T337 Groundwater and Surface-Water Arsenic: From Source to Sink II

Wednesday, 22 October 2014
1:00 PM - 5:00 PM
110

SORPTION OF ARSENIC WITHIN AQUIFER SEDIMENTS AND PROCESSES OF BIOACCUMULATION AND LOCALIZATION OF ARSENIC WITHIN RICE GROWN IN THESE SEDIMENTS FROM BANGLADESH AND INDIA

Paper number: T337-13
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

Arsenic contamination in water continues to adversely affect millions of people occupying the Bengal Delta. Multiple geogenic processes contribute to the release and mobilization of As and control the spatial variation of low and high-As localizations. The current study focuses on As sorption and release mechanisms from sediment fractions to groundwaters within aquifers. It also probes the extent of bioaccumulation, speciation, and localization of As within rice cultivated in these soils with high As irrigation waters. Results indicate contents of organic matter (OM) within sediments, and dominance of Fe and Mn together play a key role in sorption of As. Extractions from core sediments collected in contrasting low and high-As areas indicate residual and Fe-oxyhydroxide fractions dominating As adsorption. OM-adsorbed As, Fe and Mn were quantified by NaOCl extractions on the sediments. Leftover dissolved organic carbon (DOC) from the above extracts demonstrated sediment-bound organics varying from shallow to deep parts even within the high-As areas. Positive correlations were observed between total As (AsT) in groundwater and dissolved Fe-Mn ratios; AsT and DOC in groundwater; and bulk As and TOC of sediments.

Rice samples collected from low and high-As areas (n=14) and domestically purchased (n=10) were de-husked, dried, ground, and microwave digested. IC-ICP-DRC-MS analyses show a diverse range of As uptake by rice grains cultivated in both dry and wet seasons. Our results indicate rice grains with long and slender (LS) physical dimensions bioconcentrated on average more As than short and stocky (SS) grains. Rice samples that exceeded 125μg/kg AsT (n=10) were selected for water digestion and HPLC-ICP-MS analysis for speciation. Organic As (MMA, DMA) and As (V) were undetectable at <1μg/kg. As (III) was the dominant species, detected in 40% of samples in concentrations between 6.8 μg/kg and 52.3 μg/kg. µXANES and µXRF analyses were conducted to further investigate As speciation and map As localization to reveal important uptake mechanisms within rice grains.