Risk assessment and source identification of toxic metals in some commonly consumed fishes from a subtropical wetland system: Implications and monitoring.
Heavy metal pollution in wetland ecosystems poses serious threats to aquatic biodiversity and human health, particularly in agricultural regions with limited environmental monitoring. This study assesses the distribution, sources, and health risks of eight trace metals: lead (Pb), cadmium (Cd), chromium (Cr), manganese (Mn), nickel (Ni), mercury (Hg), copper (Cu), and zinc (Zn) in the Khaliajury haor, a critical wetland in Netrokona, Bangladesh. From June to December 2024, samples of surface water, sediment, and ten commonly consumed fish species were collected across five sampling stations following standard QA/QC procedures. Metal concentrations were compared with national and international guidelines, and source identification was performed along with pollution indices (Igeo, PLI, PER) and health risks (THQ, HI, CR). In surface water, Mn and Cu exceeded permissible limits at all stations. Cr and Hg in sediment surpassed the toxicity reference value (TRV) at every site, while Cd, Ni, and Cu were elevated at multiple locations. However, negative Igeo values and PLI scores below 1 indicated uncontaminated sediment status with low potential ecological risk (PER). In fish tissues, Mn exceeded maximum allowable concentrations (MAC) in seven of ten species, followed by Pb in five species, and Cr and Cd each in two species. Although THQ and HI values remained below 1, suggesting negligible non-carcinogenic risk, cancer risk (CR) values for Pb, Cd, Cr, and Ni exceeded the USEPA upper acceptable threshold of 10⁻4 across all species, implying potential lifetime carcinogenic risk to consumers. Multivariate analysis (correlation matrix and PCA) displayed that bioaccumulation of heavy metals sourced from agricultural runoffs, anthropogenic activities, wastewaters and environmental processes, that travel through different trophic levels in the wetland system. These findings underscore the need for systematic biomonitoring, source identification, and risk communication for communities dependent on haor fisheries.