LINKS BETWEEN ARSENIC SOLUBILITY, MICROBIAL METABOLISM, AND VOLATILIZATION IN PADDY SOILS
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Arsenic (As) volatilization has been studied intensively since it was discovered in the early 19th century and is gradually recognized as a potential low-cost and low-impact remediation method to remove As contamination in soils. Up to date, As volatilization has been detected and measured in various environments, and microorganisms such as fungi, bacteria, archaea, and eukaryotic algae, have been linked to arsine generation. However, the pathway of As volatilization is not clear yet, and what microbial groups are involved and their functions are also needed to be studied. Here, the soil incubation experiments with a chemo-trap system were conducted to quantify and qualify arsine production in different conditions for nine weeks in order to determine how As volatilization rate would change under different microbial metabolisms. Two testable hypotheses were brought up that: (1) sulfate reducers are the main drivers for As volatilization and methanogens can inhibit As volatilization by reducing the abundance of methylated As, and (2) methylation is the rate-limiting step in the process of As volatilization. Six experimental groups were set up by changing amendments to the synthetic porewater, among which Molybdate (Mo) was chosen as the sulfate reducing bacteria (SRB) inhibitor while 2_bromoethanesulfonate (BES) was used to inhibit methanogens. The group with dimethylarsinic acid (DMA) to replace arsenite (As(_)) was measured the highest arsine flux, indicating that As volatilization is limited by the availability of methylated As species. Compare to the control group where 1.16 ± 0.20% of aqueous As was volatilized, the fraction reached 5.33 ± 0.59% in BES condition. Meanwhile, Mo group produced a similar As flux and amount of arsine to the control in the first seven weeks. These observations can lead to the tentative conclusions that As methanogens may correlate with As demethylation, limiting the extent of As volatilization, and SRB did not have a clear link with As volatilization.