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  • 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 withexposure 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.


  • 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.


The Public Health Action Plan for the site contains a description of actions that have been or will be taken by ATSDR and/or other government agencies at the site. The purpose of the Public Health Action Plan is to ensure that this public health assessment not only identifies public health hazards, but provides a plan of action designed to mitigate and prevent adverse human health effects resulting from exposure to hazardous substances in the environment. Included is a commitment on the part of ATSDR to follow up on this plan to ensure its implementation. The public health actions that have been completed are as follows:

  • ATSDR published four health consultations evaluating public health implications related to Libby asbestos.
  • ATSDR implemented two rounds of medical testing for signs of asbestos-related disease.
  • ATSDR conducted a site visit to verify site conditions and gather pertinent information and data for the site.
  • ATSDR and EPA maintained personnel in an information center in Libby to inform the community about site-related health and environmental activities.
  • EPA conducted emergency removals of many contaminated areas in and around Libby.
  • ATSDR held a public availability session to gather health concerns from the Libby community.
  • ATSDR presented results of the combined two rounds of medical testing performed in 2000 and 2001, the updated mortality review, and the computed tomography (CT) study to the Libby community.

The public health actions to be implemented follow:

  • MDPHHS will provide ongoing medical testing in Libby to qualified individuals, with funding and technical assistance provided by ATSDR.
  • ATSDR will work with MDPHHS to develop a registry to track former workers of the vermiculite mine and their household contacts. ATSDR will assess the feasibility of including other populations in the registry.
  • EPA will continue investigating and cleaning up the site as needed.
  • ATSDR will produce an addendum to this PHA evaluating the public health impact of the mine site (OU3). This addendum will be produced during EPA's RI activities for OU3.

ATSDR will reevaluate and expand this plan when needed. New environmental, toxicological, or health outcome data or the results of implementing the above proposed actions could determine the need for additional actions at this site.

Public health issues similar to those at the Libby Asbestos NPL site are occurring at several sites across the country. These were not discussed here because the public health assessment is a site-specific document. ATSDR has addressed and will continue to address questions related to amphibole asbestos released from Libby vermiculite processing sites, the World Trade Center collapse, natural deposits in various locations, and others. For specifics on ATSDR's activities with these sites, please contact the ATSDR Office of Policy and External Affairs at 1-888-422-8737.


Jill J. Dyken, Ph.D., P.E.
Environmental Health Scientist
Superfund Site Assessment Branch
Division of Health Assessment and Consultation

John Wheeler, Ph.D., DABT
Exposure Investigation and Consultation Branch
Division of Health Assessment and Consultation

Dan Strausbaugh
Regional Representative
Region 8, Montana Office
Office of Regional Operations

Maria Teran-MacIver
Health Communication Specialist
Community Involvement Branch
Division of Health Assessment and Consultation

Kristina Larson, MHEd., CHES
Senior Health Education Specialist
Health Education Branch
Division of Health Education and Promotion

Vikas Kapil, D.O., MPH
Senior Medical Officer
Division of Health Studies
Office of the Director


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  2. Agency for Toxic Substances and Disease Registry. Health consultation for Libby Asbestos. Atlanta, GA: US Department of Healthand Human Services. December 22, 1999.

  3. Agency for Toxic Substances and Disease Registry. Health consultation on mortality from asbestosis in Libby, Montana for LibbyAsbestos site. Atlanta, GA: US Department of Health and Human Services. December 12, 2000.

  4. Agency for Toxic Substances and Disease Registry. Health consultation on export plant and screening plant for Libby Asbestos site.Atlanta, GA: US Department of Health and Human Services. May 22, 2000.

  5. Agency for Toxic Substances and Disease Registry. Health consultation on Libby export plant and screening plant removal plans.Atlanta, GA: US Department of Health and Human Services. November 3, 2000.

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  10. McDonald JC, McDonald AD, Armstrong B, Sebastien P. Cohort study of mortality of vermiculite miners exposed to tremolite. Br JInd Med 1986;43:436-444.

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  19. Agency for Toxic Substances and Disease Registry. Preliminary findings of Libby, Montana computed tomography study. URL: Accessed October 29, 2002.

  20. US Environmental Protection Agency. Administrative record for Libby Asbestos Superfund site export/screening plant and supplement.Denver, CO: US Environmental Protection Agency, Region 8. Provided electronically in May, 2002.

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  26. US Environmental Protection Agency. Integrated risk information system (for asbestos). URL: Accessed July 31, 2002.

  27. US Environmental Protection Agency. Toxic air pollutants Web site. URL: Accessed October 29, 2002.

  28. National Institute of Occupational Safety and Health. Online NIOSH pocket guide to chemical hazards. URL: Accessed July 16, 2002.

  29. American Conference of Government Industrial Hygienists. 2000 Threshold limit values for chemical substances and physical agentsand biological exposure indices. Cincinnati, OH: 2000.

  30. US Environmental Protection Agency. National primary drinking water regulations. URL: Accessed July 16, 2002.

  31. Montana Department of Environmental Quality. Circular WQB-7. Montana numeric water quality standards. September 1999. URL: Accessed July 16, 2002.

  32. McDonald JC, Harris J, Armstrong B. Cohort mortality study of vermiculite miners exposed to fibrous tremolite: an update. Ann OccHyg 2002;40:93-94.

  33. Wright RS, Abraham JL, Harber P, Burnett BR, Morris P, West P. Fatal asbestosis 50 years after brief high intensity exposure in avermiculite expansion plant. Am J Respir Crit Care Med 2002;165:1145-1149.

  34. Libby Community Advisory Group. Meeting summary for October 10, 2002 (report by Wendy Thomi on behalf of EPA). URL: Accessed April 3, 2003.

  35. Libby Community Advisory Group. Meeting summary for October 10, 2002 (report by Dr. Michael Spence, Montana Medical Officer). URL: Accessed October 24, 2002.

  36. Middleton E. (ed.) Allergy: principles and practice, 5th ed., p. 489. Mosby: 1998.

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  38. Ferber D. Monkey virus link to cancer grows stronger. Science 2002;296:1012-15.

  39. Klein G. Simian virus 40 and the human mesothelium. Proc Natl Acad Sci USA 2000; 97:9830-31.

  40. Toyooka S, Carbone M, Toyooka KO, Bocchetta M, Shivapurkar N, Minna JD, Gazdar AF. Progressive aberrant methylation of theRASSF1A gene in simian virus 40 infected human mesothelial cells. Oncogene 2002;21:4340-44.

  41. Carbone M. Introduction [to special volume on SV40]. Semin Cancer Biol 2001;11: 1-3.

  42. Jasani B, Cristaudo A, Emri SA, Gazdar AF, Gibbs A, Krynska B, Miller C, Mutti L, Radu C, Tognon M, Procoio A. Association ofSV40 with human tumours. Semin Cancer Biol 2001;11:49-61.

  43. Klein G, Powers A, Croce C. Meeting report: association of SV40 with human tumors. Oncogene 2002;21:1141-49.

  44. Nelson NJ. Debate on the link between SV40 and human cancer continues. J Natl Cancer Inst 2001;93:1284-86.

  45. Procopio A, Strizzi L, Vianale G, Betta P, Puntoni R, Fontana V, Tassi G, Gareri F, Mutti L. Simian virus 40 sequences are a negativeprognostic cofactor in patients with malignant pleural mesothelioma. Genes Chromosomes Cancer 2000;29:173-79.

  46. Stratton K Almario DA McCormick MC eds. Immunization safety review: SV40 contamination of polio vaccine and cancer.Washington: The National Academies Press, October 22, 2002. URL: Accessed October 25, 2002.

  47. US Environmental Protection Agency. NPL site fact sheet, Libby Groundwater site, Libby, Lincoln County, Montana. Helena, MT:EPA Region 8, Superfund; Revised October 23, 2002. URL: Accessed on October 25, 2002.

  48. Williams RC Agency for Toxic Substances and Disease Registry. Letter to J. Wardell of EPA Region 8 Montana office concerningLibby groundwater NPL site. Atlanta, GA: US Department of Health and Human Services. January 14, 1994.

  49. US Environmental Protection Agency. Current and revised standards for ozone and particulate matter. URL: Accessed on April 1, 2003.

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How a chemical enters a person's blood after the chemical has been swallowed, has come into contact with the skin, or has been breathed in.

Acute Exposure:
Contact with a chemical that happens once or only for a limited period of time. ATSDR defines acute exposures as those that might last up to 14 days.

Additive Effect:
A response to a chemical mixture, or combination of substances, that might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

Adverse Health Effect:
A change in body function or the structures of cells that can lead to disease or health problems.

A large group of silicate minerals with more than 40-50 members. The molecular structure of all amphiboles consists of two chains of SiO4 molecules that are linked together at the oxygen atoms. In the earth's crust, amphibole minerals are mostly nonasbestiform; asbestiform amphiboles are relatively rare. See definitions of asbestiform, mineral, and mineral habit.

Antagonistic Effect:
A response to a mixture of chemicals or combination of substances that is less than might be expected if the known effects of individual chemicals, seen at specific doses, were added together.

A habit of crystal aggregates displaying the characteristics of asbestos: groups of separable, long, thin, strong, and flexible fibers often arranged in parallel in a column or in matted masses. See definitions of mineral and mineral habit. Mineralogists call asbestiform amphibole minerals by their mineral name followed by "asbestos." Thus, asbestiform tremolite is called tremolite asbestos.

A group of highly fibrous minerals with separable, long, thin fibers often arranged in parallel in a column or in matted masses. Separated asbestos fibers are generally strong enough and flexible enough to be spun and woven, are heat resistant, and are chemically inert. See definitions of fibrous and mineral. Currently, U.S. regulatory agencies recognize six asbestos minerals: the serpentine mineral, chrysotile; and five asbestiform amphibole minerals, actinolite asbestos, tremolite asbestos, anthophyllite asbestos, amosite asbestos (also known as asbestiform cummingtonite-grunerite), and crocidolite asbestos(also known as asbestiform riebeckite). Proposals have been made to update asbestos regulations to include other asbestiform amphibole minerals such as winchite asbestos and richterite asbestos.

Interstitial fibrosis of the pulmonary parenchymal tissue in which asbestos bodies (fibers coated with protein and iron) or uncoated fibers can be detected. Pulmonary fibrosis refers to a scar-like tissue in the lung which does not expand and contract like normal tissue. This makes breathing difficult. Blood flow to the lung can also be decreased, and this causes the heart to enlarge. People with asbestosis have shortness of breath, often accompanied by a persistent cough. Asbestosis is a slow-developing disease that can eventually lead to disability or death in people who have been exposed to high amounts of asbestos over a long period. Asbestosis is not usually of concern to people exposed to low levels of asbestos.

The Agency for Toxic Substances and Disease Registry. ATSDR is a federal health agency in Atlanta, Georgia that deals with hazardous substance and waste site issues. ATSDR gives people information about harmful chemicals in their environment and tells people how to protect themselves from coming into contact with chemicals.

Background Level:
An average or expected amount of a chemical in a specific environment, or amounts of chemicals that occur naturally in a specific environment.

See Relative Bioavailability.

Used in public health, things that humans would eat--including animals, fish and plants.

A group of diseases which occur when cells in the body become abnormal and grow, or multiply, out of control

Cancer Slope Factor (CSF):
The slope of the dose-response curve for cancer. Multiplying the CSF by the dose gives a prediction of excess cancer risk for a contaminant.

Any substance shown to cause tumors or cancer in experimental studies.

Chronic Exposure:
A contact with a substance or chemical that happens over a long period of time. ATSDR considers exposures of more than one year to be chronic.

Cleavage Fragment:
Microscopic particles formed when large pieces of nonasbestiform amphiboles are crushed, as could occur in mining and milling of ores. Within a population of nonasbestiform amphibole cleavage fragments, a fraction of the particles could fit the definition of a fiber adopted for counting purposes. Populations of asbestos fibers can be readily distinguished from populations of nonasbestiform cleavage fragments, but sometimes it can be difficult to distinguish an isolated nonasbestiform cleavage fragment from an isolated asbestos fiber. See definitions of asbestiform, fiber, fibrous, and mineral habit.

Completed Exposure Pathway:
See Exposure Pathway.

Community Assistance Panel (CAP):
A group of people from the community and health and environmental agencies who work together on issues and problems at hazardous waste sites.

Comparison Value (CV):
Concentrations of substances in air, water, food, and soil which are unlikely, upon exposure, to cause adverse health effects. Comparison values are used by health assessors to select which substances and environmental media (air, water, food and soil) need additional evaluation while health concerns or effects are investigated.

Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA):
Congress enacted CERCLA in 1980. The act is also known as Superfund. This act addresses releases of hazardous substances into the environment, the cleanup of these substances, and hazardous waste sites. This act created ATSDR and gave it the responsibility to look into health issues related to hazardous waste sites.

How much or the amount of a substance present in a certain amount of soil, water, air, or food.

See Environmental Contaminant.

Delayed Health Effect:
A disease or injury that happens as a result of exposures that occurred far in the past.

Dermal Contact:
A chemical getting onto your skin (see Route of Exposure).

The amount of a substance to which a person might be exposed, usually on a daily basis. Dose is often explained as "amount of substance(s) per body weight per day."

Dose / Response:
The relationship between the amount of exposure (dose) and the resultant change in body function or health.

The amount of time (days, months, years) that a person is exposed to a chemical.

Environmental Contaminant:
A substance (chemical) that gets into a system (person, animal, or the environment) in amounts higher than the Background Level, or what would be expected.

Environmental Media:
Usually refers to the air, water, and soil in which chemicals of interest are found. Sometimes refers to the plants and animals eaten by humans. Environmental Media is the second part of an Exposure Pathway.

US Environmental Protection Agency (EPA):
The federal agency that develops and enforces environmental laws to protect the environment and the public's health.

The study of the different factors that determine how often, in how many people, and in which people will disease occur.

Coming into contact with a chemical substance. (For the three ways people can come in contact with substances, see Route of Exposure.)

Exposure Assessment:
The process of finding the ways people come in contact with chemicals, how often and how long they come in contact with chemicals, and the amounts of chemicals with which they come in contact.

Exposure Pathway:
A description of the way a chemical moves from its source (where it began) to where and how people can come into contact with (or get exposed to) the chemical.

ATSDR defines an exposure pathway as having 5 parts:

  1. Source of Contamination,
  2. Environmental Media and Transport Mechanism,
  3. Point of Exposure,
  4. Route of Exposure, and
  5. Receptor Population.

When all 5 parts of an exposure pathway are present, it is called a Completed Exposure Pathway. Each of these 5 terms is defined in this Glossary.

Any slender, elongated mineral structure or particle. For the purposes of counting asbestos fibers in air samples, regulatory agencies commonly count particles that have lengths >5 µm and length:width ratios >3:1 as fibers. For detecting asbestos fibers in bulk building materials, particles with length:width ratios >5:1 are counted as fibers.

A cumulative exposure measure calculated by multiplying a worker's duration of exposure (measured in years) by the average air concentration during the period of exposure (measured in number of fibers/mL of air). Epidemiologic studies of groups of asbestos-exposed workers commonly express exposure in these units.

A mineral habit with crystals that look like fibers. A mineral with a fibrous habit is not asbestiform if the fibers are not separable and are not long, thin, strong, and flexible.

How often a person is exposed to a chemical over time; for example, every day, once a week, twice a month.

Hazardous Waste:
Substances that have been released or thrown away into the environment and, under certain conditions, could be harmful to people who come into contact with them.

Health Effect:
ATSDR deals only with Adverse Health Effects (see definition in this Glossary).

Indeterminate Public Health Hazard:
The category is used in Public Health Assessment documents for sites where important information is lacking (missing or has not yet been gathered) about site-related chemical exposures.

Swallowing something, as in eating or drinking. It is a way a chemical can enter your body (see Route of Exposure).

Breathing. It is a way a chemical can enter your body (see Route of Exposure).

A term used as an adjective relating to spaces within a tissue or organ. Pulmonary interstitial fibrosis refers to fibrosis (scarring) developing within lung tissue.

Lowest Observed Adverse Effect Level. The lowest dose of a chemical in a study, or group of studies, that has caused harmful health effects in people or animals.

See Cancer.

Cancer of the thin lining surrounding the lung (the pleura) or the abdominal cavity (the peritoneum). Mesotheliomas are rare cancers in the general population.

Any naturally occurring, inorganic substance with a crystal structure. Naturally occurring, inorganic substances without a crystal structure (such as amorphous silica) are called mineraloids.

Mineral Habit:
The shape or morphology that single crystals or crystal aggregates take during crystal formation. Mineral habit is influenced by the environment during crystal formation. Habits of single crystals include prismatic, acicular, platy, and fiber. Habits of crystal aggregates include asbestiform, fibrous, lamellar, and columnar.

Minimal Risk Level. An estimate of daily human exposure--by a specified route and length of time--to a dose of chemical that is likely to be without a measurable risk of adverse, noncancerous effects. An MRL should not be used as a predictor of adverse health effects.

The National Priorities List. Mandated by Superfund, the NPL is a list kept by the U.S. Environmental Protection Agency (EPA) of the most serious uncontrolled or abandoned hazardous waste sites in the country. An NPL site needs to be cleaned up or at least looked at to see if people can be exposed to chemicals from the site.

No Observed Adverse Effect Level. The highest dose of a chemical in a study, or group of studies, not causing harmful health effects in people or animals.

No Apparent Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where exposure to site-related chemicals could have occurred in the past or is still occurring but the exposures are not at levels expected to cause adverse health effects.

No Public Health Hazard:
The category is used in ATSDR's Public Health Assessment documents for sites where there is evidence of an absence of exposure to site-related chemicals.

The functional cells or tissue of a gland or organ; for example, the lung parenchyma. The major lung parenchymal abnormality associated with exposure to asbestos is the development of scar-like tissue referred to as pulmonary interstitial fibrosis or asbestosis.

Public Health Assessment. A report or document that looks at chemicals at a hazardous waste site and tells if people could be harmed from coming into contact with those chemicals. The PHA also tells if possible further public health actions are needed.

A thin lining or membrane around the lungs or chest cavity. This lining can become thickened or calcified in asbestos-related disease.

Having to do with or involving the pleura.

Pleural abnormalities:
Abnormal or diseased changes occurring in the pleura. Pleural abnormalities associated with exposure to asbestos include pleural plaques, pleural thickening or calcifications, and pleural effusion.

Pleural calcification:
As a result of chronic inflammation and scarring, pleura becomes thickened and can calcify. White calcified areas can be seen on the pleura by X-ray.

Pleural cavity:
The cavity, defined by a thin membrane (the pleural membrane or pleura), which contains the lungs.

Pleural effusion:
Cells (fluid) can ooze or weep from the lung tissue into the space between the lungs and the chest cavity (pleural space) causing a pleural effusion. The effusion fluid can be clear or bloody. Pleural effusions might be an early sign of asbestos exposure or mesothelioma and should be evaluated.

Pleural plaques:
Localized or diffuse areas of thickening of the pleura (lining of the lungs) or chest cavity. Pleural plaques are detected by chest x-ray, and appear as opaque, shiny, and rounded lesions.

Pleural thickening:
Thickening or scarring of the pleura that might be associated with asbestos exposure. In severe cases, the normally thin pleura can become thickened like an orange peel and restrict breathing.

A line or column of air or water containing chemicals moving from the source to areas farther away. A plume can be a column or clouds of smoke from a chimney or contaminated underground water sources or contaminated surface water (such as lakes, ponds and streams).

Point of Exposure:
The place where someone can come into contact with a contaminated environmental medium (air, water, food, or soil). Some examples include the area of a playground that has contaminated dirt, a contaminated spring used for drinking water, or the backyard area where someone might breathe contaminated air.

A group of people living in a certain area; or the number of people in a certain area.

Potentially Responsible Party. A company, government, or person responsible for causing the pollution at a hazardous waste site. PRPs are expected to help pay for site cleanup.

Public Health Assessment(s):
See PHA.

Public Health Hazard:
The category is used in PHAs for sites with certain physical features or evidence of chronic, site-related chemical exposure that could result in adverse health effects.

Public Health Hazard Criteria:
PHA categories given to a site which tell whether people could be harmed by conditions at the site. Each are defined in the Glossary. The categories are:
- Urgent Public Health Hazard
- Public Health Hazard
- Indeterminate Public Health Hazard
- No Apparent Public Health Hazard
- No Public Health Hazard

Pulmonary interstitial fibrosis:
Scar-like tissue that develops in the lung parenchymal tissue in response to inhalation of dusts of certain types of substances such as asbestos.

Receptor Population:
People who live or work in the path of one or more chemicals, and who could come into contact with them (See Exposure Pathway).

Reference Dose (RfD):
An estimate, with safety factors (see safety factor) built in, of the daily, lifetime exposure of human populations to a possible hazard that is not likely to cause harm to the person.

Relative Bioavailability:
The amount of a compound that can be absorbed from a particular medium (such as soil) compared to the amount absorbed from a reference material (such as water). Expressed in percentage form.

Route of Exposure:
The way a chemical can get into a person's body. The three exposure routes are:
- breathing (also called inhalation),
- eating or drinking (also called ingestion), and
- getting something on the skin (also called dermal contact).

Safety Factor:
Also called Uncertainty Factor. When scientists don't have enough information to decide if an exposure will cause harm to people, they use "safety factors" and formulas in place of the unknown data. These factors and formulas can help determine the amount of a chemical that is not likely to cause harm to people.

In 1986 the Superfund Amendments and Reauthorization Act amended CERCLA (see CERCLA) and expanded the health-related responsibilities of ATSDR. CERCLA as amended by SARA directs ATSDR to look into the health effects resulting from chemical exposures at hazardous waste sites.

Sample Size:
The number of people that are needed for a health study.

A small number of people chosen from a larger population (see Population).

Igneous or metamorphic rock chiefly composed of serpentine minerals such as chrysotile or lizardite. Chrysotile, when found, can occur in localities with serpentinite rock.

Source (of Contamination):
The place where a chemical comes from, such as a landfill, pond, creek, incinerator, tank, or drum. Contaminant source is the first part of an Exposure Pathway.

Special Populations:
People who could be more sensitive to chemical exposures because of certain factors such as age, a disease they already have, occupation, sex, or certain behaviors (like cigarette smoking). Children, pregnant women, and older persons are often considered special populations.

A branch of mathematics involving collecting, looking at, and summarizing data or information.

Superfund Site:
See NPL.

A way to collect information or data from a group of people (population). Surveys can be done by phone, by mail, or in person. ATSDR cannot do surveys of more than nine people without approval from the U.S. Department of Health and Human Services.

Synergistic Effect:
A health effect from an exposure to more than one chemical, where one of the chemicals worsens the effect of another chemical. The combined effect of the chemicals acting together are greater than the effects of the chemicals acting by themselves.

Harmful. Any substance or chemical can be toxic at a certain dose (amount). The dose is what determines the potential harm of a chemical and whether it would cause someone to get sick.

The study of the harmful effects of chemicals on humans or animals.

Tremolite asbestos:
A special form of the amphibole mineral, tremolite, that displays separable, long, thin fibers often arranged in parallel in a column or in matted masses. The fibers are generally strong enough and flexible enough to be spun and woven, are heat resistant, and are chemically inert.

Abnormal growth of tissue or cells that have formed a lump or mass.

Ultramafic rock:
Igneous rock composed chiefly of dark-colored ferromagnesian silicate minerals. Asbestiform amphiboles, when found, can occur in localities with ultramafic rock.

Uncertainty Factor:
See Safety Factor.

Urgent Public Health Hazard:
This category is used in ATSDR's Public Health Assessment documents for sites that have certain physical features or evidence of short-term (less than 1 year), site-related chemical exposure that could result in adverse health effects. This category requires quick intervention to stop people from being exposed.

A mineral belonging to the mica group of silicate minerals. Vermiculite has water molecules located between the silicate layers in the crystal structure. When heated, vermiculite expands to form a light-weight material that has been used for home and building insulation, as a soil amendment, and as a packing material. The process of heating and expanding vermiculite is called exfoliation or "popping." Raw vermiculite ore is processed to produce vermiculite concentrate, which is shipped to exfoliating plants to produce the finished vermiculite product.


Click here to view Appendix B in PDF format [PDF, 436kb]


A community member requested ATSDR to provide a list of board-certified pulmonologists in the Libby area. ATSDR performed a search on the American Board of Medical Specialties' (ABMS') database at . to locate physicians in Montana, Idaho, and Washington who were board-certified in the subspecialty pulmonary disease. Listed below are those certified physicians whose address at the time of the search was within 350 miles of Libby, Montana. This information is provided with the permission of ABMS solely for theconvenience of the Libby community. ATSDR does not endorse any individual physician listed and will not pay for any services provided by the listed physicians.

The search was performed on October 25, 2002. Due to the possibility of reporting and processing delays, and because the list might have been updated since the search, the accuracy and completeness of the information cannot be guaranteed. Neither ATSDR nor ABMS can be held responsible for incomplete or inaccurate information. Physician certification information in the ABMS database is updated periodically with data provided by its member boards. 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.

William Bernard Bekemeyer JrMissoulaMontana
Richard Dyer BlevinsGreat FallsMontana
Ryland P. ByrdButteMontana
Thomas Shull LemireMissoulaMontana
C. Paul LoehnenMissoulaMontana
Brent Parker PistoreseKalispellMontana
Keith Janes PopovichButteMontana
Sripathi RamakrishnaHelenaMontana
Henry Dominic CovelliCoeur D'AleneIdaho
Hugh Franscisco HaegelinLewistonIdaho
Luke Anthony PlutoLewistonIdaho
Paul Albert AllenRichlandWashington
Scot Llewellyn BradleySpokaneWashington
Timothy Edward BruyaSpokaneWashington
Richard B. ByrdSpokaneWashington
Timothy Michael ChestnutSpokaneWashington
Richard Wayne FeltWalla WallaWashington
Todd Robert GreenSpokaneWashington
Samuel Greg JosephSpokaneWashington
William Scott KlipperKennewickWashington
Lawrence Edward KlockSpokaneWashington
Richard James LambertSpokaneWashington
Robert Edward MossSpokaneWashington
John NaylorSpokaneWashington
Robert Paul StevensWenatcheeWashington
Donald Duncan StoreySpokaneWashington
Gladson M. VazPascoWashington
Alan Coombs WhitehouseSpokaneWashington


Note: Most of the comments received were in letter form. This appendix contains the points made in the text of the received letters, but rearranged so that separate points could be addressed. We attempted to keep original wording as much as possible.

Comments from Dr. Bruce Case, McGill University:

A1: The report of "three mesothelioma cases" of which two were WRG workers is misleading (although not necessarily wrong for the time frame and population covered by the ATSDR study). Numbers of asbestosis cases reported also do not appear to realistically conform with numbers of respiratory non-malignant deaths reported by McDonald et al. in the two studies published to date on mortality in the WRG cohort alone, let alone any cases outside that small cohort, although of course many non-malignant respiratory disease deaths are notasbestosis deaths.

In fact, there has already in the open literature been a publication of 12 known cases of mesothelioma with an additional three possible cases, also determined from death certificates, all in WRG workers in the original cohort reported by McDonald et al. in 1986 and updated in 2002 in the Annals of Occupational Hygiene.

Response: ATSDR's mortality review was based on death certificates of people who lived in the area around Libby at the time of death. This review was emphasized because the focus of this public health assessment is on the community of Libby, not only the workers followed in cohort studies. We are aware that there were many more cases of disease than were tabulated in the mortality review. We have discussed this fact and the limitations of death certificate reviews several times with the Libby community. Based on our ongoing dialogue, we feelthat the community understands the complexities of the review and will not be misled by the raw numbers cited.

Further review of the data from the McDonald study and from the ATSDR mortality review shows that the percentage of workers who died of mesothelioma was similar (2.9% vs. 3.1%) for the two studies. In addition, the percentage of workers dying of nonmalignant respiratory disease in the McDonald study (12.4%) was in the same general range as the percentage of workers who died of asbestosis in the ATSDR mortality review (17.1%) [32,17].

We have added additional information on the worker cohort studies and upcoming research mentioned by this commenter to the Mortality and Evaluation subsections of the Health Outcome Data section of the document.

A2: I am reliably informed that [McDonald et al.] has now completed their dose-response assessment for respiratory disease and exposure and the ATSDR statement that "the exact level of risk associated with low-level exposure to asbestos cannot be determined because of uncertainties in the analysis and toxicology of Libby asbestos" is now false….In fact, the level of risk associated with low-level exposure to Libby amphibole asbestos (with confidence intervals), complete with dose-response relationships down to very low levels of exposure,has now been determined…. Any publication by ATSDR of their public health assessment without this information will be misleading to all concerned, especially to residents of Libby, WRG ex-workers and their household contacts.

Response: The author of this document contacted Dr. J. Corbett McDonald to request the unpublished data referenced by the commenter. Dr. McDonald responded that the latest update on the cohort has been submitted for publication and he is unable to provide details of the results until it is accepted. Therefore, we are unable to address this comment.

A3: Your assumption that workers have lower [Note: ATSDR assumed this commenter meant higher] exposure levels, while understandable, is often, and definitely in this case, wrong, at least in part. Dose-response relationships can usually only be developed with respect to a well-characterized cohort where both exposure and response (whether mortality or incidence) are available. Many workers have little exposure; some have none. In addition, most community exposure is in fact derived from the worker' exposures, secondarily. Finally, the pilesof the Libby amphibole in the community may well have provided higher levels of exposure to some classes of "residents" than to some classes of "workers"; an arbitrary and misleading separation in my view, as it is exposure and dose that matters, not what you call a class of individuals. It is therefore possible to get the definitive answers from the study of workers - and only from the study of workers.

Response: Community members as a whole would have much less exposure than workers. Individual community members with high exposures would have risk similar to workers, of course, but the risk for those with low exposures, much lower than the workers, can't be quantified even though we assume they experience some risk. This is at least partially due to the difficulties in estimating exposures of community members. The study of workers is not expected to give definitive answers for community members with very low exposures.

A4: It would be even better if the US Government could provide them with health care by declaring the Environmental Emergency or Public Health Emergency that the Office of Management and Budget appears to have precluded, if newspaper articles are accurate.

Response: ATSDR has had no discussion with the Office of Management and Budget regarding a public health emergency. ATSDR has been able to perform its activities in the community of Libby without declaring a public health emergency.

A5: The exposure problems which are developing in parts of the Sierra foothills with respect to tremolite exposure are directly related, will eventually produce even more disease than that seen at Libby (due to the much larger population base), and should be mentioned.

Response: Your comment is noted. The Public Health Assessment is a site-specific document produced as part of the Superfund process to assist the community and EPA understand exposures taking place at one specific site.

Comments from a private citizen:

B1: Our children and population in Libby are still being exposed to tremolite asbestos fibers, everyday since 1999 and before but since 1999 when Libby was "found out" to be dying from W.R. Grace's deadly dust, nothing has been done to address the exposure to our young and old. Are our children being exposed to enough tremolite asbestos fibers to kill them, today?

Response: ATSDR concluded that the areas previously found to be contaminated with Libby asbestos fibers that have been cleaned up by EPA pose no apparent public health hazard, that is, health effects are extremely unlikely from contact with those areas. However, "source areas", as defined by EPA to include areas with high levels of Libby asbestos-contaminated vermiculite, that have not yet been cleaned up do pose a public health hazard, especially to sensitive populations such as children and people who have already been exposed for manyyears. As these areas are cleaned up through the Superfund process, the risk to children who are in those areas will decrease. Keeping children away from known source areas will essentially reduce their risk to zero.

B2: How many innocent children and people [have] been exposed to enough in the last three years, to [tremolite asbestos fibers], to cause cancer? I know there are many. We are not protecting/saving the population of Libby from a deadly fiber that has no cure and kills you, period.

Response: Past exposures to Libby asbestos at harmful levels undoubtedly occurred. However, over the past three years, the majority of the most harmful materials were removed through the Superfund Emergency Removal program, and long-term cleanup has been occurring through the Superfund Remedial program for the past several months. The risk to residents, including children, has already been greatly reduced, and as cleanup at the site continues, the risk will be even further reduced.

B3: Can Libby ever be cleaned up to be a safe and healthy environment for humans to live and breathe, I think not when the extent of contamination consists of 70 years of millions of pounds of [tremolite asbestos fibers] dumped on Libby and that it's everywhere since this deadly dust is known to travel airborne up to 30 miles. Why wouldn't this [tremolite asbestos fibers] exist everywhere. Well, it does.

Response: The site can be cleaned up so that the air in Libby is at least as clean if not cleaner than many other towns and cities in the United States. Although it is impossible to remove every single fiber, cleaning up the site will minimize people's exposure to Libby asbestos, thereby minimizing the chance for future health effects.

B4: One major concern I have which must be addressed is the fact: children exposed to [tremolite asbestos fibers] at a early age and up to 6 months exposure are at risk of having mesothelioma.

Response: Asbestos fibers are thought to have similar health effects for children and adults. However, because of the long latency period, children are expected to have a longer time in which to exhibit adverse health effects. Because the major sources of exposure to Libby asbestos have been removed through the site cleanup, children today have very little risk of developing any asbestos-related health effects.

B5: Our children should be relocated because Libby is a unhealthy environment for all who breathe.

Response: It is not necessary to relocate any residents of Libby, because the town and site are being cleaned up. The risk of health effects has already been greatly reduced with the emergency removals, and further cleanup under Superfund will reduce the risk even further.

B6: Libby Montana must be declared a public health emergency for all the right and just reasons. The people exposed deserve the best of everything including protection and a government for us people.

Response: There is no precedent for declaring a public health emergency. ATSDR and EPA have been able to accomplish their goals, including performing medical testing, informing the public of the hazard, and cleaning up the site waste, soil, and residences throughout Libby, without declaring a public health emergency.

B7: It's cheaper to move and save the people than to clean up a mine and a town that has created death.

Response: Past exposures in Libby have led to increased rates of disease and death. However, the site cleanup has been and will be effective in protecting the public health from further exposures, so that relocating people is not necessary.

This commenter attached several letters to the editor; a summary of the concerns expressed in those letters follows:

BL1: Are unborn babies being exposed to asbestos through exposure of the mother?

Response: Asbestos fibers do not pass through the placenta to unborn children.

BL2: Are babies exposed to asbestos when nearby vehicles create visible dust?

Response: Sampling by EPA and others indicates that asbestos in Libby soils is only detected around source areas, such as waste piles, places where contaminated vermiculite was added to gardens or driveway. Unless the babies are near these areas when dust is generated, they will not be exposed to detectable levels of asbestos.

BL3: [Considering] the size of a baby's lungs [I know that] small levels of tremolite asbestos fibers inhaled are more than enough to cause damage.

Response: Not enough is known about how very low levels of Libby asbestos might cause lung damage and/or lead to disease. Research in this area is one of the recommendations of this public health assessment.

BL4: Are our children being exposed to asbestos today?

Response: Unless children are in the immediate vicinity of current source areas, they are not exposed to asbestos. Ambient air in Libby, as well as air around areas that have already been cleaned up, are safe for children and adults to breathe.

BL5: Just living in Libby, exposure to asbestos is a known fact…even today, contamination of tremolite asbestos is a reality.

Response: Libby does still contain areas where there is asbestos contamination. These areas have been targeted for the cleanup that is ongoing.

BL6: Children and adults who played football, baseball, track, who ran and rolled, and played and wrestled in the contamination also brought the asbestos home to contaminate the home and family members unknowingly and unprotected, just as the mine workers brought it home.

Response: This is true, although the exposures would be lower than for workers' household contacts.

BL7: Knowing that this asbestos travels air borne up to 30 miles, [I am not convinced that it is safe if] tests show no asbestos found 20 to 50 feet from a contaminated site.

Response: Sampling by EPA and others indicates that asbestos in Libby soils is only detected around source areas, such as waste piles or places where contaminated vermiculite was added to gardens or driveway. There is no indication that detectable levels of asbestos were ever found in areas away from known sources. While it is true that asbestos fibers may be carried through the air, presumably the fibers are spread out so much that the levels in soil elsewhere are too low to detect, and therefore not likely to result in increased risk.

BL8: Logging Rainy Creek drainage exposed all the workers to deadly levels of tremolite asbestos.

Response: ATSDR does not have access to any asbestos testing of either soil or air during logging operations in the Rainy Creek drainage, so it is impossible to tell whether the loggers were exposed to harmful levels of asbestos. Based on testing results from Libby, asbestos contamination is not evenly distributed throughout the area.

BL9: Girl Scouts were exposed to harmful levels of asbestos when they swept the sidewalks of Libby.

Response: Sampling by EPA and others indicates that asbestos in Libby soils is only detected around source areas, such as waste piles or places where contaminated vermiculite was added to gardens or driveway. There is no indication that detectable levels of asbestos were present in general dust on the streets of Libby.

BL10: Any dust (whether created by vehicular traffic, wind, or other activities) in Libby is harmful.

Response: Sampling by EPA and others indicates that asbestos in Libby soils is only detected around source areas, such as waste piles or places where contaminated vermiculite was added to gardens or driveways. In addition, sampling of sediment cores from a local lake did not show a layer of asbestos fiber (which would have been expected if asbestos contamination was widespread over the area). There is no indication that detectable levels of asbestos were present in general dust on the streets of Libby.

Dust blown by the wind or created by vehicles traveling on unpaved roads generally falls into the category of coarse particles (larger than 2.5 micrometers in diameter). Coarse particles are of health concern because they can penetrate into the sensitive regions of the respiratory tract. (Fine particles less than 2.5 micrometers in diameter are linked to more serious effects such as persistent coughs and wheezing). The EPA has set an ambient air quality standard for particulate matter up to 10 micrometers in diameter of 50 micrograms per cubicmeter averaged over one year or 150 micrograms per cubic meter averaged over a 24-hour period [ref pm stds].

Comments from W.R. Grace:

C1: No risk assessment supports ATSDR's conclusions about risk.

Response: A risk assessment is not required for conducting a public health assessment; in fact the CERCLA legislation specifically requires that public health assessments performed for National Priorities List (NPL) sites be completed "promptly and, to the maximum extent practicable, before the completion of the remedial investigation and feasibility study at the facility concerned" [42 U.S.C. § 104(i)(6)(D)]. ATSDR used multiple lines of evidence, including environmental sampling data, current site conditions, screening level risk assessments,current toxicological information, health outcome data, and community concerns, to make conclusions about the site.

C2: The mortality study indicates that low level environmental exposures are not associated with asbestos-related mortality.

Response: It is generally recognized that occupational exposures are higher than exposures in the general population, and therefore we expect to see initial effects from the exposure in occupationally-exposed individuals. The finding that asbestos-related deaths were not elevated for non-occupationally exposed people cannot prove that no association exists. A number of alternative factors may contribute to result in the same finding. For example, traditional occupational diseases may be under-diagnosed or underreported for people with noknown occupational exposure, the latency period may be longer for low-level exposures, or people who did not work at the mine may have been more likely to move away from the Libby area before adverse health effects could develop.

C3: All of the relevant findings of the ATSDR medical testing study should be described.

  1. The screening program does not provide evidence of a risk of asbestos-related disease from the potential levels of exposure to asbestosthat existed in 1999, when EPA arrived in Libby, nearly a decade after the vermiculite operations ceased.
  2. Pathways including having vermiculite insulation in homes, handling vermiculite insulation, using vermiculite for gardening, and usingvermiculite around the home were not statistically significant in the medical testing program evaluation, indicating that these pathways were not associated with pleural abnormalities.
  3. Pleural abnormalities shown on chest x-rays can result from many other causes. Because ATSDR does not know the percentage ofpleural abnormalities not associated with asbestos exposure, ATSDR should not suggest that "additional cases of asbestos-related disease may occur in coming years." ATSDR's statement that "it is reasonable to assume that people who exhibit pleural abnormalities could be at a higher risk for asbestos-related diseases, such as asbestosis and lung cancers," is simply speculation.
  4. The screening study found minimal restrictive abnormalities only in historical pathways, and no statistically significant increase ofabnormalities in interstitial lung tissue that is associated with asbestosis.

Response: The purpose of the review of the medical screening was to summarize the information that we used in making our conclusions. The screening program was not designed to diagnose asbestos-related diseases. While results of the screening program do not directly indicate present risk for any individual, the results support our inference, based on multiple lines of evidence, that risks continued to exist to the population of Libby long after vermiculite operations ceased. The pathways listed in (ii) were not statistically significant whenanalyzed individually; however, exposure to Libby asbestos through multiple pathways, including those listed, increased the likelihood of pleural abnormalities. From this, we inferred that these pathways, some of which still exist, contribute to the overall risk to residents of Libby.

The general rate of pleural abnormalities in populations not exposed to respiratory hazards ranges from 0.8% to 4% [50,51] . It is true that many other factors can lead to pleural abnormalities; however, the major difference between the Libby population and the general U.S. population is the exposure to Libby asbestos over many years. The Libby population tested is not more obese than the general U.S. population (1), and if former mine workers are excluded from the results of medical screening, there are still 1,000 people out of 6,303 (or 16%)who tested positive for a pleural abnormality. This is significantly higher than would be expected in the general population and is not likely explained completely by differences in procedures of the medical screening.

Due to these considerations, we assumed that the increased rate of pleural abnormalities in Libby was mostly due to exposure to Libby asbestos. This is a reasonable assumption. Because people who were exposed to asbestos have a higher risk of developing asbestos-related disease, it is not speculative to state that a higher rate of these diseases can be expected in the population of Libby.

Results of the pulmonary function testing were discussed on page 18 of the public comment public health assessment. We have added a statement that no statistically significant increase in interstitial abnormalities was found.

C4: The assessment should have been conducted prior to other ATSDR studies.

Response: The relevant part of the paragraph in the CERCLA legislation referred to is from 42 U.S.C. § 104(i)(6)(G):

(G) The purpose of health assessments under this subsection shall be to assist in determining whether actions under paragraph (11) of this subsection should be taken to reduce human exposure to hazardous substances from a facility and whether additional information on human exposure and associated health risks is needed and should be acquired by conducting epidemiological studies under paragraph (7), establishing a registry under paragraph (8), establishing a health surveillance program under paragraph (9), or through other means….

While a health assessment may indicate the need for further actions, the health assessment is not required to perform actions necessary to protect public health around facilities where there is a documented release of hazardous substances. When the Libby Asbestos site was proposed to the NPL on February 26, 2002, ATSDR began working on this public health assessment to meet the requirement of 42 U.S.C. § 104(i)(6)(A):

(A) The Administrator of ATSDR shall perform a health assessment for each facility on the National Priorities List established under section 9605. Such health assessment shall be completed not later than December 10, 1988, for each facility proposed for inclusion on such list prior to the date of the enactment of the Superfund Amendments and Reauthorization act of 1986 or not later than one year after the date of proposal for inclusion on such list for each facility proposed for inclusion on such list after such date of enactment.

Further, please note that ATSDR's annual appropriations language provides:

Provided, that notwithstanding any other provision of law, in lieu of performing a health assessment under section 104(i)(6) of CERCLA, the Administrator of ATSDR may conduct other appropriate health studies, evaluations, or activities, including, without limitation, biomedical testing, clinical evaluations, medical monitoring, and referral to accredited health care providers: Provided further, that in performing any such health assessment or health study, evaluation, or activity, the Administrator of ATSDR shall not be bound by the deadlines in section 104(i)(6)(A) of CERCLA.

1. 67% of participants in the medical screening program were overweight (body mass index (BMI) greater than 25), and 32% were obese (BMI greater than 30 [18]. 1999-2000 data from the National Health and Nutrition Examination Survey (NHANES) indicates that 64% of US adults over age 20 years were overweight, and 30% were obese [52].

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