Water management such as drainage for creating aerobic conditions is considered to be an adequate method for reducing the accumulation of arsenic (As) in rice grains; however, it is difficult to conduct drainage operations in some areas that experience a lengthy rainy season as well as in soils with poor drainage. In this regard, application of oxygen-releasing compounds (ORCs) may be an alternative method for maintaining aerobic conditions even under flooding in paddy soils. Therefore, a pot experiment was conducted to investigate the effects of application of an ORC, calcium peroxide (CaO2), on the growth and accumulation of As in rice plants grown in As-contaminated paddy soils. The rice plants were grown in two soils with different characteristics and As levels, and all of the tested soils were treated with 0, 5, 10, and 20 g CaO2 kg-1. Results revealed that the concentration of As and the distribution of arsenite in the pore water of all tested soils was reduced by CaO2 application. In addition, the grain yields increased and the concentration of inorganic As in brown rice decreased by 25-45% upon CaO2 treatment of low-As-level soils (<16 mg kg-1). However, the effect of CaO2 application on the accumulation of inorganic As in brown rice in As-enriched soils (>78 mg kg-1) could not found in this study, due to the rice plant suffered from serious As phytotoxicity. It suggests that CaO2 amendment may be suitable for reducing the As concentration of rice grains grown in low-As-level paddy soils, but for As-enriched soils, the proposed CaO2 application method is not feasible.
Keywords: Arsenic; Calcium peroxide; Inorganic arsenic; Paddy soil; Rice grain.
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