Effects and mechanisms of meta-sodium silicate amendments on lead uptake and accumulation by rice.

The objectives of this research were to study the effects of NaSiO application on the uptake, translocation, and accumulation of Pb in rice and to investigate the mechanisms of Pb immobilization by NaSiO in paddy rice soils and rice plants. Pot experiments were conducted using a Cd-Pb-Zn-polluted soil and Oryza sativa L. ssp. indica cv. Donglian 5. L-edge X-ray absorption spectroscopy was used to identify Pb species in soils and roots. The results showed that the application of NaSiO increased soil pH and available soil Si but decreased DTPA-extractable Pb in the soil. High dose of NaSiO (12.5 g/kg) reduced the Pb level in brown rice as it inhibited Pb transfer from soil to rice grains, especially Pb transfer from the root to the stem. The Pb X-ray absorption near-edge spectroscopic analysis revealed that application of high dose of NaSiO increased Pb-ferrihydrite and PbSiO precipitates in the soil and in the root while it reduced Pb-humic acids (Pb-HAs) in the soil and Pb-pectin in the root. The decrease in Pb availability in the soil can be partly attributed to increase the precipitation of PbSiO and the association of Pb with Fe oxides in the soil. The inhibition of the root-to-stem translocation of Pb was partially due to the precipitation of PbSiO on the root surfaces or inside the roots.