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 ≈ BCR1 > DTPA > NH₄NO₃ ≈ 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, non-significant 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.