Abstract: An incubation test was conducted to study the transformation of exogenous dimethylarsenic acid (DMA), monomethylarsenic acid (MMA), and arsenate ［As(V)］ in soil under the condition of 35% of  water-holding capacity. After added into soil, the concentrations of test arsenic forms all showed a decreasing trend with time. The DMA and MMA were mainly demethylated, and after 120 days incubation at constant temperature and humidity, transformed into As(V). A small amount of MMA was detected in the treatment with added DMA on the 120th day of incubation, and a small amount of DMA was detected in the treatment with added MMA during the period of 7-60 days incubation. By the end of the incubation test, the concentrations of added DMA and MMA in soil decreased significantly (P<0.01), with the decrement being 99.5% and 94.3% and the concentration of transformed As(V) increased by 4.61 and 5.15 times, respectively. Comparing with DMA and MMA, the As(V) after added into soil had less form transformation.

Key words: aerobic condition, soil, arsenic form, transformation, Collichthy lucidus, the Yangtze Estuary, diet composition, feeding habit, seasonal variation.