S177: Microbial arsenic transformations in subsurface environments and their effect on water quality as observed in New Jersey

Microbial oxidation and reduction of arsenic are acknowledged mechanisms by which arsenic can be transformed in the environment.  This has profound implications in specific locales where groundwater is a drinking water source and is associated with arsenic-rich minerals such as found  in Bangladesh, Cambodia, China, India.  Different areas of the U.S., including regions in New Jersey also have high groundwater arsenic levels that exceed U.S. EPA and WHO drinking water standards.  The Passaic and Lockatong Formations contains up to 4% arsenic by weight, and up to 136 mg/kg arsenic is found in the Inner Coastal Plain.  Using both culture dependent and independent methods, respiratory arsenate reducers have been demonstrated in the groundwater from both locations.  Detection of the arsenic respiratory reductase gene arrA correlates with groundwater chemistry.   Strains identified include Desulfosporosinus sp., Alkaliphilis oremlandii and Geobacter.  The latter is consistent with the groundwater chemistry that indicates iron reduction in the Inner Coastal Plain samples and suggests that this could be an additional mechanism for arsenic release into groundwater.  Rapid arsenate reduction only takes place in the presence of active microbes.  This is demonstrated by field data showing that the highest levels of arsenic in groundwater samples are found where microbial activity is driven by extraneous organic input.  Thus arsenic in the subsurface environment can undergo multiple microbial transformations.