GROUNDWATER-SEDIMENT SORPTION MECHANISMS AND BIOACCUMULATION OF ARSENIC IN RICE WITHIN WEST BENGAL, INDIA

Geogenic arsenic (As) contamination in the Bengal Delta aquifer system continues to adversely affect public health since the late 1970s discovery. The notion that multiple phenomena contribute to As release and varying spatial concentrations is a widely accepted theory. This study focuses on As sorption and release mechanisms of sediment fractions within groundwater as well as As bioaccumulation within rice grown in West Bengal, India (Murshidabad district). The result indicates organic matter (OM) in sediments to play an important role As sorption, as well as dominance of iron (Fe) and manganese (Mn) within these sediments. Extensive extraction of sediments from high and low As areas in Murshidabad indicate residual and Fe-oxyhydroxide fractions to dominate As adsorptions for the high and low As cores. OM-adsorbed As, Fe and Mn were quantified by NaOCl extractions on the sediments. Leftover dissolved organic carbon (DOC) from the extracts showed sediment bound organics varying from shallow to deep aquifers within the high As areas. Positive correlations were observed between As in groundwater and dissolved Fe/Mn ratios, As and DOC in groundwater, and As and TOC of sediments. ICP-OES analyses of extracted, sediment-bound organic carbon indicates As concentrations up to 188 µg/L. Rice samples (n=14) collected from high and low As areas were de-husked, dried, ground and digested via microwave (MARSXpress, CEM, NC). IC-ICP-DRC-MS analyses show a diverse range of As uptake by rice grains (long+slender and short+stalky) cultivated in both dry and wet seasons. Analyses on locally purchased rice varieties (n=10) were conducted as well. A 2012 Consumer Reports study of rice varieties (n=32) obtained within the USA revealed total inorganic As [As(III+V)] levels as high as 214 ug/L. Availability of water with safe As levels is less common in the more abundant shallow (<40m) aquifers characteristic of OM-rich Holocene sediment compared to deeper aquifers with higher oxidized older Pleistocene sediment and little-no OM (Datta et al., 2011). Inhabitants exposed to As-contaminated water are susceptible to arsenicosis, severe skin lesions and terminal illnesses such as cancers of internal organs and respiratory diseases. Exposure to As through water and rice continue to threaten the health of tens of millions within the region.