| Source | GAC-MAC-CSPG-CSSS Halifax 2005, building bridges - across science, through time, around the world: abstracts/AGC-AMC-SCGP-SCSS Halifax 2005, Jeter des ponts entre les disciplines scientifiques, les
époques, et unifier le monde : recueil des résumés; GAC-MAC-CSPG-CSSS Joint Meeting, Abstracts vol. 30, 2005 p. 148 |
| Abstract | Historical stamp milling and mercury amalgamation activities at lode gold mines in southern Nova Scotia have generated tailings deposits containing Hg, As, and other potentially toxic elements. From
1861 to the mid-1940s, gold was produced from 64 mining districts in the southern part of the province. Most of the gold was recovered using mercury amalgamation, and an estimated 10-25% of the Hg used was lost to the tailings and to the atmosphere.
In addition to Hg added during amalgamation, toxic metal(oid)s (primarily As) also occur naturally in the ore, and may exist at high concentrations in the mine wastes. The present study is a multi-disciplinary, multi-partner
investigation of the
dispersion, transformation, and fate of metals and metalloids in freshwater and marine environments surrounding
abandoned gold mines in Nova Scotia. In 2003 and 2004, samples of tailings, soil, till, rock, sediment, water, and/or vegetation
were
collected at 15 past-producing mines. Chemical analyses of 520 tailings and sediment samples show high concentrations of Hg (<5
:g/kg to 350 mg/kg), as well as other potentially toxic elements (e.g. As, 9 mg/kg to 31 wt.%). The highest Hg
concentrations are found
near mill structures, reflecting Hg loss during amalgamation and retorting. Droplets of elemental mercury and particles of amalgam
have been observed in the tailings at several locations; however, mercury may also exist
in various secondary phases, or may be sorbed
to mineral surfaces and/or organic material. Water chemistry data indicate that the dissolved concentrations of As are very high at some
locations (range: 0.2–6600 :g/L; median 100 :g/L; n = 122),
as compared to background values of generally <25 :g/L. Dissolved Hg
levels range from 1 to 60 ng/L, and show a significant positive correlation with dissolved organic carbon at most sites. In general, the
dissolved Hg concentrations in surface
waters are relatively low (i.e. <20 ng/L) even in close proximity to tailings with high (i.e. >1000
:g/kg) levels of Hg, suggesting that most of the Hg is present in relatively insoluble forms. Ongoing studies are characterizing the
background
levels, seasonal variability, speciation, mobility, and bioaccumulation of metal(loid)s in both freshwater and marine systems.
A wide variety of methods are being employed, including sequential extractions, biological sampling (fish, frogs, clams,
invertebrates,
mice), and sediment/water toxicity testing. Results from this project will be used to assess the potential risks associated with these sites, and will support better informed land-management decisions. |