Gas-exchange chamber analysis of elemental mercury deposition/emission to alluvium, ore, and mine tailings

Deposition of mercury (Hg) from the atmosphere is an important source of this contaminant to terrestrial ecosystems. Once deposited, all forms of Hg can be retained or emitted back to the atmosphere. Distinguishing between volatilization of geogenic or indigenous Hg and that deposited from the atmosphere is difficult. Field flux measurements in the general area of two industrial scale gold mining operations, showed local deposition of Hg emitted from point and nonpoint sources, and subsequent re-emission. The work presented in this paper investigated deposition/emission of elemental Hg to and from alluvium and two mine materials before, during, and after exposure to high air concentrations, for both wet and dry conditions, using a laboratory gas exchange chamber and a Hg permeation source. In general, results showed a range in mean elemental Hg deposition velocities ranging from 0.13 to 0.46cms^-1 that varied with material. A significant influence of atmospheric ozone (O₃) on flux was observed that depended on the material and whether wet or dry. A synergistic relationship existed between O₃ and light promoting Hg flux, and flux was also influenced by material grain size, chemistry, and primary mineralogy.