Small mammals as a bioindicator of mercury in a biodiversity hotspot - The Hengduan Mountains, China

Due to toxicities, capacities for long-range transportation, bioaccumulation, and biomagnification, mercury (Hg) presents a unique concern to wildlife in remote ecosystems, including "the roof of the world". Large carnivorous predators are thought to be exposed to elevated Hg due to their high trophic positions, but the direct assessment for Hg contamination is a challenge. Given the poorly understood Hg exposure in these carnivores, establishing a reliable and straightforward assessment would be essential to identify targeted species at Hg exposure risk for effective conservation, particularly in fragile biodiversity hotspots. Small mammals are abundant and serve as prey for large top predators. Combined with local observations, we provided an assessment to estimate the daily Hg exposure via consumption of small mammals for large carnivorous mammals recorded in the Hengduan Mountains, a world biodiversity hotspot, China. Within an altitude span from 2043 to 4251 m a.s.l., the average topsoil total mercury concentration (hereafter [THg]) was 44.65 +/- 25.80 mu g/kg (mean +/- sd; 10.54 - 135.15 mu g/ kg, n = 41), while the hair [THg] in small mammals was 104.66 +/- 91.96 mu g/kg (mean +/- sd; 7.73 to 385.70 mu g/ kg, n = 13). Furthermore, the daily intake of Hg was calculated among the 22 investigated/historical-recorded carnivore mammals belonging to 5 families. We found a large variance in daily intake of Hg via small mammals: Felidae (median: 205.93 mu g/day) > Ursidae (135.02 mu g/day) > Canidae (92.92 mu g/day) > Viverridae (19.88 mu g/ day) > Mustelidae (7.18 mu g/day). Specifically, Tiger Panthera tigris was found with the highest Hg daily intake (1701.39 mu g/day) via consuming small mammals, while species belonging to Mustelidae generally have low Hg daily intake (<3 mu g/day). This study provides a feasible approach to identifying species at environmental Hg risk in this fragile remote high-elevation region. The limitations and future improvements were discussed.