Exposure to ionizing radiation and liver histopathology in the tree frogs of Chornobyl (Ukraine)

Abstract

Ionizing radiation has the potential to damage organic molecules and decrease the health and survival of wildlife. The accident at the Chornobyl Nuclear Plant (Ukraine, 1986) led to the largest release of radioactive material to the environment. Among the different organs of a vertebrate, the liver plays a crucial role in detoxification processes, and has been used as a biomarker to investigate cellular damage in ecotoxicological research. Here, we examined the impact of the exposure to the current levels of ionizing radiation present in the Chornobyl Exclusion Zone on the liver of Eastern tree frogs (Hyla orientalis). We quantified the area of melanomacrophage cells and morphological variables of hepatocytes, two cell types often used to estimate damage caused by pollutants in vertebrates. First, we investigated whether these hepatic parameters were indicative of frog (individual) condition. Then, we analyzed the effect of individual absorbed dose rates and ambient radiation levels on frog livers. Most of the studied parameters were correlated with individual body condition (a good predictor of amphibian fitness and survival). We did not detect marked morphological lesions in the liver of frogs captured in medium-high radiation environments. The area occupied by melanomacrophages and the morphology of hepatocytes did not change across a gradient of radiocontamination covering two orders of magnitude. Once accounting for body condition and sampling locality, the area of melanomacrophages was lower in areas with high radiation levels. Finally, the area occupied by melanomacrophages was not linked to dorsal skin coloration. Our results indicate that current levels of radiation experienced by tree frogs in Chornobyl do not cause histopathological damage in their liver. These results agree with previous physiological work in the species in the Chornobyl area, and encourage further molecular and physiological research to fully disentangle the current impact of the Chornobyl accident on wildlife.

Keywords: Amphibians; Ecotoxicity; Hepatic melanomacrophages; Hepatological biomarkers; Histopathology; Radioactivity.