Comparison of bio-beads combined with Pseudomonas edaphica and three phosphate materials for lead immobilization: Performance, mechanism and plant growth

Phosphate materials (PMs) combine with phosphate solubilizing bacteria play an essential roles in lead (Pb) immobilization, but their resulting ability to reduce Pb bioavailability may vary depending on PMs used. In this study, Pseudomonas edaphica GAU -665 and three PMs: tricalcium phosphate, calcium phytate and nanohydroxyapatite were respectively encapsulated into bio-beads by sodium alginate, which immobilization efficiency of Pb 2+ were 99.11%, 97.76% and 99.02% at initial Pb 2+ concentration of 200 mg L -1 , respectively. The Pb 2+ immobilization performance of bio-beads under different conditions and their organic acids secreted were examined. Most Pb 2+ was immobilized by bio-beads through combined functions of adsorption, precipitation, ion exchange and biomineralization, accompanied by the formation of more stable compounds such as Pb 3 (PO 4 ) 2 , Pb 5 (PO 4 ) 3 OH and Pb 5 (PO 4 ) 3 Cl. Meanwhile, pot experimental results indicated that the inoculation of CPhy (calcium phytate) bio-beads with PSB have highest biomass and root growth of oat ( Avena sativa L.) in Pbstressed compared with CK, which increased the content of chlorophyll b (167.51%) in shoot. In addition, the CPhy bio-beads enhance the peroxidase, catalase activities and reduce the malondialdehyde content to alleviating lead physiological toxicity in oat, which reductions the Pb accumulation in shoot (52.06%) and root (81.04%), and increased the residual fraction of Pb by 165.80% in soil. These findings suggest the bio-beads combined with P. edaphica GAU -665 and calcium phytate is an efficient Pb immobilization material and provided feasible way to improve safety agricultural production and Pb-contaminated soil remediation.