Cadmium (Cd) yellow pigments (mainly the CdS) are lightfast, stable at high temperatures, intensely colored and migration-resistant so they are widely used in the coloring of engineering plastics, painting, and ceramics, which may be related to the soil Cd pollution. Moreover, Cd accumulation in rice grains poses a potential health risk via the food chain and was also the major contributor to the human intake of Cd worldwide, especially in Asia. Therefore, based on diffusive gradient in thin-film (DGT) and planar optodes (PO), the two-dimensional dynamics and toxicity of Cd and the mechanism in situ that control the solubility of Cd yellow pigment and Cd bioavailability in rice rhizosphere were investigated for better evaluating environmental exposure. The results showed that although Cd yellow pigment was insoluble complex, Cd can be released from the Cd yellow pigment and entered into the soil solution, which can be influenced by the bacterial activity. The rice rhizosphere altered solubility of the Cd yellow pigment and Cd distribution in the rhizosphere, enhancing the potential risk of Cd yellow pigment. Different O₂ saturation in the rhizosphere can influence bioavailability of Cd from Cd yellow pigment through the change of Fe(II) mobilization and the oxidation of S^2- to SO₄^2-. An acidification and chelation in the rhizosphere may be also one of the reason for enhancing Cd concentration in the rhizosphere than the bulk soil. High-throughput sequencing also indicated that the toxicity of Cd yellow pigment was related to the microbial activity. Summary, the insoluble Cd yellow pigment can increase the risk of Cd uptake in rice. In future, it is possible to investigate in situ the stability of remediation treatments and remobilization of Cd yellow pigment with the extension of the time in rice rhizosphere.

[1]: Corresponding authors, 0086–25–89680632, esluojun@nju.edu.cn