Distribution and bioaccumulation of heavy metals in water, sediment, and native fish of Mahananda River, Bangladesh with the human health implications

This study elucidated the status of heavy metal pollution and its potential human health risks due to consumption of contaminated fish from the Mahananda River, an important transboundary river in Bangladesh, which is getting continuous pollution from industries, pesticides, and municipal waste. For this purpose, five sampling stations named Alampur, Boalia, Chowdala, Batha Market, and Char Anupnagar were selected based on industrial location, paddy culture area responsible for pesticide contamination, and municipal areas. These sites were also selected by considering the upstream and downstream of this river. Water, sediment, and 12 indigenous fish, including Glossogobius giuris, Puntius sophore, Amblypharyngodon mola, Gudusia chapra, Eutropiichthys vacha, Macrognathus pancalus, Rita rita, Mystus tengara, Channa punctata, Puntius sarana, Cirrhina reba , and Mystus cavasius, were analyzed to evaluate heavy metal bioaccumulation in muscle and head tissues. In water, mercury was significantly higher in Alampur due to the industrial area and upstream of the river; however, chromium was higher in Batha market due to the dumping station and tannery wastage. Sediment was moderately polluted with cadmium and arsenic. Among different fish species, carnivorous species, Channa punctata and Rita rita, were mostly contaminated with Hg and Pb; however, Cirrhina reba was mostly polluted with Cu, Cr, and Mn due to feeding on benthic organisms. The contamination factor followed the order Zn > Mn > Ni > Cr > Cu > Pb > Co > As > Hg > Cd. There was a strong positive relation among Hg, Cu, Pb, and Cd due to anthropogenic contamination from industrial discharge, urban runoff, municipal waste, and upstream and downstream fragmentation of this river. Health risk assessment showed that the carcinogenic risk of Cr is associated with the consumption of contaminated fish species of the studied river area. An integrated evaluation of heavy metal contamination across water, sediment, and native fish species, with species-specific bioaccumulation and human health risks in Mahananda River has been revealed. Considering this pollution, an integrated river management is needed to minimize this ecological degradation and pollution of this river. Environmental implications of this study This study showed ecologically significant heavy metals pollution in the Mahananda River where sediment acts as long-term pollution source and fishes serving as bio indicators of trophic transfer. Higher metal pollution in carnivorous and benthic feeder fish species exhibited higher human health risk for their consumption. This continuous contamination threatens aquatic biodiversity, fisheries sustainability, and ecosystem stability in this transboundary river like Mahananda, Bangladesh. Effective management and continuous monitoring is essential minimize further ecological degradation and ensuring sustainable ecosystem resilience.