Multivariate and Spatial Analysis of Arsenic Mobilization Pathways in Groundwater: Insights from Darrang District, Assam, India

This study investigates the spatial distribution and potential mobilization pathway of arsenic (As) in the groundwater of Darrang district, Assam, India. A total of 107 groundwater samples were collected from hand tube wells across 18 locations and analyzed for 15 physicochemical parameters; these included pH, Eh, electrical conductivity, total dissolved solids, major ions, and heavy metals (As and Fe). Distribution maps of certain key parameters were prepared using a Garmin CHX 60 device. Prevailing research gaps were identified, and accordingly, a systematic investigation was made to understand the probable pathway of As dissolution. Most samples were mildly acidic to near-neutral under anoxic conditions, with 25 samples containing As in the range of 10–60 µg/L, exceeding the WHO/BIS arsenic guideline value (10 µg/L). Multivariate statistical techniques, cluster analysis (CA), principal component analysis (PCA), and factor analysis (FA) were conducted to determine correlations among all parameters to identify arsenic controlling geochemical factors. CA categorized all the parameters into three clusters and predicted a strong association between arsenic and iron, suggesting a similar geogenic origin. PCA/FA extracted four principal factors explaining 71.23% of the variance, with Factor 1 (28.23% contribution) indicating the comobilization of As and Fe under anoxic conditions. All these observations supported reductive dissolution of iron oxides as the most significant factor governing arsenic mobilization in the studied area. NO3− might play a significant role in transitional redox reactions and hence influence arsenic speciation and mobility. Thus, novel insights into arsenic mobilization in Darrang district can be visualized, where reductive dissolution of iron oxides plays a dominant role. This offers a paradigm for focused groundwater quality monitoring in sedimentary aquifers that are arsenic-prone.