The photo-aging of polyvinyl chloride microplastics under different UV irradiations

Microplastics (MPs) pollution is becoming a global environmental problem due to the ubiquity. Knowledge about transformation process of MPs under ultraviolet (UV) irradiation was critical to understanding the environmental fate of these particles. In this study, the photo-aging characteristics and mechanisms of polyvinyl chloride (PVC) under different UV irradiations in the air or water condition were comprehensively investigated. When the PVC was exposed to the UVA, UVB and UVC irradiation, the surface morphology, functional group, crystal structure, and elemental composition of PVC were systematically characterized. With the increasing of aging time, the PVC was identified as more oxygen-containing functional groups, higher carbonyl index, and higher crystallinity, especially under the UVC irradiation. Based on the Two-dimensional correlation Fourier transform infrared spectroscopy (2D-FTIR-COS), the active sites and aging sequence of functional groups were confirmed under UVA, UVB and UVC irradiation. The reactive oxygen species (ROS) were produced and increased with the aging time as the whole. Corresponding to the aging results, the intensity of ROS and toxicity from leaching under UVC irradiation was greater than that under UVA or UVB. These findings provide direct evidences of photo-aging processes of MPs and the potential ecological risks resulting from aging in the aquatic environments.