Persistent Effects of Naturally Aged Polyethylene Terephthalate Microplastics on Physalaemus cuvieri Tadpoles: The Toxic Legacy Beyond Exposure

Abstract

The increasing presence of microplastics (MPs) in aquatic ecosystems has raised concerns, mainly due to their adverse effects on aquatic organisms such as amphibians. This study evaluated the effects of exposure to naturally-aged polyethylene terephthalate (PET) microplastics on Physalaemus cuvieri tadpoles to investigate particle retention and toxicological impacts after cessation of exposure. The MPs were characterized through scanning electron microscopy and Raman spectroscopy analysis, and the weathering action was confirmed. Furthermore, our results indicated a significant increase in the mortality of tadpoles exposed to PET-MPs and partial retention of MPs after depuration. A higher Redox Balance Index (involving ROS levels and SOD and CAT activity) observed in the PET-MPs group at the end of the depuration period reveals a greater redox imbalance in these tadpoles. On the other hand, exposure to MPs induced neurochemical dysfunctions, such as reduced dopamine levels and increased AChE/BChE ratio, which were evident even after the end of exposure. Furthermore, the increase in total protein levels was observed throughout the experiment only in the control group. Finally, multivariate analyses (PCA and discriminant analysis) confirmed the occurrence of a phenomenon called the “legacy effect,” showing a clear separation between groups in the distinct phases of the experiment. In addition, multivariate linear regression analysis revealed a significant influence of MPs on the response of the animals only at the end of the exposure period, suggesting that the response observed at the end of depuration was cumulative, reflecting the damage induced during exposure. Thus, it is concluded that exposure to naturally-aged PET-MPs generates cumulative toxic effects in P. cuvieri, even after removing the pollutant, reinforcing the need for mitigation strategies to minimize the prolonged impacts of MPs on aquatic ecosystems.