Mercury Research
Ore deposit research, geochemical modeling, and remote sensing are used to understand the impact of historic mining and prioritize remediation
Mercury has been recognized as a serious environmental contaminant for many years
MERCURY CONTAMINATION ISSUES
Scientists sampling for mercury using precautions
to avoid sample contamination from their hands and clothing. This entails
the use of lint-free suits, plastic gloves, hoods, and stringently cleaned
sampling equipment. Risks to Human Health
- Consumption of contaminated fish
- Improper handling of contaminated sediments
- Inhalation of mercury vapors
- Low risk in municipal drinking water
- Some mine waters unsafe for consumption
A tunnel sluice with mercury contaminated sediments.
Challenges for Land Management
- Public access to contaminated areas
- Physically hazardous sites
- Environmental consequences of resource development
- Remediation of affected sites
Environmental Fate of Mercury
- “Hot spots” at mine sites
- Contaminated sediments
- Transport to downstream areas
- Bio-accumulation in food chain
The discovery of commercial mercury ore bodies in the Coast Ranges of California led to the development and operation of numerous mines from the 1840's to the early 1960's. The California Coast Ranges was one of the most productive mercury districts in the world. USGS study includes sampling water, sediment and biota at mine sites identified as mercury “hot spots”, where risks to human health and the environment can be reduced through remediation. The New Idria mercury district, one of the major production centers is currently the site of remediation effort by BLM. Past mining operations has lead to significant increases in environmental mercury concentrations in affected soil, sediment, plants, fish, and other animals. The USGS and BLM are jointly funding studies in the District and have thus far characterized mine tailings and established baseline mercury concentration and speciation in watersheds impacted by mercury mines.
The 1848 discovery of gold in the Sierra Nevada created a ready market for mercury produced by mines in the California Coast Ranges. Miners used mercury to recover gold at both placer and hard rock mines. The vast majority of mercury lost to the environment in California was from placer-gold mines, which used hydraulic, drift, and dredging methods. Mercury contamination from historic gold mining districts represents a potential risk to human health and the environment.
An interagency group of scientists from the USGS, BLM, USFS, and State and local agencies are working together to determine the distribution, transport, fate of mercury and methyl mercury in the vicinity of historic placer-gold mines. The overall purpose of the study is to provide unbiased scientific information on potential impacts of mercury and arsenic from abandoned and inactive mine sites, as a sound basis for effective resource management by land management agencies. One of the study areas is the low-sulfide gold quartz deposits and placers in the Sierra Nevada Foothills in California.
A map showing the Bear River and South Yuba River, CA watersheds.
The Bear River and South Yuba River watersheds have been selected by the USGS, BLM, and USFS, as well as State and local agencies for detailed studies of mercury distribution in relation to historic mine sites. Elevated mercury concentrations in present-day mine waters and sediments indicate that hundreds to thousands of pounds of mercury remain at each of the many sites affected by hydraulic mining. High mercury levels in fish, amphibians, and invertebrates downstream of the hydraulic mines are a consequence of historic mercury use. Depending of results of the present study and the availability of funds, follow-up activities may include investigations of the costs and benefits of remediation in areas impacted by mercury use in hydraulic mining.
A map showing the locations of mercury mines and deposits in southwestern Alaska.
Mercury deposits are scattered over a wide region in southwestern Alaska covering several tens of thousands of square kilometers. Several of the mercury deposits have been mined in the past, but most of the deposits are small and undisturbed. Southwestern Alaska has no major sources of industrial mercury; however, mercury is highly concentrated around mineral deposits in the region. Thus, the presence of mercury deposits is a potential hazard to residents and wildlife because drainage from the deposits enters streams and rivers that are part of local ecosystems.
A sample of cinnabar, showing above as red. Cinnabar, a mercury sulfide mineral, is the most common mercury ore mineral in the deposits. Liquid mercury also occurs naturally in some locations.
To evaluate the environmental concerns of these mercury deposits, USGS scientists measured the concentration of mercury in sediment, water, soil, vegetation, and fish collected around some of the mercury deposits. These data were then compared with those from streams in unmineralized (background) areas. Stream sediment samples collected near some mines are highly enriched in mercury, which are a result of erosion of cinnabar into the streams. The formation of acid drainage below some mineral deposits containing sulfide minerals can be of concern; however, cinnabar is highly insoluble in water and does not easily form acid drainage during weathering. Thus, acid formation in streams below the mercury mines and deposits in southwestern Alaska is probably insignificant.
Products from this study include data and publications (USGS Bulletin 2156, journal articles) on mercury in vegetation and soils at abandoned mercury mines in southwest Alaska. The BLM and Alaska Department of Environmental Conservation are using the results of these studies to develop guidance for establishing cleanup at the sites and determining priorities for focusing cleanup efforts.
