Impacting the Mobility of Phosphate for Remediation of Lead Contaminated Soils.

Chemical immobilization of lead using phosphate amendments is a proven cost-effective method for the remediation of contaminated soil. Application rates needed to effectively immobilize lead (Pb) also result in the accumulation of fixed phosphorus in smelter-contaminated soil. The purpose of this study is to evaluate the influence of surface applied amendments on phosphorus adsorption in a Pb-contaminated soil. Phosphorus distribution in the soil was characterized using a five step sequential chemical extraction, with the sum of these five fractions representing total soil inorganic P. In order to evaluate the influence of surface applied amendments (Sodium Oxalate (NaOx) or Avail®) on the distribution of soil inorganic P, both a field trial and incubation study were conducted with nine treatments and three replications. The following treatments were applied: (1) Triple super phosphate (TSP), (2) Vermicompost (VC), (3) VC/NaOx (application of VC with surface applied NaOx), (4) VC/Avail (application of VC with surface applied Avail), (5) TSP/Avail, (6) TSP/NaOx, (7) NaOx, (8) Avail, and (9) Control. Preliminary results from the field trial reveal that VC/Avail and VC/NaOx resulted in reduced recovery of Aluminum-bound P (Al-P) compared to VC alone, with 18% and 20% of P associated with Al for VC/Avail and VC/NaOx respectively, while VC application alone resulted in 27% of cumulative soil P being associated with the Al-P fraction. The incubation study revealed a similar pattern of P distribution within the Al-P fraction with 24% of total inorganic P associated with Al for VC application alone, compared to 22% and 19% for VC/NaOx and VC/Avail, respectively. Application of VC in conjunction with the surface amendments evaluated in this study resulted in a reduction of Al-P in both the field and incubation trials, suggesting greater phosphorus availability which may lead to a reduction of bioavailable Pb in these soils.