Chronic Exposure to Heavy Metals Induces Nuclear Abnormalities and Micronuclei in Erythrocytes of the Marsh Frog (Pelophylax ridibundus Pallas, 1771)

Amphibians have big potential as bioindicators based on their combined life cycle as aquatic and terrestrial form. They can play the role of prey or predator, making them a key element in toxic substances transfer between aquatic and terrestrial habitats. The nuclear abnormalities (NAs) in amphibians' erythrocytes in recent years have been used as a successful biomarker for anthropogenic pollution. The NAs including micronuclei in erythrocytes of the marsh frog (P. ridibundus) have been studied to assess the cytotoxic and genotoxic effect in heavy metal polluted area in situ. Here we assess the cyto- and genotoxic potential of the polluted waters (Chaya River) close to the lead-zinc smelter near Plovdiv (Bulgaria) situated in an area that has been contaminated with heavy metals for 60 years. Frogs from Strandzha Natural Park were used as a negative control. Peripheral blood smears have been dyed with acridine orange. NAs of the following types: notched nuclei, nuclear buds and blebbed nuclei have shown the highest frequency. There is no sexual dependence in the formation of different types of NAs. The significant differences (P≤0.0001) in the mean Total NAs (‰) in erythrocytes of marsh frogs from the polluted area compared to the total NAs from the background region “Strandzha” NP demonstrate the presence of in vivo active cytotoxic and genotoxic agents in the impacted area. The obtained results for NAs in erythrocytes of P. ridibundus are evidence for successful application of NAs as a biomarker in amphibians for the purpose of biomonitoring.