Migration and transformation of cadmium in rice - soil under different nitrogen sources in polymetallic sulfide mining areas

We conducted pot experiments to assess the bioavailability of cadmium (Cd) in contaminated rhizosphere soil and accumulation in rice organs in response to nitrogen (N) supply ((NH(4))(2)SO(4), NH(4)NO(3), NH(4)Cl). The results showed that the concentration of bioavailable Cd in rice rhizosphere soil was (NH(4))(2)SO(4) treatment > NH(4)Cl treatment > NH(4)NO(3) treatment at the same level of N application and growth period; the Cd concentration in rice roots was (NH(4))(2)SO(4) treatment > NH(4)NO(3) treatment > NH(4)Cl treatment; and the Cd concentration in rice straw was NH(4)NO(3) treatment > NH(4)Cl. The Cd concentration in rice roots, straws, and seeds at the maturity stage was (NH(4))(2)SO(4) treatment > NH(4)Cl treatment. With the same N fertilizer, excessive N promoted Cd accumulation in rice at later growth stages. This suggested that sulfate (SO(4)(2−)) influenced Cd concentration in rice. NH(4)Cl application maintained a low Cd level in different rice organs with the same N level. This confirmed that NH(4)Cl is a safe N source for rice planting in polymetallic sulfide mining areas. The study concludes that appropriate NH(4)Cl levels for Cd-contaminated paddy soil with high-S-content could obtain rice grains with Cd concentrations below the food safety standards (0.2 or 0.4 mg·kg(−1)).