Effect of Si on As Speciation and Distribution in Rice near the Shimen Realgar Mine

Abstract

Protection of natural water and cultivated crops from contamination in mining-affected areas is a problem in many regions. Wastewater and waste residuals from the Shimen realgar mine in Hunan Province, China, pose a high risk of arsenic (As) poisoning. The potassium silicate (PS)-assisted mechanisms of As mobility and accumulation reduction in a paddy soil–plant system were investigated. In a vegetation experiment, rice was grown in moderately and highly As-polluted soil (30.6 and 66.9 mg kg−1 of As, correspondingly) with and without PS. Total As and silicon (Si) in roots, shoots, and grains and the forms of As in the grains were analyzed. Sequential extraction of the As in the soil showed that the PS significantly reduced the mobility of As in the soil and its accumulation by rice. Several PS-mediated mechanisms were discussed: (1) dissolution of PS monosilicic acid enhances the sorption capacity of Si-based minerals for As; (2) increased pH in the soil solution provides higher As sorption by soil; (3) Si-induced competitive inhibition of As(III) transport initiated by Lsi1 and Lsi2. The results indicate the potential of using soluble Si to reduce As mobility and biotoxicity at sites with high levels of As in wastewater, tailings, and waste residuals.