Collaborative Research: Biogeochemical Controls on the Dynamics of Organoarsenic Transformation

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Organoarsenic compounds are widespread in nature, occurring in freshwater and marine as well as terrestrial environments. Organisms, including bacteria, fungi, algae, invertebrates, vertebrates and even humans, can biotransform arsenic (As), converting inorganic to organic As, and in some cases vice-versa, producing a range of structurally simple to complex organoarsenic compounds in the environment. In addition to natural sources, organoarsenicals have been synthesized for agricultural, medicinal, and military uses. The use of organoarsenicals in the poultry industry, for example, has increased dramatically as the industry has grown. Roxarsone (3-nitro 4-hydroxybenzene arsonic acid) is added to poultry feed up to 45.5g per ton for the purpose of improving weight gain, feed efficiency, and pigmentation. When roxarsone is removed from feed for a 5-d period before slaughter, As concentrations in tissue are below the USFDA limit of 0.5 mg/kg. The majority (95%) of the As is excreted from the animal, resulting in elevated As (15 to 77 mg/kg) in poultry litter. Because poultry litter is rich in nutrients, more than 90% of it is land-applied as fertilizer. The disposal of poultry waste through land application results in release of an estimated 10^6kg of As to the environment. Recent work has demonstrated that As in poultry litter is highly water soluble and thus potentially mobile. Biotransformation of roxarsone and other organoarsenicals has been documented in the laboratory, but to date, there is little known about the ultimate fate of roxarsone, and other organoarsenicals, in watersheds. The goal of our proposed research is to examine the biogeochemical controls on organoarsenic transformation in a watershed within the Delmarva Peninsula, a region of intense poultry production. Our main hypothesis is that organoarsenic transformation is carried out by diverse microbial populations under a range of biogeochemical conditions. We will conduct intensive field monitoring of soil, ground, and surface waters before and after litter application to determine the concentration and form of As in each of these water types. We will use biochemical and molecular techniques to identify and characterize microbial communities in the water samples and to examine the impact of biogeochemical conditions on microbial community structure. To enhance public understanding of water quality, we will work with students, teacher, and community groups on water quality sampling projects on two river systems, one in a mostly forested and rural area (New River, Southwestern VA) and another impacted by agricultural and industrial land uses in an urban area (Allegheny, Monongahela, and Ohio Rivers, Pittsburgh, PA).