Co-exposure to different sized polystyrene microplastics and benzo[a]pyrene affected inflammation in zebrafish andbronchial-associated cells

In recent years, emerging research has revealed that microplastics (MPs) can pollute the air. Cellulose and plastic fibers have been found in the lungs of patients with lung cancer, indicating that MPs can “travel” through the atmosphere into the respiratory tract. Due to the hydrophobicity and relatively large surface area of MPs, the biotoxicity of MPs is greatly enhanced by their adsorption and enrichment in persistent organic pollutants (POPs). With the rapid development of the economy, emissions from coal burning and automobile exhaust have made polycyclic aromatic hydrocarbon (PAHs) one of the key pollutants in urban air that cannot be ignored. Epidemiological studies have shown that PAH exposure is associated with the development of respiratory diseases, such as bronchitis and asthma, in children. The aim of this study was to investigate the inflammatory effects of co-exposure to different size polystyrene MPs (PS-MPs) and benzo[a]pyrene (BaP) on adult zebrafish gills and bronchial-related cells to provide basic information for assessment of the potential health risks of combined exposure to the human respiratory system. PS-MPs (with size of 0.5 and 5 μm) and BaP were co-administered to embryos for 7 d, adult zebrafish for 14 d, and HBE cells and HBMSCs for 48 h. The relative expression levels of inflammatory cytokine genes in the different exposure groups were determined by real-time polymerase chain reaction (PCR). The ingestion of microplastics into fish bodies and cells was observed by stereoscope and confocal microscopy, respectively. Result shows that microplastics of two sizes could be ingested by zebrafish embryos. When exposed only to 0.5-μm PS-MPs, relative expression of the TNF-α, IL-6, and IL-8 genes was significantly increased compared with that in the control; relative expression of the IFN-γ gene was largely increased in the gills of zebrafish in 5-μm PS-MP-exposed group. Moreover, relative expression of the IFN-γ, IL-6 and IL-8 genes in the group co-exposed to BaP and 0.5-μm PS-MPs was higher than that in BaP group. In addition, 0.5-μm PS-MPs could be ingested by both cell lines. Upon exposure to 0.5-μm PS-MPs alone, relative expression of genes TNF-α, IL-6, and IL-8 was considerably increased compared with that in the control HBE cells. In HBSMCs, upon exposure to 0.5-μm PS-MPs alone, relative expression of the TNF-α, IL-8, and IL-1β genes was substantially increased compared with that in the control group. Compared with that following exposure to BaP alone, relative expression of the IFN-γ and IL-6 genes in HBSMCs in 0.5-μm PS-MPs and BaP co-exposure group was remarkably increased, indicating a possible combined effect; however, co-exposure of 5-μm PS-MPs and BaP weakened the proinflammatory function of BaP and especially influenced relative expression of the TNF-α and IL-8 genes. In addition, none of the co-exposure groups of HBE cells showed obvious combined effects. The corollary is that particle size may affect the ingestion of PS-MPs in cells. In addition, the size-dependent effects of PS-MPs influence the accumulation of organic pollutants and their biotoxicity.