Seasonal dynamics of heavy metal accumulation in Wallago attu tissues from a transboundary riverine system and associated health implications

In the Shari-Goyain River, every year, hilly flash flood carries wastewater emitted from coal mining activities that result in water pollution and massive killing of fish, causing human health hazards from consumption. Therefore, this study assessed seasonal accumulation of eight heavy metals (HMs), namely Cd, Cu, Fe, Mn, Ni, Pb, Se and Zn in tissues (gill, gonad, kidney, liver, and muscle) of Wallago attu from the exposed site of this river versus a control site (the Piyain River) by using atomic absorption spectrophotometry, and evaluated the potential health risks for consumers. Metal accumulation levels in different tissues varied significantly among diverse tissues (p < 0.05) of liver > gonad > kidney > gill > muscle in the exposed site, and kidney > gill > liver > gonad > muscle in the control site. The highest concentrations of HMs (p < 0.05) in all tissues were detected in pre-monsoon, followed by winter, post-monsoon, and monsoon. Among the metals, Fe (up to 421.7 mg/kg in kidney) and Zn (up to 148.8 mg/kg in gills) exhibited the highest accumulation, whereas Cd showed the lowest levels (as low as 0.14 mg/kg in muscle). Principal component analysis linked HM pollution primarily to coal mine drainage, with Ni, Fe, Se, Pb, Cd, and Cu as dominant contributors. The presence of strong coefficients and vector arrows indicating pairwise collinearities among certain HMs (Cd-Cu, Pb-Se, and Fe-Ni) further indicated that these metals have similar sources and behaviors within the river. For all seasons and sampling sites, the total hazard quotient indicated a low likelihood of non-carcinogenic health risks. However, the consumption of fish from the Shari-Goyain River poses elevated risk in the pre-monsoon and winter compared to the other seasons. To protect the health and safety of local consumers and to support sustainable aquatic ecosystems, future research should prioritize long-term monitoring of HMs in this aquatic system and the development of mitigation solutions for coal mining pollution.