The ubiquitous presence of microplastics (MPs) in aquatic ecosystems is a growing concern. The ability to adsorb a variety of pollutants on its surface, including heavy metals, accentuates the magnitude of its impacts. The widespread contamination by MPs highlights the need to investigate the toxicological interactions of these polymers with heavy metals. Besides, there is still a gap in knowledge regarding the toxic effects of this mixture on microbiological interactions. This study intended to evaluate the combined effects of MPs and copper on the intestinal microbiota. Polyethylene (PE) and polystyrene (PS) MPs were selected because of their extensive use and high accumulation in aquatic environments. For this, zebrafish (Danio rerio) were exposed for 21 days, to copper (Cu-25 μg/L), microplastics (PE and PS, 1mg/L), and the respective mixtures (PE-Cu and PS-Cu), to evaluate their effect on the intestinal wall ultrastructure and the intestinal microbiota. The histopathological evaluation revealed changes, including necrosis, degeneration of intestinal folds, edema, infiltration of inflammatory cells, and goblet cells hyperplasia. Considering the intestinal microbiota, P. shigelloides was the microorganism present in the highest percentage (47%) and a multidrug resistance profile was observed in 67.6% of the isolated microorganisms. The highest resistance rates were observed in response to β lactam antibiotics, aminoglycosides, and tetracyclines. This work has provided valuable insights into the intricate interaction between MPs and copper in the induction of histological changes, and antibiotic susceptibility.

This work is supported by National Funds by FCT - Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020.