Influence of ultraviolet-aging and adsorbed pollutants on toxicological effects of polyvinyl chloride microplastics to zebrafish

Microplastics (MPs) undergo various aging processes and interact with diverse pollutants in the environment. In the present study, we investigated the influence of ultraviolet (UV) aging on the adsorption of organic pollutants by polyvinyl chloride microplastics (mPVC) and explored toxicity variations among pristine, aged, and pollutant-loaded mPVCs to zebrafish. Irradiation of UV for 30 d significantly changed the physiochemical properties of mPVC, leading to more oxygen-containing groups and free radicals (O-1(2), .O-2((sic)), and .OH) on mPVC surfaces. The aging process reduced the adsorption of mPVC against a hydrophobic compound chlorpyrifos (CPF) but enhanced the adsorption against a moderately hydrophilic compound erythromycin (ERY). Ingestion of CPF-and ERY-loaded mPVCs resulted in bioaccumulation of the two compounds in zebrafish, suggesting a carrier effect of mPVCs. In toxicity tests, the aged mPVC caused severer gut damages, stronger oxidative stresses, and greater interference with the gut microbiota in zebrafish than the pristine mPVC. The CPF and ERY-loaded mPVCs produced lower oxidative stresses in zebrafish than mPVCs alone, due to fewer radicals on mPVC surfaces after the adsorption of organic contaminants. Notably, the CPF and ERY-loaded mPVCs presented greater effects on fish swimming behaviors and gut microbial compositions, which was associated with the released CPF and ERY from mPVCs within the zebrafish. Overall, the present study demonstrated significant influences of UV-aging and the adsorbed pollutants on the toxicological effects of MPs and highlighted the necessity to perform toxicity studies of MPs using more environmentally relevant MPs.

Automated summary

In this study, the influence of UV aging on the adsorption of organic pollutants by mPVC and the toxicity variations among different types of mPVCs to zebrafish were investigated. UV irradiation significantly changed the physiochemical properties of mPVC, resulting in more oxygen-containing groups and free radicals on the surfaces. Aging reduced the adsorption of mPVC against a hydrophobic compound but enhanced the adsorption against a moderately hydrophilic compound. Ingestion of pollutant-loaded mPVCs led to bioaccumulation in zebrafish and caused severer gut damages and oxidative stresses. The study highlights the need for using environmentally relevant mPVCs in toxicity studies of MPs.