Effective lead immobilization by phosphate rock solubilization mediated by phosphate rock amendment and phosphate solubilizing bacteria

Lead can be immobilized in contaminated soils by phosphate rock (PR) amendment, but its efficiency is generally limited by low solubility of PR. Our study aimed to elucidate whether phosphate solubilizing bacteria (PSB) can promote Pb immobilization through PR solubilization. Results showed that P. ananatis HCR2 and B. thuringiensis GL-1 could effectively solubilize PR by producing citric, glucose, and α-Ketoglutaric acids. In broth assay, phosphate solubilized from PR by PSB rapidly reacted with Pb2+ and formed insoluble lead compounds, as confirmed by scanning electron microscope, energy dispersive X-ray, and X-ray photoelectron spectroscopy. Pot experiment using lettuce (Lactuca sativa L.) and diffusive gradients in thin films (DGT) verified the effectiveness of soil remediation using PR amendment and PSB inoculation, as plant shoot biomass and net photosynthetic rate as well as soil bioavailable phosphate concentration have significantly increased, while the phytoavailability of Pb, Cd, and Zn greatly reduced. This study suggested that PR amendment combined with PSB inoculation could be applied for remediation of agricultural fields contaminated with multiple heavy metals.