ORGANIC CARBON AND ARSENIC FRACTIONATION AND SORPTION MECHANISMS WITHIN GROUNDWATER-SEDIMENT INTERFACE WITHIN WEST BENGAL AQUIFERS

Naturally occurring, inorganic arsenic within the Bengal Delta aquifer system adversely affects millions of people within the region by exposure to high arsenic-concentrated groundwater. Organic carbon and its role in sorption mechanisms of oxyanions and later release into the groundwater is probed in this work. As concentrations range below India’s health standard of 50µg/L and exceed 4000µg/L occurring dominantly as As^III (>83%) species within the study area of Murshidabad, West Bengal, India. Patients within the study area are susceptible to arsenicosis and acquired severe skin lesions as well as terminal illnesses such as lung cancer. Major exposure pathways include consumption of contaminated drinking water and rice paddies capable of accumulating 0.08-0.2mg/L As. We probe into the extent of As, Mn and Fe adsorption onto extracted organic matter from the sediments. Loss on Ignition and moisture content of the sediments are also correlated with the organic matter content. We show a direct correlation of extent of As release from sediments to Fe/Mn ratios along with a positive correlation between [As] and OC content of the sediments. TOC measured in the supernatant after extracting 1gm of sediment with NaOCl indicates a similar trend as dissolved organic carbon (DOC) in the associated groundwater samples. DOC and dissolved organic nitrogen in the tubewell waters (collected from close to the sediment core collection points) show a cluster of high values within an intermediate depth (15-30m) within these aquifers. These can indicate both organic carbon and nitrogen having a source from the local sewage and recent organic matter even to that depth of ~30m. Organic matter characterization somewhat indicates both terrestrially derived organic component and bacterial mediated OM in the shallow aquifers. Deeper aquifers (>45m) indicate slightly higher bacterial component in the groundwaters.