Reducing leachability and bioaccessibility of lead in soils using a new class of stabilized iron phosphate nanoparticles

This study prepared and tested a new class of iron phosphate (vivianite) nanoparticles synthesized with sodium carboxymethyl cellulose (CMC) as a stabilizer for in situ immobilization of lead (Pb2+) in soils. Batch test results showed that the CMC-stabilized nanoparticles can effectively reduce the TCLP (toxicity characteristic leaching procedure) leachability and PBET (physiologically-based extraction test) bioaccessibility of Pb2+ in three representative soils (calcareous, neutral, and acidic). When the soils were treated for 56 days at a dosage ranging from 0.61 to 3.0 mg/g-soil as PO43-, the TCLP leachability of Pb2+ was reduced by 85–95%, whereas the bioaccessibility was lowered by 31–47%. Results from a sequential extraction procedure showed a 33–93% decrease of exchangeable Pb2+ and carbonate-bound fractions, and an increase in residual-Pb2+ fraction when Pb2+-spiked soils were amended with the nanoparticles. Addition of chloride in the treatment further decreased the TCLP-leachable Pb2+ in soils, suggesting the formation of chloro-pyromorphite minerals. Compared to soluble phosphate used for in situ metal immobilization, application of the iron phosphate nanoparticles results in ∼50% reduction in phosphate leaching into the environment.