Arsenic-sulfur speciation - a potential key to understanding arsenic accumulation and mobilisation in sulfidic aquifers of Bangladesh
Final Report Abstract
- Depth-dependent monitoring showed maximum arsenic concentrations up to 300 ug/L at 85 to 115 ft depth where clay lenses, partially rich in peat fragments, interlayer the reduced, gray fine sand aquifer - Sorption capacity for arsenate was found to be lower in the reduced upper aquifer compared to the oxidized lower aquifer (280 ft depth with arsenic concentrations of 70 ug/L), where spiked arsenite is partially oxidized; in competition with phosphate arsenate is mobilized quicker from the reduced upper aquifer than from the oxidized lower aquifer - Monitoring seasonal changes in hydrogeochemistry at different depths with a high temporal resolution showed both significant short-term variations as well as an overall gradual increase in total arsenic concentrations between May and November, seen even more pronounced in a significant increase of arsenite concentrations and mirrored by a decrease in phosphate concentrations, especially in the critical depths of 85 to 115 ft - Monothioarsenate was formed besides arsenite and arsenate contributing up to 20% to total arsenic; no other thioarsenates were detected at sulfide concentrations < 0.14 mg/L - Classical hydride generation-based arsenic speciation methods are unable to separate monothioarsenate; it is co-determined with arsenate which is especially critical as it was found that monothioarsenate is easier mobilized from both the reduced and the oxidized aquifer than arsenate - Phosphorous speciation revealed a so-far unidentified species besides phosphate that became the dominant P-species in some of the wells (with up to 70% of total P) - Observation of quick changes in hydrogeochemistry, especially total arsenic concentrations and arsenic speciation, over time and pronounced increase between May and November in depths of 85 to 115 ft, where the highest arsenic concentrations occur - Detection of an additional, partially dominant phosphorous species besides phosphate
Publications
- (2008) Column experiments simulating various scenarios for arsenic mobilization in Bangladesh.- Freiberg Online Geoscience FOG Vol. 18, ISSN 1434-7512
Lißner H
