ENVR 117 |
| Arsenic mobilization from solid phase Fe (III) hydroxides is an issue of concern, as water-borne arsenic can migrate into pristine environments, endangering aquatic and human life. The mobility of arsenic is known to increase under bio-reductive conditions due to multiple factors of pH and redox. Microbial activity is also known to induce greater arsenic mobilization via Fe (II) reduction, which consequently results in arsenic dissociation from the solid phase. In addition, direct microbial arsenic reduction can also occur. Since iron hydroxides have a lower binding capacity for As (III) as compared to As (V), soluble arsenic levels increase. In this study, we seek to elucidate the biogeochemical mechanisms that control arsenic mobilization and biotransformation in granular ferric hydroxide (GFH)-coated sand under abiotic and biotic induced conditions. GFH-coated sand (~1,000 mg/kg As) was subjected to abiotic desorption studies at different pH and redox. It was observed that arsenic and iron leaching showed strong pH dependence, with maximum arsenic release at extreme pH conditions. In general, abiotic reducing conditions did not play a significant role in arsenic or iron solubilization. A native wetland sulfate reducing bacteria, Sulfurospirillum barnesii strain SES-3, and a microbial consortia (consisting of aerobes, anaerobes, methanogens and sulfate reducers) from a municipal landfill leachate were used to induce bacterial activity. Under reducing conditions invoked either by S. barnesii or methanogens, our observation indicates that arsenic retention and release from GFH-coated sand is controlled by complex pathways of Fe (III) transformation. It was also observed that arsenic release was higher in the abiotic experiments than in the biotic ones. Solid phase analysis with X-ray absorption fine structure (EXAFS) is presented. |
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General Papers
6:00 PM-8:00 PM, Wednesday, August 22, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Environmental Chemistry |