CO-OCCURRING TRACE ELEMENTS (CTES) OF POTENTIAL HUMAN HEALTH CONCERN IN ARSENIC CONTAMINATED AQUIFERS IN THE BENGAL BASIN

The mobilization of co-occurring trace elements (CTEs) in aquifers with known metal(loid) contamination may exacerbate potential human health threats where release mechanisms are not geochemically limited. This study investigates the co-mobilization of the potentially toxic CTEs antimony (Sb), molybdenum (Mo), vanadium (V), uranium (U), and selenium (Se) with arsenic (As) and iron (Fe) in contrasting high and low As aquifers surrounding the river Bhagirathi in Murshidabad, West Bengal, India. Groundwater samples from Holocene (high As) and Pleistocene (low As) aquifers in West Bengal were analyzed for CTEs using high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). The results revealed that the groundwater from Holocene aquifer contains groundwater with compositions reflective of carbonate mineral dissolution and silicate mineral weathering, along with clear signs of Fe reduction and associated mobilization of As, Sb, Mo, V, and U. Relatively oxic groundwater in the Pleistocene aquifer underlying the study sites on the west side of the river showed minimal Fe reduction and signatures of carbonate mineral dissolution and silicate mineral weathering, or evaporite mineral dissolution. In groundwater samples from the more oxic Pleistocene aquifer, concentrations of As, Sb, Mo, and V were substantially lower than in the Holocene aquifer, however, U concentrations were relatively higher where carbonate mineral dissolution predominated. Compelling positive correlations between Fe and CTEs in the Holocene but not in the Pleistocene aquifer implicated Fe reductive processes as the probable pathway for CTEs release. We hypothesize that carbonate mineral dissolution mobilizes U in the absence of Fe reduction, and that U solubility in the reducing Holocene aquifer may be facilitated by carbonate mineral dissolution products (e.g., Ca, HCO3-, CO32-) that promote U complexation and the inhibition of (bio) immobilization pathways. We therefore argue that – despite moderately low concentrations of CTEs in the current study – mechanistic modeling efforts and more extensive monitoring of trace metal (loid)s should be performed to ensure that drinking water supplies do not pose additional health threats in the coming years.