Elevated mercury wet deposition in the biodiversity hotspot of southwestern China.

The West China Rain Zone (WCRZ), one of worldwide biodiversity hotspots, is vulnerable to pollutant exposure. Mercury (Hg), as a global toxic pollutant, could enter into this ecosystem by wet and dry deposition, potentially posing ecological risks. Therefore, it is essential to investigate the patterns, controlling factors, and source contributions of Hg deposition in this region. This study presents a three-year comprehensive analysis of atmospheric Hg wet deposition at Mt. Emei of this biodiversity hotspot region. Results revealed the elevated Hg concentrations with volume-weighted mean concentration (VWMC) of 15.6 ± 9.8 ng L and deposition fluxes of 47.8 ± 4.3 μg m in the WCRZ. The wet deposition flux was twice the magnitude of dry deposition flux in this region. This value exceeded the deposition levels observed in many other regions globally, with WCRZ deposition levels being 1.1-15.6 times that of other biodiversity hotspots worldwide. Source apportionment analysis revealed that Hg in wet deposition predominantly originated from local anthropogenic sources. The transboundary Hg of anthropogenic sources in South Asia contributed to ∼20% of Hg source contribution during winter periods. Finally, we suggest the elevated Hg wet deposition inducing a potentially ecological risk to wildlife in this biodiversity hotspot regions of Southwest China.