A MIMICKED IN-SITU REMEDIATION STUDY OF METAL-CONTAMINATED SOILS WITH EMPHASIS ON CADMIUM AND LEAD

The capacity of several additives, ie., lime, Thomas phosphate basic slag (TBS), hydrous iron oxides (HFO), hydrous manganese oxides (HMO), and Beringite, added to soil to fix Cd or ph, was evaluated using two pot experiments in tandem with soil extractions. Three soils from France with metal contents ranging from 0.17 to 108 mg Cd kg(-1) soil dry weight (DW) and 47 to 1112 mg Pb kg(-1) soil DW were studied. Metal sources were: sludge-borne metals (Soil A), fallout from a smelter (Soil B), and emission from a tetraethyl Pb production facility (Soil C). Ryegrass (Lolium spp.) or tobacco (Nicotiana tabacum L) shoots were harvested. The addition of HMO decreased to a maximum extent Cd in ryegrass and tobacco for Soils A and B, but did not suppress the differences in Cd uptake between the two plant species. Use of HMO reduced Pb concentrations only in ryegrass shoots. Thomas phosphate basic slag lowered Pb bioavailability in Soils B and C. The addition of HMO into Soils A and B reduced Cd concentrations in water, 0.1 M Ca(NO3)(2), or 0.43 M acetic acid (HOAc) extracts, but not in 0.05 M EDTA pH 7 extracts. Water and sequential extractions were employed on Soil C: HMO caused the most reduction in ph water-soluble and HOAc-extractable fractions, and rendered Pb less extractable with H2O2 and more with HONH3Cl. The decrease of Cd- and Pb soluble fractions was reflected in their suppressed bioavailability. Among the screened additives, HMO exhibited a most promising potential to reduce either Cd or Pb transfer from soil to soil solution or their entry into the food chain vis plant uptake. This material would be promising for in-situ remediation technologies geared to restore Cd- and Pb-contaminated soils. However, little is known about the kinetics and persistence of this chemical under field conditions.