Distribution of environmental lead in brown bear body compartments

Lead (Pb) is a very stable inorganic environmental pollutant exchanged between blood, mineralized and soft tissue compartments upon absorption. Comprehensive distribution of Pb in the body of brown bears (Ursus arctos) has not been previously investigated. The need for such a study arose upon earlier reports suggesting that 1-5% of the bear population might be at risk of adverse effects caused by hepatic and renal Pb levels over threshold levels established for terrestrial mammals. Therefore, the aim of this study was to explore the bone as the principal deposition compartment and marker of long-term exposure to Pb, and soft tissues (heart, kidney, liver, lungs, muscle and spleen) that reflect recent exposure, but also endogenous Pb sources. Lead was quantified in tissues of 40 brown bears hunted in 2015 according to the Brown Bear Management Plan in Croatia. The highest Pb levels were found in the kidney cortex (median, 4398 µg/kg dry mass), followed by the femoral bone (2502-3980), liver (1761), lungs (303), spleen (209), heart (22.7) and muscle (11.1). Microdistribution inside the bone revealed higher Pb in the compact (3980 µg/kg) than trabecular bone (2502 µg/kg) at the same location (femoral metaphysis). Also, the Pb level differed depending on the location on the bone (epiphysis vs. metaphysis and metaphysis vs. diaphysis). Age was a significant factor in prediction of bone Pb, which was higher in adults compared to young animals. Unlike soft tissues, the femoral bone of brown bears was confirmed as a good biomarker of Pb, known for its accumulative nature.