ObjectiveDiphenylarsinic acid (DPAA) is one of the main degradation products of arsenic-containing chemical weapons in the environment. The objective of this study was to investigate the effects of iron and sulfate reduction on the mobilization and thionation of DPAA in soil.MethodAcrisol from a peanut field and woodland was selected for soil incubation experiment, and both were spiked with DPAA and different concentrations of sodium lactate (C source) and sodium sulfate (S source) under flooded condition. Four treatments were established in the current study, treatment one (S-C-) was created without the addition of S or C sources, treatment two (S+C-) only received 426 μg·g^-1 S, treatment three (S+C+) received 426 μg·g^-1 S and 1 300 μg·g^-1 C, and treatment four (S+C++) received 426 μg·g^-1 S and 2 170 μg·g^-1 C. Samples of the soil and supernatant were collected for the analysis of DPAA, Fe²⁺, HCl-extractable Fe²⁺, SO₄^2-, sulfide, pH, Eh and bacterial community structure.ResultResults for the peanut field indicated that the mobilization of DPAA was significantly enhanced in the S+C+ and S+C++ treatments due to the addition of carbon, as compared to S-C- and S+C- treatments without carbon. This difference was likely caused by the elevated Fe reduction (> 45%) due to lactate addition, which then promoted DPAA mobilization. In comparison to other treatments, sulfate reduction was most significant in the S+C+ treatment of the peanut field (with the concentration of dissolved sulfide reaching 11.28 mg·L^-1 after 13 weeks of incubation), where the removal rate (59.6%) of DPAA was the highest and DPAA was primarily thionated. However, the increased Fe reduction and decreased sulfate reduction in the S+C++ treatment were not conducive to the thionation of DPAA. Unlike peanut land, the mobilization and thionation of DPAA were not observed in woodland regardless of the addition of sodium lactate and sulfate. This difference can be explained by the lower degree of Fe reduction (< 25%) and the absence of sulfate reduction (without the detection of dissolved sulfide) in woodland. The relative abundances of Clostridium, Bacillus and Desulfosporosinus were significantly higher in the peanut field soil than those in woodland. This probably promoted the occurrence of iron and sulfate reduction, respectively, and both processes ultimately had a stronger influence on the mobilization and thionation of DPAA.ConclusionGenerally, instead of the stimulating effect of Fe reduction on DPAA mobilization, the degree of sulfate reduction and the concentration of sulfide in the liquid phase is a more significant factor in determining DPAA thionaiton in Acrisol under flooded condition. The findings will serve as a theoretical foundation for the in-depth understanding of the environmental behavior of DPAA as well as the development of biostimulation remediation solutions for DPAA-contaminated Acrisol.