Immobilization of Lead by Alishewanella sp. WH16-1 in Pot Experiments of Pb-Contaminated Paddy Soil

Abstract

This study investigates the effectiveness and mechanism of decreasing the bioavailability of Pb in bacterial culture and in pot experiments of Pb-contaminated paddy soil by Alishewanella sp. WH16-1. The WH16-1 strain was isolated from mine soil and exhibited high resistances to many heavy metals, especially to Pb2+ (2070 mg/L) and Cr (VI) (2340 mg/L). During cultivation of the WH16-1 strain with the addition of 100 mg/L Pb2+, Pb2+ was precipitated, and 84.13 % of Pb2+ was removed in 72 h. The precipitant was observed by transmission electron microscopy (TEM) and further confirmed to be PbS by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The WH16-1 strain was incubated in Pb2+-added paddy soil pot experiments for 60 days and compared with the uninoculated Pb2+-added paddy soil. Comparison showed that the exchangeable and carbonate-bound Pb in the paddy soil decreased by 14.04 and 10.69 % (P < 0.05), respectively. The Fe-Mn oxide-bound Pb, organic matter-bound Pb and the residual Pb increased by 4.47, 19.40, and 22.78 % (P < 0.05), respectively. Compared with the uninoculated Pb2+-added paddy soil, the dry weight of rice significantly increased by 28.59 %, and the Pb concentrations in rice, husk, leaves, and culms in Pb2+-added paddy soil pot experiment incubated with the WH16-1 strain significantly decreased by 26.18, 26.94, 26.61, and 25.56 % (P < 0.05), respectively. These results suggest that Alishewanella sp. WH16-1 can reduce the bioavailability of Pb in soil. This bacterium may be applicable for the biological stabilization of Pb in Pb-contaminated paddy soil.