Submitted to: Environmental Engineering Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/22/2011
Publication Date: 5/17/2011
Citation: Hua, B., Yan, W., Wang, J., Deng, B., Yang, J. 2011. Arsenic accumulation in rice grains: Effects of cultivars and water management practices. Environmental Engineering Science. 28(8):591-596. Interpretive Summary: Arsenic (As) is listed as one of the top health hazards by the International Agency for Research on Cancer (IARC), which is linked to bladder, lung, skin, and prostate cancers. Human exposure to As is primarily through the intake of drinking water and foods, such as rice grains, that contain an elevated amount of As. Accumulation of As in rice plant tissues and grains was reported resulting from the soils or irrigation waters containing an elevated level of As. Rice growing in the anoxic environment was found to store the highest amount of As among all grain crops. In Arkansas, the elevated As in the soils resulting from a long historical application of As-containing pesticides, such as monosodium methanearsonate (MSMA), could induce the straighhead-like symptom, a physiological disorder of rice with which rice heads remain up at maturity because of lack of grain development. As a result, As accumulation in rice plants would have profound, adverse impacts on the quality, security, marketability, and profitability of rice products. The objectives of this study were to (i) evaluate As susceptibility and uptake of three rice cultivars in MSMA-elevated soil; (ii) determine As extractability in relation to iron (Fe) redox status in the soil under two water management conditions through field experiments; and (iii) test the hypothesis that Fe redox transformation controls the MSMA-As solubility and extractability through laboratory study.
Technical Abstract: Arsenic (As) accumulation in rice grains is a threat to human health and marketability of rice products. The accumulation has been linked to the elevated As in soil resulting from pesticide application and/or irrigation water quality. In an effort to minimize As uptake by rice grain and occurrence of As-induced rice straighthead disease, field experiments were conducted to investigate As accumulation in rice grains of three cultivars and As extractability in monosodium methanearsonate (MSMA)-treated soil under saturated and flooded water management practices. Results indicated that As concentration in rice grains was cultivar-dependent and influenced by water management. Soil flooding would substantially enhance As accumulation with a great variation among cultivars. Extractable As in the soil was positively correlated with DCB (a solution of sodium dithionite-sodium citrate-sodium bicarbonate)-extractable Fe and P, suggesting a strong association of As with ferric (hydr)oxide and/or iron phosphate. Additional laboratory experiments showed a strong affinity between synthetic ferric (hydr)oxide and MSMA, which could be accounted for by As adsorption on the surface of ferric (hydr)oxide and/or As partitioning into the mineral structure. This study demonstrated that the selection of less As-responsive rice cultivars and saturated water management in paddy field could be effective means to minimize As accumulation in rice grains and the occurrence of rice straighthead disease.