Determining Optimum Extractants to Evaluate Cd Bioavailability in Paddy Field.

Heavy metal pollution in agricultural field is a critical problem in Korea because of increased concern about crop safety issue. In addition, evaluating bioavailability of heavy metal in agricultural field is also important. Therefore, the main objective of this research was to determine optimum extractants for evaluating bioavailability of Cd in paddy field where chemical amendments, lime and steel slag, were applied for remediation purpose. Four different extractants, 0.1M HCl, 0.005M DTPA, 0.01M CaCl₂, 1M NH₄NO₃ were used to examine Cd bioavailability in soil and Cd concentration in rice grain was also measured with Inductively Coupled Plasma (ICP) after extracting with wet digestion method. Result showed that no significant decrease of bioavailable Cd concentration in control was observed while bioavailability of Cd was decreased when lime and steel slag were applied in paddy field. For lime application, decreased ratio of bioavailable Cd was varied depending on extractants such as 0.1M HCl (60%), 0.005M DTPA(68%), 0.01M CaCl₂(98%), 1M NH₄NO₃(80%). In case of steel slag, decreased ratio of bioavailable Cd was 0.1M HCl (28%), 0.005M DTPA(32%), 0.01M CaCl₂(98%), 1M NH₄NO₃(92%). Correlation analysis between Cd concentration in soil and rice grain showed that NH4NO3 (R² = 0.92) was highly correlated followed by CaCl₂ (R²=0.84) in lime applied field. In conclusion, application of lime and steel slag showed promising method for decreasing bioavailability of heavy metals in soil and NH₄NO₃ would be used as optimum extractant to evaluate heavy metal bioavailability.