&EPA
United States
Environmental Protection
Agency
Determining Toxicity Values of
Libby Amphibole Asbestos
May 2011
The purpose of this fact sheet is to describe EPA's course
of action for establishing Libby Amphibole asbestos (LA)-
specific toxicity values. It also summarizes site history and
explains the role of toxicity values in risk assessment.
Site History and Cleanup Progress
The Libby Asbestos site in northwest Montana includes
the towns of Libby and Troy. In the 1920s, the Zonolite
Company formed and began mining vermiculite at a mine
seven miles northeast of Libby. In 1963, W.R. Grace
bought Zonolite's mining operations and expanded mining
activities. Vermiculite was widely used in building
insulation and as a soil conditioner. Both the ore and the
processed vermiculite from the W.R. Grace mine were
contaminated with a form of asbestos, now referred to as
LA. The mine was closed in 1990 for economic reasons.
Asbestos consists of microscopic fibers that are hazardous
to humans when inhaled. Many people in Libby have died
of illness caused by LA exposure.
EPA determined that an imminent and substantial
endangerment to public health exists in Libby due to LA
contamination. Since 1999, EPA has worked diligently to
investigate and remove contamination and reduce health
risks.
EPA has made progress in reducing the threat of asbestos
on the ground and in the air. The most recent ambient air
quality report published in 2009 indicates that LA air
concentrations are approximately 10,000 times lower than
the reported air concentrations in downtown Libby when
the mine and milling plants were operating.
As of October 2010, EPA has safely removed over
825,000 cubic yards of asbestos-contaminated soil from
1,463 commercial and residential properties in Libby. The
Montana Department of Environmental Quality (MDEQ)
also has conducted removal actions at 84 properties in
Troy.
Over 22,100 cubic yards of vermiculite attic insulation and
43,160 cubic yards of contaminated debris have also been
removed from the Libby and Troy area. EPA continues to
implement removal actions to reduce exposures and to
collect additional data to support the risk assessment.
LA Toxicity Values
The Libby community requested that the final risk
assessment and cleanup decisions be based on LA-specific
toxicity data. EPA uses its Integrated Risk Information
System (IRIS) process for adopting toxicity values to
make sure that the toxicity values represent the best
science available. While the IRIS process moves forward,
the Agency will make public draft LA toxicity values that
resulted from scientific review within EPA. This
information will serve as a basis for starting discussions
with the community about how the draft values affect our
understanding of site risks and options for addressing
them.
There are currently no LA-specific toxicity values. An
IRIS value for asbestos was established in 1986 for cancer
effects. This value was established based on studies of the
health effects of exposure to a range of types of asbestos,
including chrysotile, tremolite, amosite and crocidolite.
Both lung cancer and mesothelioma were considered in
the 1986 analysis. EPA does not have a quantitative
estimate of noncancer effects of LA or other asbestos in
IRIS. EPA toxicologists have worked over the past years
to develop toxicity values for LA including the following:
1. A cancer Inhalation Unit Risk or IUR value
quantifies the exposure-response relationship for
cancer from breathing LA in the air. Asbestos-
related cancer health effects include malignant
mesothelioma, an incurable, fatal cancer of the
chest cavity, and an increased risk of all lung
cancers.
2. Non-cancer risk evaluations are based on a value
referred to as the Reference Concentration or RfC.
This is an estimated exposure that is likely to be
without an appreciable risk of harm. Asbestos-
related non-cancer illnesses include pleural
abnormalities and asbestosis, a debilitating
respiratory illness caused by progressive scarring
of lung tissues. The increase in pleural anomalies
in workers is the basis for the draft RfC value.
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The data used to develop LA-specific toxicity values were
obtained from Libby miners and others that were exposed
to LA at work, including those at the Marysville, Ohio
plant, one of the plants that processed Libby vermiculite.
Components of the Libby Risk Assessment
A Superfund risk assessment is a formal, scientific
process, led by experienced toxicologists, to quantify
health risks to residents, workers, and recreationalists.
EPA's risk assessment process has four steps:
1. Data collection. Compiles data on site history,
exposure potential, and contaminant distribution.
2. Exposure assessment. Estimates how much and in
what ways exposures may occur. Inhalation of LA is
the major pathway for human exposure.
3. Toxicity assessment. Addresses the potential of
contaminants to cause harmful effects in humans.
4. Risk characterization. Estimates the risk to human
health using data from both the exposure and toxicity
assessments.
Libby Toxicity Assessment
The toxicity assessment is a key part of the human health
risk assessment that determines the relationship between
the dose of Libby amphibole and its biological response -
for both cancer and non-cancer effects.
Next Steps in the LA Toxicity Value Process
Since February 2011, EPA's scientists nationwide have
been reviewing the data and methodologies used to
develop draft toxicity values. These values will be
submitted to other federal agencies for peer review in
spring 2011.
The current schedule anticipates that the IRIS review
process will be completed in 2012. While the IRIS
process is underway, EPA will use draft toxicity values to
begin conversations with the Libby and Troy residents
about remedy options.
Moving Forward with Cleanup
EPA will carry on its efforts to clean up years of
contamination left by W.R. Grace. While there is much
less asbestos contamination in Libby than there was 10
years ago, there are still potential risks from exposure to
asbestos-contaminated vermiculite. That is why EPA is
taking a combined approach of "action" (indoor and
outdoor cleanups at targeted properties) and
"investigations and studies" to continue to reduce
exposure and support final remedy decisions.
EPA is committed to reducing exposure to LA in Libby
and will continue to work closely with our federal, state
and local partners as cleanup efforts progress. The Libby
cleanup will remain one of the Agency's highest priorities
in the years ahead.
The Libby Human Health Risk Assessment
Combined with site-specific exposure information
(including activity-based sampling data), the LA-specific
toxicity values will be used to estimate health risks in
Libby. EPA will develop a risk assessment that reflects the
cumulative exposures experienced by Libby residents.
This risk assessment will evaluate exposures to adults,
teenagers, and children conducting a variety of activities
throughout the Libby Valley such as housework, playing
in the yard or at school, walking, bicycling, or working in
an office or outside.
Four Steps of Risk Assessment
Toxicity
Assessment
Data Collection
& Evaluation
Risk
Characterization
Exposure
Assessment
For additional information about the Libby Asbestos
Toxicity and Risk Assessments, please visit EPA's
Libby website at www.epa.gov/libby/ or contact:
Deborah McKean
EPA Toxicologist
303-312-6178
mckean.deborah@epa.gov
Libby Faulk
EPA Community Involvement Coordinator
303-312-6083
faulk.libby@epa.gov
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