Microbial Arsenic Transformation in Near Subsurface Environments

In the first part of this study, environmental bacterial arsenic transformation was investigated in anthropogenically arsenic contaminated subsurface sediments from the former Vineland Chemical Company in Vineland, NJ. Subsurface sediments from the vadose (371 mg/kg arsenic) and aquifer (81 mg/kg arsenic) zones and an off-site surface sediment (0.7 mg/kg arsenic; control) were used as inocula for enrichment cultures with selective media to assess for microbial arsenic metabolic activity. Arsenite (As(III)), monomethyl arsenic acid (MMA) and dimethyl arsenic acid (DMA) were provided as electron donors, while arsenate (As(V)) was provided as an electron acceptor. An anion exchange chromatography method with conductivity and UV/Vis detection was developed and utilized to investigate arsenic transformations under each selective condition. While demethylation and arsenite oxidation were not observed, there was strong As(V) reduction to As(III) activity in the enrichments amended with lactate and As(V). Polymerase chain reaction (PCR) was used to amplify arrA and arsC genes, followed by cloning and sequencing. Both vadose and aquifer enrichments gave positive results for arrA (respiratory arsenate reductase) and arsC (arsenic resistance), while only arsC amplified from the off-site. Both 16S rRNA genes and the ribosomal intergenic spacer (RIS) genes were used to assess community diversity. The results indicate a diverse community with As(V) respiring bacteria. In the second part of this study, the utility of ion chromatography (IC) in speciating inorganic (As(V), As(III)) and organic (MMA, DMA) was assessed. The As(V) and roxarsone respiring Alkaliphilus oremlandii OhILAs was cultured and the spent medium analyzed. Under the conditions used, OhILAs failed to produce any As(III) and As(V) when grown on roxarsone and lactate; however, As(V) to As(III) reduction was observed when grown in the presence of lactate and As(V). In the third part of this study, microcosms were used to assess bacterial arsenic transformation in cores from a coal ash impoundment. A medium was formulated based on the water chemistry of the system. As(V) respiration was detected at all four depths tested (0-2m; 2-4m, 4-6m, and 8-10m), with the surface sediments showing the greatest rates