Environ. Sci. Technol. 2004, 38, 1977-1983
Atmospheric Mercury Emissions and Speciation at the Sulphur Bank Mercury Mine Superfund Site, Northern California DAVID M. NACHT,† M A E S E X A U E R G U S T I N , * ,† M A R K A . E N G L E , †,‡ RICHARD E. ZEHNER,† AND ANTHONY D. GIGLINI† Department of Environmental and Resource Sciences, MS 370, University of Nevada, Reno, Nevada 89557, and Tetra Tech EM Inc., 1325 Automotive Way, Suite 200, Reno, Nevada 89502
One pathway for release of mercury (Hg) from naturally enriched sites is emission to the atmosphere. Elemental Hg, when emitted, will enter the global atmospheric pool. In contrast, if reactive gaseous Hg or Hg2+ (as HgCl2, HgBr2, or HgOH2) is formed, it will most likely be deposited locally. This study focused on the measurement of elemental Hg flux and reactive gaseous Hg concentrations at the Sulphur Bank Superfund Site, an area of natural Hg enrichment with anthropogenic disturbance and ongoing geothermal activity. Mean Hg emissions ranged from 14 to 11000 ng m-2 h-1, with the highest emissions from anthropogenically disturbed materials. Reactive gaseous Hg concentrations were the highest ever reported for a natural setting (0.376 ng m-3). Measured Hg fluxes were used within a Geographic Information System to estimate mercury releases to the atmosphere from the site. Results indicated ∼17 kg of Hg y-1 of is emitted to the atmosphere from the 3.8 km2 area, with half from mine waste, ore, and tailing piles and half from relatively undisturbed naturally enriched substrate.
Introduction Mercury (Hg) is emitted to the atmosphere from anthropogenic and natural, point and nonpoint sources (1-4). Anthropogenic sources include utility boilers, metal refineries, mining activities, and waste incinerators (1, 4, 5). Natural source emissions occur from geothermal vents, volcanoes, and naturally enriched substrates (3, 6). Pirrone et al. (7) recently suggested that, on a global scale, natural and anthropogenic emissions each contributed one-third to the atmosphere while re-emission or recycling of previously deposited Hg contributed the last third. Earlier studies suggested that anthropogenic emissions were significantly greater than natural emissions and applied a flux of ∼1.1 ng of Hg m-2 h-1 to naturally enriched areas (1, 8). However, recent work indicates that this value may underestimate Hg emissions from global Hg belts (9-13). The impact of natural source emissions will depend on the amount of Hg released and the speciation of emissions. Gaseous elemental Hg (Hg°) will enter the atmospheric pool * Corresponding author phone: (775) 784-4203; fax: (775) 7844789; e-mail:
[email protected]. † University of Nevada. ‡ Tetra Tech EM Inc. 10.1021/es0304244 CCC: $27.50 Published on Web 02/20/2004
2004 American Chemical Society
and be globally distributed. Reactive gaseous mercury (RGM) species, or Hg2+ as compounds such as HgCl2 and HgBr2, are at least 105 times more water soluble and much more chemically reactive than Hg°, and exhibit high dry deposition velocities (1-5 cm s-1) (4, 17). This form is more likely to be deposited to local and regional ecosystems. Natural sources emit primarily Hg° to the atmosphere (14); however, no data have been published regarding the presence of RGM at naturally enriched sites. Recent research has demonstrated that a small component (
