Toxicological Impact of Polyethylene Terephthalate ( <scp>PET</scp> ) Microfragments and Microfibers on the Gut of Zebrafish ( <scp> <i>Danio rerio</i> </scp> , Hamilton, 1822): Insights Into Gastrointestinal Health

Plastic has been recognized as a major toxicological problem, but the recent detection of microplastics (MPs) in human fluids and tissues has raised global concern. MPs, mainly fibers and fragments, have been found in oceans, rivers, and lakes. Due to their small size (< 5 mm), aquatic organisms can accidentally ingest them and may ultimately reach humans through the food chain. This study assessed the gut response of Danio rerio exposed to different concentrations and shapes-microfibers (M.Fb.) and microfragments (M.Fg.)-polyethylene terephthalate (PET) MPs via feeding. Adult fish (n = 114) were exposed to 30 MPs for 24 h (acute toxicity) and to 1 or 6 MPs per feed per day for 15 and 30 days (chronic toxicity). The acute test revealed longer gut retention time for M.Fb. than M.Fg. Chronic exposure led to the detection of M.Fg. in gut sections. Histopathological analysis showed coalescence of villi, epithelial detachment, epithelial degeneration, muscle layer displacement, dysplasia, hypertrophy, hyperplasia, and necrosis, particularly at 6 MPs per feed. The histopathological alteration index (HAI) indicated greater damage with higher MP exposure, especially from M.Fb. Overall, these results suggest that in addition to concentration, the shape of the MPs also influences their impact on fish gut health, with M.Fb. exhibiting more severe effects of M.Fg.on the gut.