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Libby is the county seat of Lincoln County, in northwest Montana. Vermiculite was mined from "Zonolite Mountain" near Libby from the early 1920s until 1990 and was processed for export in and around the town of Libby. The vermiculite mined in Libby is contaminated with amphibole asbestos fibers (Libby asbestos). Mining and processing operations, as well as home use of Libby vermiculite products, resulted in the spreading of Libby asbestos throughout the town. Unusually high numbers of people in Libby have been diagnosed with asbestos-related respiratory disease; deaths from asbestos-related respiratory diseases are also elevated. Since 1999, the Environmental Protection Agency's (EPA's) Emergency Response Branch has been conducting sampling and removals to address the most highly contaminated areas in the Libby valley. Since the proposal of the Libby Asbestos site to the National Priorities List (NPL), these activities have been transitioning over to the Superfund Branch for long-term cleanup.

People were exposed to Libby asbestos by many different exposure pathways in the past, and as long as source materials are present, the possibility for further exposure remains. Source materials are defined as any material (including waste rock, soil, building materials, or insulation) containing Libby asbestos which, when disturbed, could produce elevated levels of Libby asbestos fibers in air. The size of source areas can range from the residential scale to the industrial scale. However, many of the largest and most highly contaminated areas have been or are being cleaned up. As of late fall 2002, characterization of contamination in Libby homes and businesses to prioritize cleanups through the EPA Superfund program is almost complete.

On the basis of available information, the Agency for Toxic Substances and Disease Registry (ATSDR) has concluded that:

  • People in the Libby area were exposed to hazardous levels of asbestos in the past.
  • People in the Libby area have elevated levels of disease, and death, associated with exposure to asbestos.
  • People could still be exposed to hazardous levels of asbestos near current source areas. These levels could be especially hazardous to sensitive populations, including people who have been exposed for many years already, smokers, and young children.
  • The exact level of risk associated with low-level exposure to asbestos cannot be determined due to uncertainties in the analysis and toxicology of Libby asbestos. Nevertheless, continuing exposures to Libby asbestos pose an unacceptable risk to residents and workers who have already been exposed for many years.
  • The cleanup actions undertaken by EPA are protective of public health.

ATSDR makes the following recommendations:

  • Continue to investigate and clean up the site to reduce or remove continuing sources of Libby asbestos.
  • Provide ongoing medical testing in Libby to qualified individuals.
  • More research is needed, specifically: toxicological investigation of the risks associated with low-level exposure to asbestos, especially Libby asbestos; clinical research on treatments for mesothelioma and asbestosis; and epidemiology studies to better characterize the link between exposure to asbestos and disease.
  • Conduct health education for the community, especially concerning smoking and asbestos.
  • Create a registry to track former workers, their household contacts, and residents exposed to Libby asbestos.
  • Continue to provide information to the community about the hazards of Libby asbestos.
  • Continue to provide information on how to diagnose and treat asbestos-related diseases to the local medical community.


Libby Asbestos was proposed for the National Priorities List (NPL) on February 26, 2002 and listed on October 24, 2002. The Agency for Toxic Substances and Disease Registry (ATSDR) is required by Congress to conduct public health assessments (PHAs) on all sites proposed for the NPL. In this PHA, ATSDR evaluates the public health implications of the Libby Asbestos site using available environmental data, potential exposure scenarios, community health concerns, and health outcome data. This document also recommends actions to prevent, reduce, or further identify the possibility for site-related adverse health effects.


The background, site description, and site operational history comes from Environmental Protection Agency (EPA) and ATSDR documents [1,2,3,4,5].

Libby is the county seat of Lincoln County, located in northwest Montana. In 1881 gold prospectors discovered vermiculite, a type of platy weathered mica mineral, on "Zonolite Mountain," 7 miles northeast of Libby. From the early 1920s until 1990, vermiculite was mined for use in a variety of products. Raw vermiculite ore is used in gypsum wallboard, cinder blocks, and many other products, and exfoliated vermiculite is used as loose fill insulation, as a fertilizer carrier, and as an aggregate for concrete. Exfoliated vermiculite is formed by heating the ore to approximately 2,000 degrees Fahrenheit (ºF), which explosively vaporizes the water contained within the mineral structure and causes the vermiculite to expand by a factor of 10 to 15. Direct export and exfoliation (expansion) prior to shipping occurred in locations in and around the town of Libby.

The vermiculite mined from Zonolite Mountain is contaminated with asbestos fibers, including the asbestos varieties tremolite and actinolite, and contains the related fibrous asbestiform minerals winchite, richterite, and ferro-edenite [6]. Collectively, the asbestiform minerals contaminating the vermiculite are referred to as Libby asbestos. Mining and processing operations, as well as home use of waste rock and products from the mine, resulted in the spreading of Libby asbestos throughout the town. Hundreds of people in Libby, including former mine workers, their families, and other residents, have exhibited signs and symptoms of asbestos-related disease. Since 1999, in response to reports of widespread disease among Libby residents, EPA's Region 8 Emergency Response Branch has been conducting sampling and removals to address the most highly contaminated areas in the Libby valley. Since the Libby area was proposed for the NPL in February 2002, these activities are transitioning to EPA's Superfund Branch for long-term cleanup.

Site Description

The Libby Asbestos site (the site) is located in Libby, Montana. Figure 1 shows the site location and features. Libby lies in the northwest corner of Montana in Lincoln County approximately 35 miles east of the Idaho border and 65 miles south of the Canadian border. Libby is bounded to the north by the Kootenai River and surrounded to the south by the Cabinet Mountains and the Cabinet Mountain Wilderness area. The site lies within Sections 3 and 10, T30N, R31W of the Libby Quadrangle in Lincoln County, Montana.

Site Locations and Features
Figure 1. Site Locations and Features

The site comprises the vermiculite mine on Zonolite Mountain, the former screening plant and the former export plant (two former vermiculite processing centers), the road between the former screening plant and the mine site (Rainy Creek Road), and homes and other businesses which could have become contaminated with Libby asbestos fibers as a result of the mining and processing operations in and around Libby. For long-term management purposes, EPA has divided the site into two operable units (OUs). OU3 includes the mine site and Rainy Creek Road, and OU4 includes the remainder of the Libby valley [1].

Because OU4 includes homes and other areas where continuing exposure to asbestos fibers is likely, and because EPA is focusing its current remedial investigation (RI) activities on this unit, this PHA will consider only OU4. The mine and road in OU3 are of less concern at present because access is limited by a barricade at the lower entrance to Rainy Creek Road. OU3 will be considered at a later date.

Site Operational History

In the early 1920s, initial mining operations began on the vermiculite ore body 7 miles northeast of Libby. Full-scale operation began later that decade under the name of Universal Zonolite Insulation Company (Zonolite). The vermiculite ore was strip-mined using conventional mining equipment. The ore was processed onsite in a dry mill to remove waste rock and overburden material and then transported to the former screening plant at the foot of Zonolite Mountain, where it was sorted into size fractions. After the sorting process, the material was shipped throughout the United States, either for direct use in products or for expansion prior to use in products. Two expansion sites were also located in Libby: the former export plant immediately west of Highway 37 where it crosses the Kootenai River and the former expansion plant at the end of Lincoln Road, near 5th Street (this plant was shut down in the early 1950s).

In 1963, W.R. Grace purchased Zonolite and continued mining operations. In 1975, Grace added a wet milling process which operated in tandem with the dry mill until the dry mill was shut down in 1985. Expansion operations at the export plant ceased sometime before 1981, although the area was still used to bag and export milled ore until mining operations stopped in 1990. In the years of operation, the Libby mine produced millions of tons of vermiculite, providing about 80% of the world's supply.


According to U.S. Census 2000 information, 10,362 persons live within the zip code area including Libby, Montana (59923) [7]. Figure 2 shows that the demographic profile of the population residing in the area around Libby selected for asbestos screening by EPA includes a population of 8,668. The population is mostly (95%) white. About 1.5% of the population is Native American, less than 1% is Black, Asian, Native Hawaiian or other Pacific Islanders or other, and about 2% of the population is two or more races.

It should be noted that some mine workers lived in the smaller towns of Troy and Eureka, Montana. Also, some mine workers moved to the town of Elko, Nevada, after the Libby mine shut down. The demographics of people affected in these communities are expected to be similar to those of Libby.

Demographic Map
Figure 2. Demographic Map

Land and Natural Resource Use

Located in the far northwestern corner of Montana, Libby lies in a valley carved by the Kootenai River on the northeastern edge of the Cabinet Mountain Range. Libby's elevation is 2,066 feet, and it is surrounded by the Kootenai National Forest. The Libby Dam confines the Kootenai River about 17 miles north of town to create the 90-mile long Lake Koocanusa, which extends north into Canada. Montana Highway 37 parallels the Kootenai River and Lake Koocanusa and connects Libby to U.S. Highway 93 to the north. U.S. Highway 2 runs through Libby and connects Libby to the nearest towns of Kalispell, 90 miles to the southeast, and Troy, 18 miles to the northwest. The Burlington Northern Railroad maintains the railroad that runs through Libby connecting Libby to Whitefish, Montana and Spokane, Washington. Freight service runs daily and Amtrak service is available 4 days a week. Libby also has a small airport with a 5,000 foot runway [8].

Libby contains neighborhoods and commercial and industrial areas in relative proximity to each other. Outside the town the terrain quickly becomes mountainous, forested, and rural. Away from the two main roads, population is sparse. Major area industries include forestry, forest products, and tourism.

People in Libby engage in typical residential activities as well as activities related to work at commercial and industrial facilities in town. The areas outside of town are used for hiking, fishing, hunting, and other recreational activities. Logging also takes place in the forested areas.

Drinking water for the city of Libby comes from the Flower Creek reservoir, which is approximately 3 miles southwest of town. People in the area surrounding Libby might use groundwater wells for their drinking water (personal communication, Jim Christiansen, U.S. Environmental Protection Agency, July 2002).

In some areas the Libby valley has a vertical relief as high as 4,000 feet and is subject to severe temperature inversions during many times of the year. These physical characteristics can result in the trapping of particulates and other air pollutants in the Libby valley [3].

Previous Reports and Studies

This PHA builds on the many previous studies and reports already in existence regarding Libby asbestos and the impact asbestos has had on health in Libby and the surrounding area. The information in the following documents was used as background for this report:

  • Articles began appearing in the scientific literature in the late 1970s and 1980s reporting elevated levels of asbestos-related diseases in workers of the Libby vermiculite mine [9,10,11,12]. In 1999, concern for the workers, their families, and residents of Libby was brought to the public's attention in the media [13]. ATSDR became involved with Libby at this time.
  • To address public health concerns regarding asbestos exposure in Libby, ATSDR has cooperated with EPA, the Montana Department of Public Health and Human Services (MDPHHS), the Lincoln County Environmental Health Department, and the Montana Department of Environmental Quality in the Libby Community Environmental Health Project.
  • In December 1999, ATSDR published a health consultation regarding EPA Region 8's proposal to use an asbestos sampling protocol developed by EPA Region 1 to assess levels of contamination in Libby [2]. ATSDR concurred with the use of this protocol.
  • In May 2000, ATSDR published a health consultation regarding the health hazards associated with asbestos contamination at the former screening plant and at the former export plant [4]. ATSDR concluded that the contamination posed a public health hazard and that time critical removals by EPA were warranted.
  • In November 2000, ATSDR published a health consultation evaluating proposed plans for the removal of asbestos contamination at the former screening plant and the former export plant [5]. ATSDR found the plans to be protective of public health. ATSDR also made recommendations to minimize the chances of asbestos exposure to workers or the community during the removal.
  • In August 2001, ATSDR and cooperative partners in the Libby Community Environmental Health Project released a report on the results of the first round of medical testing of Libby residents and former residents for asbestos-related health effects [14]. The testing program was undertaken in cooperation with other agencies to identify the asbestos-related health effects of participants exposed to asbestos and to refer these individuals for additional medical evaluation as needed. Results were combined with later testing results and are discussed below.
  • In September 2001, ATSDR released a chemical-specific health consultation on tremolite asbestos and other related types of asbestos [15]. This consultation served as an addendum to ATSDR's toxicological profile on asbestos and was produced to address public health concerns regarding the fibrous amphibole found in Libby vermiculite.
  • In December 2001, an EPA toxicologist published a memorandum to the Libby on-scene coordinator which included a discussion of potential risks from exposure to Libby asbestos in residential settings [16]. The memo concluded that "amphibole mineral fibers in source materials in residential and commercial areas of Libby pose an imminent and substantial endangerment to public health."
  • In May 2002, EPA published a sampling and analysis plan for its contaminant screening study, part of the RI activities for OU4 [1]. This report outlines EPA's plan for screening each property in the Libby valley for potential sources of Libby asbestos. ATSDR was given the opportunity to comment on a draft of this document and agreed that the proposed plan was reasonable.
  • In August 2002, ATSDR published a health consultation updating results of a December 2000 analysis of Libby area mortality statistics [17,3]. This review was conducted to generate an accurate representation of mortality potentially associated with historical asbestos exposure in the Libby area. For the period reviewed in the report (1979-1998), mortality in Libby resulting from asbestosis was 40 to 80 times higher than expected, and lung cancer was 20% to 30% higher than expected. Mesothelioma mortality was also elevated, but it could not be quantified. State and national statistics on this disease are not routinely published. Still, because the disease is so rare, any cases are viewed as an elevation. Most of the asbestosis and mesothelomia deaths (11/12 and 2/3, respectively) were among former workers of the vermiculite mine and processing operations.
  • In September 2002, ATSDR provided preliminary results of combined medical testing performed in 2000 and 2001 [18]. Of the 6,668 participants who received chest x-rays in the two rounds of testing, 18% showed pleural abnormalities. Fifty-one percent (51%) of the 365 former workers showed pleural abnormalities. By comparison, in the United States the rate of pleural abnormalities in non-asbestos exposed groups ranges from 0.2% to 2.3%.
  • In conjunction with the medical testing performed in 2000 and 2001, ATSDR conducted a study on the usefulness of computed tomography (CT) scans in identifying lung problems associated with asbestos exposure for people whose chest x-rays were indeterminate (e.g., those where only 1 of 3 B-readers found abnormalities). The preliminary results of this study showed that CT scans identified pleural abnormalities in some people whose chest x-rays were indeterminate [19]. The study did not indicate whether CT scans are better than chest x-rays in detecting pleural abnormalities.


Data Used

The preparation of this report involved the review and summary of numerous previous studies and data summaries. Generally, the conclusions reached herein are based on three types of data:

  1. Analytical data--reported in several documents available in EPA's administrative record (AR) for the site [20].
  2. Community concerns--collected by ATSDR representatives in Libby. Also, some community concerns were obtained during a public availability session held in Libby on September 27 and 28, 2002.
  3. Health outcome data--as reported in ATSDR's mortality statistics review and in the ATSDR report on the community medical testing program [3,17,14,18].

All the above data were considered in determining conclusions and recommendations for the site.

Contaminant of Concern

The Libby vermiculite contains a characteristic profile of asbestiform minerals, including tremolite, actinolite, winchite, richterite, and ferro-edenite. The contaminant of concern, comprising the various types of asbestiform minerals detected in vermiculite from the Libby mine, is referred to as Libby asbestos. The following sections give more information about asbestos in general and the materials making up Libby asbestos specifically.

This document is atypical compared to most PHAs in that only one contaminant is considered. If, in the course of the RI activities for this site, other contaminants are identified that could contribute substantially to health risks in the community, they will be evaluated in an addendum to this document.

Asbestos Overview
This description comes mostly from ATSDR's toxicological profile for asbestos [15]. Asbestos is a general name applied to a group of silicate minerals consisting of thin, separable fibers in a parallel arrangement. Different criteria are used to identify asbestos fibers, depending on the context. In general, the Occupational Safety and Health Administration (OSHA) regulates as fibers those particles of the regulated mineral classes (see below) longer than 5 µm in length, with aspect ratios (length: width) of at least 3:1, and which are not "cleavage fragments," i.e., crystalline particles exempt from regulation [6].

Asbestos minerals fall into two classes: serpentine and amphibole. Serpentine asbestos has relatively long and flexible crystalline fibers and includes chrysotile, the predominant type of commercial asbestos. Amphibole asbestos minerals are brittle and have a rod- or needle-like shape. Amphibole minerals regulated as asbestos by OSHA include five classes: fibrous tremolite, actinolite, anthophyllite, crocidolite, and amosite. However, other amphibole minerals, including winchite, richterite, and others, can exhibit fibrous asbestiform properties.

Asbestos fibers do not have any detectable odor or taste. They do not dissolve in water or evaporate and are resistant to heat, fire, and chemical and biological degradation.

The vermiculite mined at Libby contains amphibole asbestos, with a characteristic composition including tremolite, actinolite, richterite, and winchite--Libby asbestos. The raw ore was estimated to contain up to 26% Libby asbestos [21]. For most of the mine's operation, Libby asbestos was considered a byproduct of little or no value and was not used commercially. Nevertheless, the mining and processing of Libby asbestos -contaminated vermiculite resulted in the contamination of many areas in and around Libby with Libby asbestos.

Asbestos Health Effects
Breathing any type of asbestos increases the risk of the following health effects.

Malignant mesothelioma—Cancer of the lining of the lung (pleura) and abdominal cavity. This cancer can spread to tissues surrounding the lungs or other organs. Virtually all mesothelioma cases are attributable to asbestos exposure [15].

Lung cancer—Cancer of the lung tissue. The exact mechanism relating asbestos exposure with lung cancer is not completely understood. The combination of tobacco smoking and asbestos exposure greatly increases the risk of developing lung cancer [15].

Noncancer effects—these include 1) asbestosis, where asbestos fibers lodged in the lung cause scarring and reduce lung function; 2) pleural plaques, localized or diffuse areas of thickening of the pleura (lining of the lung); 3) pleural thickening, extensive thickening of the pleura which restricts breathing; 4) pleural calcification, calcium deposition on pleural areas thickened from chronic inflammation and scarring; and 5) pleural effusions, fluid buildup in the pleural space between the lungs and the chest cavity [15].

Insufficient evidence exists to conclude whether inhalation of asbestos increases the risk of cancers at sites other than the lungs, pleura, and abdominal cavity [15].

It has been suggested that amphibole asbestos is more toxic than chrysotile asbestos, mainly due to physical characteristics which allow chrysotile to be broken down and cleared from the lung, whereas amphibole is not removed and builds up to high levels in lung tissue [22]. The resulting increased duration of exposure to amphibole asbestos is thought to significantly increase the risk of mesothelioma and, to a lesser extent, asbestosis and lung cancer [22]. OSHA, however, continues to regulate chrysotile and amphibole asbestos as one substance, because both types increase the risk of disease [23].

Evidence suggesting that the different types of asbestos fibers vary in carcinogenic potency and site specificity is limited by the lack of information on fiber exposure by mineral type [24]. Other data indicate that differences in fiber size distribution and other process differences can contribute at least as much to the observed variation in risk as does the fiber type itself [24,25].

Ingestion of asbestos causes little or no risk of noncancer effects [15]. However, some evidence suggests that acute oral exposure can induce precursor lesions of colon cancer, and that chronic oral exposure can lead to an increased risk of gastrointestinal tumors [15]. ATSDR found no elevation in the number of deaths from gastrointestinal cancers in the Libby area compared to Montana and the United States [17].

Asbestos, Immunological Changes, and Autoimmune Disease

Community members expressed concerns about autoimmune diseases such as rheumatoid arthritis, lupus, or fibromyalgia being caused by asbestos exposure. ATSDR's toxicological profile for asbestos reviews information in the literature about possible immunological effects of exposure to asbestos. The toxicological profile summarizes its findings in the following excerpted passage [15]:

Studies of workers suffering from asbestos-related diseases such as asbestosis or mesothelioma indicate that the cellular immune system in such patients can be depressed. This is an effect of particular interest and concern since impaired immune surveillance may contribute to the increased incidence of cancer in asbestos-exposed people. Moreover, variation in immune system functional capability might be an important determinant of why some people develop cancer or asbestosis while others, with approximately equal exposures, do not. However, it is very difficult to distinguish whether the alterations in immune function noted in such studies are the cause or the result of asbestos-induced disease. The frequency of impaired cellular immunity in exposed workers without clinically-apparent disease is generally low, although some studies have noted alterations in lymphocyte distribution and impairment of natural killer (NK) cells. This could mean that the immunological changes do not occur until the disease develops (i.e., the changes are the result of the disease). Alternatively, it could mean that workers with immune systems that are not impaired by asbestos do not get serious disease, while workers whose immune systems are injured by asbestos do tend to develop disease (i.e., effects on the immune system are the cause of the disease). Available data do not allow a firm distinction between these alternatives at present, but the possible immunotoxic effects of asbestos are of clear concern. Results from animal studies provide supporting evidence of direct and indirect effects of asbestos on the immune system, although the specific roles of these effects in the etiology of asbestos-induced pulmonary diseases are not well understood and are under current investigation. For example, experiments with mice indicate that asbestos exposure decreases the number and cytotoxic activity of interstitial pulmonary NK cells and that genetically impaired cell-mediated immunity may be a predisposing factor in asbestos fibrosis.

Also, according to the toxicological profile, "concentrations of autoantibodies (rheumatoid factor, antinuclear antibodies) tend to be abnormally high in asbestos-exposed workers. . . . In some cases, increased autoantibodies can lead to rheumatoid arthritis (Caplan's Syndrome), although this is more common in coal miners and workers with other pneumoconioses than in workers with asbestosis. . . . Immunological abnormalities are usually mild or absent in asbestos-exposed workers who have not developed clinical signs of asbestosis. . . ." [Note: secondary references have been omitted for brevity. Further information and secondary references are given in the toxicological profile, which is available online at:]

In summary, not enough evidence exists to say whether asbestos exposure or resulting asbestos-related disease could increase a person's likelihood of experiencing autoimmune disease. Still, the associations that have been discovered between immunological changes and asbestos exposure indicate that this question deserves further research.

Methods for Measuring Asbestos Content
Measuring asbestos content in air samples and in bulk materials that could become airborne involves both quantification of fibers and determination of mineral content of the fibers to identify whether they are asbestiform. For air samples, fiber quantification is traditionally done through phase contrast microscopy (PCM), by counting fibers longer than 5 µm and with an aspect ratio (length:width) greater than 3:1. This is the standard method by which regulatory limits were developed [15]. Disadvantages of this method include the inability to detect fibers smaller than 0.25 µm in diameter and the inability to distinguish between asbestos and nonasbestos fibers [15].

Asbestos content in bulk samples is often determined using polarized light microscopy (PLM), a method that uses polarized light to compare refractive indices of minerals and can distinguish between asbestos and nonasbestos fibers and between different types of asbestos. Fibers are quantified through PCM, and then mineral species are determined using polarizing elements added to the light path. The PLM method is also limited by resolution–fibers finer than about 1 µm in diameter cannot be identified by PLM.

Scanning electron microscopy (SEM) and, more commonly, transmission electron microscopy (TEM) are more sensitive methods and can detect smaller fibers than light microscopic techniques. TEM allows the use of electron diffraction and energy-dispersive x-ray methods, which give information on crystal structure and elemental composition, respectively [15]. This information can be used to determine the elemental composition of the visualized fibers. SEM does not allow measurement of electron diffraction patterns. One disadvantage of electron microscopic methods is that it is difficult to determine bulk asbestos concentration [15].

To compare SEM and TEM measurements with regulatory limits, they are multiplied by conversion factors to give PCM equivalent fiber concentrations. The correlation between PCM fiber counts and TEM mass measurements is very poor. A conversion between TEM mass and PCM fiber count of 30 (µg/m3)/(f/cc) was adopted as a conversion factor, but this value is highly uncertain because it represents an average of conversions ranging from 5 to 150 (µg/m3)/(f/cc) [26]. The correlation between PCM fiber counts and TEM fiber counts is also very uncertain, and no generally applicable conversion factor exists for these two measurements [26]. Generally, a combination of PCM and TEM is used to describe the fiber population in a particular sample.

Counting fibers using the regulatory definitions does not adequately describe risk of health effects, as fiber size, shape, and composition can contribute collectively to risks in ways that are still being elucidated. For example, shorter fibers appear to deposit preferentially in the deep lung, but longer fibers can disproportionately increase the risk of mesothelioma [15,24]. Some of the unregulated amphibole minerals can exhibit asbestiform characteristics and contribute to risk. Fiber diameters greater than 2 µm are considered above the upper limit of respirability and do not contribute significantly to risk [24]. Methods are being developed to assess the risks posed by varying types of asbestos and are currently undergoing peer review [24].

EPA is currently working with several contract laboratories and others to develop, refine, and test a number of methods for screening bulk soil samples. The methods under investigation include PLM, infrared (IR), and SEM (personal communication, Jim Christiansen, U.S. Environmental Protection Agency, November 2002).

Current Standards, Regulations, and Recommendations for Asbestos
For industrial applications, OSHA has defined as an asbestos-containing material any material with greater than 1% bulk concentration of asbestos. It is important to note that 1% is not a health-based level, but instead represents the practical detection limit in the 1970s when the regulations were made.

Friable asbestos (asbestos which is crumbly and can be broken down to suspendable fibers) is listed as a Hazardous Air Pollutant on EPA's Toxic Release Inventory [27]. This requires companies releasing friable asbestos at concentrations greater than a 0.1% de minimus limit to report the release under Section 313 of the Emergency Planning and Community Right-to Know Act.

OSHA has set a permissible exposure limit (PEL) of 0.1 fibers per cubic centimeter (f/cc) for asbestos fibers greater than 5 µm in length and with an aspect ratio (length:width) greater than 3:1, as determined by PCM. This value represents a time-weighted average (TWA) exposure level based on 8 hours a day for a 40-hour work week. In addition, OSHA has defined an excursion limit in which no worker should be exposed in excess of 1 f/cc as averaged over a sampling period of 30 minutes [28].

The National Institute of Occupational Safety and Health (NIOSH) set a recommended exposure limit (REL) of 0.1 f/cc for asbestos fibers greater than 5 µm in length. This REL is a TWA for up to a 10-hour workday in a 40-hour work week [28]. The American Conference of Government Industrial Hygienists (ACGIH) has also adopted a TWA of 0.1 f/cc as its threshold limit value [29].

EPA has set a maximum contaminant level (MCL) for asbestos fibers in water as 7,000,000 fibers longer than 10 µm in length per liter, based on an increased risk of developing benign intestinal polyps [30]. The state of Montana, and several other states, uses the same value as a human health water quality standard for surface water and groundwater [31].

Asbestos is a known human carcinogen. EPA has calculated an inhalation unit risk for cancer (cancer slope factor) of 0.23 per f/cc of asbestos. This value estimates additive risk of lung cancer and mesothelioma using a relative risk model for lung cancer and an absolute risk model for mesothelioma. Using this value, one can calculate average lifetime asbestos fiber air concentrations corresponding to specified risk levels. The concentration resulting in an increased risk of 1 in 10,000 is 0.0004 f/cc. The concentration resulting in an increased risk of 1 in 1,000,000 is 0.000004 f/cc. The unit risks were based on measurements with phase contract microscopy and should not be applied directly to measurements made with other analytical techniques. Also, the unit risk should not be used if the air concentration exceeds 0.04 f/cc, because above this concentration the slope factor can differ from that stated [26].

Exposure Pathways

An exposure pathway is the process by which an individual is exposed to contaminants originating from a contamination source. An exposure pathway consists of the following five elements: 1) a source of contamination, 2) a media such as air or soil through which the contaminant is transported, 3) a point of exposure where people can contact the contaminant, 4) a route of exposure by which the contaminant enters or contacts the body, and 5) a receptor population. A pathway is considered complete if all five elements are present and connected. The following sections describe the exposure pathways identified at the site.

The highest risk at the site, both now and in the past, is from inhalation of asbestos fibers. Several inhalation exposure pathways were identified, and they are discussed briefly in the next section.

Present Inhalation Exposure Pathways

Residential indoor–Residents can inhale Libby asbestos-contaminated household dust, Libby asbestos -contaminated building materials or insulation disturbed during renovations or work in attics, or deteriorating Libby asbestos-contaminated building materials or insulation falling into living areas.

Residential outdoor–Residents can inhale Libby asbestos while gardening in soil amended with Libby asbestos-contaminated vermiculite, driving over Libby asbestos-contaminated fill in driveways, and/or playing in Libby asbestos-contaminated soil.

Occupational–Cleanup workers can be exposed to Libby asbestos during remedial activities through disturbing Libby asbestos-contaminated vermiculite, soil, building materials, or insulation.

In a memorandum, EPA documented that 1) normal activities such as those listed above can suspend Libby asbestos fibers into the breathing zone, 2) the level of exposure a person experiences is dependent on the level of activity as well as the level of Libby asbestos in the soil, and 3) exposures resulting from the above activities can at times exceed OSHA or risk-based standards [16]. The calculations in this memorandum were for screening purposes only. However, given the uncertainties involved in the risk assumptions, measurement techniques, and toxicology of Libby asbestos fibers, ATSDR considers this analysis adequate for demonstrating that a risk exists.

Potential present exposure pathways include breathing ambient air in the Libby area and breathing around undisturbed building materials or insulation. For these pathways, exposures are not expected to be high enough to cause significant additional health risks compared to the exposure pathways described above.

Past Inhalation Exposure Pathways

Occupational--Workers were exposed to high levels of Libby asbestos in the air at the mine, during transport and handling operations, and during processing operations such as exfoliation. Asbestos levels in air at the mine were measured as high as 100 f/cc [16]. Anecdotal information indicates that workers did not often wear personal protective equipment such as respirators.

Household contact--Relatives of workers were exposed to Libby asbestos from dirty clothing and cars of workers returning from the mine.

Vermiculite piles--Children played in open piles of Libby asbestos-contaminated vermiculite, such as those near the ball fields and export plant.

Residential outdoor--Residents inhaled Libby asbestos while gardening in soil amended with Libby asbestos-contaminated vermiculite, driving over Libby asbestos-contaminated fill in driveways, and/or playing in contaminated soil. This pathway includes inhalation of Libby asbestos-contaminated fill used at local schools, because residents could also have been exposed there.

Residential indoor--Residents inhaled Libby asbestos-contaminated household dust, Libby asbestos-contaminated insulation being sprayed into attics and walls or disturbed during past renovations, or deteriorating Libby asbestos-contaminated building materials or insulation falling into living areas.

Ambient air--Historical levels of asbestos in the ambient air in Libby were higher than the current OSHA standard of 0.1 f/cc [16]. These historical results are uncertain due to the scarcity of sampling, a lack of differentiation between asbestos and nonasbestos fibers, and the low sensitivity of the analytical method used. However, the results still indicate a potentially higher risk of health effects, especially for residents who were exposed continuously and through multiple pathways.

The limited information on historical concentrations of Libby asbestos in air and appropriate exposure assumptions to make for activities that happened long ago make it even more difficult to determine quantitative risk for the past exposure pathways. Nevertheless, it is known that the likelihood of someone inhaling Libby asbestos was much higher while the mine and processing facilities were in operation. Also, as described below, health outcome data shows that people exposed to Libby asbestos have higher rates of asbestos-related disease. Therefore, no calculations are necessary to conclude that the risk of health effects was unusually high for the past exposures in Libby.

Pathways Eliminated From Consideration

Ingestion of Drinking Water
A ban on private wells is in place in the city of Libby because of groundwater contamination from a source unrelated to asbestos. The city of Libby's drinking water is drawn from Flower Creek Reservoir. This reservoir is southwest and upstream of town; thus it is not close to or downstream from Zonolite Mountain or the processing facilities associated with the vermiculite mine. In 2000, no asbestos fibers were detected in sampling of influent and effluent water at the water treatment plant [20]. In the areas outside Libby, some people drink groundwater from private wells. According to EPA officials, private wells in and around Libby have not been tested for asbestos (personal communication, Jim Christiansen, U.S. Environmental Protection Agency, July 2002). Because asbestos fibers are not readily transported through soil, it is unlikely that contamination from waste piles, processing operations, or vermiculite in soil would reach the groundwater. Therefore, because site-related asbestos contamination is unlikely, and because the inhalation pathways described above are the major contributors to risk, in this PHA the drinking water pathway was eliminated from further consideration.

Soil and Waste Incidental Ingestion
Incidental ingestion of Libby asbestos-contaminated soils, vermiculite, and/or wastes was not considered because the health risk from this pathway is minor in comparison to the inhalation pathways described above. This assumption is supported by the results of ATSDR's mortality review, which found deaths from lung diseases (related to inhalation) elevated, while at the same time no increase in gastrointestinal cancers (related to ingestion) was found.

Dermal Exposure Pathways
No dermal exposure (skin contact) pathways were considered. The health risks associated with this route of exposure are minor in comparison to the inhalation pathways described above.

Health Outcome Data

The Superfund law requires consideration of health outcome data in a public health assessment. Health outcome data can include mortality information (e.g., the number of people dying from a certain disease) or morbidity information (e.g., the number of people in an area getting a certain disease or illness). The Libby Asbestos site meets the four criteria necessary to perform a thorough evaluation of health outcome data:

  1. A completed human exposure pathway--as described previously, several completed human exposure pathways exist at the site, specifically those related to inhalation of asbestos fibers.
  2. Contaminant levels high enough to result in measurable health effects--many reports of measured health effects caused by exposure to asbestos exist and will be detailed below.
  3. Enough people in the completed pathway for the health effect to be measured--workers, their families, and residents in the Libby area were and are potential receptors for the asbestos inhalation pathway.
  4. A health outcome database in which disease rates for populations of concern can be identified--information used includes death certificate data and results of medical testing conducted by ATSDR and other agencies.

Both morbidity and mortality information have been evaluated in other ATSDR reports [14,17,3,18]. The conclusions of these reviews are summarized below.

Morbidity Information - Medical Testing Results
In response to the reports of asbestos-related illness in the Libby community, ATSDR developed a community-based medical testing program. The testing was a part of the Libby Community Environmental Health Project and was carried out with the cooperation of the Department of Health and Human Services Region 8 office, EPA, MDPHHS, the Lincoln County Environmental Health Department, and the Lincoln County Public Health Officer.

Those eligible for participation in the program included former workers and contractors of the vermiculite mine, household contacts of former workers, and people who had been in the Libby area for a 6-month period prior to December 31, 1990. The testing included a questionnaire, chest x-rays for adult participants, and lung function tests. Two rounds of testing were offered; the first round was in summer 2000 and tested 6,149 persons, and a second round was offered in summer 2001 to test people who had missed the first round; 1,158 persons were tested in this round.

In September 2002 a report was made available that summarized preliminary results of the combined 2000 and 2001 testing [18]. Eighteen percent of the participants had pleural abnormalities reported by at least 2 out of 3 certified B-readers who analyzed the x-rays. Of former mine workers, 51% showed pleural abnormalities. The factors most strongly related to having pleural abnormalities were being a former mine worker, being male, and being a female household contact of a former mine worker. Exposure to asbestos via multiple exposure pathways also increased the chances of finding pleural abnormalities. Pulmonary function testing showed that 1.8% of the participants had moderate to severe restriction in breathing capacity. The strongest risk factors for restrictive changes in pulmonary function included current cigarette smoking, being a former mine worker, chest surgery, having a high body mass index, and age. No statistically significant increase in interstitial abnormalities was found.

Mortality Information - Death Certificate Review
As part of its response to reports of asbestos-related illnesses in Libby, ATSDR reviewed mortality statistics from the Libby area for the years 1979-1998. Death certificates were reviewed, and mortality rates and standard mortality ratios were determined for underlying causes of death associated with asbestos exposure. These included nonmalignant respiratory diseases, lung cancer, mesothelioma, digestive cancer, and pulmonary circulation diseases. The initial findings were released in a December 2000 health consultation [3]. Asbestosis mortality in the area was 40 to 60 times higher than expected, and mesothelioma cases were also elevated. The degree to which mesothelioma was elevated could not be quantitatively determined because state and national statistics on this rare disease are not routinely available. Other causes of death, including lung cancer, digestive cancer, and diseases of pulmonary circulation, were not significantly elevated over the time period studied.

Recently, it was discovered that several death certificates were inadvertently omitted from the initial review, due to differences in reporting procedures in certificates from before 1980. Therefore, ATSDR reanalyzed the statistics from 1979 to 1998, including the newly identified certificates. ATSDR released the updated health consultation in August 2002 [17]. The updated analysis showed that the elevation of asbestosis was even greater than previously found, with mortality in Libby 40 to 80 times higher than expected. In addition, lung cancer was found to be 20% to 30% higher than expected. Again, mesothelioma was elevated, but difficult to quantify. Other causes of death, including digestive cancer and diseases of pulmonary circulation, were not significantly elevated.

The updated mortality review included a comparison of death certificate data with employment information obtained from employee records from the mining and milling facilities in Libby. This analysis showed that 92% (11/12) of the asbestosis deaths, 17% (21/124) of the lung cancer deaths, and two out of three mesothelioma deaths were former employees of the vermiculite facility.

Death certificate reviews have inherent limitations. They tend to underestimate mortality for specific causes--contributing diseases are not always reported. Also, it is generally recognized that occupational and environmental diseases are under-reported. Thus, it is expected that mortality in Libby from asbestos-related disease is even higher than shown in the death certificate review. ATSDR has also received anecdotal information from Libby residents that more people in Libby have contracted and died from asbestos-related illness since 1998, the last year covered in the ATSDR mortality review.

Cohort studies following Libby vermiculite mine workers as a group (including workers who moved away from the Libby area) have reported similarly high rates of mortality from asbestos-related diseases as in the ATSDR community-focused study [32,10,12]. One study has reported 12 confirmed mesothelioma cases out of 406 workers as of 2002 [32].


Determining a quantitative risk of health effects to Libby community members from exposure to Libby asbestos is difficult for several reasons. First, significant uncertainties and conflicts in the methods used to analyze asbestos exist. Also, the exact level of health concern for different sizes and types of asbestos remains controversial due to limitations in toxicological information currently available. Analytical techniques and toxicology issues specifically related to the Libby asbestos from the Libby vermiculite mine are areas deserving substantial further research. It has been reported to ATSDR that McDonald et al. have quantified risks from very low-level exposures to Libby asbestos based on worker cohort studies (personal communication, Bruce Case, McGill University, February 2003). At the time of the writing of this report, this study was unpublished and not available for review (personal communication, J. Corbett McDonald, (UK) National Heart and Lung Institute, February 2003). It is not known whether this risk quantitation would be applicable to community exposures, the vast majority of which are much lower than worker exposures. In addition, we still do not have enough information to estimate community exposures leading to risk.

Despite these uncertainties, given the health outcome data presented above, it is likely that continuing exposure to Libby asbestos increases the risk of malignant and nonmalignant respiratory disease.

The mortality review showed that almost all the deaths from asbestos-related disease occurred in former workers of the vermiculite facility or their household contacts. It is not surprising that the workers would show the highest mortality, as they were exposed to the highest concentrations of asbestos for the longest period of time. The greater level of exposure combined with the long exposure duration (average length of employment was close to 20 years) would increase the risk of disease and effectively reduce the latency period before onset of disease.

People who had lower exposures or shorter durations of exposure--or both--could exhibit longer latency periods before the onset of disease. For example, a recent case report described a patient who had a brief (summer employment for two years) but high intensity exposure to Libby asbestos. About 30 years later, the patient showed pleural abnormalities on chest x-rays but had no symptoms of asbestos-related disease for another 10 years, when fatal asbestosis quickly set in [33]. No direct causal relationship between pleural abnormalities and asbestos-related diseases has ever been demonstrated. However, both conditions are associated with asbestos exposure, and it is reasonable to assume that people who exhibit pleural abnormalities could be at higher risk for asbestos-related diseases, including asbestosis and lung cancers. The elevated number of pleural abnormalities, in both former workers and other residents around Libby, suggests that additional cases of asbestos-related disease may occur in coming years.

Summary of Removal and Remedial Actions Completed and Proposed

Because risk is based on exposure level and duration, the risk of asbestos-related health effects can be effectively reduced by interrupting continuing exposures to Libby asbestos. EPA has been and continues to perform emergency removal and remedial activities to interrupt major sources of Libby asbestos and Libby asbestos-contaminated materials in and around Libby. This section reviews these activities with respect to their effectiveness in protecting public health.

Mine Site–Because the mine site is in a remote area, it is unlikely that people will have large, continuing exposure to asbestos there. To minimize the chance of exposure, EPA has paved Rainy Creek Road, closed the entrance to Rainy Creek Road, and placed warning signs at the road entrance and around the mine. Although further investigation and cleanup of the mine site is expected, at this time these actions will be protective of public health.

Screening Plant / Export Plant–EPA provided ATSDR with plans for removal of contamination at these facilities. ATSDR reviewed the plans and determined that they would be protective of public health [5]. Remediation of both of these sites is complete [34].

Schools–Cleanup of school grounds has occurred. Cleanup of school running tracks is also complete [34].

Residential and Commercial Properties–EPA published a Sampling and Analysis Plan for prioritizing residential and commercial properties for cleanup [1]. ATSDR reviewed this plan and found it would be protective of public health. To assure proper disposal of waste materials from the residential cleanup activities, EPA is constructing a special cell in the county landfill.

The contaminant screening study is complete. Of the screened properties, approximately 6% have indoor visible vermiculite in insulation or building materials, about 31% have visible vermiculite outdoors in gardens or yards, and about 6% have both. Two hundred eighty-one property owners denied EPA access for screening. Residential cleanups are underway, but the final determination of how many properties will be cleaned is awaiting results of the soil samples collected during the contaminant screening study (personal communication, Jeff Montera, Camp Dresser & McKee and Jim Christiansen, U.S. Environmental Protection Agency, November 2002).

Children's Health Considerations

ATSDR recognizes that infants and children might be more vulnerable to exposures than adults in communities faced with environmental contamination. Because children depend completely on adults for risk identification and management decisions, ATSDR is committed to evaluating their special interests at the site as part of the ATSDR Child Health Initiative.

The effects of asbestos on children are thought to be similar to adults. However, children could be especially vulnerable to asbestos exposures because:

  • children are more likely to disturb fiber-laden soils or indoor dust while playing,
  • children are closer to the ground and thus more likely to breathe contaminated soils or dust,
  • children have faster breathing rates that may increase the level of exposure to asbestos, and
  • children could be more at risk than those exposed later in life because of the long latency period between exposure and onset of asbestos-related respiratory disease.

Many of the most highly contaminated areas have been addressed through emergency removals. Thus, children today have a lower risk of health effects than children in the past.

Community Health Concerns

Community concerns about the health effects of asbestos exposure have been identified through ATSDR's activities in Libby. Concerns have been expressed during Community Advisory Group (CAG) meetings and other interactions with community members. ATSDR has also maintained a presence in Libby at EPA's Information Center and encouraged people to share their concerns. ATSDR held public availability sessions on September 27 and 28, 2002, to give community members a chance to share concerns about the site that they feel have not been addressed. Approximately 13 community members shared concerns at these public availability sessions.

The health-related concerns identified through these community interactions are listed and addressed below:

(1) Concern: I have been diagnosed as having asbestosis. What can I do now to keep myself healthy and protect myself from a worsening condition?

(1) Response: It is important for you to follow up with your personal physician on an ongoing basis. In addition, ATSDR has developed a brochure entitled "Living With Asbestos-Related Illness: A Self-Care Guide," which describes actions people can take to improve their health and quality of life. This brochure is included in Appendix B of this document.

(2) Concern: What is the procedure for getting further x-rays done? Do I need a written order from my doctor?

(2) Response: You should consult your doctor for a referral if, based on your occupational and/or medical history, he or she recommends a chest x-ray. You can also utilize the medical services at the Center for Asbestos-Related Disease (CARD) clinic in Libby. Periodic screening will also be performed for eligible persons. Contact Dr. Michael Spence, Montana State Medical Officer, for information on the testing program.

(3) Concern: I would like a listing of board-certified pulmonologists in the area who would be able to treat my asbestosis. Will someone be setting up a practice in Libby? If I get sicker, I might not be able to drive as far as I do now.

(3) Response: ATSDR staff performed a search on October 25, 2002 for medical doctors in Montana, Idaho, and Washington licensed in the subspecialty of pulmonary disease on the Web site of the American Board of Medical Specialties ( ). ATSDR received permission from ABMS to provide the search results as a community service with the understanding that the search results were for consumer use only.

The names and locations of licensed pulmonary disease physicians whose addresses were within 350 miles of Libby are included in Appendix C. ATSDR does not endorse any individual physician listed and will not pay for any services provided by the listed physicians. In addition, although the physician certification information in the ABMS database is updated periodically with data provided by its member boards, due to the possibility of reporting and processing delays, the accuracy and completeness of the list cannot be guaranteed. Neither ATSDR nor ABMS can be held responsible for incomplete or inaccurate information. For updated information, consumers can register to perform searches on the ABMS Web site, or they can verify the certification of a physician by calling 1-866-ASK-ABMS.

ATSDR does not know whether any pulmonologist will set up practice in Libby.

(4) Concern: I have a general concern with the predominance of cancer here.

(4) Response: As described earlier, ATSDR found that deaths from lung cancer and from mesothelioma were elevated in the Libby area when compared with the state of Montana and with the United States as a whole. Deaths from digestive cancers were not higher than expected. Past exposure of people to asbestos is associated with increased risk of mesothelioma and lung cancer. The removal of asbestos sources from the community is expected to eventually result in fewer cases of mesothelioma and lung cancer. However, the long latency period between exposure and onset of disease suggests that people who were exposed in the past could continue to develop asbestos-related cancers for some time to come.

Other types of cancer are not associated with exposure to asbestos. Risk factors that could contribute to a person's risk of developing cancer include genetics, age, lifestyle, diet, and smoking history. People who feel they have an elevated risk of cancer should consult their health care provider for additional information, precautions, or preventative measures.

(5) Concern: More research needs to be done on treatments and a cure for asbestosis and other asbestos-related disease.

(5) Response: Your comment is noted, and some potential resources for information on current research projects are listed in this response. Information on current research studies on many diseases, including asbestos-related diseases, can be found on the National Institutes of Health (NIH) Clinical Trials Database at URL . Another potential resource is the National Library of Medicine's PubMed search engine, available at URL which allows searches by keyword of citations in the biomedical literature.

ATSDR does not perform or provide funding for clinical studies pertaining to the treatment of disease, but we do fund scientific research on mechanisms of toxicity. Results from these studies can eventually assist in the understanding of disease etiology, progression, and possible treatment. In addition, ATSDR Toxicological Profiles identify data needs for methods of reducing toxic effects, and we may support or fund future research in this area.

(6) Concern: The CT study results prove that more than one B-reader is needed to make a determination on chest x-ray. The state of Montana has said it will use only one B-reader. ATSDR should maintain the lead for the ongoing medical screening to ensure that the same protocol is used for the ongoing screening as was used in the 2000 and 2001 testing.

(6) Response: According to Montana State Medical Officer Dr. Michael Spence, at this time one B-reader is planned for ongoing screening [35]. The plan is to continue screening periodically those people who previously had negative screening results, as well as people who were not previously screened. Multiple readings over the period of several years should ensure that disease is detected even using only one B-reader. All other protocols and eligibility criteria will be identical to those used in the 2000 and 2001 medical screening.

(7) Concern: Both x-ray and CT scans should be used for screening to identify the full extent of the problem.

(7) Response: The chest x-ray is a standard screening test for workers exposed to asbestos dusts. Radiation dose to the patient from a CT scan is much greater than that from a chest x-ray. The periodic x-ray screening as proposed by the state of Montana should adequately identify the extent of asbestos-related disease in the community. However, CT scans may be considered to further screen high-risk persons who have questionable chest x-rays.

(8) Concern: More health education on smoking cessation specifically targeted to the Libby community is needed. Programs should emphasize that a person's risk of developing lung cancer after asbestos exposure is greatly increased if he or she smokes. Program materials or information should be easily accessible to the community (for example, published in the local newspaper).

(8) Response: Contact the state of Montana for information on their smoking cessation program.

(9) Concern: Smoking cessation patches should be provided free of charge to smokers in the community.

(9) Response: Your suggestion is noted. ATSDR agrees with the need to encourage people in Libby to stop smoking, as quitting would greatly reduce their risk of developing lung cancer. Patches cost about the same as cigarettes, so people can switch without financial assistance.

(10) Concern: The Libby Center for Asbestos-Related Diseases needs the new, state-of-the-art cancer detection equipment I saw reviewed on a science program on television.

(10) Response: ATSDR staff were unable to locate information on the cancer detection equipment the commenter mentioned. We found reference to several different types of blood tests for enzymes produced by cancerous cells that would allow early detection. It is possible that earlier detection of mesothelioma and lung cancers could increase survival rates. However, to our knowledge, no screening method exists that has been proven to increase survival rates.

(11) Concern: Twenty-three members of my immediate family had or have asbestos-related disease.

(11) Response: ATSDR recognizes that the Libby community has faced a tragic and unfair burden due to the diseases caused by the exposure of people to asbestos over many years. The actions that have been and are being taken should prevent future contributions to cumulative exposures.

(12) Concern: Anecdotal account of person dying from mesothelioma recently who had no occupational or household contact--only exposure from deteriorating insulation.

(12) Response: Information about the histories of persons diagnosed with mesothelioma in the Libby community will further our knowledge about how the disease is caused. However, it is difficult to determine exactly how and how much people were exposed to Libby asbestos in the past. Many other pathways, including ambient air and neighborhood waste piles, could have contributed to this person's exposure in the past.

(13) Concern: Does asbestos cause autoimmune disorders such as lupus, rheumatoid arthritis, and fibromyalgia?

(13) Response: Not enough information exists at this time to determine whether asbestos causes autoimmune diseases. A number of studies have shown that asbestosis is associated with immunological changes that could theoretically make a person more susceptible to autoimmune disorders. According to a recent allergy textbook, "immunologic abnormalities in animal models and patients with asbestosis include abnormal lymphocyte accumulation in the lower respiratory tract, abnormal T-lymphocyte subsets in BAL [bronchoalveolar lavage] fluid, evidence of decreased cell-mediated immunity, and diminished suppressor T cell function." The text continues, however, "Correlation of these abnormalities (systemic or local) with the clinical features of asbestosis . . . has not been clearly demonstrated" [36]. In other words, it is not known at this time whether the changes are causally linked to the asbestosis or exposure to asbestos. It is also possible that people who have autoimmune abnormalities could be more likely to develop asbestos-related disease. Please see page 12 of this document for a more detailed treatment of this subject.

(14) Concern: I would like to see a discussion of the SV40 virus and other viruses known to affect development of cancers. Is there any record of whether SV40-contaminated vaccine was distributed in Libby? Please comment on additional risk to Libby in light of the latency periods involved.

(14) Response: The information in this response comes from a number of review articles found through a search on the online database PubMed, a service of the National Library of Medicine which provides access to MEDLINE citations dating to the 1960s [37,38,39,40,41,42,43,44,45]. SV40 is a simian (monkey) virus that has known oncogenic (tumor-causing) properties, including causing mesothelioma in hamsters. SV40-infected monkey cells were inadvertently used to produce polio vaccines from 1954 to 1961, resulting in the exposure of wide populations to infectious SV40 until around 1963. The exact means by which SV40 initially entered the population and/or how it may have spread is unclear; SV40 has been detected in people who were either too old or too young to receive the infected vaccines.

When the polio vaccine contamination was first discovered, epidemiological studies did not indicate any short-or long-term effects in the humans exposed. SV40 became an important tool in molecular laboratories and contributed to the elucidation of many cellular mechanisms. The development of the polymerase chain reaction (PCR) allowed researchers to detect very small amounts of genetic material, and through the use of this technique it has been found that a significant fraction (up to 60%) of some cancers (especially mesotheliomas, brain, and bone cancers) contain SV40 DNA. Many scientists initially thought the detections were "false positives" caused by laboratory contamination, but further multi-laboratory studies using adequate controls have added strength to the finding. SV40 has been shown to cause the above rare cancers in animals.

Whether and how SV40 actually causes cancer in humans is under active investigation. SV40 is known to induce DNA alterations and interfere with programmed cell death of defective cells. The combination of (amphibole) asbestos with SV40 could synergistically increase the risk of mesothelioma. It has been postulated that asbestos has immunosuppressant properties that allow SV40 to replicate and cause mutagenic changes for a longer time without killing mesothelial cells, increasing the likelihood of a cell becoming cancerous.

The Immunization Safety Review Committee of the Institute of Medicine recently released an evaluation of the evidence on possible causal relationships between contamination of the polio vaccine with SV40 and cancer. The committee concluded that "the evidence is inadequate to accept or reject a causal relationship between SV40-containing polio vaccines and cancer" [46].

No research was found showing whether SV40 decreases the latency period of onset of mesothelioma (over 30 years on average). SV40 is not associated with lung cancer or other asbestos-related diseases.

For Libby, it is impossible to determine if an additional risk of mesothelioma might result from SV40. No known record exists of whether SV40-contaminated vaccines were actually distributed there. Time of vaccination does not necessarily prove exposure, because it is estimated that only 10 to 30% of the polio vaccine produced actually contained infectious virus. However, the possibility of additional risk does exist, since some people would have been vaccinated during the time that contaminated vaccines were in general distribution. Regardless of whether a person is infected with SV40, removing the sources of exposure to asbestos will even further reduce the very low risk of developing mesothelioma.

(15) Concern: People in Libby were exposed to pollutants from drinking water contaminated by another Superfund site before it was cleaned up. Is there a relationship or synergistic effect between other carcinogens and mineral fibers or viruses?

(15) Response: The commenter is referring to the Libby Groundwater NPL site, consisting of soil and groundwater contaminated with wood treating fluids at the former Champion lumber and plywood mill (now occupied by Stimson Lumber) [47]. The contamination at this site was discovered in 1979 when, shortly after installation of private wells in the area, homeowners noticed a strong creosote odor in their water. The groundwater contained pentachlorophenol (PCP), polycyclic aromatic hydrocarbons, and heavy metals. The site was listed on the NPL in 1983. Homeowners were connected to municipal water, existing private wells were plugged and abandoned, and the source-contaminated soils were excavated and treated. A city ordinance now prohibits the installation of new wells for drinking water or irrigation. ATSDR concluded in 1993 that the site poses no apparent public health hazard [48]. The main contaminant of concern in the groundwater was PCP, which is toxic to the liver, thyroid, immune and reproductive systems, and developing organisms. PCP is not expected to interact with asbestos, which affects a different target organ (the lungs and respiratory system). When inhaled, some PAHs and metals have the same target organs as asbestos; however, the major route of exposure for the Libby Groundwater site was ingestion, so no interactions are likely to have occurred.

Asbestos and smoking are known to increase the risk of lung cancer and asbestosis more than predicted by additivity. It is not known whether the effect is a result of synergistic interactions of asbestos and carcinogens inhaled in smoke, reduced lung clearance in smokers leading to higher lung burden of asbestos, or both [15]. The previous response discussed possible interactions of asbestos and the SV40 virus; no information was found on interaction of asbestos with other carcinogens or viruses.

(16) Concern: ATSDR must follow through on their mandate as described on p. 181 of the Toxicological Profile for Asbestos, "Section 104(i)(5) of CERCLA, as amended, directs the Administrator of ATSDR (in consultation with the Administrator of EPA and agencies and programs of the Public Health Service) to assess whether adequate information on the health effects of asbestos is available. Where adequate information is not available, ATSDR, in conjunction with the National Toxicology Program (NTP), is required to assure the initiation of a program of research designed to determine the health effects (and techniques for developing methods to determine such health effects) of asbestos."

(16) Response: ATSDR has met this requirement by producing the document Priority Data Needs for Asbestos, which also describes the ATSDR substance-specific applied research program for asbestos. This document is currently awaiting peer review. Copies of the final document can be obtained by contacting ATSDR, Division of Toxicology, Mail Stop E-29, Atlanta GA 30333.

(17) Concern: Initial contact with community members for participation in the registry should be done by someone locally, face-to-face, if possible. It is difficult to give confidential personal information over the telephone, and this reduces participation. We need full participation to get the best information from the study.

(17) Response: Initial contacts for the registry are being made by telephone interviews. This registry is targeting all former workers and their household contacts, not just workers in Libby. Because the workers are located all over the country, telephone interviews are necessary to prevent any bias that might be introduced if some people were interviewed face-to-face and others by telephone. As of October 19, 2002, 1,171 workers and household contacts had been interviewed out of an estimated total of 6,000. It is anticipated that an excellent rate of participation will be achieved by the projected end of the contract in April 2003.

(18) Concern: What is the risk to residents, children, and visitors from vermiculite insulation dust potentially sifting into living spaces?

(18) Response: If the insulation does not contain asbestos, it poses no risk of asbestos-related illnesses. However, any vermiculite insulation in Libby can be assumed to contain asbestos. If the insulation remains undisturbed, it is not considered to pose a significant risk. However, if the insulation is creating dust, the dust may contain microscopic asbestos fibers which increase the risk of asbestos-related health effects when breathed in. The exact level of risk depends on how many fibers were breathed in and how long the exposure lasted. In addition, a person's response to exposure differs and could be based upon genetic makeup and certain lifestyle activities, particularly smoking. People who suspect they have been exposed to asbestos fibers, especially if the exposure was long-term, should consult a physician experienced in occupational and environmental medicine or pulmonary medicine.

(19) Concern: I am very sick with asbestosis. Why was I not assigned a higher priority in EPA's testing and cleanup?

(19) Response: The following information is taken from EPA's Question and Answer Web page on Libby ( ).

EPA must continue to clean up properties based on two primary factors:

1. Conditions at the property based on sample results and visual inspections. Homes will be generally prioritized using these criteria:

    (higher priority)
  • multiple sources of Libby asbestos and high levels detected
  • single source of Libby asbestos and high levels detected
  • potential for immediate contact with Zonolite
  • home sale pending on home with Zonolite or low levels detected
  • Zonolite present only

  • (lower priority)

2. Location of the property. At times, homes with conditions dictating a lower priority may get cleaned up faster because it's near a higher priority home. This will cut cleanup time and is the only way EPA can clean so many properties in just a few years.

Until your home is cleaned up, EPA gives the following advice (also from EPA's Q&A web page):

If you have or suspect that you have Zonolite insulation in your home, the safest course of action is to leave the material alone. Avoid any activities that may spread vermiculite and asbestos into your living space such as using the attic for storage. Likewise, seal any spaces, cracks or gaps in the ceiling or around light fixtures through which asbestos could escape from the attic. If you decide to remove or must otherwise disturb the material due to a renovation project, please consult with an experienced asbestos contractor.

(20) Concern: Concern that there are no health-based risk values other than for cancer.

(20) Response: ATSDR recommends in this document that toxicological investigation of the risks associated with low-level exposure to asbestos, specifically with the chemical makeup and fiber size of Libby asbestos, be performed. This research would allow development of more health-based risk values.

(21) Concern: Concern that regulation of asbestos is not protective of public health because it is not regulated as an air pollutant.

(21) Response: Friable asbestos (asbestos which is crumbly and can be broken down to suspendable fibers) is listed as a Hazardous Air Pollutant on EPA's Toxic Release Inventory [27]. This requires companies that release friable asbestos at concentrations greater than a 0.1% de minimus limit to report the release under Section 313 of the Emergency Planning and Community Right-to Know Act. Asbestos is not one of the six "criteria pollutants" used by EPA as indicators of air quality throughout the United States.

ATSDR, as an advisory health agency, does not make or enforce laws.

(22) Concern: I think all the government agencies here are doing a terrific job.

(22) Response: Thank you for your comment. We will continue to work with the local community and other agencies to address public health issues at this site.

(23-27) Economic Concerns

  • The community members who participate in research need to have coverage provided to protect them from complications that might arise due to their participation in the advancement of the science.
  • My concern is with the progression of the disease and the care issues involved; I fear there will be no one to pay for care.
  • I am not sick now, but I am concerned about the potential cost if I develop asbestos-related disease at a later date. Will Grace money be available until my Medicare starts? Will there be government funds available if Grace goes bankrupt?
  • I have concerns regarding the long-term health care costs related to asbestosis, and additional diseases I have that have not been definitively linked to asbestos exposure.
  • I am concerned on the economic impact this has had on the community.

(23-27) Response: Your concerns are noted. ATSDR recognizes that the people of Libby have suffered economic as well as human losses. We are concerned that more people who have been exposed to asbestos may develop asbestos-related disease. ATSDR does not have the authority to pay for or provide medical care or to make judgments about who should pay for care.

The Libby Asbestos Public Health Assessment was available for public review and comment from December 30, 2002 until March 14, 2003, on the Internet, at the Lincoln County Library in Libby, and at the EPA Information Center in Libby. The public comment period was announced to local media outlets. The PHA was also sent to federal, state, and local officials. The findings of the PHA were presented by ATSDR staff at the February 13, 2003 CAG meeting in Libby, Montana. The written public comments received are listed and addressed in Appendix D.


On the basis of known past exposures and resulting disease rates, to protect public health it is prudent to reduce known continuing exposures to Libby asbestos. ATSDR concludes that locations where Libby asbestos -contaminated vermiculite has the potential to become airborne during people's normal activities pose a current public health hazard to the people of Libby.

ATSDR has also evaluated the cleanup actions and plans for cleanup taken by EPA. These actions, provided confirmation testing indicates effective reduction of Libby asbestos levels, have been and will be protective of public health by reducing continuing Libby asbestos exposures. Areas that have been cleaned up as described are not likely to pose a hazard. Although very small amounts of asbestos could still be present, the potential for significant exposure is expected to be very small. Therefore, ATSDR characterizes these areas as no apparent public health hazard.

On the basis of historical information and current health outcome data, ATSDR concludes that the site was a past public health hazard. Workers at the mine, their household contacts, and people not occupationally exposed at the mine were exposed to airborne Libby asbestos at unsafe levels. This exposure has resulted in significantly elevated levels of asbestos-related disease in the area.

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