Establishing baselines for metal and metalloid accumulation in black (Ursus americanus) and grizzly bears (Ursus arctos horribilis) in Montana.

Metal(loid) contamination remains a concern for wildlife inhabiting landscapes influenced by legacy and ongoing mining. Blood (n = 24) and hair (n = 27) samples were collected from black bears (Ursus americanus) and grizzly bears (Ursus arctos horribilis) in Montana's Cabinet-Yaak Ecosystem (CYE), with a preliminary comparison using hair from two grizzly bears in the Northern Continental Divide Ecosystem (NCDE). Analyses focused on 10 target metal(loid)s (As, Cd, Cu, Hg, Mn, Pb, Rb, Se, U, and Zn), although U was below the detection limit in blood. Most concentrations were within published reference ranges, although some individual As, Cd, and Pb measurements exceeded screening or effect-associated values derived from other species; the toxicological relevance of these comparisons for bears remains uncertain. Cu, Hg, Se, and Zn concentrations were generally within published reference ranges, whereas Mn was highly variable, potentially reflecting geologic or anthropogenic influences. Multivariate blood and hair element profiles differed between black and grizzly bears, although within-species variability produced partial overlap. Rb and U concentrations also exhibited species-associated patterns, but their ecological basis could not be determined because diet and habitat use were not measured directly. Blood-hair associations were weak for most metal(loid)s, consistent with differences in temporal integration and element-specific incorporation and turnover between matrices. Compared with published data from other bear populations, CYE bears exhibited relatively high As, Mn, and Pb concentrations, potentially reflecting regional geochemistry or land use, although specific exposure sources were not identified. Hair concentrations in the two NCDE grizzly bears were generally comparable to those in CYE bears, except that Cu concentrations were higher; however, these comparisons are preliminary given the limited NCDE sample size. These findings establish baseline metal(loid) concentrations for CYE bears and identify priorities for targeted monitoring of spatial patterns, potential sources, and biological significance.