Mukul Sharma Current Research Interests in Isotope Geochemistry

• Near surface geochemistry of osmium
• Generation of oceanic lithosphere: the role of mantle heterogeneities
• Magma Differentiation and Source Characteristics of Continental Flood Basalts
• Early evolution of the earth: the terrestrial record of 146Sm
• Study on continental weathering using osmium isotopes
• Variations in Solar Magnetic Activity and the Sun-Climate Connection
• Tracing the source of groundwater arsenic in Bangladesh Delta
• Geochemical and isotopic studies of cosmic dust
• Near surface geochemistry of osmium
• Osmium and Iridium Transport through Estuarine Environments

Tracing the source of groundwater arsenic in Bangladesh Delta

The occurrence of high arsenic in the alluvial aquifers in the Bengal Delta Plain in Bangladesh as well as in the east-Indian state of West Bengal has emerged as an issue of great concern during the past decade because of its impact on the health of a large cross section of the population, reliant on groundwater for potable supplies. The aquifers from which the arsenic-rich groundwater is derived are the Holocene sediments comprising sequences of sand, silt and clay deposited and subsequently reworked by the Ganges, the Brahmaputra, and the Meghna. Two principal contradictory hypotheses have been proposed concerning the origin of arsenic in groundwater in the Bengal Delta Plain: (1) arsenic is derived from the oxidation of As-rich pyrite in the shallow aquifer as a result of lowering of water table due to over-abstraction of groundwater for irrigation, and (2) arsenic is derived as a result of reductive de-sorption from surface reactive mineral phases such as iron oxy-hydroxides, present ubiquitously as coatings on the aquifer sediments in response to changes in the redox conditions, caused by return flow from rice fields and/or wetland cultivation as well as due to over-abstraction of groundwater. In collaboration with Dr. P. Bhattacharya (Royal Institute of Technology, Sweden) we are investigating the Os isotopes in selected groundwater samples with variable As-enrichment. The objectives of this study are two fold: (1) tracing the sources of Os and possibly As given that the Os derived from arsenopyrite will have a different isotopic composition compared to that derived from iron-oxyhydroxide, (2) deducing the present-day Os flux into the oceans from modern-deltas.