Hydro-chemical assessment of fluoride and nitrate in groundwater from east and west coasts of Bangladesh and India

Groundwater from the coastal alluvial plain is the primary water source in coastal areas. Its contaminants, such as nitrate and fluoride, are significant concerns for freshwater supply and human health issues. Although spatiotemporal variability of nitrate and fluoride levels has been analyzed individually in the Indo-Bangladesh coastal region, their drivers and hydro-chemical analysis have scarcely been studied. Thus, to assess the groundwater quality, hydro-chemistry, and drivers in coastal alluvial aquifers, 123 groundwater samples were collected from the east (Bangladesh) and west coasts (India) for assessment of nitrate and fluoride levels and major physiochemical parameters. Multivariate statistical and hydro-chemical analysis and public health risk appraisal were carried out for this purpose. The results showed that 25% (East coast) and 22.39% (West coast) of groundwater samples surpassed the allowable limit of fluoride with a maximum concentration of up to 16.11 mg/L and the tolerable nitrate limit slightly exceeded 10 mg/L. Furthermore, we note that industrial waste, synthetic pesticides, and agricultural fertilizer triggered the leaching of nitrate into groundwater, while the release of fluoride into groundwater was possibly due to evaporite dissolution, carbonate mineral weathering, and ion exchange processes on both coasts. About 28.36% (26.79%) of groundwater samples possessed poor quality on the east (west) coasts. Considering the uncertainties of the variables, the mean hazard quotient ingestion values of fluoride faced by children (adults) were 10.5 (1.39) and 5.56 (6.9 x 10-1), respectively, on the east (west) coasts, demonstrating a high non-carcinogenic risk to people, particularly, children, who cannot be neglected. Children had two times higher health risks than the adult inhabitants in both regions studied. Probabilistic models can reveal health risks more extensively than deterministic models. This study came up with strategies for improving sustainable groundwater quality and managing health risks in coastal regions.