Foliar uptake of atmospheric cadmium in rice: The importance of deposition forms for translocation and grain accumulation

Atmospheric deposition is a significant source of cadmium (Cd) contamination in rice, yet studies on the foliar uptake and accumulation of its different chemical forms remain limited. In this study, two rice varieties with a significant difference of leaf cuticle were cultivated and exposed to three different chemical forms of Cd (CdCl 2 , CdO and PM-Cd) via foliar application at the grain-filling stage. The Cd content in rice tissues, its subcellular localization and chemical speciation in leaves, and the cuticular wax composition of different varieties were analyzed. The results showed that the ionic CdCl 2 was better retained by the epidermal waxes and thus absorbed. The accumulation of Cd in rice grains varied significantly depending on its chemical form, following the order of CdCl 2 > PM-Cd > CdO treatment. Under CdO-exposed conditions, Cd primarily accumulated in the cell wall, with a predominance of the residual fraction of Cd. In contrast, CdCl 2 exposure resulted in higher Cd bioavailability, as evidenced by increased proportions of inorganic Cd and water-extractable Cd. The leaf epidermal wax deposited and retained approximately 1/2–2/3 of the Cd, with the ZJZ17 variety (higher epidermal wax content) showing greater grain Cd accumulation than XZX24. This study concludes that higher plant cuticular wax content leads to greater Cd accumulation in rice, with CdCl 2 identified as the most easily absorbed form among different types of Cd. These findings contribute to combating atmospheric Cd pollution, ensuring food safety, and providing new directions for future research.