The effect of microbial processes on the mobilization of arsenic (As) from the Cheyenne River at Cherry Creek (CC) was investigated using aqueous speciation chemistry, spectroscopy measurements and NextGen Illumina sequencing. Elevated concentrations of As measured in mining impacted riverbank sediments from CC were in the range of 96-259 mg kg-1. Illumina analyses of the sediments detected 0.3% in mixed cultures to be dissimilatory arsenic-reducing bacteria (DARB) and arsenic oxidizing bacteria (AOB) of the total microbial communities. Microbial batch experiments were conducted under anaerobic and aerobic cycling conditions with and without the addition of electron donors (glucose and urea) to evaluate the effects of redox processes on the mobilization of As. The highest release of total arsenic was 4,478 ug L-1 under aerobic conditions with glucose as an electron (e-) donor. A maximum release of 191 ug L-1 As(III) was also measured in treatments with glucose as an e- donor under anaerobic conditions. The release coincided with a 54% decrease in As(III) detected at the surface of the sediment using X-ray photoelectron spectroscopy (XPS). All other treatments show total As release below 223 ug L-1, indicating that glucose as an e- donor aids in mobilizing As from sediments. Active sediments with the urea treatment released a maximum of 7.46 ug L-1 as dimethylarsinic acid (DMA), which is a methylated species of As that was not detected in any of the other experiments. Inorganic species of As (III and IV) are more toxic than methylated (DMA and MMA) but the detection of methylated As in these experiments may play a role in the transformations of As between species. The results of these investigations on As mobility have important implications for environmental exposure and risk assessments.

Investigation of the effect of microbial processes on arsenic stability in sediments from Cheyenne River, South Dakota, USA

2019 Spring National Meeting

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