Barrier function of zebrafish embryonic chorions against microplastics and nanoplastics and its impact on embryo development

Embryonic stage is important for the development of aquatic animals, and embryonic chorion is an efficient barrier against exogenous pollutants. The efficient barrier function of zebrafish (Danio rerio) embryonic chorions against micro- and nano- polystyrene (PS) particles was observed. Embryonic chorions presented high affinity to PS particles. The covering layer of PS particles on the outer surface of chorions affected the patency of pores in chorions, and the nano- PS particles exerted a considerable effect. The accelerated heart rate and blood flow velocity in the embryos indicated that the PS particles adhering to embryonic chorions might cause an internal hypoxic microenvironment in the embryos. The coating of PS particles on embryonic chorions also resulted in delayed hatching of the embryos. The observed development toxicity induced by the nano- and micro-PS particles was confirmed via the expressions of metabolic pathways related to antioxidant system. The pathways of biosynthesis of unsaturated fatty acid, linoleic acid metabolism and alanine, and aspartate and glutamate metabolism extensively altered when the embryos were exposed to PS particles, especially to the nano-PS particles. Although micro- and nano- plastic particles can be efficiently blocked by embryonic chorions, they can still affect the early development of aquatic organisms.