Tim Walker, MS, RS, CIH, Division of Health Assessment and Consultation
In 1881, miners searching for gold unearthed a micalike material from an area outside of Libby, Montana. At the time, they did not know what they had uncovered. It was not until 1919 that Edward Alley, a local businessman from Libby, discovered the unique properties of this material. While he was walking through an abandoned mine, his torch contacted the surface of the mine, resulting in an expansion or "popping" of the ore into a material later known as vermiculite. This unique material was marketed for many uses, such as loose-fill insulation, a fertilizer carrier, a soil conditioner, and an aggregate in many products such as gypsum wall board and numerous construction products.
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Vermiculite ore from Libby was mined beginning in the 1920s. In 1963, W.R. Grace purchased the mine and expanded operations. During the 1960s-1980s, millions of tons of vermiculite ore were shipped to 30 states and six foreign countries. The ore from Libby was contaminated with asbestos, and evidence of adverse health effects began to appear in workers employed at the mine, mill, and refining processes in Libby. Investigations in the 1980s found that those workers had increased rates of asbestosis, mesothelioma, and lung cancer. At a
fertilizer plant in Marysville, Ohio, that received ore from Libby, asbestos-related lung abnormalities were identified among workers. During early mining operations in Libby, airborne levels of asbestos were measured at levels >100 fibers per cubic centimeter (f/cc) of air. In downtown Libby, concentrations of airborne asbestos exceeded the federal Occupational Safety and Health Administration (OSHA) permissible exposure limit of 0.1 f/cc.
In 2000, as the U.S. Environmental Protection Agency (EPA) initiated clean-up actions in Libby, and as the Agency for Toxic Substances and Disease Registry (ATSDR) began health screening of former workers and residents, an effort was under way throughout the United States to investigate facilities that received asbestos-contaminated ore from the W.R. Grace mine. Approximately 300 sites across the country were identified as possible recipients of the vermiculite ore. Working with EPA, ATSDR has begun to evaluate all of these sites to determine whether asbestos contamination is present at levels that pose a public health risk.
Of all types of vermiculite processing facilities, exfoliation plants are most likely to have resulted in the greatest amounts of environmental contamination and exposure. Exfoliation plants heated the vermiculite ore to approximately 2,000°F (1,093°C), creating the expanded vermiculite used for a variety of products, including loose-fill insulation in homes. Significant concentrations of asbestos fibers might have been released into communities near these plants through stack emissions. ATSDR is evaluating past exposure to airborne asbestos around these plants by looking at asbestos-related disease rates.
Current exposure to asbestos-contaminated vermiculite is also being assessed at the facilities that received Libby vermiculite ore. EPA and ATSDR are working together to gather information on these sites. Where appropriate, environmental sampling of the air and soil is being conducted to assess the current level of exposure around former vermiculite facilities. In addition, the National Institute for Occupational Safety and Health (NIOSH) is evaluating active vermiculite facilities that are receiving ore from mines other than Libby.
Collecting environmental data is only the first step in the identification process. Current exposure models used to assess risk to asbestos in air and soil do not incorporate much of the knowledge acquired during the last 15 years. Much has been learned regarding asbestos fiber types and biologic mechanisms. This information needs to be incorporated into any future exposure models to give meaningful information regarding risk. In addition, environmental sampling methodologies must be developed to best measure and collect the kind of information that will be useful to health professionals who are assessing the data. The ultimate goal of this effort is to identify sites where unacceptable exposures to asbestos might be occurring, so that exposure at these sites can be mitigated to a safe level. ATSDR will work with EPA and other federal agencies to serve affected populations by providing health education and meeting other needs as appropriate.