Ena Oster, University of Zagreb, Faculty of Veterinary Medicine

Mercury (Hg) is a globally distributed contaminant that accumulates in wildlife tissues and can cause nephrotoxic, haematotoxic, neurotoxic, and negative reproductive effects even at low levels. From a practical perspective, hair sampling represents one of the most suitable methods for monitoring metal(loid) exposure in animals due to its accessibility and potential for non-invasive collection. The aim of this study was to examine the relationship between Hg concentrations in hair and kidney tissue in brown bears (Ursus arctos). Total Hg concentrations were determined in cut hair and kidney cortex samples from free-ranging brown bears (N = 79) from the Dinara-Pindos population, hunted or traffic-killed in Croatia between 2009 and 2022. Mercury concentrations in kidneys ranged from 0.191 to 9.20 mg/kg dry weight (mean ± SD: 1.56 ± 1.83 mg/kg; median: 0.968 mg/kg), while hair Hg concentrations ranged from 0.023 to 1.11 mg/kg dry weight (mean ± SD: 0.244 ± 0.177 mg/kg; median: 0.191 mg/kg). A positive correlation was found between Hg concentrations in hair and kidneys (r = 0.636, p < 0.001). Linear regression analysis further supported a significant linear association between the two matrices (adjusted R2 = 0.396, F(1,77) = 52.238, p < 0.001). Although hair and kidney tissues reflect Hg exposure over different temporal scales, the observed relationship indicates that hair Hg concentrations can provide information on relative differences in renal Hg exposure at the population level. These findings highlight the utility of hair as a practical, ethical, and non-invasive approach for evaluating mercury exposure in free-ranging brown bears.