewater treatment plant, which is confirmed by sediment and water analyses. The remaining examined heavy metals enter the water body only after the discharge of untreated wastewater, typically following heavy rain events, and can only be determined through immediate water sample analysis. Transported by water flow, these heavy metal elements eventually sediment to the bottom of the water body and bind to the sediment present there. Consequently, they are no longer detectable in the water at a later time but can be identified through sediment analysis.\u003c/p\u003e \u003cp\u003eTo assess an increase in contamination in the water body, an additional examination of a less polluted reference section in the upper part of the water body is necessary. This approach helps reduce the influence of other sources of heavy metals, such as the geogenic background, especially when comparing with other water bodies.\u003c/p\u003e \u003cp\u003eIn a majority of the examined water bodies, an increase in zinc and copper concentrations in the water course compared to the respective reference sections was observed. This once again indicates a relationship between the discharge of municipal wastewater and the rise in heavy metal concentrations in the sediment. The existing variations, such as higher concentrations in reference sections, indicate that these sections might also be previously contaminated. Therefore, a precise selection of sampling sites, preferably those with minimal contamination, as well as before-and-after comparisons, is recommended.\u003c/p\u003e \u003cp\u003eGammarids, also known as freshwater amphipods, can serve as bioindicators for heavy metal contamination related to anthropogenic inputs, providing a comprehensive view of heavy metal pollution in the sampled sections of water bodies. However, no direct correlation could be established between the measurement values of gammarids and the influence of anthropogenic discharge points. Moreover, the detected levels of heavy metals at a specific section of the water body could not be confirmed by averaging individual measurements as the weight of the collected organisms was only sufficient for a single gammarid sample. Additionally, not all sampling sites could be investigated using gammarid samples due to the absence of these organisms in some sections of the study area. However, these limitations were not encountered in assessing heavy metal contamination using sediment analysis. The standardized analysis of heavy metals in sediment cannot be substituted by the assessment of heavy metals in gammarids, as there is only a low correlation observed between the heavy metal levels in gammarids and the sediment measurement values.\u003c/p\u003e \u003cp\u003eDespite these limitations, the observed heavy metal contaminations in gammarids have greater significance for the aquatic ecosystem compared to sediment pollution. Ultimately, the examined gammarids play a key role in water bodies as decomposers of organic substances and prey organisms in the food chain, reaching up to fish. They are commonly found ubiquitously in smaller water bodies with a large number of individuals. Furthermore, both German and European regulations stipulate that results from biota surveys (fish, crustaceans, molluscs) are favored in the chemical status assessment (Directive 2013/39/EU 2013).\u003c/p\u003e \u003cp\u003eThe results of this study indicate that gammarids can serve as bioindicators for heavy metal pollution in water bodies, provided that the described limitations are taken into account. Further investigations should assess the extent to which they could serve as an alternative to standardized electrofishing methods.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eEthics approval and consent to participate: Not applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication: Not applicable\u003c/p\u003e\n\u003cp\u003eAvailability of data and material: \"The datasets supporting the conclusions of this article are included within the article\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eCompeting interests: All co-authors have seen and agree with the contents of the manuscript and there is no financial interest to report. We certify that the submission is original work and is not under review for any other publication.\u003c/p\u003e\n\u003cp\u003eFunding: Not applicable\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAuthors' contributions: Lukas Plaß, Felix Heid and Ute Windisch performed the data calculations, participated in its coordination and drafted the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003eAcknowledgements: Special thanks go to the Technische Hochschule Mittelhessen for providing the laboratory and material.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eARGE Elbe - Arbeitsgemeinschaft f\u0026uuml;r die Reinhaltung der Elbe (1980): Schwermetalldaten der Elbe von Schnackenburg bis zur Nordsee. Hamburg\u003c/li\u003e\n\u003cli\u003eBayerischer Landtag (2022): Drucksache 18/19568 vom 25.02.2022. 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(1984): Ammonia-treated barley straw and rolled barley offered either together, in a mixed ration, or successively to beef steers. Animal Feed Science and Technology 10 (4):247-255\u003c/li\u003e\n\u003cli\u003eWindisch, U., Springer, F., Stahl, T. (2020): Freshwater amphipods (\u003cem\u003eGammarus pulex/fossarum\u003c/em\u003e) and brown trout as bioindicators for PFC contamination with regard to the aquatic ecological status of a small stream. Environmental Sciences Europe 32:108-122\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"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":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"heavy metals, copper, mercury, zinc, anthropogenic discharges, untreated sewage, small streams, sediment, water, Gammarus pulex, Gammarus fossarum, Gammarus roeselii, bioindicator, accumulation, benthic invertebrates","lastPublishedDoi":"10.21203/rs.3.rs-3832560/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3832560/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe entry of heavy metals into rivers affects both the water quality and the biocoenosis of the water bodies. Heavy metals that are discharged with wastewater are distributed with the current and can be stored downstream in the sediment of the watercourse and absorbed by aquatic organisms.\u003c/p\u003e \u003cp\u003eThe aim of the study is to examine how heavy metals entering water bodies are found in samples of water, sediment, and freshwater amphipods (Gammarus spp.). Several smaller rivers in Hesse and Bavaria are being investigated, establishing a connection to existing wastewater discharge points.\u003c/p\u003e \u003cp\u003eFor the examined rivers, it is determined that the concentration of heavy metals in sediment is about 10,000 times higher than in a scoop sample of water from the same section of the water body. In the species \u003cem\u003eGammarus fossarum\u003c/em\u003e, \u003cem\u003eG. pulex\u003c/em\u003e and \u003cem\u003eG. roeselii\u003c/em\u003e, heavy metal concentrations are about 1,000 times higher than those found in the investigated river water. A comparison of heavy metal contents in gammarids and in sediment shows no linear relationship. Gammarids inhabit the bottom of water bodies and the bank area, accumulating heavy metals with their food throughout their lifetime. Due to their high abundance, they serve as accumulation indicators in most smaller rivers. However, the sampling process is labor-intensive, requiring sufficient sample weight and the removal of other macrozoobenthos species. Sampling sediment in water bodies with gravel or fine sediment requires less effort. Water samples can be obtained quickly from any water body.\u003c/p\u003e \u003cp\u003eThe investigations of the K\u0026ouml;ssein and R\u0026ouml;slau rivers in Bavaria, known for their mercury contamination, show a decrease in heavy metal concentrations over a period of about ten years. Due to the low flow velocity at the W\u0026ouml;lsauerhammer weir, elevated levels can still be observed in the settled sediment. Dredging the riverbed and securing the banks of previously heavily contaminated sections lead to an overall decrease in concentrations throughout the river system.\u003c/p\u003e \u003cp\u003eSediment analyses from several sampling sites along the Wieseck river near Trohe, where untreated sewage was discharged for a week, indicate that an increase in heavy metal contamination due to the event can still be detected about a year later.\u003c/p\u003e \u003cp\u003eThe example of Rosbach in the Taunus region illustrates the suitability of combining different types of samples. Water analysis shows an increase in heavy metal concentrations (including zinc) downstream of a wastewater treatment plant's discharge point, which can be found in the sediment further along the watercourse.\u003c/p\u003e \u003cp\u003eThe examination of water samples is mainly suitable for short-term monitoring of known contamination events. Conversely, environmental media such as sediment and Gammarus spp. can be used to assess past wastewater discharges. The increase in heavy metal contamination in water bodies due to wastewater discharges is confirmed for both sediment and gammarids.\u003c/p\u003e","manuscriptTitle":"Comparison of heavy metal contamination in sediment, water and Gammarus spp. (Crustacea: Amphipoda) in small streams with respect to anthropogenic discharges","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-08 09:01:12","doi":"10.21203/rs.3.rs-3832560/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ae1c53b4-fe7d-4702-9b94-6c5259d6e848","owner":[],"postedDate":"January 8th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-31T11:23:33+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-08 09:01:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3832560","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3832560","identity":"rs-3832560","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}