Abstract:

There is an urgent need for cadmium pollution transfer risk and soil nutrient restoration technology in rice field in karst mining area of South China. To explore the effect of nutritional passivator on cadmium (Cd) contaminated paddy soil in mining areas, and to clarify its effect on the morphological transformation, bioavailability and soil quality of cadmium in the rhizosphere soil of rice, the in-situ remediation experiment of paddy soil was carried out. Three treatments were set up, including no passivator (T₁), inorganic nutritional passivator (T₂) and organic-inorganic nutritional passivator (T₃). The gradient diffusion film (DGT) technique was used to study the bioavailability of Cd and Cd transformation in rhizosphere soil of the paddy field, and the biological correlation between Cd transformation, bioavailability of Cd and soil quality was evaluated in rhizosphere soil of the paddy field. The results showed that: (1) nutritional passivator affected the ratio of cadmium formation in cadmium-contaminated paddy soil. Nutritional passivator could promote the transformation of exchangeable cadmium to residual cadmium in soil. Nutritional passivator reduced the proportion of exchangeable cadmium content. Compared with T₁ (control), the T₂ and T₃ decreased the proportion of exchangeable cadmium content in soil by 14.71% and 5.88%, respectively. Nutritional passivator increased the proportion of reducible cadmium content. Compared with T₁ (control), the T₂ and T₃ increased the proportion of reducible cadmium content in soil by 8.51% and 6.38%, respectively. Nutritional passivator increased the proportion of residual cadmium content. Compared with T₁ (control), the T₂ increased the proportion of residual cadmium content in soil by 10%, T₃ had no obvious changes. (2) The bioavailability of Cd in rhizosphere soil of Cd-polluted paddy fields was reduced by treatment with nutritional passivator. Compared with T₁ (control), the T₂ and T₃ treatments decreased bioavailability significantly by 54.21% and 50.47% at harvest stages. (3) Nutritional passivator improved soil quality in soil of Cd-polluted paddy fields. Compared with T₁ (control), the T₂ and T₃ increased soil organic matter, pH and cation exchange capacity by 7.37%, 7.50% and 5.29%, 17.06% and 12.24%, 11.10%, respectively. Nutritional passivator could restore polluted soil and improve soil quality synchronously.

Key words: contaminated paddy fields, in-situ immobilization, Cd form transformation, nutritional passivator, karst mining area