Assessing the Effect of Polyethylene Microplastics in the Freshwater Leech (Annelida, Hirudinida) Through Integrated Biomarkers and Histopathological Analysis.

Microplastics (MPs) are contaminants of emerging concern, and the study of their effects on several species, especially freshwater organisms, has not been exhausted. , a freshwater leech, was used as a model in this study for the assessment of the potentially toxic effects of polyethylene microplastics (PE-MPs) 40-48 µm in size under controlled laboratory conditions. PE-MP toxicity was assessed in the examined leech using four increasing concentrations (1, 10, 100, and 1000 µg/L) during an exposure period of 7 days. Oxidative damage was detected through the increase in malondialdehyde (MDA) levels, reflecting the occurrence of lipid peroxidation. The activities of enzymes involved in the antioxidant response, such as catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx), increased. Furthermore, the histopathology of the body wall, muscle cells, botryoidal cells, and ovaries was assessed to understand and evaluate the acute toxicity of PE-MPs. The histopathological changes detected in PE-MP-treated leeches varied in a concentration-dependent manner. Overall, this research indicated that even at environmentally relevant concentrations, PE-MPs had biological effects on the studied leeches and, consequently, on the freshwater invertebrate clade. This finding could provide novel insights into the effects of plastic pollution on freshwater ecosystems, particularly on invertebrate health and biodiversity.