Using phosphorus and zeolite to immobilize lead in two contrasting contaminated urban soils

Lead (Pb) contamination of urban soil is a threat to human health, and reducing the risk of Pb-contaminated soil is a continuing international concern. Soil stabilization technique has been considered as a promising remediation technique to facilitate the immobilization of Pb in soil. The purpose of this study was to evaluate the effects of different amendments, including H3PO4, Ca(H2PO4)(2), H3PO4 + Ca(H2PO4)(2), and zeolite on Pb levels in two naturally contaminated urban soils. Pb speciation and bioavailability was evaluated by the sequential extraction test (SET) and the toxicity characteristic leaching procedure (TCLP) after a two-month incubation. The application of phosphorus amendments significantly reduced the TCLP-Pb concentration in two soil types and the SET-Pb in Soil 1 (alkaline but with high Pb level), whereas the zeolite amendment diminished the SET-Pb in two soil types and the TCLP-Pb in Soil 1. Nevertheless, regardless of the soil type, the application of phosphorus amendments resulted in a significant increase of residual Pb. These phosphate amendments may be a viable strategy in the in situ remediation of Pb contamination in urban soils.