Geochemical Controls on Arsenic Mobility in Groundwater and Sediments from the Ganges-Brahmaputra-Meghna Delta: Implications for Human Health and Remediation

Abstract:

This comprehensive study investigates the geochemical controls on arsenic (As) mobility in groundwater and sediments from the Ganges-Brahmaputra-Meghna (GBM) Delta, one of the world’s largest arsenic-affected regions. A total of 216 groundwater samples and 108 sediment cores (0–30 m depth) were collected from 72 sampling sites across Bangladesh and West Bengal (India) between 2021–2023. Groundwater As concentrations range from 0.01 to 586 μg/L (average=83.4 μg/L), with 78% of samples exceeding the WHO drinking water guideline (10 μg/L). Sediment As concentrations vary from 2.3 to 48.7 mg/kg (average=15.6 mg/kg), predominantly associated with iron (Fe)-oxyhydroxides (42%), organic matter (OM) (28%), and sulfide minerals (19%). Geochemical analyses reveal that As mobility is primarily controlled by reductive dissolution of Fe-oxyhydroxides, driven by microbial decomposition of OM in anoxic conditions (Eh < -100 mV, pH=6.5–8.2). Secondary controls include pH-dependent sorption, competitive anion exchange (PO₄³⁻, HCO₃⁻), and sediment mineralogy (clay content, calcite abundance). Stable sulfur isotopes (δ³⁴S) of sediment sulfides (-12.8‰ to 4.3‰ VCDT) confirm microbial sulfate reduction as a key process for As sequestration. Human health risk assessment indicates high non-carcinogenic (hazard quotient >1) and carcinogenic (carcinogenic risk >10⁻⁴) risks for 92% of the study population. This study identifies geochemical proxies (Eh, Fe²⁺, OM content, PO₄³⁻) for As-rich groundwater and proposes context-specific remediation strategies, including Fe-oxide amended filters and managed aquifer recharge. The findings provide critical insights for sustainable groundwater management in arsenic-affected deltaic regions globally.