Nuclear abnormalities and DNA damage indicate different genotoxic stress responses of marsh frogs (Pelophylax ridibundus, Pallas 1771) to industrial and agricultural water pollution in South Bulgaria

Amphibians are continuously exposed to pollutants and anthropogenic stressors in their natural habitats, representing a significant challenge to their survival. This study aimed to quantify the extent of DNA damage caused by chronic industrial and agrochemical surface water pollution in wild populations of the marsh frog (Pelophylax ridibundus). The observed genotoxic effects on the marsh frog DNA, manifesting as abnormalities in erythrocyte nuclei, micronuclei, and DNA strand breaks, demonstrate a clear cause-and-effect relationship with surface water parameters, heavy metals, metalloids, and pesticides. The most prevalent nuclear abnormalities observed were notched and blebbed nuclei and nuclear buds, indicative of chromosomal instability. The significant correlation between cadmium, lead, and copper contamination and the increased frequency of DNA breakage in the marsh frogs from the industrial site indicates that heavy metal contamination has a higher genotoxic potential than pesticide contamination. These findings underscore the vulnerability of amphibians inhabiting heavy metal-contaminated wetlands to genotoxic stress due to their lower tolerance to environmental genotoxins. Therefore, using in situ assays to detect erythrocyte nuclear abnormalities and DNA damage in P. ridibundus could serve as a reliable indicator of environmental quality and provide early detection of anthropogenic pollution.