In-situ immobilization of cadmium and lead by different amendments in two contaminated soils

Different soil amendments, including 1% zeolite, 1% bentonite, 5% Penghu soil (PHS), 5% Penghu soil + 1% manganese oxide (PHS + MO), 1% MO, and 1.5% silicate slag (SS), were used to immobilize Cd and Pb in two contaminated soils evaluated by single and sequential extractions and by uptake of Chinese cabbage (Brassica Chinensis L.). Results indicated that the PHS and MO significantly (p < 0.05) reduced the 0.1 M HCl extractable Cd and Pb in the two contaminated soils. All amendment treatments did not change the organic and residual amounts of Cd and Pb in soils A and B, but the PHS and PHS + MO treatments significantly reduced the exchangeable amounts of Cd and Pb in the two soils as measured by sequential extraction. The combination of PHS and MO amendments was associated with a high pH value and negative soil surface charge showed the best immobilizing efficiency of Cd and Pb in this study. All soil amendments investigated did not increase the dry matter weight of the plant, and most of them decreased the uptake of Cd and Pb, especially for the PHS and MO. The PHS and MO treatments reduced the extractability of Cd and Pb in two soils and their uptake by the plant, but only the Pb content in Chinese cabbage from the amended soils was less than the background levels of heavy metals in leaf vegetables of Taiwan.