Desorption of Bisphenol A and Dibutyl Phthalate from the Surfaces of Polyamide Microplastics: Crucial Role of Hydrophobicity

Plasticizers are widespread pollutants that can accumulate in microplastics (MPs), increasing environmental risks upon their desorption. Exploring their desorption mechanisms from coexisting MPs is crucial for predicting their fate, which remains unclear. In this study, polyamide microplastics (PAMPs) were used to investigate the desorption of bisphenol A (BPA) and dibutyl phthalate (DBP) in freshwater. The effects of water chemistry, aging of PAMPs (NaClO, Fenton, and UV treatments), and coexisting plasticizers were considered. Results indicated that BPA and DBP desorption was mainly controlled by the heterogeneous diffusion process, which was enhanced under higher alkalinity and temperature. Coexisting cations inhibited DBP desorption due to their low solubility. Moreover, PAMPs could be corroded by NaClO, resulting in increased hydrophobicity and thus inhibiting desorption, whereas Fenton and UV aging promoted it. Oxygen-containing groups and surface hydrophobicity of aged PAMPs played key roles in the process. The plasticizers were first proven to be easier to desorb from oxidation-aged MP surfaces. Moreover, DBP desorption decreased with increasing BPA, suggesting that interactions among coexisting pollutants affect plasticizers’ fate. These findings provided theoretical references for predicting the fate of plasticizers when MPs coexist in freshwater environments.