Microplastic pollution is of public concern for global environmental health, aquaculture, and fisheries. Toxicity studies have shown that microplastic ingestion may cause intestinal damage, microbiota dysbiosis, and disturb the lipid and energy metabolism in fish. To determine the impact of environmentally relevant, chronic, low dose microplastic fibers on fish health, medaka larvae, and juveniles were exposed to five concentrations of polyethylene (PE) fibers for 21 days through the feed. Fish growth and condition were assessed to determine the overall impact on fish health. To identify impaired energy intake, the gastrointestinal tract (GIT) integrity was evaluated at the molecular and cellular levels. Microbiota analysis was performed by comparing the top seven most abundant phyla present in both larval and juvenile fish exposed to 0, 1.5, and 3 PE fibers/fish/day. A shift in the phyla Proteobacteria and Bacteroidetes were observed. Larval samples demonstrated decreased proteobacteria abundance, while juvenile samples displayed an increase in abundance. Relative gene expression of key digestive genes from GIT tissue was quantified using real time-quantitative polymerase chain reaction. An effect on digestive gene expression potentially affecting nutrient absorption and antioxidant production was indicated via a significant decrease of solute carrier family 6 member 6 expression in larvae exposed to 6 fibers/fish/day. No significant molecular changes were observed in juvenile GIT tissue, although a non-monotonous dose-response was observed. GIT morphology was analyzed using histomorphological observations of the GIT mucus and cell types. No significant impairment of the GIT epithelial layers was observed in larvae or juveniles. To assess growth and condition, Fulton’s condition factor was measured. No differences were observed in larval or juvenile growth. Comparisons of different developmental stages allowed for identifying vulnerable developmental stages for microplastic exposure; larvae were more susceptible to molecular changes, while shifts in juvenile microbial communities were similar to changes reported post-polystyrene microplastic sphere exposure. This study is one of the first to provide toxicological data on the risk of PE fiber ingestion during fish development stages. Results indicate no imminent threat to fish condition at current measured environmental levels of microplastics; however, close monitoring of vital spawning grounds for commercially important fishes is recommended.

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Microplastic pollution has been recognized as a potential threat to environmental and human health. Recent studies have shown that microplastics reside in all ecosystems and contaminate human food/water sources. Microplastic exposure has been shown to result in adverse effects related to endocrine disruption; however, data are limited regarding how exposure to current environmental levels of microplastics during development may impact reproductive health. To determine the impact of environmentally relevant, chronic, low‐dose microplastic fibers on fish reproductive health, juvenile Japanese medaka were exposed to five concentrations of polyethylene fibers for 21 days, and reproductive maturity was examined to assess the later life consequences. Fecundity, fertility, and hatching rate were evaluated to determine the organismal level impacts. Gonadal tissue integrity and stage were assessed to provide insights into potential tissue level changes. Expression of key reproductive genes in male and female gonads provided a molecular level assessment. A significant delay in hatching was observed, indicating cross‐generational and organismal level impacts. A significant decrease in 11‐beta‐dehydrogenase isozyme 2 (HSD11 β2) gene expression in male medaka indicated adverse effects at the molecular level. A decrease in male expression of HSD11 β2 could have an impact on sperm quality because this enzyme is crucial for conversion of testosterone into the androgen 11‐ketotestosterone. Our study is one of the first to demonstrate subtle impacts of virgin microplastic exposure during development on later life reproductive health. The results suggest a possible risk of polyethylene fiber exposure for wild fish during reproductive development, and populations should be monitored closely, specifically in spawning and nursery regions. Environ Toxicol Chem 2022;41:2848–2858. © 2022 SETAC

Over the years, an increase in mass plastic production has caused growing concerns about the adverse effects that plastic nanoparticles (NPs) in the environment may have on human health. There are many knowledge gaps regarding the effects that NPs have on human health. Accurate studies prove challenging due to the hurdles in obtaining reliable model particles, performing accurate in vitro toxicology assessments, and visualizing results accurately. Numerous studies published in peer-reviewed literature have used commercially available NPs to represent environmental nanoplastic pollution. The commercial NPs with fluorescent tags were often used since they are easy to be monitored in cellular and organismal studies. However, the legitimacy of these commercial NP products has been questioned due to concerns about surface modifications altering interactions at the nano-bio interfaces, and the possibility that surface-bound fluorophores may detach and result in optical artifacts. Additionally, polystyrene is not the only polymer that should be investigated. We synthesized an orange, fluorescent organic dye and incorporated the dye into PMMA NPs to investigate skin cell uptake and in vivo biodistribution in a fish embryo model. We also compare the uptake results with that of the commonly used polystyrene particles and discuss possible mechanisms of uptake. Results revealed that 1) PMMA NPs can pass into embryos and potentially accumulate in larval bodies, and 2) commercially available sulfate-modified NPs and PMMA NPs accumulate similarly in fluorescently labeled fibroblast cells, however, PMMA NPs accumulate more localized intracellularly.