Microbial Controls on the Mobilization and Speciation of Arsenic from Newark Basin Shale

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ABSTRACT OF RESEARCHMICROBIAL CONTROLS ON THE MOBILIZATION AND SPECIATION OF ARSENIC FROM NEWARK BASIN SHALEThe North American Rift Basin spans part of New Jersey (Newark Basin) and has arsenic containing red, gray and black shale. In a recent study conducted by the NJ Geological Survey, it was determined that 15-30% of the wells from this area had arsenic levels exceeding 10 g/L and up to 215g/L. Human exposure to arsenic within the environment is typically through drinking water and the consumption of water with arsenic concentrations greater than 10 mg/L greatly increases an individual's risk of developing lung and bladder cancer (NRC, 2001). As a result, the U.S. Environmental Protection Agency (EPA) has proposed a reduction in the maximum contaminant level (MCL) for arsenic in drinking water from 50 mg/L to 10 mg/L (USEPA, 2001). Arsenic mobilization in the Newark Basin could be due to the oxidation of pyrite in black and gray shale, and/or release of arsenic from hematite or other iron oxides in red shale (Serfes et al, 2004). Although chemical and physical processes play a role in the weathering of these minerals, there is also evidence that microorganisms may be essential to the process. The hypothesis of this proposal is that microorganisms play a defining role in the mobilization and speciation of arsenic in the Newark Basin and its groundwater. Three objectives will be undertaken: 1) To compare the community structure of attached and suspended microorganisms associated with gray/black shale and with red shale found in the Newark Basin. It is hypothesized that pyrite-impacted aquifers will have a different microbial community structure than those impacted by hematite. These differences will help us identify the specific organisms critical to arsenic mobilization. 2) To examine the degree to which microbes enhance arsenic mobilization at ambient (circumneutral) pH from native pyrite and hematite. It is proposed that iron oxidizers facilitate the release of arsenic from pyrite and that iron reducers may mobilize arsenic from hematite under anoxic conditions. In addition, it is proposed that arsenic oxidizers and reducers are active in controlling the relative abundance of As(V) and As(III) and thereby affecting arsenic transport and distribution. The organisms involved in arsenic mobilization and speciation will be identified and characterized. 3) To identify iron-utilizing microbes associated with the pyrite and/or hematite shale and arsenic-utilizing microbes involved in the speciation of arsenic from the Newark Basin using biomolecular markers based on 16S rDNA sequence. Fluorescent in-situ hybridization (FISH) and scanning electron microscopy (SEM) will be used to observe the spatial distribution of both iron and arsenic active microbes on surfaces of black and red shale. It is proposed that the organisms will associate with specific minerals in the shale, for example, iron oxidizers will attach to pyrite and arsenite oxidizers will be associated with As(V)-enriched iron oxides. Understanding the role that the microbial community plays in mobilizing As from the geologic media will constitute a new contribution to our basic knowledge of biogeological weathering and trace element cycling in the earth's environment. Understanding the processes that lead to the mobilization of arsenic from naturally-enriched minerals is essential to predicting and protecting the quality of drinking water supplies. Although this project is directed at the arsenic issue in the Newark Basin in New Jersey, the Eastern Rift Basin of North America is a major formation in the mid-Atlantic and northeast region of the US and other similar sedimentary basins around the world are sources of drinking water.