Mercury contamination in the European green toad Bufotes viridis in Vienna, Austria.

Mercury (Hg) contamination affects all ecosystems worldwide. Its deleterious effects on wildlife and humans encompass a diversity of impacts from individual to population levels. In the present study, we quantified Hg concentration across various tissues (blood, brain, muscle, and toe) of green toads (Bufotes viridis) and investigated the use of toe clips as a proxy of Hg concentration in internal tissues, including the brain. Our results show distinct patterns of Hg contamination across tissues, with the highest Hg concentration in the blood with 1.496 ± 0.772 µg.g^-1 dry weight (dw), followed by muscle tissue with 0.687 ± 0.376 µg.g^-1 dw, brain tissue with 0.542 ± 0.319 µg.g^-1 dw, and toes with 0.229 ± 0.143 µg.g^-1 dw. A strong relationship has been found between toe and brain Hg concentrations (R² = 0.857, p < 0.001). These results emphasize the potential of toe clipping as a reliable, non-lethal method for predicting brain Hg concentrations in the green toad. Further, results open the possibility of assessing the potential association between Hg contamination and the cognitive performance of amphibians.