Effects of leachates from black recycled polyethylene plastics on mRNA expression of genes involved in adipogenesis and endocrine pathways in zebrafish embryos

Black recycled polyethylene pellets were collected from India, Nigeria and Taiwan. These pellet samples were used to create water leachates (in zebrafish medium at 10 and 30 g/L for 24 or 48 h), which were then used to expose zebrafish embryos (up to 120 h post fertilization), followed by fish embryo toxicity (FET) tests, mRNA analyses and larval swimming behavior assessments. The leachates were analyzed for chemicals using Liquid Chromatography-Mass Spectrometry techniques. Zebrafish experiments revealed upregulation in mRNA expression in genes associated with endocrine regulation including thyroid hormone systems as well as adipogenesis and lipid metabolism. FET and behavior tests did not show significant impacts. Chemical analyses identified 84 different substances in the leachates, including plastics additives as well as other non-intentionally added substances such as pesticides and pharmaceuticals. These findings have implications for the use of recycled plastics, especially in products where they may come into contact with humans or other organisms, exposing individuals or the environment to harmful chemical mixtures with potentially adverse health effects. The complex mixture of chemicals in these recycled plastics highlights the need for improved transparency and traceability across the plastics lifecycle, and the importance of limiting use of hazardous chemicals in plastics.