UNDERSTANDING THE ARSENIC MOBILITY IN THE SUTLEJ-INDUS RIVER BASIN USING LABORATORY-BASED INCUBATION EXPERIMENTS OF THE BEAS RIVER SEDIMENTS

Arsenic (As) is a naturally occurring carcinogen that has affected lives of millions of people who rely on groundwater for their water consumption needs. The As-contaminated shallow aquifers common along the alluvial deposits of the major rivers like Ganga, Brahmaputra, and Indus. The primary mechanism of As mobility is microbially mediated reductive dissolution of As-bearing sediments fueled by labile organic matter. The Himalayan rocks containing As-rich minerals are hypothesized to be the main source of As, but the mineralogical association of As with the transported sediments in the higher energy rivers like Beas is relatively understudied. In this study, we quantified the As in the sediments of the Beas River, a major tributary of the Indus River system. Sediment samples were collected from the six sites along the Beas River and a laboratory-based seven days incubation experiment was performed by creating oxic and anoxic conditions to Fe and As mobilization. After the seven days, the samples were centrifuged and analysed for cations, anions, trace elements, dissolved organic carbon and nitrogen. The results showed that the Beas River sediments contain on average 11.6±1.5 g/kg of Fe, 3.68±0.95 mg/kg of As and 1.37±0.5% of organic matter. All the six samples leached dissolved solids amounting to 44 μS/cm of specific conductance under both aerobic and anaerobic conditions. The sediments samples leached 0.23-0.62 mg/kg of As (4 - 24 % of AsT) and 0.39-9.34 mg/kg of Fe (0-0.08% of FeT) under aerobic conditions, compared to 0.03-0.39 mg/kg of As (1-13% of AsT) and 0.4-3.6 mg/kg of Fe (0-0.03% of FeT) under anaerobic conditions. The samples also contained around 5.83±4.22 mg/l of DOC and 0.56±0.33 mg/l of TDN. These results show that, across all sites, there was no significant difference in mobility of Fe and As under aerobic and anaerobic conditions. The observed mobility of Fe and As in this experiment therefore appears to be related to surficial processes rather than redox reactions. Naturally, the anaerobic conditions are created by oxidation of organic matter, unlike forced N₂ anaerobic conditions in this experiment. Findings of this study will improve our understanding about the transport of As-bearing sediments and their mobilization.