In the soil environment, arsenic can exist in both inorganic and organic forms. The foremost organic forms of arsenic are dimethylarsinate (DMA) and monomethylarsonate (MMA), whereas As(V) and As(III) are the inorganic forms found in soil. Baig et al. ranked the toxicity of arsenic in the following order: As(III) > As(V) > MMA > DMA. Inorganic forms of arsenic can be transformed into organic forms through the biomethylation process in soil. Regarding bioavailability to plants, the arrangement of arsenic species is as follows: DMA < As(V) < MMA < As(III). Although rice roots can absorb all species of arsenic, the intake rate of inorganic species is much higher than organic forms. As(V) is transported by roots using phosphate transport channels, whereas As(III), along with methylated-As species, is captured by aquaporin channels. The behavior of arsenic (As) in paddy soil varies depending on the flooded or non-flooded conditions. As(III) dominates in flooded conditions, accounting for 87%–94% of the total As, whereas As(V) dominates in non-flooded soil, constituting 73%–96% of the total As. Several soil chemical properties, such as organic carbon, pH, oxide minerals, and clay content, play a significant role in determining As toxicity, solubility, and bioavailability in the soil ecosystem. The cumulative impact of soil properties like clay, AlOx, FeOx, eCEC, pH, and OC on As bioavailability in soil has been observed by S. Zhang et al. and X. Zhang et al.
Author(s) Details:
Young-Cheol Chang,
Course of Chemical and Biological Engineering, Division of Sustainable and Environmental Engineering, Muroran Institute of Technology, 27-1 Mizumoto, Muroran 050-8585, Japan.
