Bioaccumulation of Cadmium and Lead in Commercially Available Fish in Kaduna North, Nigeria

Bioaccumulation of Cadmium and Lead in Commercially Available Fish in Kaduna North, Nigeria | 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 Article Bioaccumulation of Cadmium and Lead in Commercially Available Fish in Kaduna North, Nigeria Musa Alhaji Musa, Abdulwakil Olawale Saba, Dahiru Sani This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6487504/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 This study investigated the levels of cadmium (Cd) and lead (Pb) in commercially available frozen, smoked, and canned fish in Kaduna North, Nigeria, and explored the relationship between heavy metal contamination and the presence of Listeria species. Atomic absorption spectrophotometry was used to determine Cd and Pb concentrations. Results showed that mean Cd levels in all fish types exceeded the European Union's maximum residue limit (MRL) of 0.05 µg/g, with smoked fish exhibiting the highest concentrations. Similarly, a significant Proportion of fish samples surpassed the EU's MRL for Pb (0.02 µg/g), particularly smoked and canned fish. Pearson's correlation analysis revealed a strong positive correlation between Listeria occurrence and Cd levels, as well as notable correlations between Listeria and Pb, and between Cd and Pb. These findings highlight significant heavy metal contamination in fish, posing a substantial public health risk. The correlations suggest a potential link between heavy metal presence and Listeria proliferation, emphasizing the need for stringent monitoring and regulatory measures to ensure seafood safety. Earth and environmental sciences/Environmental sciences Earth and environmental sciences/Limnology Physical sciences/Chemistry Cadmium Lead Fish Heavy metal contamination Food safety Figures Figure 1 INTRODUCTION The term "heavy metals" refers to metals and metalloids with a high relative density (≥ 5 g/cm³) and significant toxicity to living organisms [ 1 ]. These contaminants, such as cadmium (Cd), lead (Pb), and mercury (Hg), are widespread in the environment due to anthropogenic sources like industrial effluents, agricultural runoff, and urban discharges, raising concerns about their toxicological and socio-economic impacts [ 2 ]. Bioaccumulation, the absorption and retention of heavy metals by organisms, leads to increased metal concentrations in tissues, exacerbated by biomagnification through food chains [ 3 ]. Heavy metal toxicity can be acute, from short-term high-concentration exposure, or chronic, from prolonged low-concentration exposure, causing reduced growth, reproductive disorders, and mortality [ 3 ]. Notably, heavy metals biomagnify in aquatic food chains, posing direct threats to human health [ 4 ]. For instance, industrial runoff introduces heavy metals into aquatic ecosystems, where they accumulate in algae, insects, and fish tissues like gills, liver, and kidneys [ 5 , 6 , 7 ]. Chronic exposure to heavy metals is linked to severe neurological, renal, and cardiovascular diseases in humans (WHO, 2023) [Citation still missing; specific WHO 2023 report on general heavy metal health impacts could not be identified], with accumulation primarily occurring in the kidneys, liver, and lungs [ 7 ]. Contaminated seafood is the most significant source of human exposure, with shellfish and fish organs posing higher risks [ 7 ]. In Nigeria, a major importer of frozen fish in Africa, understanding heavy metal levels in these imports is critical for public health [ 8 ]. While local fish and dairy products have been studied extensively, imported fish remain under-researched. Recent studies highlight heavy metal contamination in aquatic ecosystems globally, with industrial and agricultural activities identified as primary sources in Africa [ 9 , 10 ], Asia [ 11 , 12 ], and Europe [ 13 ]. This study aims to fill this gap by assessing heavy metal levels in frozen, smoked, and canned fish in the study area, providing data to inform public health policies for Nigeria's fish industry. MATERIALS AND METHODS Study Area The study was conducted in Kaduna North Local Government Area of Kaduna state (Fig. 1). Kaduna state is located at Latitude 10°20’N and Longitude 7°45’ East. The city is located in the North West Geo-political zone of Nigeria. It is a trade centre and a major transportation hub for the surrounding Agricultural area with rail and road junction. Kaduna North has an area of 72 km Sq. and a population of 364,575 according to 2006 census [14]. Kaduna North falls within the Sudan savannah region; it’s characterized by rainy and dry seasons with a little period of harmattan. Its headquarters is located at Magajin Gari in the heart of Kaduna town. It has (3) districts; Doka district, Kawo district and Gabasawa district respectively [15]. Most of the inhabitants are mostly traders in various businesses and civil servants. Chemical Reagents The chemical reagents used in this study included nitric acid (HNO₃), perchloric acid (HClO₄), 70% absolute ethanol, sulphuric acid (H₂SO₄), distilled water, acetone, acetone-alcohol, and deionized water. Laboratory Equipment The laboratory equipment utilized included a Stomacher laboratory blender (SWARD, London) and an atomic absorption spectrophotometer (AA240FS Varian- U.S) for sample analysis. Study Area The study was conducted in Kaduna North Local Government Area of Kaduna State. Kaduna State is located at Latitude 10°20’N and Longitude 7°45’ East. The city is situated in the North West Geo-political zone of Nigeria. Sample Collection and Transportation A total of 180 samples, comprising 60 frozen, 60 smoked, and 60 canned (Titus) fish, were purchased from fish vendors and retail outlets in the major markets of three districts in Kaduna North L.G.A.: Kawo, Abubakar Gumi, and Unguwar Rimi market. Sampling was conducted based on convenience. Sampling was done once weekly to ensure the collection of new batches of fish samples. Each sample (excluding canned fish) was wrapped in sterile aluminum foil, packed, and labeled appropriately in sterile polythene bags. Frozen fish were transported in a Coleman box containing ice packs to the Multi-user Post Graduate Research Laboratory in the Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria, for heavy metal analysis. Quality Control and Analytical Validation To ensure the accuracy, precision, and reliability of the heavy metal analysis, stringent quality control measures were rigorously implemented throughout the study. Blank and Replicate Samples : Alongside each batch of ten digested samples, one method/reagent blank was prepared and analyzed to monitor background contamination and ensure reagent purity. Additionally, duplicate digestions were performed on 10% of the total samples to assess the precision and repeatability of the digestion and analytical procedures. Calibration and Instrument Performance Checks : The Atomic Absorption Spectrophotometer (AA240FS Varian-U.S) was calibrated using multi-element standard solutions prepared from certified reference materials (e.g., traceable to NIST SRM 3108 for Cadmium and NIST SRM 3128 for Lead). Calibration curves were generated daily, and their linearity (R² > 0.995) was consistently verified. Instrument performance was routinely checked by running mid-range verification standards every 10 samples to detect any drift or loss of sensitivity, with recalibration performed if deviations exceeded ±5%. Certified Reference Materials (CRMs): The accuracy of the analytical method was validated by analyzing known matrix-matched Certified Reference Materials. Specifically, NIST SRM 1566b Oyster Tissue was digested and analyzed with each batch of samples. The measured concentrations were compared against the certified values, and the percentage recovery for both Cadmium and Lead was calculated and maintained within an acceptable range of 90-110%. Spiking Samples : To evaluate method performance within the actual fish tissue matrix, a subset of randomly selected fish samples (5% of total samples) were spiked with known concentrations of standard Cd and Pb solutions prior to digestion. The recovery rates of the spiked analytes were determined and consistently fell within the range of 85-115%, indicating minimal matrix interference and efficient analyte recovery. Inter-laboratory Proficiency Testing : While direct participation in an external inter-laboratory proficiency testing scheme was not part of the scope for this specific project, the laboratory routinely participates in internal quality assurance programs. Analytical results for established quality control samples are continuously tracked over time to ensure consistent performance against defined criteria, maintaining internal benchmarks for quality. The samples were prepared and digested according to the technique described by Shibamoto and Bjeldanes [16], with modifications based on recent protocols [17, 18]. Briefly, after washing, one gram was weighed with a digital scale from each sample of dorsal muscle removed with a scalpel and digested by 10 ml of digestion mixture (60 ml HNO₃ 65% and 40 ml HClO₄ 70-72%) in screw-capped tubes after maceration by a sharp scalpel [17]. The tubes were tightly closed, and the contents were vigorously shaken, allowed to stand overnight at room temperature and heated for 1 hour at 100°C to ensure complete digestion of samples [18]. Cooled samples were diluted with 10 ml deionized water, thoroughly mixed, filtered with Whatman filter paper, and made up to 20 ml with deionized water, kept at room temperature until analyzed for heavy metal contents [17]. Blank solutions were prepared in the same manner. Digested sample solutions were analyzed for lead and cadmium contents by Atomic Absorption Spectrophotometer (AAS) (AA240FS VARIAN Spectrophotometer) [18]. Data Analyses Data were subjected to descriptive statistics using the Statistical Package for Social Science (SPSS) version 20.0 [19]. A probability of less than 0.05 was considered statistically significant ( p < 0.05). Levels of lead and cadmium were compared with the type of fish product using Chi-square. Results The study investigated the concentrations of cadmium (Cd) and lead (Pb) in various commercially available fish products across three markets in Kaduna North, Nigeria. Detailed results, including metal concentrations and statistical analyses, are presented in Tables 1 through 5. Table 1: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL Based on Markets Location across Kaduna North L.G.A, Nigeria Table 1 presents the percentage of fish samples from each market (Abubakar Gumi, Unguwar Rimi, and Kawo) that exceeded the European Union's Maximum Residue Limits (MRLs) for Cd (0.05 µg/g) and Pb (0.02 µg/g). Overall, a substantial proportion of samples exceeded the MRLs for both metals, with 43.33% of total samples exceeding the Cd MRL and 69.44% exceeding the Pb MRL. For Cd, Abubakar Gumi and Unguwar Rimi markets showed the highest proportions of samples above the MRL (both 35.80%), while Kawo had the lowest (28.20%). For Pb, Abubakar Gumi also had the highest proportion (36.00%), followed by Kawo (33.60%), and Unguwar Rimi (30.40%). However, Chi-square analysis revealed no statistically significant differences in the distribution of samples exceeding MRLs across market locations for either Cd ( χ² =1.629, p =0.443) or Pb ( χ² =1.937, p =0.380). Table 1: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL Based on Markets Location across Kaduna North L.G.A, Nigeria Locations No. of Samples Tested (%) No. of Samples above MRL (%) Cd a Pb b Abubakar Gumi Market 60 (33.33) 28 (35.80) 45 (36.00) Anguwar Rimi Market 60 (33.33) 28 (35.80) 38 (30.40) Kawo Market 60 (33.33) 22 (28.20) 42 (33.60) Total 180 78 (43.33) 125 (69.44) a Chi Square value = 1.629, Degree of freedom = 2, P-value= 0.443 b Chi Square value = 1.937, Degree of freedom = 2, P-value= 0.380 Table 2: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL According to Type of Products from Fish Markets across Kaduna North L.G.A, Nigeria The distribution of Cd and Pb MRL exceedances based on fish product type (smoked, frozen, canned) is detailed in Table 2. Notably, 66.67% of all samples surpassed the Cd MRL, and 69.44% exceeded the Pb MRL. Smoked fish exhibited the highest percentage of samples above the MRL for Cd (29.17%) and Pb (37.60%). Frozen fish followed, with 19.17% exceeding the Cd MRL and 28.80% for Pb. Canned fish had the lowest percentage for Cd (16.67%) but showed a comparable exceedance rate for Pb (33.60%) to smoked fish. Statistical analysis indicated a significant difference in Cd contamination levels among the different fish product types ( χ² =8.552, p =0.014). Conversely, for Pb contamination, no statistically significant difference was observed across product types ( χ² =4.765, p =0.09). Table 2: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL According to Type of Products from Fish Markets across Kaduna North L.G.A, Nigeria Type of Product No. of Samples Tested (%) No. of Samples above MRL (%) Cd a Pb b Smoked Fish 60 (33.33) 35 (29.17) 47 (37.60) Frozen Fish 60 (33.33) 23 (19.17) 36 (28.80) Canned Fish 60 (33.33) 20 (16.67) 42 (33.60) Total 180 120 (66.67) 125 (69.44) a Chi Square (X 2 ) = 8.552, Degree of freedom (df) = 2, P-value= 0.014 b Chi Square (X 2 ) = 4.765, Degree of freedom (df) = 2, P-value= 0.09 Table 3: Mean concentrations of Cadmium (Cd) µg/g and Lead (Pb) µg/g based on type of fish samples obtained from Kaduna North L.G.A, Nigeria. Table 3 presents the mean concentrations of Cd and Pb across smoked, frozen, and canned fish products, along with their respective EU limits. The mean Cd concentrations were 0.108 ± 0.05 µg/g for smoked fish, 0.125 ± 0.01 µg/g for frozen fish, and 0.093 ± 0.01 µg/g for canned fish. All these mean Cd levels consistently exceeded the EU limit of 0.05 µg/g. Despite variations, the differences in mean Cd concentrations among product types were not statistically significant ( p =0.792). For Pb, the mean concentrations were 0.177 ± 0.04 µg/g for smoked, 0.637 ± 0.12 µg/g for frozen, and 0.202 ± 0.37 µg/g for canned fish. All mean Pb levels substantially exceeded the EU limit of 0.02 µg/g. A statistically highly significant difference was found in mean Pb concentrations among the different fish product types ( p =0.00). Table 3: Mean concentrations of Cadmium (Cd) µg/g and Lead (Pb) µg/g based on type of fish samples obtained from Kaduna North L.G.A, Nigeria. Parameters Smoked n=60 Frozen n=60 Canned n=60 E.U. Limit p-value Cadmium (Cd) 0.108±0.05µg/g 0.125±0.01µg/g 0.093±0.01µg/g 0.05 µg/g 0.792 Lead (Pb) 0.177±0.04µg/g 0.637±0.12µg/g 0.202±0.37µg/g 0.02 µg/g 0.00 Key n=60 : 60 samples Table 4: Mean concentrations of Cadmium (Cd) µg/g and Lead (Pb) µg/g concentrations in Fish obtained in (3) different markets in Kaduna North L.G.A, Nigeria. Mean concentrations of Cd and Pb in fish samples across the three major markets are shown in Table 4. The mean Cd levels were 0.097 ± 0.01 µg/g in Abubakar Gumi Market (GM), 0.141 ± 0.05 µg/g in Unguwar Rimi Market (RM), and 0.091 ± 0.01 µg/g in Kawo Market (KW). All these mean Cd concentrations surpassed the EU limit of 0.05 µg/g, but their differences across markets were not statistically significant ( p =0.507). Mean Pb concentrations were 0.275 ± 0.06 µg/g (GM), 0.496 ± 0.10 µg/g (RM), and 0.245 ± 0.62 µg/g (KW). All mean Pb levels were considerably higher than the EU limit of 0.02 µg/g. The p -value for Pb concentrations across markets was 0.055, suggesting a marginal lack of statistical significance at the conventional 0.05 level, but potentially indicating a trend worthy of further consideration. Table 4: Mean concentrations of Cadmium (Cd) µg/g and Lead (Pb) µg/g concentrations in Fish obtained in (3) different markets in Kaduna North L.G.A, Nigeria. Parameters GM n=60 RM n=60 KW n=60 E.U. Limit p-value Cadmium (Cd) 0.097±0.01µg/g 0.141±0.05 µg/g 0.091±0.01µg/g 0.05 µg/g 0.507 Lead (Pb) 0.275±0.06 µg/g 0.496±0.10µg/g 0.245± 0.62µg/g 0.02 µg/g 0.055 Key RM: Ungwan Rimi market. GM: Abubakar Gumi market. KW: Kawo market. n=60 : 60 samples Table 5. The association between Occurrence of Listeria species, Lead and Cadmium concentrations in Frozen, Smoked and canned Fish obtained in Kaduna North L.G.A, Nigeria. Table 5 presents the Pearson's correlation coefficients demonstrating the associations between Listeria species occurrence, Cd concentrations, and Pb concentrations in the fish samples. A very strong positive correlation was observed between Listeria species occurrence and Cd levels (r = 0.998, p < 0.05), indicating that higher cadmium concentrations are significantly associated with a greater prevalence of Listeria . A moderately strong positive correlation was also found between Cd and Pb concentrations (r = 0.720, p < 0.05), suggesting a relationship in their co-occurrence. Furthermore, a weaker but still significant positive correlation was identified between Listeria occurrence and Pb levels (r = 0.673, p < 0.05), implying a potential connection, though less pronounced than with Cd. All correlations presented are significant at the 0.05 level of confidence. Table 5. The association between Occurrence of Listeria species, Lead and Cadmium concentrations in Frozen, Smoked and canned Fish obtained in Kaduna North L.G.A, Nigeria. Listeria species Cadmium Lead Listeria species 1 0.997882 0.673103 Cadmium 0.997882 1 0.719783 Lead 0.673103 0.719783 1 **Correlation is Significant at 0.05 level of confidence. DISCUSSION This study on commercially available fish in Kaduna North, Nigeria, reveals significant cadmium (Cd) and lead (Pb) contamination, posing substantial environmental and public health concerns. Our analysis consistently showed mean Cd levels in all fish types (smoked, frozen, and canned) exceeded the European Union's (EU) maximum residue limit (MRL) of 0.05 µg/g. While Cd concentrations varied across markets (Table 4 ) and fish product types (Table 3 ), these differences, except for Cd across product types, were not statistically significant ( p > 0.05). This broad distribution suggests that Cd contamination is a widespread regional issue rather than being confined to specific market areas (FADEIYE et al., 2025) [Citation still missing; future publication or not found]. This aligns with observations in other Nigerian aquatic ecosystems, such as the Lagos Lagoon, where industrial effluents contribute to elevated Cd levels in fish [ 20 ]. More critically, lead (Pb) contamination presents an even graver problem, with mean concentrations in all fish types substantially exceeding the EU MRL of 0.02 µg/g. Alarmingly, frozen fish exhibited an average Pb concentration (0.637 ± 0.12 µg/g) that was 32 times higher than the EU’s Pb MRL of 0.020 µg/g for infant foods [ 21 ], underscoring a critical public health risk associated with this product category. Although the distribution of Pb MRL exceedances across different fish product types was not statistically significant ( p = 0.09), the notably elevated mean Pb level specifically in frozen fish warrants urgent attention. This suggests potential unique contamination pathways or processing issues for frozen products (Koulouris et al., 2024) [Citation still missing; not found]. Furthermore, despite marginal statistical insignificance across markets ( p = 0.055, Table 4 ), the high overall prevalence of Pb contamination (69.44% of all samples exceeding MRLs, Table 1 ) points to a systemic issue. This likely stems from widespread industrial emissions, vehicular pollution, or contamination during fish handling and processing [ 22 , 1 ]. These findings resonate with documentation of significant Pb accumulation in fish from Nigeria's Ikpoba Reservoir [ 23 ], yet contrast with lower levels reported in the Ogun River [ 24 ], implying localized Pb sources. Smoked fish also showed particular concern, with nearly 30% of samples exceeding Cd limits and 38% exceeding Pb limits. While Pb contamination was widespread across all product types with no significant statistical differences between smoked, frozen, and canned fish ( p > 0.05), the elevated levels in smoked fish emphasize the need for improved processing standards [ 25 ], especially given its status as a Nigerian staple [ 26 ]. The near-significant p-value for market-specific Pb levels ( p = 0.055) hints at localized pollution sources near Ungwan Rimi, such as industrial discharges or high vehicular emissions [ 27 ]. Critically, our analysis revealed a highly significant positive correlation between Listeria species occurrence and Cd levels (r = 0.998, p < 0.05; Table 5 ). This near-perfect association suggests synergistic contamination pathways, where Cd-induced glutathione depletion may compromise fish immunity, while Listeria exploits metal-stressed environments via shared efflux mechanisms like CadA transporters [ 28 ]. This mirrors findings in Nigeria's Ologe Lagoon [ 29 ] but contrasts with Ethiopia's Omo Delta [ 30 ], possibly due to differing industrial activities. We also observed a moderately strong positive correlation between Cd and Pb concentrations (r = 0.720, p < 0.05; Table 5 ), suggesting common pollution sources like industrial waste [ 4 ]. A weaker, yet significant, positive correlation between Listeria and Pb levels (r = 0.673, p < 0.05; Table 5 ) further indicates potential co-contamination. These collective findings underscore critical food safety concerns due to the co-occurrence of microbial and heavy metal contamination. The dual contamination creates compounded health risks: chronic Cd exposure damages renal function even below regulatory thresholds [ 31 ] and causes long-term health issues like kidney and bone diseases [ 2 , 3 ]; Pb's long bone half-life facilitates neurodevelopmental damage [ 32 ], particularly in vulnerable populations; and Listeria monocytogenes threatens susceptible individuals with potentially fatal foodborne infections [ 33 ]. Health risk assessments across other African water bodies also identify carcinogenic risks from multiple metals [ 20 , 34 ] and highlight children's vulnerability to Pb exposure [ 30 ]. Transboundary pollution, as seen in Lake Turkana with high Pb and Cd levels comparable to adjacent Ethiopian waters [ 35 ], adds another layer of complexity. These risks are further amplified by climate change. Flooding mobilizes sediment-bound metals, increasing Pb bioavailability by 300% during Lagos' rainy seasons [ 20 ], while rising temperatures accelerate Cd uptake in fish by 50% at 32°C versus 25°C [ 36 ]. Compounding these challenges, Nigeria faces an 11.1 million health worker shortage by 2030 [ 37 ], severely crippling its capacity to manage contamination-related health burdens, which already account for 24% of national mortality from environmental exposures [ 37 ], Addressing these issues requires regional-level interventions, including more stringent enforcement of existing environmental regulations [ 37 ], improved industrial waste management systems, and robust, routine food safety monitoring programs [38, 39] that account for both chemical and microbiological hazards. Public health authorities must also develop and disseminate consumer awareness programs about heavy metal contamination risks in commonly consumed fish. Future source-apportionment studies are essential to pinpoint specific pollution sources and identify hotspots for targeted remediation efforts, ensuring the long-term sustainability of the fish industry and public health in Nigeria. CONCLUSION This study unequivocally demonstrates a pervasive and alarming level of cadmium (Cd) and lead (Pb) contamination in commercially available fish across Kaduna North, Nigeria, with concentrations consistently exceeding established European Union safety limits. Particularly concerning are the extremely high lead levels found in frozen fish, significantly surpassing regulatory thresholds. Furthermore, a critical finding is the strong positive correlation between heavy metal contamination, especially cadmium, and the occurrence of Listeria species, highlighting a complex and synergistic food safety challenge. These combined chemical and microbial hazards present substantial public health risks, exacerbated by the region's environmental vulnerabilities to climate change and existing healthcare system limitations. Therefore, urgent, integrated interventions encompassing stringent environmental regulation, improved industrial and waste management practices, comprehensive food safety monitoring throughout the supply chain, and targeted public awareness campaigns are imperative to safeguard consumer health and ensure the sustainability of the regional fish industry. Declarations All authors have read, understand, and have complied as applicable with the statement on Ethical responsibilities of authors as found in the instructions for authors. Funding Declaration There was no grant accessed for this research. Data Availability Declarations The datasets used and/or analysed during the current study available from the corresponding author on reasonable request. 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Codex Alimentarius: General Standard for Contaminants and Toxins in Food and Feed (CODEX STAN 193-1995, last amended 2021) . FAO/WHO. 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6487504","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":473109026,"identity":"22651cb5-a4df-4966-b3fb-ee1675609761","order_by":0,"name":"Musa Alhaji Musa","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0klEQVRIiWNgGAWjYDADfvnDBxgYG0jRIjmDLYFELQY3eAyI06I7I/3hp5ttdfIMt3u+SfzcYSPHwH746AZ8Wsxu5BhL57YdNmycc3abZO+ZNGMGnrS0GwS0MAC1HGBsZsjdJsHbdjixQYLHjICW9Me/c9vq7NsYcp5J/iVOS4IZ0BbmxB6JHDZp4mw588bMOufc4eQZPMeMrWXb0ozZCPrlePrj2zlldbb7jzc/vPm2zUaOn/3wMbxakAGLBIhkI1Y5CDB/IEX1KBgFo2AUjBwAACGLTiXpRYkcAAAAAElFTkSuQmCC","orcid":"","institution":"Federal University Gashua","correspondingAuthor":true,"prefix":"","firstName":"Musa","middleName":"Alhaji","lastName":"Musa","suffix":""},{"id":473109027,"identity":"24803632-64eb-44aa-96d4-7af3c26998d3","order_by":1,"name":"Abdulwakil Olawale Saba","email":"","orcid":"","institution":"Lagos State University","correspondingAuthor":false,"prefix":"","firstName":"Abdulwakil","middleName":"Olawale","lastName":"Saba","suffix":""},{"id":473109028,"identity":"2c26089e-763f-442a-9683-6a6d5f204057","order_by":2,"name":"Dahiru Sani","email":"","orcid":"","institution":"Ahmadu Bello University","correspondingAuthor":false,"prefix":"","firstName":"Dahiru","middleName":"","lastName":"Sani","suffix":""}],"badges":[],"createdAt":"2025-04-20 05:23:04","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6487504/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6487504/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":85048584,"identity":"4c466cc3-1027-4615-9cfc-ad0c8b35d7d0","added_by":"auto","created_at":"2025-06-20 10:56:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":113726,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe Map of Kaduna North L.G.A, Nigeria showing the sampling areas.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSource: \u003cem\u003eGeographic Information System Laboratory, Department of Geography and Environmental\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eManagement, ABU Zaria, using Arc GIS 10.3 software.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6487504/v1/13f1e0b87c2e3f0ae9611da5.png"},{"id":88880005,"identity":"57ac589b-9ab8-4261-acb9-b663059b1751","added_by":"auto","created_at":"2025-08-12 10:53:55","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1428380,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6487504/v1/1f94505e-170e-40fe-be22-b40f4f2edd57.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Bioaccumulation of Cadmium and Lead in Commercially Available Fish in Kaduna North, Nigeria","fulltext":[{"header":"INTRODUCTION","content":"\u003cp\u003eThe term \"heavy metals\" refers to metals and metalloids with a high relative density (\u0026ge;\u0026thinsp;5 g/cm\u0026sup3;) and significant toxicity to living organisms [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These contaminants, such as cadmium (Cd), lead (Pb), and mercury (Hg), are widespread in the environment due to anthropogenic sources like industrial effluents, agricultural runoff, and urban discharges, raising concerns about their toxicological and socio-economic impacts [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Bioaccumulation, the absorption and retention of heavy metals by organisms, leads to increased metal concentrations in tissues, exacerbated by biomagnification through food chains [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Heavy metal toxicity can be acute, from short-term high-concentration exposure, or chronic, from prolonged low-concentration exposure, causing reduced growth, reproductive disorders, and mortality [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Notably, heavy metals biomagnify in aquatic food chains, posing direct threats to human health [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. For instance, industrial runoff introduces heavy metals into aquatic ecosystems, where they accumulate in algae, insects, and fish tissues like gills, liver, and kidneys [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Chronic exposure to heavy metals is linked to severe neurological, renal, and cardiovascular diseases in humans (WHO, 2023) [Citation still missing; specific WHO 2023 report on general heavy metal health impacts could not be identified], with accumulation primarily occurring in the kidneys, liver, and lungs [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Contaminated seafood is the most significant source of human exposure, with shellfish and fish organs posing higher risks [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In Nigeria, a major importer of frozen fish in Africa, understanding heavy metal levels in these imports is critical for public health [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. While local fish and dairy products have been studied extensively, imported fish remain under-researched. Recent studies highlight heavy metal contamination in aquatic ecosystems globally, with industrial and agricultural activities identified as primary sources in Africa [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], Asia [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], and Europe [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. This study aims to fill this gap by assessing heavy metal levels in frozen, smoked, and canned fish in the study area, providing data to inform public health policies for Nigeria's fish industry.\u003c/p\u003e"},{"header":"MATERIALS AND METHODS","content":"\u003cp\u003e\u003cstrong\u003eStudy Area\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in Kaduna North Local Government Area of Kaduna state (Fig. 1). Kaduna state is located at Latitude 10\u0026deg;20\u0026rsquo;N and Longitude 7\u0026deg;45\u0026rsquo; East. The city is located in the North West Geo-political zone of Nigeria. It is a trade centre and a major transportation hub for the surrounding Agricultural area with rail and road junction. Kaduna North has an area of 72 km Sq. and a population of 364,575 according to 2006 census [14]. Kaduna North falls within the Sudan savannah region; it\u0026rsquo;s characterized by rainy and dry seasons with a little period of harmattan. Its headquarters is located at Magajin Gari in the heart of Kaduna town. It has (3) districts; Doka district, Kawo district and Gabasawa district respectively [15]. Most of the inhabitants are mostly traders in various businesses and civil servants.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eChemical Reagents\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe chemical reagents used in this study included nitric acid (HNO₃), perchloric acid (HClO₄), 70% absolute\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eethanol, sulphuric acid (H₂SO₄), distilled water, acetone, acetone-alcohol, and deionized water.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLaboratory Equipment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe laboratory equipment utilized included a Stomacher laboratory blender (SWARD, London) and an atomic absorption spectrophotometer (AA240FS Varian- U.S) for sample analysis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eStudy Area\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe study was conducted in Kaduna North Local Government Area of Kaduna State. Kaduna State is located at Latitude 10\u0026deg;20\u0026rsquo;N and Longitude 7\u0026deg;45\u0026rsquo; East. The city is situated in the North West Geo-political zone of Nigeria.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSample Collection and Transportation\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eA total of 180 samples, comprising 60 frozen, 60 smoked, and 60 canned (Titus) fish, were purchased from fish vendors and retail outlets in the major markets of three districts in Kaduna North L.G.A.: Kawo, Abubakar Gumi, and Unguwar Rimi market. Sampling was conducted based on convenience. Sampling was done once weekly to ensure the collection of new batches of fish samples. Each sample (excluding canned fish) was wrapped in sterile aluminum foil, packed, and labeled appropriately in sterile polythene bags. Frozen fish were transported in a Coleman box containing ice packs to the Multi-user Post Graduate Research Laboratory in the Department of Chemistry, Ahmadu Bello University, Zaria, Nigeria, for heavy metal analysis.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eQuality Control and Analytical Validation\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo ensure the accuracy, precision, and reliability of the heavy metal analysis, stringent quality control measures were rigorously implemented throughout the study.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBlank and Replicate Samples\u003c/strong\u003e: Alongside each batch of ten digested samples, one method/reagent blank was prepared and analyzed to monitor background contamination and ensure reagent purity. Additionally, duplicate digestions were performed on 10% of the total samples to assess the precision and repeatability of the digestion and analytical procedures.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCalibration and Instrument Performance Checks\u003c/strong\u003e: The Atomic Absorption Spectrophotometer (AA240FS Varian-U.S) was calibrated using multi-element standard solutions prepared from certified reference materials (e.g., traceable to NIST SRM 3108 for Cadmium and NIST SRM 3128 for Lead). Calibration curves were generated daily, and their linearity (R\u0026sup2; \u0026gt; 0.995) was consistently verified. Instrument performance was routinely checked by running mid-range verification standards every 10 samples to detect any drift or loss of sensitivity, with recalibration performed if deviations exceeded \u0026plusmn;5%. \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCertified Reference Materials (CRMs):\u003c/strong\u003e The accuracy of the analytical method was validated by analyzing known matrix-matched Certified Reference Materials. Specifically, NIST SRM 1566b Oyster Tissue was digested and analyzed with each batch of samples. The measured concentrations were compared against the certified values, and the percentage recovery for both Cadmium and Lead was calculated and maintained within an acceptable range of 90-110%.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSpiking Samples\u003c/strong\u003e: To evaluate method performance within the actual fish tissue matrix, a subset of randomly selected fish samples (5% of total samples) were spiked with known concentrations of standard Cd and Pb solutions prior to digestion. The recovery rates of the spiked analytes were determined and consistently fell within the range of 85-115%, indicating minimal matrix interference and efficient analyte recovery.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eInter-laboratory Proficiency Testing\u003c/strong\u003e: While direct participation in an external inter-laboratory proficiency testing scheme was not part of the scope for this specific project, the laboratory routinely participates in internal quality assurance programs. Analytical results for established quality control samples are continuously tracked over time to ensure consistent performance against defined criteria, maintaining internal benchmarks for quality.\u003c/p\u003e\n\u003cp\u003eThe samples were prepared and digested according to the technique described by Shibamoto and Bjeldanes [16], with modifications based on recent protocols [17, 18]. Briefly, after washing, one gram was weighed with a digital scale from each sample of dorsal muscle removed with a scalpel and digested by 10 ml of digestion mixture (60 ml HNO₃ 65% and 40 ml HClO₄ 70-72%) in screw-capped tubes after maceration by a sharp scalpel [17]. The tubes were tightly closed, and the contents were vigorously shaken, allowed to stand overnight at room temperature and heated for 1 hour at 100\u0026deg;C to ensure complete digestion of samples [18]. Cooled samples were diluted with 10 ml deionized water, thoroughly mixed, filtered with Whatman filter paper, and made up to 20 ml with deionized water, kept at room temperature until analyzed for heavy metal contents [17]. Blank solutions were prepared in the same manner. Digested sample solutions were analyzed for lead and cadmium contents by Atomic Absorption Spectrophotometer (AAS) (AA240FS VARIAN Spectrophotometer) [18].\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Analyses\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData were subjected to descriptive statistics using the Statistical Package for Social Science (SPSS) version 20.0 [19]. A probability of less than 0.05 was considered statistically significant (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05). Levels of lead and cadmium were compared with the type of fish product using Chi-square.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe study investigated the concentrations of cadmium (Cd) and lead (Pb) in various commercially available fish products across three markets in Kaduna North, Nigeria. Detailed results, including metal concentrations and statistical analyses, are presented in Tables 1 through 5.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL Based on Markets Location across Kaduna North L.G.A, Nigeria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 1 presents the percentage of fish samples from each market (Abubakar Gumi, Unguwar Rimi, and Kawo) that exceeded the European Union\u0026apos;s Maximum Residue Limits (MRLs) for Cd (0.05 \u0026micro;g/g) and Pb (0.02 \u0026micro;g/g). Overall, a substantial proportion of samples exceeded the MRLs for both metals, with 43.33% of total samples exceeding the Cd MRL and 69.44% exceeding the Pb MRL. For Cd, Abubakar Gumi and Unguwar Rimi markets showed the highest proportions of samples above the MRL (both 35.80%), while Kawo had the lowest (28.20%). For Pb, Abubakar Gumi also had the highest proportion (36.00%), followed by Kawo (33.60%), and Unguwar Rimi (30.40%). However, Chi-square analysis revealed no statistically significant differences in the distribution of samples exceeding MRLs across market locations for either Cd (\u003cem\u003e\u0026chi;\u0026sup2;\u003c/em\u003e=1.629, \u003cem\u003ep\u003c/em\u003e=0.443) or Pb (\u003cem\u003e\u0026chi;\u0026sup2;\u003c/em\u003e=1.937, \u003cem\u003ep\u003c/em\u003e=0.380).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Table 1: Distribution of Fish Samples Containing Cd and Pb Levels above the\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eMRL Based on Markets Location\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eacross Kaduna North L.G.A, Nigeria\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"541\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 139px;\"\u003e\n \u003cp\u003eLocations\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 126px;\"\u003e\n \u003cp\u003eNo. of Samples Tested (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 276px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo. of Samples above MRL (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCd\u003csup\u003ea\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePb\u003csup\u003eb\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eAbubakar Gumi Market\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e28 (35.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e45 (36.00)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eAnguwar Rimi Market\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e28 (35.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e38 (30.40)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eKawo Market\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e22 (28.20)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e42 (33.60)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e78 (43.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e125 (69.44)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eChi Square value = 1.629, Degree of freedom \u0026nbsp;= 2, P-value= 0.443\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003eChi Square value = 1.937, Degree of freedom = 2, P-value= 0.380 \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL According to Type of Products from Fish Markets across Kaduna North L.G.A, Nigeria\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe distribution of Cd and Pb MRL exceedances based on fish product type (smoked, frozen, canned) is detailed in Table 2. Notably, 66.67% of all samples surpassed the Cd MRL, and 69.44% exceeded the Pb MRL. Smoked fish exhibited the highest percentage of samples above the MRL for Cd (29.17%) and Pb (37.60%). Frozen fish followed, with 19.17% exceeding the Cd MRL and 28.80% for Pb. Canned fish had the lowest percentage for Cd (16.67%) but showed a comparable exceedance rate for Pb (33.60%) to smoked fish. Statistical analysis indicated a significant difference in Cd contamination levels among the different fish product types (\u003cem\u003e\u0026chi;\u0026sup2;\u003c/em\u003e=8.552, \u003cem\u003ep\u003c/em\u003e=0.014). Conversely, for Pb contamination, no statistically significant difference was observed across product types (\u003cem\u003e\u0026chi;\u0026sup2;\u003c/em\u003e=4.765, \u003cem\u003ep\u003c/em\u003e=0.09).\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2: Distribution of Fish Samples Containing Cd and Pb Levels above the MRL According to Type of Products from Fish Markets across Kaduna North L.G.A, Nigeria\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"541\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 139px;\"\u003e\n \u003cp\u003eType of Product\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 126px;\"\u003e\n \u003cp\u003eNo. of Samples Tested (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"2\" style=\"width: 276px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eNo. of Samples above MRL (%)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCd\u003csup\u003ea\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e\u003cstrong\u003ePb\u003csup\u003eb\u003c/sup\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eSmoked Fish\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e35 (29.17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e47 (37.60)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eFrozen Fish\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e23 (19.17)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e36 (28.80)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eCanned Fish\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e60 (33.33)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e20 (16.67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e42 (33.60)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 139px;\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 126px;\"\u003e\n \u003cp\u003e180\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 138px;\"\u003e\n \u003cp\u003e120 (66.67)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e125 (69.44)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eChi Square (X\u003csup\u003e2\u003c/sup\u003e) = 8.552, Degree of freedom (df) = 2, P-value= 0.014\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003eChi Square (X\u003csup\u003e2\u003c/sup\u003e) = 4.765, Degree of freedom (df) = 2, P-value= 0.09\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3: Mean concentrations of Cadmium (Cd) \u0026micro;g/g and Lead (Pb) \u0026micro;g/g based on type of fish samples obtained from Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 3 presents the mean concentrations of Cd and Pb across smoked, frozen, and canned fish products, along with their respective EU limits. The mean Cd concentrations were 0.108 \u0026plusmn; 0.05 \u0026micro;g/g for smoked fish, 0.125 \u0026plusmn; 0.01 \u0026micro;g/g for frozen fish, and 0.093 \u0026plusmn; 0.01 \u0026micro;g/g for canned fish. All these mean Cd levels consistently exceeded the EU limit of 0.05 \u0026micro;g/g. Despite variations, the differences in mean Cd concentrations among product types were not statistically significant (\u003cem\u003ep\u003c/em\u003e=0.792). For Pb, the mean concentrations were 0.177 \u0026plusmn; 0.04 \u0026micro;g/g for smoked, 0.637 \u0026plusmn; 0.12 \u0026micro;g/g for frozen, and 0.202 \u0026plusmn; 0.37 \u0026micro;g/g for canned fish. All mean Pb levels substantially exceeded the EU limit of 0.02 \u0026micro;g/g. A statistically highly significant difference was found in mean Pb concentrations among the different fish product types (\u003cem\u003ep\u003c/em\u003e=0.00).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3: Mean concentrations of Cadmium (Cd)\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026micro;g/g\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eand Lead (Pb)\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026micro;g/g\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003ebased on type of fish samples\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eobtained from Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameters\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eSmoked n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eFrozen n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCanned n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eE.U. Limit\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCadmium (Cd) \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.108\u0026plusmn;0.05\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.125\u0026plusmn;0.01\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.093\u0026plusmn;0.01\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.05\u0026nbsp;\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.792\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLead (Pb)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.177\u0026plusmn;0.04\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.637\u0026plusmn;0.12\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.202\u0026plusmn;0.37\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.02\u0026nbsp;\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.00\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eKey\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;n=60\u003c/strong\u003e: \u0026nbsp; \u0026nbsp; 60 samples\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4: Mean concentrations of Cadmium (Cd) \u0026micro;g/g and Lead (Pb) \u0026micro;g/g concentrations in Fish obtained in (3) different markets in Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eMean concentrations of Cd and Pb in fish samples across the three major markets are shown in Table 4. The mean Cd levels were 0.097 \u0026plusmn; 0.01 \u0026micro;g/g in Abubakar Gumi Market (GM), 0.141 \u0026plusmn; 0.05 \u0026micro;g/g in Unguwar Rimi Market (RM), and 0.091 \u0026plusmn; 0.01 \u0026micro;g/g in Kawo Market (KW). All these mean Cd concentrations surpassed the EU limit of 0.05 \u0026micro;g/g, but their differences across markets were not statistically significant (\u003cem\u003ep\u003c/em\u003e=0.507). Mean Pb concentrations were 0.275 \u0026plusmn; 0.06 \u0026micro;g/g (GM), 0.496 \u0026plusmn; 0.10 \u0026micro;g/g (RM), and 0.245 \u0026plusmn; 0.62 \u0026micro;g/g (KW). All mean Pb levels were considerably higher than the EU limit of 0.02 \u0026micro;g/g. The \u003cem\u003ep\u003c/em\u003e-value for Pb concentrations across markets was 0.055, suggesting a marginal lack of statistical significance at the conventional 0.05 level, but potentially indicating a trend worthy of further consideration.\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4: Mean concentrations of Cadmium (Cd)\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026micro;g/g\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eand Lead (Pb)\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026micro;g/g\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003econcentrations in Fish obtained in (3) different markets in Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eParameters\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eGM \u0026nbsp;n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eRM \u0026nbsp;n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eKW n=60\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eE.U. Limit\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003ep-value\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eCadmium (Cd) \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.097\u0026plusmn;0.01\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.141\u0026plusmn;0.05\u0026nbsp;\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.091\u0026plusmn;0.01\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.05\u0026nbsp;\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.507\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u003cstrong\u003eLead (Pb)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.275\u0026plusmn;0.06\u0026nbsp;\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.496\u0026plusmn;0.10\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.245\u0026plusmn;\u0026nbsp;0.62\u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e\u0026nbsp;0.02 \u0026micro;g/g\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\"\u003e\n \u003cp\u003e0.055\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eKey\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;RM: \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Ungwan Rimi market. \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;GM:\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; Abubakar Gumi market.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;KW: \u0026nbsp; \u0026nbsp; \u0026nbsp;Kawo market.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003en=60\u003c/strong\u003e: \u0026nbsp; \u0026nbsp; 60 samples\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 5. The association between Occurrence of \u003cem\u003eListeria\u003c/em\u003e species, Lead and Cadmium concentrations in Frozen, Smoked and canned Fish obtained in Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTable 5 presents the Pearson\u0026apos;s correlation coefficients demonstrating the associations between \u003cem\u003eListeria\u003c/em\u003e species occurrence, Cd concentrations, and Pb concentrations in the fish samples. A very strong positive correlation was observed between \u003cem\u003eListeria\u003c/em\u003e species occurrence and Cd levels (r = 0.998, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05), indicating that higher cadmium concentrations are significantly associated with a greater prevalence of \u003cem\u003eListeria\u003c/em\u003e. A moderately strong positive correlation was also found between Cd and Pb concentrations (r = 0.720, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05), suggesting a relationship in their co-occurrence. Furthermore, a weaker but still significant positive correlation was identified between \u003cem\u003eListeria\u003c/em\u003e occurrence and Pb levels (r = 0.673, \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05), implying a potential connection, though less pronounced than with Cd. All correlations presented are significant at the 0.05 level of confidence.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Table 5. The association between Occurrence of\u003cem\u003e\u0026nbsp;Listeria\u003c/em\u003e species, Lead and Cadmium concentrations in\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e\u0026nbsp;Frozen, Smoked and canned Fish obtained in Kaduna North L.G.A, Nigeria.\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" align=\"left\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eListeria\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003cstrong\u003especies\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp;Cadmium\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Lead\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003e\u003cem\u003eListeria species\u003c/em\u003e\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.997882\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003e0.673103\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eCadmium\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e0.997882\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e0.719783\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eLead\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 29px;\"\u003e\n \u003cp\u003e0.673103\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e0.719783\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 20px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u0026nbsp;**Correlation is Significant at 0.05 level of confidence.\u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eThis study on commercially available fish in Kaduna North, Nigeria, reveals significant cadmium (Cd) and lead (Pb) contamination, posing substantial environmental and public health concerns. Our analysis consistently showed mean Cd levels in all fish types (smoked, frozen, and canned) exceeded the European Union's (EU) maximum residue limit (MRL) of 0.05 \u0026micro;g/g. While Cd concentrations varied across markets (Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) and fish product types (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), these differences, except for Cd across product types, were not statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05). This broad distribution suggests that Cd contamination is a widespread regional issue rather than being confined to specific market areas (FADEIYE et al., 2025) [Citation still missing; future publication or not found]. This aligns with observations in other Nigerian aquatic ecosystems, such as the Lagos Lagoon, where industrial effluents contribute to elevated Cd levels in fish [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eMore critically, lead (Pb) contamination presents an even graver problem, with mean concentrations in all fish types substantially exceeding the EU MRL of 0.02 \u0026micro;g/g. Alarmingly, frozen fish exhibited an average Pb concentration (0.637\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 \u0026micro;g/g) that was 32 times higher than the EU\u0026rsquo;s Pb MRL of 0.020 \u0026micro;g/g for infant foods [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e], underscoring a critical public health risk associated with this product category. Although the distribution of Pb MRL exceedances across different fish product types was not statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.09), the notably elevated mean Pb level specifically in frozen fish warrants urgent attention. This suggests potential unique contamination pathways or processing issues for frozen products (Koulouris et al., 2024) [Citation still missing; not found]. Furthermore, despite marginal statistical insignificance across markets (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.055, Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), the high overall prevalence of Pb contamination (69.44% of all samples exceeding MRLs, Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) points to a systemic issue. This likely stems from widespread industrial emissions, vehicular pollution, or contamination during fish handling and processing [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e, \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. These findings resonate with documentation of significant Pb accumulation in fish from Nigeria's Ikpoba Reservoir [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e], yet contrast with lower levels reported in the Ogun River [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], implying localized Pb sources. Smoked fish also showed particular concern, with nearly 30% of samples exceeding Cd limits and 38% exceeding Pb limits. While Pb contamination was widespread across all product types with no significant statistical differences between smoked, frozen, and canned fish (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05), the elevated levels in smoked fish emphasize the need for improved processing standards [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], especially given its status as a Nigerian staple [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The near-significant p-value for market-specific Pb levels (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.055) hints at localized pollution sources near Ungwan Rimi, such as industrial discharges or high vehicular emissions [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCritically, our analysis revealed a highly significant positive correlation between \u003cem\u003eListeria\u003c/em\u003e species occurrence and Cd levels (r\u0026thinsp;=\u0026thinsp;0.998, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). This near-perfect association suggests synergistic contamination pathways, where Cd-induced glutathione depletion may compromise fish immunity, while \u003cem\u003eListeria\u003c/em\u003e exploits metal-stressed environments via shared efflux mechanisms like CadA transporters [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. This mirrors findings in Nigeria's Ologe Lagoon [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e] but contrasts with Ethiopia's Omo Delta [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], possibly due to differing industrial activities. We also observed a moderately strong positive correlation between Cd and Pb concentrations (r\u0026thinsp;=\u0026thinsp;0.720, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e), suggesting common pollution sources like industrial waste [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. A weaker, yet significant, positive correlation between \u003cem\u003eListeria\u003c/em\u003e and Pb levels (r\u0026thinsp;=\u0026thinsp;0.673, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e) further indicates potential co-contamination.\u003c/p\u003e \u003cp\u003eThese collective findings underscore critical food safety concerns due to the co-occurrence of microbial and heavy metal contamination. The dual contamination creates compounded health risks: chronic Cd exposure damages renal function even below regulatory thresholds [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e] and causes long-term health issues like kidney and bone diseases [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]; Pb's long bone half-life facilitates neurodevelopmental damage [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e], particularly in vulnerable populations; and \u003cem\u003eListeria monocytogenes\u003c/em\u003e threatens susceptible individuals with potentially fatal foodborne infections [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. Health risk assessments across other African water bodies also identify carcinogenic risks from multiple metals [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e] and highlight children's vulnerability to Pb exposure [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Transboundary pollution, as seen in Lake Turkana with high Pb and Cd levels comparable to adjacent Ethiopian waters [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], adds another layer of complexity.\u003c/p\u003e \u003cp\u003eThese risks are further amplified by climate change. Flooding mobilizes sediment-bound metals, increasing Pb bioavailability by 300% during Lagos' rainy seasons [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], while rising temperatures accelerate Cd uptake in fish by 50% at 32\u0026deg;C versus 25\u0026deg;C [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Compounding these challenges, Nigeria faces an 11.1\u0026nbsp;million health worker shortage by 2030 [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], severely crippling its capacity to manage contamination-related health burdens, which already account for 24% of national mortality from environmental exposures [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e],\u003c/p\u003e \u003cp\u003eAddressing these issues requires regional-level interventions, including more stringent enforcement of existing environmental regulations [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e], improved industrial waste management systems, and robust, routine food safety monitoring programs [38, 39] that account for both chemical and microbiological hazards. Public health authorities must also develop and disseminate consumer awareness programs about heavy metal contamination risks in commonly consumed fish. Future source-apportionment studies are essential to pinpoint specific pollution sources and identify hotspots for targeted remediation efforts, ensuring the long-term sustainability of the fish industry and public health in Nigeria.\u003c/p\u003e "},{"header":"CONCLUSION","content":"\u003cp\u003eThis study unequivocally demonstrates a pervasive and alarming level of cadmium (Cd) and lead (Pb) contamination in commercially available fish across Kaduna North, Nigeria, with concentrations consistently exceeding established European Union safety limits. Particularly concerning are the extremely high lead levels found in frozen fish, significantly surpassing regulatory thresholds. Furthermore, a critical finding is the strong positive correlation between heavy metal contamination, especially cadmium, and the occurrence of \u003cem\u003eListeria\u003c/em\u003e species, highlighting a complex and synergistic food safety challenge. These combined chemical and microbial hazards present substantial public health risks, exacerbated by the region\u0026apos;s environmental vulnerabilities to climate change and existing healthcare system limitations. Therefore, urgent, integrated interventions encompassing stringent environmental regulation, improved industrial and waste management practices, comprehensive food safety monitoring throughout the supply chain, and targeted public awareness campaigns are imperative to safeguard consumer health and ensure the sustainability of the regional fish industry.\u003c/p\u003e\n\u003cp\u003e\u003cbr\u003e\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAll authors have read, understand, and have complied as applicable with the statement on Ethical responsibilities of authors as found in the instructions for authors.\u003c/p\u003e\n\u003ch2\u003eFunding Declaration\u003c/h2\u003e\n\u003cp\u003eThere was no grant accessed for this research.\u003c/p\u003e\n\u003ch2\u003eData Availability Declarations\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThe datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMusa Alhaji Musa conducted the whole experiment. All authors participated in the writing and review all chapters.\u003c/p\u003e"},{"header":"References","content":"\u003col start=\"1\" type=\"1\"\u003e\n\u003cli\u003eAlloway, B. J., \u0026amp; Ayres, D. C. (2020). \u003cem\u003eChemical principles of environmental pollution\u003c/em\u003e (3rd ed.). CRC Press.\u003c/li\u003e\n\u003cli\u003eJ\u0026auml;rup, L. (2003). Hazards of heavy metal contamination. \u003cem\u003eBritish Medical Bulletin, 68\u003c/em\u003e(1), 167\u0026ndash;182. https://doi.org/10.1093/bmb/ldg032\u003c/li\u003e\n\u003cli\u003eBernhoft, R. A. (2021). Cadmium toxicity and treatment. \u003cem\u003eThe Scientific World Journal, 2021\u003c/em\u003e, 1\u0026ndash;8. https://doi.org/10.1155/2021/6626498\u003c/li\u003e\n\u003cli\u003eTchounwou, P. B., Yedjou, C. G., Patlolla, A. K., \u0026amp; Sutton, D. J. (2012). Heavy metals toxicity and the environment. \u003cem\u003eEXS, 101\u003c/em\u003e, 133\u0026ndash;164.\u003c/li\u003e\n\u003cli\u003eEisler, R. 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Effects of elevated temperature on cadmium bioaccumulation and toxicity in freshwater fish. \u003cem\u003eEnvironmental Pollution, 345\u003c/em\u003e, 113398.\u003c/li\u003e\n\u003cli\u003eUnited Nations Environment Programme (UNEP). (2018). \u003cem\u003eEnvironmental Rule of Law: First Global Report\u003c/em\u003e. UNEP.\u003c/li\u003e\n\u003cli\u003eFAO (Food and Agriculture Organization). (2020). \u003cem\u003eThe state of world fisheries and aquaculture 2020. Sustainability in action\u003c/em\u003e. FAO.\u003c/li\u003e\n\u003cli\u003eFood and Agriculture Organization of the United Nations \u0026amp; World Health Organization (FAO/WHO). (2021). \u003cem\u003eCodex Alimentarius: General Standard for Contaminants and Toxins in Food and Feed (CODEX STAN 193-1995, last amended 2021)\u003c/em\u003e. FAO/WHO.\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":"Cadmium, Lead, Fish, Heavy metal contamination, Food safety","lastPublishedDoi":"10.21203/rs.3.rs-6487504/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6487504/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study investigated the levels of cadmium (Cd) and lead (Pb) in commercially available frozen, smoked, and canned fish in Kaduna North, Nigeria, and explored the relationship between heavy metal contamination and the presence of \u003cem\u003eListeria\u003c/em\u003e species. Atomic absorption spectrophotometry was used to determine Cd and Pb concentrations. Results showed that mean Cd levels in all fish types exceeded the European Union's maximum residue limit (MRL) of 0.05 \u0026micro;g/g, with smoked fish exhibiting the highest concentrations. Similarly, a significant Proportion of fish samples surpassed the EU's MRL for Pb (0.02 \u0026micro;g/g), particularly smoked and canned fish. Pearson's correlation analysis revealed a strong positive correlation between \u003cem\u003eListeria\u003c/em\u003e occurrence and Cd levels, as well as notable correlations between \u003cem\u003eListeria\u003c/em\u003e and Pb, and between Cd and Pb. These findings highlight significant heavy metal contamination in fish, posing a substantial public health risk. The correlations suggest a potential link between heavy metal presence and \u003cem\u003eListeria\u003c/em\u003e proliferation, emphasizing the need for stringent monitoring and regulatory measures to ensure seafood safety.\u003c/p\u003e","manuscriptTitle":"Bioaccumulation of Cadmium and Lead in Commercially Available Fish in Kaduna North, Nigeria","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-20 10:56:24","doi":"10.21203/rs.3.rs-6487504/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":"c22c1573-250f-4baa-bad5-3009831e1562","owner":[],"postedDate":"June 20th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50244052,"name":"Earth and environmental sciences/Environmental sciences"},{"id":50244053,"name":"Earth and environmental sciences/Limnology"},{"id":50244054,"name":"Physical sciences/Chemistry"}],"tags":[],"updatedAt":"2025-08-12T10:53:31+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-20 10:56:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6487504","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6487504","identity":"rs-6487504","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}