Assessment of single extraction methods for evaluating the immobilization effect of amendments on cadmium in contaminated acidic paddy soil

Various single extractants (EDTA, DTPA, CaCl2, NaNO3 and NH4NO3) and the first step of Community Bureau of Reference (BCR1) method were used to evaluate the immobilization of Cd in contaminated acidic paddy soil by different amendments. The extractability of Cd in amended soil changed in the following order: EDTA approximate to BCR1 > DTPA > NH4NO3 approximate to CaCl2 > NaNO3. A simple correlation analysis indicated that the BCR1, CaCl2, NH4NO3, and NaNO3 methods are the best suited methods for predicting changes in the phytoavailability to rice of Cd in soil (r = 0.680 to 0.828, P < 0.001), followed by the DTPA extraction procedure (r = 0.543 to 0.666, P < 0.01). However, nonsignificant correlations were observed between soil EDTA-extractable Cd and Cd accumulated in rice. Accordingly, the BCR1, CaCl2, NH4NO3, and NaNO3 extraction procedures are recommended for evaluating the immobilization of Cd in contaminated acidic paddy soil.