The arsenic speciation transformation in artificially arsenic-contaminated fluvo-aquic soil (Beijing, China)

Arsenic (As) speciation transformation often accompanies adsorption-desorption when exogenous arsenide is poured into soil. Disregarding the speciation transformation when evaluating adsorption-desorption of As can greatly influence the experimental results. In this study, batch experiments were conducted, and the results indicated that exogenous monomethylarsonic acid (MMA) or dimethylarsinic acid (DMA) added to fluvo-aquic soil collected from agricultural area in Beijing of China, was completely converted into As(V) after cultivated for 60 or 90 days. However, when exogenous As(V) was added to the soil, no speciation transformation of As(V) was observed. Furthermore, although the total As concentration, which was 6.55 or 11.55 mg/kg in aqueous extracts of the soil to which MMA or DMA had been added, respectively, remained stable after cultivated for 30 or 60 days, the As speciation transformation of MMA or DMA into As(V) in soil still occurred. Differences in As speciation can result in different fates and behaviors of As in soil, and As speciation transformation should be taken into account when evaluating the adsorption-desorption of As.