Osmium tetroxide (OsO 4 ) is one of the most toxic air contaminants but its environmental effects are poorly understood. Here, for the first time, we present evidence of osmium uptake in a common herbivore (bank vole, Myodes glareolus) in boreal forests of northern Sweden. Voles (n=22) and fruticose arboreal pendular lichens, the potential main winter food source of the vole, were collected along a spatial gradient to the west of a steelwork in Tornio, Finland at the Finnish-Swedish border. 187 Os/ 188 Os isotope ratios increased and osmium concentrations decreased in lichens and voles along the gradient. Osmium concentrations in lichens were 10,000-fold higher than those in voles. Closest to the steelwork, concentrations were highest in kidneys rather than skin/fur that are directly exposed to airborne OsO 4 . The kidney-to-body weight ratio was higher at the two localities close to the steelwork. Even though based on a small sample size, our results for the first time demonstrate that osmium is taken up, partitioned, and accumulated in mammal tissue, and indicate that high kidney-to-body weight ratios might be induced by anthropogenic osmium.