Physiological, Biochemical, and Histopathological Alterations in Bufo Regularis Tadpoles Co-Exposed to Polyethylene Nanoplastics and Doxycycline

Amphibian larvae, due to their aquatic developmental stages, are particularly vulnerable to freshwater contaminants. Among emerging threats are polystyrene and polyethylene nanoplastics, alongside pharmaceutical pollutants such as the antibiotic doxycycline (DOX). This study investigates the individual and combined toxicological effects of polyethylene nanoplastics (PE-NPs) and DOX on tadpoles. We hypothesized that co-exposure would exacerbate adverse effects across multiple biological levels. Tadpoles were exposed for seven days to 10 mg/L PE-NPs, 40 mg/L DOX, and a combination of both. A comprehensive assessment was conducted to evaluate physiological, histopathological, and biochemical impacts. Tissues (liver, cardiac muscle, spinal cord) were examined for morphological and histopathological alterations, while a suite of biomarkers was analyzed to determine oxidative stress and neurotoxicity. Exposed tadpoles exhibited significant morphological abnormalities in blood cells, including the appearance of acanthocytes, schistocytes, and elliptocytes. Histopathological analysis revealed inflammation and degenerative necrosis in the liver, as well as degenerative changes in cardiac muscle bundles and spinal cord tissue. Biochemically, exposure to PE-NPs and DOX, both individually and in combination, induced a pronounced oxidative stress response. This was characterized by increased activity of the antioxidant enzymes catalase and superoxide dismutase, an increase in glutathione content, and elevated malondialdehyde levels, indicating lipid peroxidation. These findings demonstrate that PE-NPs and DOX, at environmentally relevant concentrations, can induce significant pathophysiological stress in amphibian larvae. The results underscore the potential ecological risk posed by the interaction of nano-plastics and antibiotics in freshwater ecosystems, highlighting a threat to amphibian health.