Skip to content
MSHA News Release No. 97-0919a
Mine Safety and Health Administration
Contact: Katharine Snyder
Phone: (703) 235-1452

Friday, September 19, 1997


Mercury contamination may present a potentially serious hazard to workers at U.S. gold and silver mines, according to the U.S. Department of Labor's Mine Safety and Health Administration (MSHA). The agency is asking the mining community to review a new draft guide to controlling mercury hazards in the gold industry and to offer comments.

"Mercury presents potentially serious health risks to workers in the precious metals industries," said Davitt McAteer, assistant secretary of labor for mine safety and health. "In addition, workers can unwittingly take mercury contamination home from the worksite and expose their families.

"We're concerned that many individuals in the gold mining industry are not fully aware of mercury's hazards and the means necessary to control the risks in these operations," McAteer said. "Mercury is an insidious hazard that requires constant vigilance. We're sharing the latest information we have on mercury hazards and best practices to reduce mercury exposure, and we are asking others in the mining community to contribute their comments."

Chronic mercury exposure can cause permanent disability in mine employees unless it is properly controlled. It can also affect the children of workers either by the reproductive damage it can cause in their parents or by exposure when their parents bring home mercury through contamination of clothing and other items. A cumulative poison, mercury can affect the brain, the central nervous system, the kidneys, and the reproductive system.

Mercury can be naturally present in ore and is produced as a byproduct of gold and silver mining. Because mercury vapor is odorless and cannot be seen, individuals often underestimate the hazard. Mercury can be absorbed through the lungs, the skin, or the digestive tract. Growing use of cyanide technology has increased recovery of byproducts such as mercury, as well as gold and silver production.

"In the past several years, MSHA has found many overexposures involving mercury," said Davitt McAteer, assistant secretary of labor for mine safety and health. "These overexposures present potentially serious health risks for workers in the gold mining industry, and for their families."

According to "Controlling Mercury Hazards in Gold Mining: A Best Practices Toolbox," in the past six years, MSHA found 86 mercury overexposures in over 690 samples taken at 72 gold and silver mines. Of the 86 overexposures, 50 percent were more than twice the exposure limit. Exposures ranged as high as 50 times the allowable limit. In addition, MSHA has found lunchrooms contaminated by mercury, as well as individuals permitted to eat in work areas exposed to the toxic material.

Practices similar to those recommended in MSHA's draft "Best Practices" document recently were adopted under a settlement agreement between MSHA and Getchell Gold Corporation. Getchell agreed to adopt an industrial hygiene protocol for the control of mercury and lead in the lunch rooms at its Getchell Mine near Golconda, Nev.

The small amount of elemental mercury that is extracted from the host ore can pose special health risks to employees who work with the gold-bearing solution purification and concentration circuit. The cyanidation process involves concentrating the precious metals and the mercury by a factor of three to four thousand to produce a small volume of high grade gold solution. Many overexposures to mercury detected by MSHA involved workers at refineries associated with mining operations.

MSHA's draft document presents "Best Practices" that can be utilized within the mining industry in controlling employees' exposures to liquid and vapor forms of mercury. The draft:

    Characterizes the problems associated with controlling mercury vapor at gold and silver mines where cyanide is used to extract the precious metals;

    Discusses good industrial hygiene practices concerning the design and operation of facilities using cyanide to extract gold and silver

    Describes the best practices and controls for reducing employees' exposures to mercury;

    Provides a source of equipment needed to control mercury and materials required for surface decontamination; and

    Provides a list of personal protective equipment to limit employees' exposures to mercury.

In addition to presenting best practices for control of mercury within the workplace, MSHA's "Best Practices" document describes methods to prevent employees' street clothes, personal items, motor vehicles and homes from being contaminated with mercury from the workplace. Potentially contaminated clothing should never be worn home for laundering or stored in the same lockers used to hold employees' street clothes. To prevent contamination, mine operators can provide employees and visitors an appropriate place to shower as well as facilities to isolate their street clothes from sources of mercury such as contaminated work clothing.

"In recent years, MSHA has conducted several studies involving mercury hazards at gold and silver operations," McAteer said. "We believe that by sharing information with miners, mine operators and health and safety professionals throughout the gold industry, miners can be better protected. We're asking all interested parties to comment on the draft and to add their own ideas on best practices for controlling mercury hazards."

According to MSHA's draft "Best Practices" document, 191 gold mines and 15 silver mines employ approximately 19,000 miners in twelve states: Alaska, Arizona, California, Colorado, Idaho, Montana, Nevada, New Mexico, South Carolina, South Dakota, Utah and Washington. Nevada has 30 percent of the total operations and 65 percent of the miners employed in gold and silver mining. California is second with 19 percent of the operations and 10 percent of the miners. MSHA inspects all U.S. mines for safety and health hazards.

Some 40 percent of U.S. gold and silver mines are joined with mineral processing mills, while additional freestanding mills, also under MSHA jurisdiction, process gold and silver ores from various mines. Many gold and silver ore processing mills incorporate refineries.

Gold production in the United States has increased approximately tenfold since 1980, with reported gold mine employment increasing from 6,000 in 1980 to more than 17,000 last year.

MSHA's draft "Best Practices Toolbox" on controlling mercury hazards in gold mining is available on the World Wide Web at or from MSHA's Division of Technical Support, Attn.: "Mercury Report," 4015 Wilson Boulevard, Arlington, VA 22203; telephone (703) 235-1580. MSHA is accepting comments on the draft "Best Practices" document until November 15; comments may be sent via e-mail to Michael L. Lynham or to MSHA's Division of Technical Support at the above address.

# # #