Mercury exposure and potential hazards through vegetation intake to large herbivores along an elevational gradient in the Central Himalayas.

Vegetation in mountains offers specific habitats for endemic wildlife while serving as a sink for long-range transported pollutants such as mercury (Hg). Over half of the atmospheric Hg is absorbed by vegetation, making it a major pathway for Hg transfer into terrestrial ecosystems. As one of the world's 22 biodiversity hotspots and situated between the major Hg emitters in Asia, the Himalayas host numerous endemic and endangered species, including large herbivores that play vital ecological roles. We investigated total Hg (THg) in vegetation across five vegetation zones along the longest elevational gradient (1800 ∼ 5400 m) in the Central Himalayas. Mean vegetation THg was 20.2 ± 10.7 ng g-1 (6.0 ∼ 62.9 ng g-1, 60 sampling sites). Overall, vegetation THg decreased significantly with elevation (y = (-0.004 ± 0.001) x + (33.5 ± 4.8), R2 = 0.13, p = 0.005), with soil THg explaining the variation most. We found 6 herbivore species inhabiting evergreen broad-leaved forest and 10 species inhabiting subalpine coniferous forest, could be facing potential Hg exposure risk in those vegetation zones. When we combine this with captive daily intake estimation of vegetation, we identified endangered high-altitude species, such as Himalayan tahr (Hemitragus jemlahicus) and kiang (Equus kiang), which could be more at Hg exposure risk under climate change due to potential habitat shrinkage. Our findings highlight that, in addition to predators, large herbivores may also face elevated Hg exposure risk due to their substantial consumption of vegetation, which is important when evaluating the Minamata Convention's effectiveness.