Hydrochemical characterization, mechanism of mobilization, and natural background level evaluation of arsenic in the aquifers of upper Gangetic plain, India

Abstract

Although arsenic (As) contamination has been extensively investigated in the aquifers of the lower and middle Gangetic plains, less attention has been given to the distribution and fate of As in the groundwater of the upper Gangetic plain, India. In the current study, groundwater samples (n = 40) were collected from Moradabad district in the upper Gangetic plain and analyzed for several physicochemical parameters to characterize the groundwater chemistry and evaluate various geogenic and anthropogenic factors controlling the occurrence, mobilization, and fate of As in the plain. Arsenic concentrations in groundwater ranged from 0.17 μg/L to 139 μg/L, with the majority of high-As groundwater associated with high Fe, Mn, and HCO3− and low NO3−, SO42−, and negative Eh values, implying that As was released via reductive dissolution of Fe and Mn oxyhydroxides in reducing conditions under the influence of organic matter degradation. Interrelationships between various geochemical variables and the natural background level (NBL) quantification of As suggested the influence of anthropogenic processes on the mobility of As in groundwater. Piper and Gibbs diagrams and various bivariate plots revealed that the majority of groundwater was of the Ca2+ − Mg2+ − HCO3− type and that the major ions in groundwater were derived from carbonate and silicate weathering, cation exchange and reverse ion exchange processes, and anthropogenic activities. Moreover, the results of principal component analysis (PCA), and hierarchical cluster analysis (HCA) also suggested geogenic and anthropogenic sources for the ion concentration in groundwater. The health risk assessment showed a higher non-carcinogenic risk for children and a higher carcinogenic risk for adults, respectively, due to the daily intake of As contaminated groundwater. Overall, this study represents the first systematic investigation of the distribution, geochemical behavior, and release process of As in groundwater in the study area and provides a strong base for future research in the alluvial aquifers of the upper Gangetic plain.