Collaborative Research: Biogeochemical Controls on the Dynamics of Organoarsenic Transformation

有机砷化合物在自然界广泛存在，存在于淡水和海洋以及陆地环境中。包括细菌、真菌、藻类、无脊椎动物、脊椎动物甚至人类在内的生物体都可以对砷进行生物转化，将无机砷转化为有机砷，在某些情况下，反之亦然，在环境中产生一系列结构简单到复杂的有机砷化合物。除了天然来源外，有机砷还被合成用于农业、医药和军事用途。例如，随着家禽业的发展，有机砷在家禽业中的使用急剧增加。洛克沙胂（3-硝基4-羟基苯胂酸）在家禽饲料中的添加量高达每吨45.5g，目的是提高增重、饲料效率和色素沉着。当在屠宰前5天将罗沙胂从饲料中去除时，组织中的As浓度低于美国食品和药物管理局0.5 mg/kg的限制。大部分（95%）砷从动物体内排出，导致家禽产仔中砷含量升高（15至77毫克/公斤）。由于禽畜粪便营养丰富，90%以上的禽畜粪便被用作土地肥料。通过申请土地处置家禽废物，估计会向环境释放10^6公斤砷。最近的研究表明，家禽粪便中的砷具有高度水溶性，因此具有潜在的流动性。洛克沙胂和其他有机砷的生物转化已经在实验室中有了记录，但到目前为止，对洛克沙胂和其他有机砷在流域中的最终命运知之甚少。我们提出的研究目标是研究生物地球化学控制有机砷转化在德尔马瓦半岛流域，一个密集的家禽生产地区。我们的主要假设是，有机砷的转化是在一系列生物地球化学条件下由不同的微生物种群进行的。我们将在施用凋落物前后对土壤、地面和地表水进行密集的实地监测，以确定每种水类型中砷的浓度和形式。我们将使用生物化学和分子技术来识别和表征水样中的微生物群落，并研究生物地球化学条件对微生物群落结构的影响。为了提高公众对水质的了解，我们将与学生、教师和社区团体合作，对两个河流系统进行水质采样项目，一个在森林和农村地区（弗吉尼亚州西南部的新河），另一个在城市地区受农业和工业用地影响（宾夕法尼亚州匹兹堡的阿勒格尼、莫农加赫拉和俄亥俄河）。

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).