Effects of Arsenic Compound Amendment on Arsenic Speciation in Rice Grain

Abstract

Rice consumption is a major source of arsenic for Asian populations. Arsenic is present in rice grain both as inorganic arsenic and as dimethylarsinic acid (DMA). It is unclear whether DMA in rice is taken up from the soil or synthesized in planta. We investigated the effect of DMA, methylarsonic acid (MMA) and arsenite amendment on arsenic speciation in rice grain grown in soil and in solution culture. We also investigated the methylation of arsenic in solution culture under suppression of bacterial activity. When rice was grown under flooded conditions after the heading stage, DMA amendment to the soil resulted in higher DMA concentration in brown rice and rice straw. In the solution culture, not only DMA amendment but also MMA or arsenite amendment increased the DMA concentration in brown rice and rice straw. DMA was detected in the solution amended by MMA or arsenite with young rice plants. When the solution included the antibacterial agent chloramphenicol, DMA concentration in the solution decreased dramatically. When only the soil was incubated with MMA or arsenite, only a slight amount of DMA was detected in the soil. These results suggest that rice rhizosphere associated bacteria would be involved in the formation of DMA in brown rice.

Biogas slurry application elevated arsenic accumulation in rice plant through increased arsenic release and methylation in paddy soil

“…More importantly, the As methylation and volatilization was influenced by the activity of relative microbes related to As transformation, altered by the input of organic matters into the soil (Huang et al 2012). It was most likely that the methylated As species in rice plants was originated from the rhizosphere under the active of relative methylating microbes in the soil (Arao et al 2011;Lomax et al 2011), so the mehylated As species in the soil solution was absorbed into rice plants, especially in the BGS addition treatments.. The extent of the increase of methylated As was much higher than the inorganic As in the rice grain and husk, due to the fact that methylated As were more liable translocating from roots and shoots to the grains (Carey et al 2011).…”

Pathways and Relative Contributions to Arsenic Volatilization from Rice Plants and Paddy Soil

“…17−19 However, recent studies have shown that the methylated As species detected in plants are most likely derived from the growth medium originated from microbial methylation. 13,16 The pathway of As methylation and biovolatilization in certain bacteria and fungi, proposed by Challenger and co-workers, 20−22 involves reduction of As(V) to As(III), followed by oxidative methyl transfer from S-adenosyl-L-methionine (SAM) to As(III) catalyzed by arsenite Sadenosylmethionine methytransferase. Arsenic reduction and methylation can continue for several steps forming methylated As species with 1−4 methyl groups.…”

Effects of microbial processes on the fate of arsenic in paddy soil

“…DMA levels detected in the solution amended by MMA or As(III) with the growth of rice seedlings decreased dramatically after the addition of antibacterial agent chloramphenicol [97]. No methylated As could be detected in plants (rice, tomato and red clover) cultured in a sterile hydroponic solution fed with inorganic As [98].…”

“…It is clear now that methylated As species in rice plant (mostly in the grain) is originated from soil, where microorganisms are responsible for the production of methylated species [97,98]. DMA levels detected in the solution amended by MMA or As(III) with the growth of rice seedlings decreased dramatically after the addition of antibacterial agent chloramphenicol [97].…”