Lead immobilization and bioavailability in microbial and root interface.

A range of both soluble and insoluble phosphate (P) compounds have been used to immobilize Pb in solution and soil. However, these compounds have limitations because of low solubility or leaching of P. Phosphate solubilizing bacteria (PSB) can be used to enhance the solubility of insoluble P compounds. The effects of PSB on the immobilization of Pb in the presence of phosphate rock (PR) and subsequent reduction in Pb uptake by Indian mustard (Brassica juncea) in nutrient agar medium and ryegrass (Lolium perenne) in soil under sterile condition were tested. Root colonization of PSB was confirmed by halo formation around the root in the medium containing tricalcium phosphate. Addition of PR in the presence of PSB immobilized Pb in both agar medium and soil, and reduced Pb translocation from root to shoot. Furthermore, shoot Pb concentrations of Indian mustard in agar medium and ryegrass in soil were decreased by 58.1% and 22.8%, respectively, compared to the control. Even though soluble P compound was the most effective in the immobilization of Pb, excess P may cause eutrophication. Therefore, PSB are suggested as a co-amendment to facilitate immobilization of Pb without causing any detrimental effect on the environment.