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BIOGEOCHEMICAL PROCESSES CONTROLLING ARSENIC SPECIATION AND BIOTRANSFORMATION IN GRANULAR FERRIC HYDROXIDE COATED SAND
Citation:
JEGADEESAN, G., P. PINTO, S. R. AL-ABED, AND CHRISTOPHER IMPELLITTERI. BIOGEOCHEMICAL PROCESSES CONTROLLING ARSENIC SPECIATION AND BIOTRANSFORMATION IN GRANULAR FERRIC HYDROXIDE COATED SAND. Presented at 234th American Chemical Society National Meeting, Boston, MA, August 19 - 23, 2007.
Impact/Purpose:
to present information
Description:
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. In general, metal oxide (hydroxides) exerts a dominating effect on the fate and transport of arsenic in surface and subsurface environments. Release of As via desorption during the onset of reducing conditions and the subsequent dissolution of As-bearing solids under extreme pH conditions are generally ascribed to be the dominant mechanisms of arsenic mobilization from solid phases. Microbial activity is also known to induce'greater arsenic mobilization via Fe (II) reduction, which consequently results in arsenic dissociation from the solid phase. Since iron hydroxides have a lower binding capacity for As (III) as compared to As (V), soluble arsenic levels increase. Microorganisms appear to commonly dominate the redox chemistry of arsenic (arsenite (As (III) and arsenate (As (V» via reduction processes Under anoxic conditions, arsenate serves as the terminal electron acceptor in the biological oxidation of organic matter. Even though, it is widely known that biotransformation of arsenic occurs primarily in the most bioaccessible (aqueous) phase, limited studies have shown the reduction of arsenic in the sorbed solid phases. Further, the biotransformation of arsenic into its organic forms (mono or di-methyl arsenate or arsenite) can also occur, which are known to be equally toxic as its inorganic counterparts. Since a variety of complex biogeochemical processes impact arsenic fate and transport, it is therefore important to understand the speciation of the arsenic in bacterial rich environments and provide a reliable assessment on their mobility due to the ensuing biological activity. In this study, we seek to elucidate the biogeochemical mechanisms that control arsenic mobilization and biotransformation in granular ferric hydroxide (GFH) coated sand unper abiotic and biotic induced conditions. GFH coated sand containing -1000 mg/kg As was subjected to arsenic desorption studies at different pH and redox conditions, In addition, 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. During the course of the experiments, arsenic speciation and mobility was monitored and the data is presented.