Arsenic and Cadmium Bioavailability to Rice ( Oryza Sativa L.) Plant in Paddy Soil : Influence of Sulfate Application

Arsenic (As) and cadmium (Cd) accumulate easily in rice grains that pose an unignorable threat to human health worldwide. The opposite releasing mechanisms of As and Cd in the soil complicate measures to reduce the accumulation of As and Cd simultaneously in rice. We performed soil incubation experiments and pot experiments to explore the effect of sulfate (100 mg kg -1 ) supply on the bioavailability of As and Cd in soil and the rice growth under three different levels of As and Cd co-contaminated soil. For soil with low sulfate background, the application of exogenous sulfate significantly reduced the concentration of As and Fe in porewater and the proportion of exchangeable Cd in the soil. The relative abundance of dsr gene increased significantly, suggesting that exogenous sulfur stimulated microbial sulfate reduction. For the soil with high sulfate background, sulfate addition accelerated the immobilization of Cd but had little effect on As solubility. Further pot experiments showed that sulfate significantly alleviated the stress of As and Cd on rice, mainly as follows: increased rice tillers, increased biomass, decreased root electrolyte leakage, and increased chlorophyll in shoots. Additionally, sulfate reduced the content of iron plaque, speculating that the rhizosphere Fe formed Fe-S secondary minerals instead of being oxidized and attached to the root surface. The accumulation of As and Cd in rice tissues was also significantly reduced, especially those grown in soils with high As and low sulfate backgrounds. These findings indicate that the application of sulfate can reduce the bioavailability of As and Cd in the soil and promote rice growth, providing a novel strategy to remediate the paddy fields co-contaminated with As and Cd