Hydrogeochemical analysis of aquifer in northwestern part of Bangladesh: implication for targeting low arsenic zone
摘要
Arsenic (As) contamination in groundwater poses a significant global threat to drinking water safety and public health. This study investigates the distribution and mobilization of As in core sediments and groundwater in the northwestern part of Bangladesh. A total of 21 borehole sediment samples and 10 groundwater samples were collected from two boreholes (BH1 and BH2), drilled to depths of 37 m and 35 m, respectively. Sediment and groundwater samples were analyzed using wavelength dispersive X-ray fluorescence and atomic absorption spectroscopy, respectively. Sediment color classified as black/grey, red/orange-brown, and white/off-white served as an indicator of geochemical conditions. The highest As concentrations were observed in black to grey sediments: 28.02 mg kg−1 at 12 m (BH1) and 163.56 mg kg−1 at 20 m (BH2). Groundwater As concentrations ranged from 0 to 1300 µg L−1, with an average 26 times higher than the Department of Environment (DoE) limit (50 µg L−1). Arsenic in sediments showed moderate correlations with Fe (R2 = 0.2064) and Mn (R2 = 0.3725), while groundwater As exhibited positive correlations with Fe (R2 = 0.2395) and Mn (R2 = 0.3957), indicating mobilization via reductive dissolution of FeOOH and MnOOH, likely facilitated by microbial activity. Principal component analysis and hierarchical cluster analysis revealed similar geochemical behavior among metals. Significantly lower As concentrations were found in oxidized reddish and yellowish sediments. The findings underscore the significance of sediment color as an indicator of As mobilization and offer practical guidance for locating low-As aquifers for safe well installation.