Use of water-treatment residue containing polysilicate-iron to stabilize arsenic in flooded soils and attenuate arsenic uptake by rice (Oryza sativa L.) plants

A pot experiment was conducted to examine how soil amendment with water-treatment residue (WTR) containing polysilicate-iron affected dissolved arsenic (As) in flooded soils and As uptake by rice plants (Oryza sativa L.). The WTR was applied at a rate of 0 (control), 5, 10 or 20tha(-1). Simple linear regression analyses showed significant negative relationships between the concentrations of dissolved As in soil solution and WTR application rates at all sampling times, probably due to adsorption of As onto ferrihydrite in the WTR. Compared to As concentrations in rice plants grown on control soil, the concentrations in plants grown on WTR-treated soils decreased by 20.1-41.6% in straw (stems and leaves), 19.8-31.7% in husk and 18.6-21.0% in grain. The regression analyses demonstrated that the concentration and content of As in rice are negatively correlated with WTR application rate. Total As content was 16.5-32.0% lower in rice shoots grown on WTR-treated soils than on control soil. The percentage of each As species in grain decreased in the following order: As(III) >> dimethylarsinic acid >> As(V). The application of WTR did not change the As speciation in grain. Silicon contents in shoot significantly increased with application of WTR, indicating the potency of WTR as a silicate fertilizer. Taken together, our results indicate that WTR containing polysilicate-iron promises to be a practical amendment for stabilizing As and attenuating As uptake by rice plants.