Impacting Phosphate Mobility in a Lead-Contaminated Urban Soil.

Chemical immobilization of lead (Pb) using phosphate amendments is a proven cost-effective method for the remediation of contaminated soil. Application rates needed to effectively immobilize Pb also result in the accumulation of fixed phosphorus (P) in contaminated soils. The purpose of this study was to evaluate the influence of surface applied organic amendments on P adsorption in a Pb-contaminated soil. Phosphorus distribution in the soil was characterized by separating inorganic P into five fractions (soluble/loosely-bound, Al, Fe, occluded and Ca). In order to evaluate the influence of surface applied amendments (sodium oxalate (NaOx) and Avail^®) on the distribution of soil inorganic P, an exploratory field trial was conducted with nine treatments and three replications. The following treatments were applied: (1) Triple super phosphate (TSP) (2) Vermicompost (TSP+VC) (3) TSP+VC+NaOx (4) TSP+VC+Avail (5) TSP+Avail (6) TSP+NaOx (7) NaOx (8) Avail and (9) Control (no application). Eight weeks after incorporation of treatments, Al- and Fe-associated P were reduced using TSP+VC+Avail, compared to an equivalent addition of P as TSP+VC. The lower amount of Bray-1 extractable P and bioaccessible Pb associated with TSP+VC+Avail compared to TSP+VC suggested that this treatment could reduce Pb bioaccessibility while lowering the environmental risk associated with a high concentration of P near the soil surface.