Seasonal contamination of heavy metals in Tawi River - Sources, fate, and health implications

• Spatial-temporal assessment of heavy metals in the Tawi River, Himalaya. • High-altitude Hg linked to atmospheric deposition and cold-trapping processes. • Built-up areas show elevated Al, Fe, Ag, and Cd, whereas monsoon driven chemical weathering enhances Al and Fe levels. • Arsenic and Hg pose seasonal health risks, with children more vulnerable than adults. The present study assesses the non-carcinogenic and carcinogenic effects of HMs in the Tawi River, with a focus on seasonal (December – S1, and July - S2) and altitudinal variation. The seasonal comparison showed higher Al and Fe concentrations in July (season 2) samples, suggesting intensified monsoon-induced weathering. However, Hg concentrations were consistently higher (in both seasons) at higher altitudes, suggesting the influence of atmospheric deposition and “ cold trapping ” processes. Further, the non-carcinogenic effects measured through hazard quotient (HQ) show minimal risk from all metals. The hazard index (HI) values for selected metal lie below 1 (HI<1), except for arsenic (in seasons 1 and 2) and Hg (in season 2 only). This reflects a seasonal weathering-induced mobilisation of arsenic during the monsoon. The carcinogenic risk (CR) analysis indicated that the samples collected during S1 showed a low to very low risk for Cr, Ni, Cd and Pb, whereas As falls into the medium-risk category, with children being more vulnerable than adults to HM exposure. Similarly, for the samples collected during S2, CR values for Cr, Ni, and As fall in the medium risk category, whereas Cd and Pb represent the very to low-risk category. These findings emphasise the urgent need for better water quality management and a focus on regular monitoring of seasonal HM measurements and increased public awareness concerning the Tawi River in the Jammu region.