Effect of phosphate amendments on the reduction of lead phytoavailability for Spinach in a calcareous soil

In order to reduce Pb phytoavailability for spinach (Spinacia oleracea L.) using P amendment, (DAP, TSP 1:1 ratio acid phosphoric and phosphate rock), a factorial experiment based on completely randomized design was conducted and analyzed 100 days after the P applications using a sequential extraction method. Sequential extraction analysis indicates that P was effective in transforming soil Pb from non-residual fractions (SS, SE, CA, Fe-Mn form and Pb in OM) to a residual fraction. Results revealed that DTPA extractable Pb was reduced in treated soils, however, among these three treatments, DAP at 9 molar ratio of P/Pb was the most effective. Results of greenhouse experiments showed that the amount of lead in aerial parts of spinach had the highest lead in 1:1 ratio of acid phosphoric and phosphat rock and the DAP had the lowest. In DAP treatment, the Pb concentrations in shoots of spinach decreased 72% as compared with the control treatment. The results suggested that P amendments especially DAP can lower the bioavailability and increase the geochemical stability of soil Pb, so it has the potential for in situ remediation in Pb-contaminated soils.