Accumulation of mercury and selenium in the brain of river otter (Lutra canadensis) and mink (Mustela vison) from Nova Scotia, Canada

Concentrations of mercury (total and methylated) and selenium were quantified in the brains of river otter and mink from southwestern Nova Scotia, where mercury concentrations in biota are known to be high. Otters from interior areas (5.2 +/- 3.9 mug/g brain d.w.) of Nova Scotia had significantly more total mercury in the brain than otters inhabiting coastal areas (2.6 +/- 2.9 mug/g brain d.w.) of the province. A significant positive relationship was observed between total mercury and selenium in brain of inland (linear regression: n = 16; r2 = 0.804; p < 0.001; Se = 1.000 THg) and coastal (linear regression: n = 10; r2 = 0.581; p = 0.010; Se = 0.900 THg) otters containing total mercury concentrations greater than 3.6 mug/g. No relationship was observed between the two elements in brain of inland or coastal mink. Inland (paired t-test: t = 8.802; df = 23; p < 0.001) and coastal (paired t-test: t = 7.533; df = 37; p < 0.001) otters were found to contain a significant amount of mercury in the brain in the inorganic form, indicating that demethylation of methylmercury is occurring in this organ in these animals. Inland and coastal otters contained approximately 18.3 +/- 10.3% and 17.5 +/- 13.4% inorganic mercury in the brain, respectively. Concentrations of total mercury and methylmercury in mink brain were not significantly different, indicating that mink do not demethylate methylmercury in the brain. If the co-accumulation of selenium with mercury in the brain or the demethylation of methylmercury in the brain represent detoxification mechanisms, then this study indicates mink may be more susceptible to mercury poisoning than otters.