Heavy Metals in Smoked Fish: A Comprehensive Review of Nutritional Implications, Health Impacts, and Public Health Challenges in Nigeria

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Bello, Oladipupo Azeezat Olawumi, Abdulmalik O. Abdulwasiu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8852012/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 Background Smoked fish is a vital protein source and livelihood in Nigeria, but traditional smoking may introduce toxic heavy metals, creating public health concerns. Objective This review synthesizes Nigerian literature on heavy metal contamination in smoked fish, examining smoking processes, nutritional implications, health risks, and public health challenges, including occupational exposure of processors. Methods A systematic search of PubMed, Scopus, ScienceDirect, Google Scholar, and ResearchGate was conducted for studies published between 2015–2025 following PRISMA guidelines. Included studies reported quantitative data on heavy metal concentrations in Nigerian smoked fish. Data on metal levels, health risk indices (THQ, HI, cancer risk), nutritional parameters, and smoking methods were extracted and synthesized thematically. Results Studies across Ondo, Ogun, Lagos, Anambra, Borno, and the Niger Delta consistently report elevated lead, cadmium, chromium, and arsenic in smoked fish, frequently exceeding regulatory limits. Traditional drum-smoking yields higher contamination than improved kilns. Smoked fish retains nutritional value, creating a risk-benefit dilemma. Health risk assessments reveal non-carcinogenic effects (HI > 1) and unacceptable cancer risks from chromium. Children are most vulnerable. A critical gap is the complete absence of research on occupational exposure of fish smokers. Conclusion Heavy metal contamination causes significant risks to consumers while processors face unstudied occupational hazards. Addressing this requires improved smoking technologies, national surveillance, occupational health integration, and community education. Food Science & Technology Health Economics & Outcomes Research Smoked fish heavy metals public health occupational exposure health risk assessment nutrition food safety 1.0 INTRODUCTION Fish smoking is a centuries-old preservation technique deeply embedded in Nigerian food culture and economy [Adeyeye, 2016 ]. It extends the shelf life of highly perishable fish, enables transportation to inland markets, and provides livelihood opportunities, particularly for women processors [Bwala & Imam, 2021 ; Adeyeye et al., 2017 ]. Smoked fish serves as a crucial source of affordable animal protein and essential micronutrients for millions of Nigerians, bridging nutritional gaps in both rural and urban diets [Obande et al., 2025 ; Oli et al., 2024 ]. However, the smoking process, particularly when conducted using traditional kilns and potentially contaminated fuelwood, introduces chemical contaminants that compromise food safety [Adeyeye, 2019 ; Ubwa et al., 2015 ]. Among the most concerning are heavy metals—lead (Pb), cadmium (Cd), chromium (Cr), and arsenic (As)—which accumulate in fish tissues during smoking and pose significant health risks to consumers [Olayinka-Olagunju, 2025 ; Osuala & Igwo-Ezikpe, 2022 ; Onoja et al., 2025 ]. Over the past decade, a growing body of Nigerian research has documented elevated heavy metal concentrations in smoked fish from various regions, with health risk assessments frequently indicating potential non-carcinogenic and carcinogenic effects [Thomas, 2024 ; Oghenochuko et al., 2022 ; Adelakun et al., 2024 ; Oloye & Odedeyi, 2025 ]. Systematic reviews have confirmed that heavy metal contamination in Nigerian aquatic foods is widespread, particularly in crude oil-impacted areas like the Niger Delta [Umeoguaju et al., 2023 ] and across Southwest Nigeria [Laoye et al., 2025 ]. Despite this accumulating evidence, a comprehensive synthesis that integrates the nutritional value , health impacts , and public health implications of heavy metal contamination specifically in smoked fish r emains lacking [Idowu, 2022 ; Nkwunonwo et al., 2020 ]. This review addresses this gap by critically examining the existing Nigerian literature on heavy metals in smoked fish through four interconnected lenses: (1) the smoking process as a source of contamination, (2) the nutritional profile of smoked fish, (3) the documented health risks to consumers, and (4) the broader public health challenges, including the overlooked occupational exposure of fish smokers. By synthesizing evidence from across Nigeria, this review aims to inform policy, guide future research, and contribute to safer fish smoking practices that protect both consumers and producers. 2.0 SMOKING PRACTICES AND HEAVY METAL CONTAMINATION 2.1 Fish Smoking in Nigeria Fish smoking in Nigeria is predominantly artisanal, employing traditional technologies that vary by region. The most common methods include drum kilns (repurposed metal oil drums), mud kilns, and wire-mesh ovens, all of which rely on direct combustion of wood or another biomass [Adeyeye, 2016 ; Adeyeye et al., 2017 ; Adeyeye, 2019 ]. While these methods are effective for preservation and impart desirable sensory characteristics, they offer limited control over temperature, smoke density, and exposure duration which are the factors that influence contaminant formation and deposition [Ubwa et al., 2015 ; Tongo et al., 2017 ]. Studies have shown that smoking methods significantly affect the quality and safety of the final product, with drum-smoking often associated with higher contaminant levels compared to improved kilns [Adeyeye et al., 2017 ]. 2.2 Sources of Heavy Metals in Smoked Fish Heavy metals in smoked fish are majorly from two primary sources: the raw fish itself and the smoking process. Fish harvested from polluted waters accumulate metals in their tissues through dietary and dermal uptake [Adesiyan et al., 2018 ; Edogbo et al., 2020 ; Enuneku et al., 2018 ]. Rivers in industrial areas - such as those in Kano [Edogbo et al., 2020 ], Southwest Nigeria [Adesiyan et al., 2018 ], and the Niger Delta [Umeoguaju et al., 2023 ; Enuneku et al., 2018 ] -have documented elevated metal levels, which are reflected in resident fish species [Oloye & Odedeyi, 2025 ; Odey et al., 2020 ]. During smoking, additional contamination can occur through various means. Firstly, wood harvested from metal-contaminated soils or treated wood may release metals during combustion, which deposit on fish surfaces [Laoye et al., 2025 ; Idowu, 2022 ]. In addition, corroded metal drums or galvanized wire meshes can leach metals such as lead, cadmium, and zinc into the fish, especially under high heat and acidic smoke conditions [Adeyeye et al., 2019 ; Nwosu et al., 2021]. Also, smoking removes moisture up to 70% weight loss, concentrating existing metals in the remaining tissue [Osuala & Igwo-Ezikpe, 2022 ; Oghenochuko et al., 2022 ]. 2.3 Evidence from Nigerian Studies Various studies across Nigeria have documented elevated heavy metal concentrations in smoked fish compared to fresh samples or regulatory limits. Table 1 summarizes heavy metal concentrations in smoked fish reported from different Nigerian regions. Table 1 Heavy Metal Concentrations in Smoked Fish from Nigerian Studies Location Fish Species Metals Detected Key Finding/limits Reference Ondo State Clarias gariepinus (smoked catfish) Fe: 149.0 ± 7.76–155.0 ± 5.10; Mn: exceeded 1 mg/kg; Ni: 0.00 ± 0.00–1.00 ± 1.41; Cd, Cr reported Exceeded limits; HI > 1; Cr cancer risk Olayinka-Olagunju, 2025 New Bussa Market Smoked Freshwater fish Chemical qualities and heavy metals evaluated Contamination linked to processing Adelakun et al., 2024 South West Nigeria local markets Fresh, frozen, smoked Multiple Smoked > fresh; children at risk Oghenochuko et al., 2022 Lagos State Catfish Cd, Pb, Zn Smoking increases metal concentration Osuala & Igwo-Ezikpe, 2022 Eke-Awka Market, Anambra State Smoked-dried fish As, Cd, Cr, Hg, Pb Health risk > 1 Onoja et al., 2025 Zaria Catfish Multiple Smoked from polluted sources > home-bred Odey et al., 2020 Ose River, Ondo Multiple Multiple Water-sediment-fish transfer Oloye & Odedeyi, 2025 Borno State Multiple Not specified Socio-economics documented Bwala & Imam, 2021 Across these studies, lead and cadmium are the most frequently detected metals exceeding regulatory limits, with chromium emerging as a metal of high concern due to its carcinogenic potential [Thomas, 2024 ; Olayinka-Olagunju, 2025 ]. The Niger Delta region shows particularly elevated levels due to crude oil pollution [Umeoguaju et al., 2023 ], while industrial areas like Kano show contamination from industrial effluents [Edogbo et al., 2020 ]. 3.0 METHODOLOGY This chapter describes the systematic approach employed to identify, screen, and synthesize relevant literature on heavy metal contamination in smoked fish from Nigeria. 3.1 Search Strategy A comprehensive literature search was conducted to identify studies on heavy metal contamination in smoked fish from Nigeria. The following electronic databases were systematically searched: PubMed, Scopus, ScienceDirect, Google Scholar, and ResearchGate. The search was conducted between February 2026 and March 2026 and covered publications from January 2015 to December 2025 to ensure relevance and currency. The search strategy employed combinations of keywords and Boolean operators. Population terms included "Nigeria" OR "Nigerian" combined with specific state names such as Ondo, Lagos, Ogun, Anambra, Borno, Niger Delta, and Southwest Nigeria. Exposure terms comprised "heavy metals," "trace metals," "toxic metals," "lead," "Pb," "cadmium," "Cd," "chromium," "Cr," "arsenic," and "As." Food terms included "smoked fish," "processed fish," "smoke-dried fish," "Clarias gariepinus," "catfish," and "tilapia." Outcome terms covered "health risk assessment," "THQ," "hazard quotient," "hazard index," "HI," "cancer risk," "nutrition," "proximate composition," and "public health." 3.2 Inclusion and Exclusion Criteria Studies were included if they met specific criteria. Eligible studies comprised original primary research or systematic reviews published in peer-reviewed journals, conducted in Nigeria or specifically focused on Nigerian smoked fish samples, and reported quantitative data on heavy metal concentrations including lead, cadmium, chromium, arsenic, or mercury in smoked fish. All included studies were published in English between January 2015 and December 2025. Studies were excluded if they examined fresh or frozen fish only without a smoked fish component, reported only polycyclic aromatic hydrocarbons, microbial contamination, or pesticide residues without metal analysis, or were conference abstracts, editorials, commentaries, or opinion pieces without original data. Studies where full text was unavailable after contacting authors and duplicate publications of the same data were also excluded. 3.3 Study Selection and PRISMA Framework The study selection process followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. The selection involved four stages: identification, screening, eligibility, and inclusion. During identification, records were retrieved from database searching using the specified keywords. In the screening stage, titles and abstracts were screened against inclusion criteria and duplicates were removed. Full-text articles were then assessed for eligibility during the third stage. Finally, studies meeting all criteria were included in the final review. 3.4 Quality Assessment The quality of included studies was assessed using an adapted checklist. Each study was evaluated on several parameters including clear description of sampling methodology covering location, sample size, and fish species; appropriate analytical methods such as atomic absorption spectrophotometry or inductively coupled plasma mass spectrometry with quality control measures; use of certified reference materials or recovery tests; reporting of detection limits; calculation of health risk indices including target hazard quotient, hazard index, and cancer risk where applicable; and transparent reporting of results including means, standard deviations, and ranges. Studies were not excluded based on quality scores, but methodological strengths and limitations were considered in the narrative synthesis. 3.5 Data Extraction The following data were extracted from each included study into a standardized spreadsheet. Bibliographic information included authors, year, journal, and digital object identifier. Study characteristics comprised location including state, specific market, river, or community; fish species sampled with common and scientific names; and smoking method such as drum kiln, mud kiln, improved kiln, or unspecified. Heavy metals analyzed were recorded along with mean concentrations in milligrams per kilogram wet weight or dry weight with standard deviations. Regulatory limits used for comparison including WHO, FAO, NAFDAC, and SON standards were noted. Health risk indices including target hazard quotient, hazard index, and cancer risk were extracted where calculated. Nutritional parameters including protein, fat, moisture, ash, and minerals were recorded if reported, along with key conclusions and recommendations from each study. 3.6 Data Synthesis Extracted data were synthesized narratively due to heterogeneity in study locations, fish species, analytical methods, and reporting formats. Findings were organized thematically corresponding to the review objectives. Geographic patterns were examined by grouping results by Nigerian region including Southwest, Southeast, North, and Niger Delta to identify regional contamination patterns. Metal prevalence was assessed by examining frequency and concentrations of specific metals including lead, cadmium, chromium, and arsenic across studies. Health risk outcomes were summarized by compiling target hazard quotient, hazard index, and cancer risk findings with particular attention to vulnerable groups. Where studies compared different smoking techniques, findings were synthesized separately to evaluate the impact of smoking methods on contamination levels. 4.0 NUTRITIONAL PROFILE AND THE RISK-BENEFIT DILEMMA 4.1 Nutritional Value of Smoked Fish Smoked fish remains a nutritionally valuable food. It provides high-quality, easily digestible protein essential for growth and tissue repair [Oli et al., 2024; Adeyeye et al., 2019]. Fish are also the primary dietary source of long-chain omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]), which support cardiovascular health, brain development, and reduce inflammation [Obande et al., 2025]. Additionally, smoked fish contributes bioavailable micronutrients. Adeyeye et 0al. [2019] documented the amino acid, vitamin, and mineral profiles of smoked fish, showing that smoking methods and fish types affect nutrient retention. Aliyu et al. [2024] reported mineral compositions in processed tilapia, while Oli et al. [2024] compared proximate composition of fresh and smoke-dried fish from Omambala River, finding that smoking preserves protein content while reducing moisture. For many low-income households in Nigeria, smoked fish represents an affordable and accessible source of these essential nutrients [Oghenochuko et al., 2022; Bwala & Imam, 2021]. 4.2 Impact of Smoking on Nutrient Content The smoking process can alter nutrient composition. Heat exposure may degrade vitamins which are sensitive to heat and cause some lipid oxidation. However, protein content is generally well-preserved, and the dehydration process concentrates nutrients alongside contaminants [Oli et al., 2024; Adeyeye et al., 2019]. Studies comparing fresh and smoked fish from the same sources are limited and thereby make a research gap. 4.3 The Risk-Benefit Calculus The co-occurrence of heavy metals in smoked fish creates a public health dilemma. While consumers derive nutritional benefits, they are simultaneously exposed to neurotoxic, nephrotoxic, and carcinogenic metals [Lawal et al., 2021; Nkwunonwo et al., 2020]. This risk-benefit analysis is particularly critical for citizens including children, pregnant women, and frequent consumers who may be at higher risk despite the nutritional advantages [Oghenochuko et al., 2022; Obande et al., 2025]. The key question is whether the levels of heavy metals documented in Nigerian smoked fish negate its nutritional value. Based on the health risk assessments reviewed in Section 5, the answer is context-dependent: for some metals and consumer groups, the risks likely exceed the benefits [Thomas, 2024; Olayinka-Olagunju, 2025; Onoja et al., 2025]. This emphasizes the urgent need for contamination reduction strategies that preserve nutritional integrity while minimizing toxic exposures. 5.0 HEALTH IMPACTS OF HEAVY METAL CONTAMINATION 5.1 Toxicological Profiles of Detected Metals Lead (Pb): A neurotoxin that affects cognitive development in children and causes cardiovascular and renal effects in adults. No safe level of exposure exists [Lawal et al., 2021 ; Nkwunonwo et al., 2020 ]. Nigerian studies consistently report Pb exceeding permissible limits in smoked fish [Olayinka-Olagunju, 2025 ; Oghenochuko et al., 2022 ; Onoja et al., 2025 ]. Cadmium (Cd): Accumulates in kidneys and bones, with a half-life of 10–30 years. Chronic exposure causes renal tubular dysfunction and osteoporosis [Lawal et al., 2021 ]. Cd is frequently detected in smoked fish from industrial and urban areas [Osuala & Igwo-Ezikpe, 2022 ; Edogbo et al., 2020 ]. Chromium (Cr): Hexavalent chromium (Cr VI) is classified as a Group 1 human carcinogen (lung, nasal). Trivalent Cr (III) is essential but toxic at high levels [Thomas, 2024 ; Olayinka-Olagunju, 2025 ]. Thomas [ 2024 ] specifically identified Cr as the metal of highest carcinogenic concern in smoked catfish from Ogun State. Arsenic (As): Inorganic arsenic is a carcinogen (skin, bladder, lung) and causes cardiovascular and neurological effects [Lawal et al., 2021 ]. Detected in Ondo State samples [Olayinka-Olagunju, 2025 ]. 5.2 Health Risk Assessment in Nigerian Smoked Fish Health risk assessment estimates potential non-carcinogenic and carcinogenic risks from dietary exposure. The Target Hazard Quotient (THQ) compares estimated exposure to a reference dose; values 1.0 indicate potential non-carcinogenic effects. The Hazard Index (HI) sums THQs for multiple metals. Cancer Risk (CR) estimates lifetime cancer probability; values 1 × 10⁻⁴ are considered unacceptable by the US EPA. Table 2 summarizes health risk indices reported in Nigerian studies. Table 2 Health Risk Assessment Findings Location Fish Species Key Findings Health Implications References Ondo State smoked catfish & grasscutter High Fe/Mn/Ni; exceeded WHO limits Non-carcinogenic risks from chronic intake Olayinka-Olagunju ( 2025 ) Niger Delta Seafood meta-analysis Elevated THQ/ILCR for heavy metals Oil-impacted regions cause systemic toxicity Umeoguaju et al. ( 2023 ) Southwest markets Smoked fish HI/THQ > 1 for key metals Higher risks in smoked vs fresh/frozen Oghenochuko et al. ( 2022 ) Abeokuta Processed catfish THQ for metals in smoked; non-carcinogenic focus Vulnerable groups at risk (e.g., nephrotoxicity) Thomas ( 2024 ) Ose River, Ondo Fish species Concentrations & risk assessment (water/sediment/fish) Bioaccumulation led to elevated HI Oloye & Odede (2025) Review Heavy metals public health General risks (carcinogenic/non-carcinogenic) Pb/Cd neuro/kidney damage in Nigeria context Lawal et al. ( 2021 ) Review Nigeria food chain review Health implications via food chain Chronic exposure risks malnutrition synergy Nkwunonwo et al. ( 2020 ) Anambra Smoked-dried fish HI > 1; non-carcinogenic adverse effects Market fish unsafe for regular consumption Onoja et al. ( 2025 ) Across the reviewed studies, a consistent pattern emerges: Non-carcinogenic risks: In Ondo State, Olayinka-Olagunju [ 2025 ] reported HI values exceeding 1.0, indicating potential adverse health effects in regular consumers. Oghenochuko et al. [ 2022 ] also found that children face higher health risks per unit body weight compared to adults, due to higher fish consumption rates and greater physiological susceptibility. Onoja et al. [ 2025 ] similarly documented HI > 1 in Anambra State. Carcinogenic risks: Thomas [ 2024 ] in Ogun State reported cancer risk values for chromium that exceeded the US EPA acceptable limit (1×10⁻⁴), classifying smoked fish consumption as a potential carcinogenic hazard. Olayinka-Olagunju [ 2025 ] also documented elevated cancer risks in Ondo State, with chromium as the primary contributor. Vulnerable groups: Children are consistently identified as the most vulnerable subpopulation [Oghenochuko et al., 2022 ; Obande et al., 2025 ]. 5.3 Regional and Temporal Patterns Comparing studies across Nigeria reveals geographic variation in contamination profiles. Northern states like Borno [Bwala & Imam, 2021 ] and Zaria [Odey et al., 2020 ] show industrial and domestic effluent impacts. Southwestern states show complex mixtures with Cr-related cancer risks [Thomas, 2024 ; Olayinka-Olagunju, 2025 ; Laoye et al., 2025 ]. The Niger Delta exhibits the most severe contamination due to crude oil pollution [Umeoguaju et al., 2023 ; Enuneku et al., 2018 ]. This likely reflects differences in local pollution sources, smoking practices, and fish species. 6.0 PUBLIC HEALTH IMPLICATIONS AND POLICY GAPS 6.1 Regulatory Landscape In Nigeria, maximum permissible limits for heavy metals in fish are established by the National Agency for Food and Drug Administration and Control (NAFDAC) and the Standards Organization of Nigeria (SON), which generally align with Codex Alimentarius and WHO/FAO standards [Ogbeide & Henry, 2024 ; Idowu, 2022 ]. However, the reviewed studies repeatedly document overruns these limits [Olayinka-Olagunju, 2025 ; Oghenochuko et al., 2022 ; Onoja et al., 2025 ; Osuala & Igwo-Ezikpe, 2022 ; Adelakun et al., 2024 ], indicating a significant gap between standards and actual food safety. 6.2 Monitoring and Enforcement Gaps Despite the evidence of contamination, Nigeria lacks a coordinated national surveillance program for heavy metals in smoked fish [Ogbeide & Henry, 2024 ; Idowu, 2022 ]. Monitoring remains scattered, limited to academic research with limited translation into regulatory action. Ogbeide and Henry [ 2024 ] rigorously assessed Nigerian policies addressing heavy metal pollution, concluding that enforcement remains weak and remediation strategies are inadequately implemented. This absence of systematic data hinders risk assessment, prevents early warning and leaves consumers unprotected. 6.3 Consumer Awareness There is a striking gap in research on consumer knowledge regarding heavy metal risks in smoked fish. Studies on microbial safety [Adetuwo et al., 2023 ] suggest that consumers may be more aware of spoilage than chemical contaminants. The findings suggest that consumers select fish based on sensory qualities (texture, color, smell) rather than safety considerations [Adeyeye, 2016 ; Bwala & Imam, 2021 ]. Without awareness, consumer pressure cannot drive safer practices. 6.4 The Overlooked Population: Occupational Exposure of Fish Smokers A major oversight in the Nigerian literature is the occupational health of fish smokers - predominantly women who spend hours daily inhaling smoke from burning wood. While studies document heavy metals and PAHs in smoked fish [Ubwa et al., 2015 ; Tongo et al., 2017 ], no study in this database assessed inhalation exposure among processors. Emerging findings from West Africa suggest that smoke contains not only particulate matter and PAHs but also volatile metals that can be inhaled or absorbed dermally [Obande et al., 2025 ; Laoye et al., 2025 ]. These workers may face health risks exceeding those of consumers, yet they remain entirely absent from food safety discourse and occupational health protections. This represents the most urgent research gap identified in this review. 6.5 Economic and Trade Implications Heavy metal contamination can affect domestic and international trade. Smoked fish is a tradable commodity within West Africa, and consistent violation of international standards could lead to export restrictions or loss of market access [Ogbeide & Henry, 2024 ]. Bwala and Imam [ 2021 ] documented the socio-economic importance of fish smoking in Borno State, highlighting that contamination could damage livelihoods. 6.6 Pathways to Intervention Addressing heavy metal contamination requires a multi-faceted approach. Promoting improved smoking kilns (e.g., Chorkor, FAO-Thiaroye) validated to reduce both PAHs and metal contamination [Adeyeye et al., 2017 ; Adeyeye, 2019 ; Ubwa et al., 2015 ]. Ensuring fuelwood is sourced from uncontaminated areas; exploring alternative biomass [Laoye et al., 2025 ; Idowu, 2022 ]. Establishing routine monitoring with clear enforcement mechanisms [Ogbeide & Henry, 2024 ]. Extending food safety frameworks to include processor protection; study inhalation risks [Obande et al., 2025 ; identified as gap]. And finally, developing culturally appropriate messaging on selecting safer smoked fish and diversifying protein sources [Nkwunonwo et al., 2020 ]. 7.0 KNOWLEDGE GAPS AND FUTURE RESEARCH DIRECTIONS This review reveals several critical gaps in the Nigerian literature on heavy metals in smoked fish. No reviewed study simultaneously measured heavy metals and comprehensive nutritional parameters (protein, fatty acids, vitamins) in the same smoked fish samples, preventing direct risk-benefit quantification. While Adeyeye et al. [ 2019 ] and Oli et al. [ 2024 ] provide nutritional data, and Olayinka-Olagunju [ 2025 ] provides metal data, they are from different samples. In addition, no studies assessed heavy metal exposure in fish smokers via inhalation or dermal routes. This is the most urgent research need, given the hours processors spend in smoke [Obande et al., 2025 ; identified in this review]. All studies are cross-sectional; no data exist on seasonal variation or long-term trends in metal contamination [Idowu, 2022 ]. No studies have evaluated whether improved kilns or fuel substitutions actually reduce metal levels in smoked fish, though PAH reduction has been studied [Ubwa et al., 2015 ; Adeyeye et al., 2017 ]. Total metal concentration does not equal absorbed dose. Studies measuring bio-accessibility (simulated digestion) would refine risk assessments [Lawal et al., 2021 ; Nkwunonwo et al., 2020 ]. Research on consumer awareness, preferences, and willingness to pay for safer smoked fish is absent [noted in Section 6]. More research is needed to distinguish metals originating from aquatic pollution versus those introduced during smoking [Laoye et al., 2025 ; Idowu, 2022 ]. Policy implementation research: Studies on why existing regulations fail and how to improve enforcement are lacking [Ogbeide & Henry, 2024 ]. Future research should prioritize these areas to generate evidence for effective interventions. 8.0 CONCLUSION This review synthesizes Nigerian evidence on heavy metal contamination in smoked fish, revealing a persistent and alarming trend. Across multiple states and studies, smoked fish contains high levels of lead, cadmium, chromium, and arsenic, frequently exceeding regulatory limits [Olayinka-Olagunju, 2025 ; Oghenochuko et al., 2022 ; Onoja et al., 2025 ; Osuala & Igwo-Ezikpe, 2022 ; Adelakun et al., 2024 ; Oloye & Odedeyi, 2025 ]. Health risk assessments show that regular consumption carries potential non-carcinogenic risks (Hazard Index > 1) and, for chromium, unacceptable cancer risks [Thomas, 2024 ; Olayinka-Olagunju, 2025 ; Onoja et al., 2025 ]. Children are particularly vulnerable due to higher consumption per body weight and greater physiological susceptibility [Oghenochuko et al., 2022 ; Obande et al., 2025 ]. Basically, this review identifies a major challenge: the occupational health of fish smokers. While consumers face dietary risks, processors - predominantly women - may face even higher risks through inhalation, yet they remain entirely absent from Nigerian research and policy [identified gap; Obande et al., 2025 ]. This lapse must be urgently addressed. Smoked fish remains an essential source of nutrition and livelihood in Nigeria [Adeyeye, 2016 ; Bwala & Imam, 2021 ; Oli et al., 2024 ]. The goal is not to eliminate smoking but to make it safe - for all. Achieving this requires investment in validated smoking technologies [Adeyeye et al., 2017 ; Ubwa et al., 2015 ], National surveillance linking metal data to health outcomes [Ogbeide & Henry, 2024 ; Idowu, 2022 ], Inclusion of occupational health in food safety frameworks [identified gap] and Community education for safer practices [Nkwunonwo et al., 2020 ]. 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Pakistan J Anal Environ Chem 23(1):118–128. http://eprints.lmu.edu.ng/4016/ Thomas OJ (2024) HEALTH RISK ASSESSMENT OF METALS IN DIFFERENTLY PROCESSED-AFRICAN MUD CATFISH (Clarias gariepinus Burchell, 1822) IN ABEOKUTA MARKETS, OGUN STATE, SOUTHWESTERN NIGERIA [Master's thesis, Federal University of Agriculture, Abeokuta]. FUNAAB Repository. https://ir.funaab.edu.ng/items/49d10637-31ba-4bc8-bdc2-d3c2807e5805/full Osuala FI, Igwo-Ezikpe MN, POLY AROMATIC HYDROCARBON CONTAMINANTS IN SMOKED AND FRESH CLARIAS GARIEPINUS (2022) Nigerian J Life Sci 6(2). https://doi.org/10.52417/njls.v6i2.329 . HEAVY METALS AND Aliyu MD, Abdulkarim M, Egbo ML, Salifu UA (2024) Biochemical, Mineral and Microbial Analysis of Differently Salted Nile Tilapia (Oreochromis niloticus). 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F1000Res 14:134. 10.12688/f1000research.160148.4 PMID: 40822873; PMCID: PMC12355173 Onoja CR, Ogbaji HO, Edodi IO, Mmuta EC, Igwegbe KC, Ogini OR, Odibo UE, Ewuola AA, Mahmoud AB, Okpoji AU (2025) Heavy Metal Contamination and Health Risk Assessment of Smoked-Dried Fish Sold in Eke-Awka Market, Anambra State, Nigeria. J Sustainable Res Dev 1(2):18–25. https://doi.org/10.69739/jsrd.v1i2.1044 Odey MO, Udiba UU, Asuk AA, Emuru EO (2020) Heavy metal contamination of african cat fish (Clarias gariepinus) from industrial effluent and domestic waste-contaminated rivers and home bred sources in Zaria, Nigeria. Afr J Biomedical Res 23(1):101–105 Idowu GA (2022) Heavy metals research in Nigeria: a review of studies and prioritization of research needs. Environ Sci Pollut Res 29:65940–65961. https://doi.org/10.1007/s11356-022-22174-x Adesiyan IM, Bisi-Johnson M, Aladesanmi OT, Okoh AI, Ogunfowokan AO (2018) Concentrations and Human Health Risk of Heavy Metals in Rivers in Southwest Nigeria. J Health Pollut 8(19):180907. 10.5696/2156-9614-8.19.180907 PMID: 30524866; PMCID: PMC6257163 Edogbo B, Okolocha E, Maikai B, Aluwong T, Uchendu C (2020) Risk analysis of heavy metal contamination in soil, vegetables and fish around Challawa area in Kano State, Nigeria. Sci Afr 7. https://doi.org/10.1016/j.sciaf.2020.e00281 Ogbeide O, Henry B (2024) Addressing Heavy Metal Pollution in Nigeria: Evaluating Policies, Assessing Impacts, and Enhancing Remediation Strategies. J Appl Sci Environ Manage 28(4):1007–1051. https://doi.org/10.4314/jasem.v28i4.5 Enuneku A, Omoruyi O, Tongo I et al (2018) Evaluating the potential health risks of heavy metal pollution in sediment and selected benthic fauna of Benin River, Southern Nigeria. Appl Water Sci 8:224. https://doi.org/10.1007/s13201-018-0873-9 Adeyeye SAO (2019) Smoking of fish: a critical review. J Culin Sci Technol 17(6):559–575. https://doi.org/10.1080/15428052.2018.1495590 Oli AU, Okeke PA, Oli CC, Ibe FN, Okogwu JD (2024) Comparative study of the proximate composition and sensory evaluation of fresh and smoke-dried fish species from River O, State A Nigeria. Newport Int J Biol Appl Sci, 5 (2), 44–50. https://doi.org/10.59298/NIJBAS/2024/5.2.445011 Obande IU, Aliyu AA, Ed-Idoko JO, Kareem AA, Pateh K, Hammed MO (2025) A review on the effects of smoked fish on the health of its consumers. Asian J Fisheries Aquat Res 27(8):8986. https://doi.org/10.9734/ajfar/2025/v27i8986 Bwala MN, Imam TS (2021) Fish smoking, preservation and socio-economic characteristics of fish smokers and traders in selected fish markets in Borno state, Nigeria. Nigerian J Fisheries 18(2):2346–2354 Adeyeye SAO, Fayemi OE, Adebayo-Oyetoro AO (2019) Amino acid, vitamin and mineral profiles of smoked fish as affected by smoking methods and fish types. J Culin Sci Technol 17(3):195–208. https://doi.org/10.1080/15428052.2017.1418693 Adetuwo OJ, Adegbehingbe KT, Rachael OT (2023) Safety Concerns on Microbes Associated with Fresh and Smoked Fish Sold in Igbokoda Fish Market, Nigeria. J Adv Microbiol 23(10):72–82. https://doi.org/10.9734/jamb/2023/v23i10758 Adeyeye SAO, Oyewole OB, Obadina OA, Omemu AM, Adeniran OE, Oyedele HA, Omoniyi SA (2017) Effect of Smoking Methods on Quality and Safety of Traditional Smoked Fish from Lagos State, Nigeria. J Culin Sci Technol 15(1):17–35. https://doi.org/10.1080/15428052.2016.1185072 Adeyeye SAO (2016) Traditional fish processing in Nigeria: a critical review. Nutr Food Sci 46(3):321–335. https://doi.org/10.1108/NFS-11-2015-0148 Ubwa ST, Abah J, Tarzaa L, Tyohemba RL, Ahile UJ (2015) Effects of traditional smoking methods on the concentrations of polynuclear aromatic hydrocarbons (PAHs) in some species of smoked fish traded in Benue State, Nigeria. J Food Res 4(2):119. 10.5539/jfr.v4n2p119 Tongo I, Ogbeide O, Ezemonye L (2017) Human health risk assessment of polycyclic aromatic hydrocarbons (PAHs) in smoked fish species from markets in Southern Nigeria. Toxicol Rep 4:55–61. https://doi.org/10.1016/j.toxrep.2016.12.006 Uzomah A, Lundebye A-K, Kjellevold M, Chuku FA, Stephen OA (2021) A Review of Chemical Contaminants in Marine and Fresh Water Fish in Nigeria. Foods, 10(9), 2013. https://doi.org/10.3390/foods10092013 Additional Declarations The authors declare no competing interests. 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-8852012","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Systematic Review","associatedPublications":[],"authors":[{"id":598638331,"identity":"2d697418-7cb5-452e-bed6-f80e6afd64aa","order_by":0,"name":"Abdullahi A. Bello","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+0lEQVRIiWNgGAWjYBACAwYeBgmGAgsGA2bmg4//VACFmJkbiNBiAETMbMkGPGdAWhiJ1cLAYybA2wYSI6DFnP3swds8BhLy5uxsaQyS82qj+duBWn5UbMOpxbInL9kaqMVwZzPzsQeG247nzjjM2MDYc+Y2bocdyDGTBmph3HCYLd0gcdux3AagFmbGNjxazr8Ba7HfcJjHTOLgnGO58wlquQGxJRGkRbKxoSZ3AyEtljPeJVvOMZBIBjos2Zjh2IHcjUAtB/H5xZw/9+CNNxU2thvOHz74mKGmLncekPHgRwVuLejgMJg8QLR6IKgjRfEoGAWjYBSMEAAAmVhZYfVi6+EAAAAASUVORK5CYII=","orcid":"https://orcid.org/0009-0008-6842-0075","institution":"Bayero University, Kano","correspondingAuthor":true,"prefix":"","firstName":"Abdullahi","middleName":"A.","lastName":"Bello","suffix":""},{"id":598638539,"identity":"86ec20e0-53e6-4fa3-84e6-fc5406f42c34","order_by":1,"name":"Oladipupo Azeezat Olawumi","email":"","orcid":"","institution":"Abiola Ajimobi Technical University, Ibadan","correspondingAuthor":false,"prefix":"","firstName":"Oladipupo","middleName":"Azeezat","lastName":"Olawumi","suffix":""},{"id":598638540,"identity":"04d0e0cf-485e-4f85-90dc-fbe09ef37c54","order_by":2,"name":"Abdulmalik O. Abdulwasiu","email":"","orcid":"","institution":"Bayern University, Kano","correspondingAuthor":false,"prefix":"","firstName":"Abdulmalik","middleName":"O.","lastName":"Abdulwasiu","suffix":""}],"badges":[],"createdAt":"2026-02-11 13:01:30","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-8852012/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8852012/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":104400509,"identity":"1e4ee032-a790-4284-b411-f5388570f608","added_by":"auto","created_at":"2026-03-11 12:10:11","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":901353,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8852012/v1/0f1bccd2-6915-4456-ab25-2cfc595fe8c8.pdf"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003eHeavy Metals in Smoked Fish: A Comprehensive Review of Nutritional Implications, Health Impacts, and Public Health Challenges in Nigeria\u003c/p\u003e","fulltext":[{"header":"1.0 INTRODUCTION","content":"\u003cp\u003eFish smoking is a centuries-old preservation technique deeply embedded in Nigerian food culture and economy [Adeyeye, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e]. It extends the shelf life of highly perishable fish, enables transportation to inland markets, and provides livelihood opportunities, particularly for women processors [Bwala \u0026amp; Imam, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e]. Smoked fish serves as a crucial source of affordable animal protein and essential micronutrients for millions of Nigerians, bridging nutritional gaps in both rural and urban diets [Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Oli et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, the smoking process, particularly when conducted using traditional kilns and potentially contaminated fuelwood, introduces chemical contaminants that compromise food safety [Adeyeye, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e]. Among the most concerning are heavy metals\u0026mdash;lead (Pb), cadmium (Cd), chromium (Cr), and arsenic (As)\u0026mdash;which accumulate in fish tissues during smoking and pose significant health risks to consumers [Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Osuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Onoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOver the past decade, a growing body of Nigerian research has documented elevated heavy metal concentrations in smoked fish from various regions, with health risk assessments frequently indicating potential non-carcinogenic and carcinogenic effects [Thomas, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Adelakun et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Oloye \u0026amp; Odedeyi, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. Systematic reviews have confirmed that heavy metal contamination in Nigerian aquatic foods is widespread, particularly in crude oil-impacted areas like the Niger Delta [Umeoguaju et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e] and across Southwest Nigeria [Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. Despite this accumulating evidence, a comprehensive synthesis that integrates the \u003cb\u003enutritional value\u003c/b\u003e, \u003cb\u003ehealth impacts\u003c/b\u003e, and \u003cb\u003epublic health implications\u003c/b\u003e of heavy metal contamination specifically in \u003cb\u003esmoked fish r\u003c/b\u003eemains lacking [Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Nkwunonwo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThis review addresses this gap by critically examining the existing Nigerian literature on heavy metals in smoked fish through four interconnected lenses: (1) the smoking process as a source of contamination, (2) the nutritional profile of smoked fish, (3) the documented health risks to consumers, and (4) the broader public health challenges, including the overlooked occupational exposure of fish smokers. By synthesizing evidence from across Nigeria, this review aims to inform policy, guide future research, and contribute to safer fish smoking practices that protect both consumers and producers.\u003c/p\u003e"},{"header":"2.0 SMOKING PRACTICES AND HEAVY METAL CONTAMINATION","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Fish Smoking in Nigeria\u003c/h2\u003e \u003cp\u003eFish smoking in Nigeria is predominantly artisanal, employing traditional technologies that vary by region. The most common methods include drum kilns (repurposed metal oil drums), mud kilns, and wire-mesh ovens, all of which rely on direct combustion of wood or another biomass [Adeyeye, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Adeyeye, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e]. While these methods are effective for preservation and impart desirable sensory characteristics, they offer limited control over temperature, smoke density, and exposure duration which are the factors that influence contaminant formation and deposition [Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Tongo et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e]. Studies have shown that smoking methods significantly affect the quality and safety of the final product, with drum-smoking often associated with higher contaminant levels compared to improved kilns [Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Sources of Heavy Metals in Smoked Fish\u003c/h2\u003e \u003cp\u003eHeavy metals in smoked fish are majorly from two primary sources: the raw fish itself and the smoking process. Fish harvested from polluted waters accumulate metals in their tissues through dietary and dermal uptake [Adesiyan et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Edogbo et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Enuneku et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e]. Rivers in industrial areas - such as those in Kano [Edogbo et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e], Southwest Nigeria [Adesiyan et al., \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2018\u003c/span\u003e], and the Niger Delta [Umeoguaju et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Enuneku et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e] -have documented elevated metal levels, which are reflected in resident fish species [Oloye \u0026amp; Odedeyi, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Odey et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eDuring smoking, additional contamination can occur through various means. Firstly, wood harvested from metal-contaminated soils or treated wood may release metals during combustion, which deposit on fish surfaces [Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e]. In addition, corroded metal drums or galvanized wire meshes can leach metals such as lead, cadmium, and zinc into the fish, especially under high heat and acidic smoke conditions [Adeyeye et al., \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Nwosu et al., 2021]. Also, smoking removes moisture up to 70% weight loss, concentrating existing metals in the remaining tissue [Osuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Evidence from Nigerian Studies\u003c/h2\u003e \u003cp\u003eVarious studies across Nigeria have documented elevated heavy metal concentrations in smoked fish compared to fresh samples or regulatory limits. Table\u0026nbsp;1 summarizes heavy metal concentrations in smoked fish reported from different Nigerian regions.\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 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHeavy Metal Concentrations in Smoked Fish from Nigerian Studies\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFish Species\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMetals Detected\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eKey Finding/limits\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReference\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOndo State\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eClarias gariepinus (smoked catfish)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFe: 149.0\u0026thinsp;\u0026plusmn;\u0026thinsp;7.76\u0026ndash;155.0\u0026thinsp;\u0026plusmn;\u0026thinsp;5.10;\u003c/p\u003e \u003cp\u003eMn: exceeded 1 mg/kg;\u003c/p\u003e \u003cp\u003eNi: 0.00\u0026thinsp;\u0026plusmn;\u0026thinsp;0.00\u0026ndash;1.00\u0026thinsp;\u0026plusmn;\u0026thinsp;1.41; Cd, Cr reported\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eExceeded limits; HI\u0026thinsp;\u0026gt;\u0026thinsp;1; Cr cancer risk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOlayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNew Bussa Market\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmoked Freshwater fish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eChemical qualities and heavy metals evaluated\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eContamination linked to processing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAdelakun et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSouth West Nigeria local markets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFresh, frozen, smoked\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMultiple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSmoked\u0026thinsp;\u0026gt;\u0026thinsp;fresh; children at risk\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLagos State\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCatfish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCd, Pb, Zn\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSmoking increases metal concentration\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOsuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEke-Awka Market, Anambra State\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmoked-dried fish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAs, Cd, Cr, Hg, Pb\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHealth risk\u0026thinsp;\u0026gt;\u0026thinsp;1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOnoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eZaria\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCatfish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMultiple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSmoked from polluted sources\u0026thinsp;\u0026gt;\u0026thinsp;home-bred\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOdey et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOse River, Ondo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMultiple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eMultiple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eWater-sediment-fish transfer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOloye \u0026amp; Odedeyi, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2025\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBorno State\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMultiple\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNot specified\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSocio-economics documented\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBwala \u0026amp; Imam, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAcross these studies, lead and cadmium are the most frequently detected metals exceeding regulatory limits, with chromium emerging as a metal of high concern due to its carcinogenic potential [Thomas, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. The Niger Delta region shows particularly elevated levels due to crude oil pollution [Umeoguaju et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e], while industrial areas like Kano show contamination from industrial effluents [Edogbo et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"3.0 METHODOLOGY","content":"\u003cp\u003eThis chapter describes the systematic approach employed to identify, screen, and synthesize relevant literature on heavy metal contamination in smoked fish from Nigeria.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Search Strategy\u003c/h2\u003e \u003cp\u003eA comprehensive literature search was conducted to identify studies on heavy metal contamination in smoked fish from Nigeria. The following electronic databases were systematically searched: PubMed, Scopus, ScienceDirect, Google Scholar, and ResearchGate. The search was conducted between February 2026 and March 2026 and covered publications from January 2015 to December 2025 to ensure relevance and currency. The search strategy employed combinations of keywords and Boolean operators. Population terms included \"Nigeria\" OR \"Nigerian\" combined with specific state names such as Ondo, Lagos, Ogun, Anambra, Borno, Niger Delta, and Southwest Nigeria. Exposure terms comprised \"heavy metals,\" \"trace metals,\" \"toxic metals,\" \"lead,\" \"Pb,\" \"cadmium,\" \"Cd,\" \"chromium,\" \"Cr,\" \"arsenic,\" and \"As.\" Food terms included \"smoked fish,\" \"processed fish,\" \"smoke-dried fish,\" \"Clarias gariepinus,\" \"catfish,\" and \"tilapia.\" Outcome terms covered \"health risk assessment,\" \"THQ,\" \"hazard quotient,\" \"hazard index,\" \"HI,\" \"cancer risk,\" \"nutrition,\" \"proximate composition,\" and \"public health.\"\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Inclusion and Exclusion Criteria\u003c/h2\u003e \u003cp\u003eStudies were included if they met specific criteria. Eligible studies comprised original primary research or systematic reviews published in peer-reviewed journals, conducted in Nigeria or specifically focused on Nigerian smoked fish samples, and reported quantitative data on heavy metal concentrations including lead, cadmium, chromium, arsenic, or mercury in smoked fish. All included studies were published in English between January 2015 and December 2025. Studies were excluded if they examined fresh or frozen fish only without a smoked fish component, reported only polycyclic aromatic hydrocarbons, microbial contamination, or pesticide residues without metal analysis, or were conference abstracts, editorials, commentaries, or opinion pieces without original data. Studies where full text was unavailable after contacting authors and duplicate publications of the same data were also excluded.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Study Selection and PRISMA Framework\u003c/h2\u003e \u003cp\u003eThe study selection process followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 guidelines. The selection involved four stages: identification, screening, eligibility, and inclusion. During identification, records were retrieved from database searching using the specified keywords. In the screening stage, titles and abstracts were screened against inclusion criteria and duplicates were removed. Full-text articles were then assessed for eligibility during the third stage. Finally, studies meeting all criteria were included in the final review.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Quality Assessment\u003c/h2\u003e \u003cp\u003eThe quality of included studies was assessed using an adapted checklist. Each study was evaluated on several parameters including clear description of sampling methodology covering location, sample size, and fish species; appropriate analytical methods such as atomic absorption spectrophotometry or inductively coupled plasma mass spectrometry with quality control measures; use of certified reference materials or recovery tests; reporting of detection limits; calculation of health risk indices including target hazard quotient, hazard index, and cancer risk where applicable; and transparent reporting of results including means, standard deviations, and ranges. Studies were not excluded based on quality scores, but methodological strengths and limitations were considered in the narrative synthesis.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Data Extraction\u003c/h2\u003e \u003cp\u003eThe following data were extracted from each included study into a standardized spreadsheet. Bibliographic information included authors, year, journal, and digital object identifier. Study characteristics comprised location including state, specific market, river, or community; fish species sampled with common and scientific names; and smoking method such as drum kiln, mud kiln, improved kiln, or unspecified. Heavy metals analyzed were recorded along with mean concentrations in milligrams per kilogram wet weight or dry weight with standard deviations. Regulatory limits used for comparison including WHO, FAO, NAFDAC, and SON standards were noted. Health risk indices including target hazard quotient, hazard index, and cancer risk were extracted where calculated. Nutritional parameters including protein, fat, moisture, ash, and minerals were recorded if reported, along with key conclusions and recommendations from each study.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Data Synthesis\u003c/h2\u003e \u003cp\u003eExtracted data were synthesized narratively due to heterogeneity in study locations, fish species, analytical methods, and reporting formats. Findings were organized thematically corresponding to the review objectives. Geographic patterns were examined by grouping results by Nigerian region including Southwest, Southeast, North, and Niger Delta to identify regional contamination patterns. Metal prevalence was assessed by examining frequency and concentrations of specific metals including lead, cadmium, chromium, and arsenic across studies. Health risk outcomes were summarized by compiling target hazard quotient, hazard index, and cancer risk findings with particular attention to vulnerable groups. Where studies compared different smoking techniques, findings were synthesized separately to evaluate the impact of smoking methods on contamination levels.\u003c/p\u003e \u003c/div\u003e"},{"header":"4.0 NUTRITIONAL PROFILE AND THE RISK-BENEFIT DILEMMA ","content":"\u003cp\u003e\u003cstrong\u003e4.1 Nutritional Value of Smoked Fish\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSmoked fish remains a nutritionally valuable food. It provides high-quality, easily digestible protein essential for growth and tissue repair [Oli et al., 2024; Adeyeye et al., 2019]. Fish are also the primary dietary source of long-chain omega-3 fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]), which support cardiovascular health, brain development, and reduce inflammation [Obande et al., 2025].\u003c/p\u003e\n\u003cp\u003eAdditionally, smoked fish contributes bioavailable micronutrients. Adeyeye et 0al. [2019] documented the amino acid, vitamin, and mineral profiles of smoked fish, showing that smoking methods and fish types affect nutrient retention. Aliyu et al. [2024] reported mineral compositions in processed tilapia, while Oli et al. [2024] compared proximate composition of fresh and smoke-dried fish from Omambala River, finding that smoking preserves protein content while reducing moisture. For many low-income households in Nigeria, smoked fish represents an affordable and accessible source of these essential nutrients [Oghenochuko et al., 2022; Bwala \u0026amp; Imam, 2021].\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.2 Impact of Smoking on Nutrient Content\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe smoking process can alter nutrient composition. Heat exposure may degrade vitamins which are sensitive to heat and cause some lipid oxidation. However, protein content is generally well-preserved, and the dehydration process concentrates nutrients alongside contaminants [Oli et al., 2024; Adeyeye et al., 2019]. Studies comparing fresh and smoked fish from the same sources are limited and thereby make a research gap.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e4.3 The Risk-Benefit Calculus\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe co-occurrence of heavy metals in smoked fish creates a public health dilemma. While consumers derive nutritional benefits, they are simultaneously exposed to neurotoxic, nephrotoxic, and carcinogenic metals [Lawal et al., 2021; Nkwunonwo et al., 2020]. This risk-benefit analysis is particularly critical for citizens including children, pregnant women, and frequent consumers who may be at higher risk despite the nutritional advantages [Oghenochuko et al., 2022; Obande et al., 2025].\u003c/p\u003e\n\u003cp\u003eThe key question is whether the levels of heavy metals documented in Nigerian smoked fish negate its nutritional value. Based on the health risk assessments reviewed in Section 5, the answer is context-dependent: for some metals and consumer groups, the risks likely exceed the benefits [Thomas, 2024; Olayinka-Olagunju, 2025; Onoja et al., 2025]. This emphasizes the urgent need for contamination reduction strategies that preserve nutritional integrity while minimizing toxic exposures.\u003c/p\u003e"},{"header":"5.0 HEALTH IMPACTS OF HEAVY METAL CONTAMINATION","content":"\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Toxicological Profiles of Detected Metals\u003c/h2\u003e \u003cp\u003eLead (Pb): A neurotoxin that affects cognitive development in children and causes cardiovascular and renal effects in adults. No safe level of exposure exists [Lawal et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nkwunonwo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e]. Nigerian studies consistently report Pb exceeding permissible limits in smoked fish [Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Onoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eCadmium (Cd): Accumulates in kidneys and bones, with a half-life of 10\u0026ndash;30 years. Chronic exposure causes renal tubular dysfunction and osteoporosis [Lawal et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e]. Cd is frequently detected in smoked fish from industrial and urban areas [Osuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Edogbo et al., \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eChromium (Cr): Hexavalent chromium (Cr VI) is classified as a Group 1 human carcinogen (lung, nasal). Trivalent Cr (III) is essential but toxic at high levels [Thomas, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. Thomas [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e] specifically identified Cr as the metal of highest carcinogenic concern in smoked catfish from Ogun State.\u003c/p\u003e \u003cp\u003eArsenic (As): Inorganic arsenic is a carcinogen (skin, bladder, lung) and causes cardiovascular and neurological effects [Lawal et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e]. Detected in Ondo State samples [Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Health Risk Assessment in Nigerian Smoked Fish\u003c/h2\u003e \u003cp\u003eHealth risk assessment estimates potential non-carcinogenic and carcinogenic risks from dietary exposure. The Target Hazard Quotient (THQ) compares estimated exposure to a reference dose; values 1.0 indicate potential non-carcinogenic effects. The Hazard Index (HI) sums THQs for multiple metals. Cancer Risk (CR) estimates lifetime cancer probability; values 1 \u0026times; 10⁻⁴ are considered unacceptable by the US EPA.\u003c/p\u003e \u003cp\u003eTable\u0026nbsp;2 summarizes health risk indices reported in Nigerian studies.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eHealth Risk Assessment Findings\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLocation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFish Species\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eKey Findings\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHealth Implications\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eReferences\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOndo State\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003esmoked catfish \u0026amp; grasscutter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHigh Fe/Mn/Ni; exceeded WHO limits\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNon-carcinogenic risks from chronic intake\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOlayinka-Olagunju (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNiger Delta\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSeafood meta-analysis\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eElevated THQ/ILCR for heavy metals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOil-impacted regions cause systemic toxicity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eUmeoguaju et al. (\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSouthwest markets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmoked fish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHI/THQ\u0026thinsp;\u0026gt;\u0026thinsp;1 for key metals\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eHigher risks in smoked vs fresh/frozen\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOghenochuko et al. (\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbeokuta\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eProcessed catfish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTHQ for metals in smoked; non-carcinogenic focus\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVulnerable groups at risk (e.g., nephrotoxicity)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eThomas (\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOse River, Ondo\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFish species\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eConcentrations \u0026amp; risk assessment (water/sediment/fish)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBioaccumulation led to elevated HI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOloye \u0026amp; Odede (2025)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReview\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHeavy metals public health\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGeneral risks (carcinogenic/non-carcinogenic)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePb/Cd neuro/kidney damage in Nigeria context\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLawal et al. (\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReview\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNigeria food chain review\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHealth implications via food chain\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eChronic exposure risks malnutrition synergy\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNkwunonwo et al. (\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnambra\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSmoked-dried fish\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHI\u0026thinsp;\u0026gt;\u0026thinsp;1; non-carcinogenic adverse effects\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMarket fish unsafe for regular consumption\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eOnoja et al. (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAcross the reviewed studies, a consistent pattern emerges:\u003c/p\u003e \u003cp\u003eNon-carcinogenic risks: In Ondo State, Olayinka-Olagunju [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e] reported HI values exceeding 1.0, indicating potential adverse health effects in regular consumers. Oghenochuko et al. [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e] also found that children face higher health risks per unit body weight compared to adults, due to higher fish consumption rates and greater physiological susceptibility. Onoja et al. [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e] similarly documented HI\u0026thinsp;\u0026gt;\u0026thinsp;1 in Anambra State.\u003c/p\u003e \u003cp\u003eCarcinogenic risks: Thomas [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e] in Ogun State reported cancer risk values for chromium that exceeded the US EPA acceptable limit (1\u0026times;10⁻⁴), classifying smoked fish consumption as a potential carcinogenic hazard. Olayinka-Olagunju [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e] also documented elevated cancer risks in Ondo State, with chromium as the primary contributor.\u003c/p\u003e \u003cp\u003eVulnerable groups: Children are consistently identified as the most vulnerable subpopulation [Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Regional and Temporal Patterns\u003c/h2\u003e \u003cp\u003eComparing studies across Nigeria reveals geographic variation in contamination profiles. Northern states like Borno [Bwala \u0026amp; Imam, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e] and Zaria [Odey et al., \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2020\u003c/span\u003e] show industrial and domestic effluent impacts. Southwestern states show complex mixtures with Cr-related cancer risks [Thomas, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. The Niger Delta exhibits the most severe contamination due to crude oil pollution [Umeoguaju et al., \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2023\u003c/span\u003e; Enuneku et al., \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2018\u003c/span\u003e]. This likely reflects differences in local pollution sources, smoking practices, and fish species.\u003c/p\u003e \u003c/div\u003e"},{"header":"6.0 PUBLIC HEALTH IMPLICATIONS AND POLICY GAPS","content":"\u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e6.1 Regulatory Landscape\u003c/h2\u003e \u003cp\u003eIn Nigeria, maximum permissible limits for heavy metals in fish are established by the National Agency for Food and Drug Administration and Control (NAFDAC) and the Standards Organization of Nigeria (SON), which generally align with Codex Alimentarius and WHO/FAO standards [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e]. However, the reviewed studies repeatedly document overruns these limits [Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Onoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Osuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Adelakun et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e], indicating a significant gap between standards and actual food safety.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e6.2 Monitoring and Enforcement Gaps\u003c/h2\u003e \u003cp\u003eDespite the evidence of contamination, Nigeria lacks a coordinated national surveillance program for heavy metals in smoked fish [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e]. Monitoring remains scattered, limited to academic research with limited translation into regulatory action. Ogbeide and Henry [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e] rigorously assessed Nigerian policies addressing heavy metal pollution, concluding that enforcement remains weak and remediation strategies are inadequately implemented. This absence of systematic data hinders risk assessment, prevents early warning and leaves consumers unprotected.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e6.3 Consumer Awareness\u003c/h2\u003e \u003cp\u003eThere is a striking gap in research on consumer knowledge regarding heavy metal risks in smoked fish. Studies on microbial safety [Adetuwo et al., \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2023\u003c/span\u003e] suggest that consumers may be more aware of spoilage than chemical contaminants. The findings suggest that consumers select fish based on sensory qualities (texture, color, smell) rather than safety considerations [Adeyeye, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Bwala \u0026amp; Imam, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e]. Without awareness, consumer pressure cannot drive safer practices.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e6.4 The Overlooked Population: Occupational Exposure of Fish Smokers\u003c/h2\u003e \u003cp\u003eA major oversight in the Nigerian literature is the occupational health of fish smokers - predominantly women who spend hours daily inhaling smoke from burning wood. While studies document heavy metals and PAHs in smoked fish [Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Tongo et al., \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2017\u003c/span\u003e], no study in this database assessed inhalation exposure among processors. Emerging findings from West Africa suggest that smoke contains not only particulate matter and PAHs but also volatile metals that can be inhaled or absorbed dermally [Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. These workers may face health risks exceeding those of consumers, yet they remain entirely absent from food safety discourse and occupational health protections. This represents the most urgent research gap identified in this review.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e6.5 Economic and Trade Implications\u003c/h2\u003e \u003cp\u003eHeavy metal contamination can affect domestic and international trade. Smoked fish is a tradable commodity within West Africa, and consistent violation of international standards could lead to export restrictions or loss of market access [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e]. Bwala and Imam [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e] documented the socio-economic importance of fish smoking in Borno State, highlighting that contamination could damage livelihoods.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec27\" class=\"Section2\"\u003e \u003ch2\u003e6.6 Pathways to Intervention\u003c/h2\u003e \u003cp\u003eAddressing heavy metal contamination requires a multi-faceted approach. Promoting improved smoking kilns (e.g., Chorkor, FAO-Thiaroye) validated to reduce both PAHs and metal contamination [Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Adeyeye, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e]. Ensuring fuelwood is sourced from uncontaminated areas; exploring alternative biomass [Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e]. Establishing routine monitoring with clear enforcement mechanisms [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e]. Extending food safety frameworks to include processor protection; study inhalation risks [Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; identified as gap]. And finally, developing culturally appropriate messaging on selecting safer smoked fish and diversifying protein sources [Nkwunonwo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e"},{"header":"7.0 KNOWLEDGE GAPS AND FUTURE RESEARCH DIRECTIONS","content":"\u003cp\u003eThis review reveals several critical gaps in the Nigerian literature on heavy metals in smoked fish.\u003c/p\u003e \u003cp\u003eNo reviewed study simultaneously measured heavy metals and comprehensive nutritional parameters (protein, fatty acids, vitamins) in the same smoked fish samples, preventing direct risk-benefit quantification. While Adeyeye et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e] and Oli et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e] provide nutritional data, and Olayinka-Olagunju [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e] provides metal data, they are from different samples. In addition, no studies assessed heavy metal exposure in fish smokers via inhalation or dermal routes. This is the most urgent research need, given the hours processors spend in smoke [Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; identified in this review]. All studies are cross-sectional; no data exist on seasonal variation or long-term trends in metal contamination [Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eNo studies have evaluated whether improved kilns or fuel substitutions actually reduce metal levels in smoked fish, though PAH reduction has been studied [Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e; Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e]. Total metal concentration does not equal absorbed dose. Studies measuring bio-accessibility (simulated digestion) would refine risk assessments [Lawal et al., \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Nkwunonwo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e]. Research on consumer awareness, preferences, and willingness to pay for safer smoked fish is absent [noted in Section 6]. More research is needed to distinguish metals originating from aquatic pollution versus those introduced during smoking [Laoye et al., \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e]. Policy implementation research: Studies on why existing regulations fail and how to improve enforcement are lacking [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e]. Future research should prioritize these areas to generate evidence for effective interventions.\u003c/p\u003e"},{"header":"8.0 CONCLUSION","content":"\u003cp\u003eThis review synthesizes Nigerian evidence on heavy metal contamination in smoked fish, revealing a persistent and alarming trend. Across multiple states and studies, smoked fish contains high levels of lead, cadmium, chromium, and arsenic, frequently exceeding regulatory limits [Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Onoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Osuala \u0026amp; Igwo-Ezikpe, \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Adelakun et al., \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Oloye \u0026amp; Odedeyi, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHealth risk assessments show that regular consumption carries potential non-carcinogenic risks (Hazard Index\u0026thinsp;\u0026gt;\u0026thinsp;1) and, for chromium, unacceptable cancer risks [Thomas, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Olayinka-Olagunju, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2025\u003c/span\u003e; Onoja et al., \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. Children are particularly vulnerable due to higher consumption per body weight and greater physiological susceptibility [Oghenochuko et al., \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eBasically, this review identifies a major challenge: the occupational health of fish smokers. While consumers face dietary risks, processors - predominantly women - may face even higher risks through inhalation, yet they remain entirely absent from Nigerian research and policy [identified gap; Obande et al., \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2025\u003c/span\u003e]. This lapse must be urgently addressed.\u003c/p\u003e \u003cp\u003eSmoked fish remains an essential source of nutrition and livelihood in Nigeria [Adeyeye, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Bwala \u0026amp; Imam, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Oli et al., \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2024\u003c/span\u003e]. The goal is not to eliminate smoking but to make it safe - for all. Achieving this requires investment in validated smoking technologies [Adeyeye et al., \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Ubwa et al., \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2015\u003c/span\u003e], National surveillance linking metal data to health outcomes [Ogbeide \u0026amp; Henry, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Idowu, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2022\u003c/span\u003e], Inclusion of occupational health in food safety frameworks [identified gap] and Community education for safer practices [Nkwunonwo et al., \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe evidence is unequivocal; urgent action is required to advance the field and address the challenges identified. 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Foods, 10(9), 2013. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/foods10092013\u003c/span\u003e\u003cspan address=\"10.3390/foods10092013\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"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":"Smoked fish, heavy metals, public health, occupational exposure, health risk assessment, nutrition, food safety","lastPublishedDoi":"10.21203/rs.3.rs-8852012/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8852012/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eSmoked fish is a vital protein source and livelihood in Nigeria, but traditional smoking may introduce toxic heavy metals, creating public health concerns.\u003c/p\u003e\u003ch2\u003eObjective\u003c/h2\u003e \u003cp\u003eThis review synthesizes Nigerian literature on heavy metal contamination in smoked fish, examining smoking processes, nutritional implications, health risks, and public health challenges, including occupational exposure of processors.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA systematic search of PubMed, Scopus, ScienceDirect, Google Scholar, and ResearchGate was conducted for studies published between 2015\u0026ndash;2025 following PRISMA guidelines. Included studies reported quantitative data on heavy metal concentrations in Nigerian smoked fish. Data on metal levels, health risk indices (THQ, HI, cancer risk), nutritional parameters, and smoking methods were extracted and synthesized thematically.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eStudies across Ondo, Ogun, Lagos, Anambra, Borno, and the Niger Delta consistently report elevated lead, cadmium, chromium, and arsenic in smoked fish, frequently exceeding regulatory limits. Traditional drum-smoking yields higher contamination than improved kilns. Smoked fish retains nutritional value, creating a risk-benefit dilemma. Health risk assessments reveal non-carcinogenic effects (HI\u0026thinsp;\u0026gt;\u0026thinsp;1) and unacceptable cancer risks from chromium. Children are most vulnerable. A critical gap is the complete absence of research on occupational exposure of fish smokers.\u003c/p\u003e\u003ch2\u003eConclusion\u003c/h2\u003e \u003cp\u003eHeavy metal contamination causes significant risks to consumers while processors face unstudied occupational hazards. Addressing this requires improved smoking technologies, national surveillance, occupational health integration, and community education.\u003c/p\u003e","manuscriptTitle":"Heavy Metals in Smoked Fish: A Comprehensive Review of Nutritional Implications, Health Impacts, and Public Health Challenges in Nigeria","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-03 07:19:32","doi":"10.21203/rs.3.rs-8852012/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":"577dd8ad-e477-43de-b4f1-84590cb0a56b","owner":[],"postedDate":"March 3rd, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":63707313,"name":"Food Science \u0026 Technology"},{"id":63707314,"name":"Health Economics \u0026 Outcomes Research"}],"tags":[],"updatedAt":"2026-03-03T07:19:32+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-03 07:19:32","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8852012","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8852012","identity":"rs-8852012","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}