Chemical Immobilization of Lead, Cadmium, Copper, and Nickel in Contaminated Soils by Phosphate Amendments

Introducing phosphorus amendments to contaminated acid and neutral soils result in pH increment, formation of insoluble phosphorus metals compounds and subsequent decrease in heavy metals availability. Little is known, however, on the performance of various phosphorus amendments in reducing heavy metals availability in carbonated soils. This experiment was conducted to evaluate effectiveness of two phosphorus amendments, triple superphosphate (TSP) and phosphate rock (PR), to change Pb, Cd, Ni, and Cu status in four artificially contaminated, mainly calcareous, soils. Addition of TSP substantially decreased Pb and Cd availability through the modification of the metals partitioning from non -residual to residual forms. In contrast, Ni availability was increased in the presence of TSP amendments. PR was relatively ineffective in metals immobilization likely due to the lower activity of apatite in calcareous soils. The greenhouse experiment well indicated the effectiveness of TSP amendment for reducing Pb and Cd mobility and phytoavailability, which may contribute to the formation of minerals semi-pyromorphite in soil and plants cell walls, but in subject of Ni, TSP may in fact have adverse effects on immobilization.