Spatial Distribution and Patterns of Airborne Mercury using Epiphytic Lichens at a Historical Gold Mine Tailings Site in Nova Scotia, Canada.

Abstract:

Mercury (Hg) contaminated gold mining waste (tailings) in Nova Scotia, Canada poses a significant risk to public and ecosystem health. Between the 1860s and 1940s, over 360 gold mines in 64 formal gold districts in Nova Scotia generated approximately three million tonnes of tailings that were released directly into terrestrial and aquatic environments near mining communities. The tailings have elevated Hg concentrations due to losses from the Hg amalgamation process that was used in extracting gold from the ore. Many of these mines were abandoned and unremediated since the 1940s, leaving a legacy of environmental contamination. Consequently, many tailings sites are largely unvegetated today, creating the potential for windblown dust. Studies to date have investigated dust chemical speciation and Hg fluxes at the sites, but no work has been done to quantify wind-borne dust and air contamination around the sites. Lichens are widely used in biomonitoring spatial patterns of dust and air quality at contaminated sites due to their ability to accumulate airborne contaminants almost entirely from wet and dry atmospheric deposition. In the summer of 2019, we sampled epiphytic lichens (Platismatia and Usnea spp.) over a series of gridded transects over both tailing and reference areas to determine the spatial distribution of airborne Hg surrounding a large gold mine tailings site near Dartmouth, Nova Scotia. Lichens were collected surrounding the Montague gold mine tailings site. The lichens were split into washed and unwashed subsets, and both analysed for Hg along with the rinse water from the washed lichen subset. Seasonal dust and elemental levels were also determined using passive air samplers and rain collectors along a stream-based transect through the main sampling grid. We will report the geographical distribution of Hg in lichen and their proximity to historical gold mining sites.