A comparative study of inorganic and methylated arsenic on absorption and transportation in rice plants

Due to the use of herbicides or pesticides and the As methylation in soil by microbes, methylated As were also detected in rice grains, on top of the inorganic As. Rice culture in solution was conducted to investigate the uptake, transportation, transformation and efflux of the inorganic As (As(III) and As(V)) and methylated As (MMA(V) and DMA(V)) species. The results showed that uptake efficiency of As into rice roots was in the order of As(III) > MMA(V) > As(V) > DMA(V), but the transportation index (T _i) from root to shoot followed the order of DMA(V) > As(III) > As(V) > MMA(V). No methylated As was observed in rice plants by the inorganic As treatments, and the demethylation of organic As in rice plants by the methylated As treatments was also in small proportion. However, a small portion of MMA(V) in rice plants was reduced to MMA(III) in the MMA(V) treatment. The DMA(V) transported much faster upwards and downwards in rice plants than the other As species in xylem sap and phloem sap, compared to its concentrations in shoots and roots. The efflux of methylated As species in roots were also much faster than the inorganic As species. The results showed that the accumulation of different As species was dependent on the absorption and transportation of As in rice plants, and also the efflux of As out of the roots.