Arsenic Accumulation and Speciation in Paddy Rice As Affected By Iron Plaque and Genotypes Grown in As-Contaminated Soils.

Arsenic (As) is a human carcinogen and the intake of As through rice (Oryza sativa L.) consumption may lead to the significant risk of cancer, therefore, reducing the As uptake and accumulation by rice plants is very important. A pot experiment was conducted to investigate the effects of iron plaque and variation of rice genotypes on the uptake and accumulation of As by paddy rice. In addition, due to As species in rice grains governing the toxicity to humans, the distribution of As species in rice grains of different genotypes also was investigated in this study. Three levels of geogenic As-contaminated soils (10.6 (L), 343.3 (M) and 512.3 (H) mg As kg soil^-1) collected from Guandu Plain of northern Taiwan and six rice genotypes commonly planted in Taiwan, including three Japonica and three Indica cultivars were used in this study. The results show that concentrations of As and Fe in pore water increased with growing time due to the reductive dissolution of iron oxides induced by high contents of organic carbon in soils. The amounts of iron plaque formation on roots were significantly different among six tested rice genotypes and iron plaque can sequester most of As uptake from soils. The variation of rice genotypes and soil As concentrations affect the amounts of As accumulated in rice grain (polished rice) and grain yields. Grain yields decreased markedly for rice grown in high As-contaminated soils (M and H soils). However, the As concentrations of grains in L soil was the highest, possibly resulting from less phytotoxicity of As to rice grown in L soil than that in M and H soils. The predominant As species was dimethylarsinic acid (DMA) and the percentage of arsenite decreased with total As concentrations in rice grains. The information obtained from this study will be useful for selecting the rice genotypes which have low As concentrations in grains for growing in As-contaminated soils.