[Potential to Ensure Safe Production from Rice Fields Polluted with Heavy Cadmium by Combining a Rice Variety with Low Cadmium Accumulation, Humic Acid, and Sepiolite].

The study investigated the potential of ensuring safe production of rice from paddy fields affected by heavy cadmium contamination. A paddy soil polluted with heavy cadmium (total Cd content of 2.52 mg·kg-1) surrounding a lead-zinc mining area in Guiyang County of Chenzhou City, Hunan province was selected for analysis. We investigated production using a low cadmium accumulation rice variety (Oryza sativa L. Jia-33) and passivation additives for heavy metal activity (including humic acid and sepiolite). Results showed that:Oryza sativa L. Jia-33 showed good low cadmium accumulation characteristics in rice fields with heavy cadmium pollution. When humic acid and sepiolite were applied (alone or combined), the accumulation of Cd in different organs of the rice declined, and the transport coefficient of Cd for stem to root and polished rice to stem also declined. The rate of decline increased with increased application dosage. The cadmium content in polished rice was lower than the limit established in the National Food Safety Standard (GB 2715-2012), when applying 5.250 t·hm-2 humic acid, 6.750 t·hm-2 sepiolite, or a combination of 1.125 t·hm-2 humic acid and 3.37 5 t·hm-2 sepiolite; Cd content in polished rice was (0.171±0.01), (0.184±0.01), and (0.181±0.01) mg·kg-1, respectively. Single or combined application of humic acid and sepiolite promoted the transformation of soil Cd to residual and Fe Mn oxide bound forms, significantly reducing the content of available Cd and the bioavailability of Cd in soil, and further reducing Cd content in all rice organs. The reduction was more effective with single application of sepiolite or combined application of humic acid and sepiolite. The effects of combined application of humic acid and sepiolite were also more beneficial for soil nutrients, while soil available phosphorus, available potassium, phosphorus, and organic matter content increased with increased application of amendments. Soil nitrogen content did not change. In conclusion, results indicate that joint application of humic acid, sepiolite, and a low Cd accumulation rice variety are best for safe production on heavy cadmium-contaminated soil.