Co-sampled fruticose and foliose epiphytic lichens as spatial biomonitors of airborne mercury and arsenic in a historical "Gold Rush" mining district

Historical gold mine tailings may have elevated total mercury (THg) and
total arsenic (TAs) concentrations. We collected and analyzed the
fruticose lichen genus Usnea and the foliose lichen genus Platismatia for
biomonitoring airborne sources of Hg and As at the historical Montague
Gold Mine District in Nova Scotia, Canada. We investigated spatial trends
of Hg and As measured from 112 Usnea (10 species) and 113 Platismatia (2
species) lichen thalli collected across four sampling grids covering both
tailings and non-tailings areas. Usnea consistently had higher THg
concentrations, while Platismatia showed higher TAs concentrations. Areas
where there was evidence of known past mining activities (i.e. mine
shafts, stamp mills, Hg-amalgamation sites) were found to be hotspots for
both Hg and As in the lichen samples collected nearby. These areas likely
received greater inputs of these elements from windblown tailings or
volatilization processes, or indirectly from the interception of these
elements by the forest edge/canopy adjacent to the tailings. A
tailing-contaminated wetland at Montague was also identified as a hotspot
for Hg, likely facilitating its redistribution into the atmosphere.
Co-sampling of a fruticose and a foliose lichen can be an effective method
for airborne monitoring of contaminants around historical mine tailing
sites.