Abstract: An incubation test was conducted to study the dynamics of exogenously supplied dimethylarsenic acid (DMA), monomethylarsonic acid (MMA), and As(V) in soil under flooding. With the increasing time of incubation, the exogenously supplied DMA and MMA were mainly transformed into As(V), and the As(V) concentration increased, being significantly higher after incubated for 150 days, compared with that after incubated for 1 day. The exogenously supplied DMA was demethylated into As(V) within 30 days, accompanied by a little As(III), while the transformation rate of exogenously supplied MMA was rather slow within 60 days, accompanied by a little As(Ⅲ) and DMA. The exogenously supplied As(V) decreased with increasing time of incubation, and its form had less change except that a little As(Ⅲ) occurred.

Key words: soil, flooding, arsenic, form transformation