Dynamics of Arsenic Co-contamination in the Groundwater of the Eastern Himalayas: The Biogeochemical Drivers and GRACE-Based Evidence

We probed the status quo of arsenic (As) and related cocontaminants like iron (Fe), fluoride (F^–), and uranium (U) reported in aquifers of the eastern Himalayan region including the northeastern Indian states, the Ganga–Brahmaputra–Meghna basins, and Bangladesh. Our study appraised the hydro-geobiological features and probable sources of cocontamination and corroborated the variability concerning the conditions in Bangladesh. Increased awareness, advanced analytical capabilities, and support from international organizations have led to the identification of new contamination sites, with As levels in some areas exceeding the permissible value of 10 μg L^–1, reaching up to 986 μg L^–1. Key factors include mineral deposits enriched with As, Fe, U, and F^– in the Indus–Tsangpo suture zone and the Siwalik Neogene sediments, influenced by iron (hydr)oxide and microbial processes, as well as growing reliance on groundwater. In northeastern India, cocontaminants are more prevalent due to diverse land use, quartzite, shale, sandstone, and clay deposits. In contrast, the contamination in Bangladesh is mainly associated with aquifer geology. Leveraging data from the Gravity Recovery and Climate Experiment (GRACE), this study identifies the significant challenge of groundwater overexploitation in both regions assessed. These findings offer opportunities to support sustainable goals, raise awareness, and implement mitigation to protect vulnerable communities.