Rice Seedlings and Microorganisms Mediate Biotransformation of Se in CdSe/ZnS Quantum Dots to Volatile Alkyl Selenides

Quantum dots (QDs) are widely applied and inevitably released into the environment. The biotransformation of Se in typical CdSe/ZnS QDs coated with glutathione (CdSe/ZnS-GSH) to volatile alkyl selenides and the fate of alkyl selenides in the hydroponically grown rice system were investigated herein. After a 10-day exposure to CdSe/ZnS-GSH (100 nmol L-1), seven alkyl selenides, dimethyl selenide (DMSe), dimethyl diselenide (DMDSe), methyl selenol (MSeH), ethylmethyl selenide (EMSe), ethylmethyl diselenide (EMDSe), dimethyl selenenyl sulfide (DMSeS), and ethylmethyl selenenyl sulfide (EMSeS), were detected in the exposure system using the suspect screening strategy. CdSe/ZnS-GSH was first biotransformed to DMSe and DMDSe by plant and microorganisms. The generated DMSe was volatilized to the gas phase, adsorbed and absorbed by leaves and stems, downward transported, and released into the hydroponic solution, whereas DMDSe tended to be adsorbed/absorbed by roots and upward transported to stems. The airborne DMSe and DMDSe also partitioned from the gas phase to the hydroponic solution. DMSe and DMDSe in the exposure system were further transformed to DMSeS, EMSeS, EMSe, EMDSe, and MSeH. This study gives a comprehensive understanding on the behaviors of Se in CdSe/ZnS-GSH in a rice plant system and provides new insights into the environmental fate of CdSe/ZnS QDs.