MOBILIZATION OF CO-OCCURRING TRACE ELEMENTS UNDER IRON-REDUCING CONDITIONS IN WEST BENGAL GROUNDWATER

Elevated levels of dissolved arsenic (As) in Bengal Basin groundwater is considered one of the greatest mass poisonings in human history. Recent studies have shown that several other co-occurring trace elements (CTEs) of health concern such as antimony (Sb), molybdenum (Mo), vanadium (V), uranium (U) and selenium (Se) may also be released into groundwater during As mobilization. Here, we present the distribution of As and CTEs in 45 groundwater samples from contrasting aquifers on either side of the river Bhagirathi in Murshidabad, West Bengal. The aquifer to the east of the river Bhagirathi is characterized by Holocene sediments and groundwater with lower redox potential, high dissolved As (3.5 ± 4.6 µM), and high dissolved iron (Fe, 73 ± 74 µM). In contrast, the aquifer on the west side is characterized by Pleistocene sediments and groundwater with higher redox potential and lower dissolved As (0.11 ± 0.14 µM) and Fe (2.4 ± 3.3 µM). Concentrations of Mo (0.04 ± 0.04 µM), Sb (0.013 ± 0.015 µM) and V (0.03 ± 0.04 µM) are significantly higher in the Holocene aquifers relative to the Pleistocene aquifers (0.005 ± 0.003 µM, 0.0009 ± 0.001 µM and 0.009 ± 0.01 µM, respectively). Interestingly, U and Se show no significant differences between the groundwater in Holocene and Pleistocene aquifers. Dissolved Fe is positively correlated with Mo, Sb, and V in Holocene groundwater and not Pleistocene groundwater, suggesting that Mo, Sb and V may be mobilized alongside As during reductive dissolution of iron-(oxy) hydroxides. Our results further suggest that concentrations of these CTEs are associated with aromatic, humic-like and terrestrially derived dissolved organic matter (DOM), possibly due to aqueous complexation between CTEs and DOM.