Effect of rainwater oxidants on As volatilization in the soil-rice system

Rainwater contains multiple oxidants, such as hydrogen peroxide (H₂O₂) and perchlorate (ClO₄^-). The aim of the study was to investigate the rainwater of trace H₂O₂ and ClO₄^- affected on the arsenic (As) methylation and volatilization in the rice paddy of As contamination (arsenite (As(III)) and roxarsone (Rox)). Heavy rainfall monitoring and simulation experiments were applied in this study. The result showed that the H₂O₂ and ClO₄^- of heavy rainfall in 2017 was 5.3-51.6 μmol/L and ND - 6.1 μg/L respectively. Because of the differences in chemical properties, H₂O₂ and ClO₄^- affected As methylation and volatilization of paddy soil in different ways. H₂O₂ performed a temporary effect on As volatilization, which was mainly in the 1st-hour and restored to the controls condition finally. However, ClO₄^- showed a persistent inhibition on As volatilization which decreased 32 %-69 % in the whole test. In general, the trend of volatilization was following the order: CK ≈ H₂O₂ > ClO₄^-. The oxidants (H₂O₂ and ClO₄^-) also could decrease As(III) in 37 %-44 % and increased As(V) in 24 %-272 %. In addition, planting rice in As contamination soil could enhance As volatilization by 36 %-334 %. These suggested that planting wetland plants on As-contaminated soil probably become a potential way to increase As volatilization.