Impact of Elevated Nitrate and Perchlorate in Irrigation Water on the Uptake, Speciation, and Accumulation of Arsenic in Rice (Oryza sativa L.)

Abstract

In the absence of adequate molecular oxygen in a continuously flooded soil, other oxidizing anions can potentially oxidize arsenite (As(III)) into arsenate (As(V)) and reduce the bioavailability of arsenic (As) to rice while maintaining high rice yield. We conducted a greenhouse study to evaluate the effect of two prevalent oxyanions (10 mg/L nitrate and/or 50 μg/L perchlorate) on the As uptake, speciation, and accumulation in a hybrid rice (XL753) at the heading and maturity stages. The presence of nitrate and/or perchlorate at the used concentrations increased the rice grain yield by 35–93% to16.6–23.8 g/pot while lowering the total As in rice grains by 34–45% to 0.81–0.97 mg/kg dry weight. Perchlorate alone led to the greatest decrease in total As. Organic As was the predominant species in rice grains, with dimethylarsinic acid (DMA) accounting for 66–76% of total As in all treatments. In contrast, inorganic As was the dominant As form in rice straws and roots, with As(V) accounting for 62.4–91.4% of total As in all treatments. The translocation and accumulation of different As species in rice tissues varied at different growth stages in the presence of two tested oxyanions, as indicated by the ratios of inorganic vs organic As and inorganic As(III) vs As(V). Overall, the presence of oxyanions in irrigation water at the tested concentrations significantly decreased the total As accumulation in rice grains, while enhancing the rice yield.