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Testimony
Before the Subcommittee
on Superfund, Toxics,
Risk, and Waste Management
Committee on Environment
and Public Works
United States Senate
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Workplace Exposure to
Asbestos Statement
of Gregory
R. Wagner, M.D. Director,
Division of Respiratory Disease Studies National
Institute for Occupational Safety and Health Centers
for Disease Control and Prevention, U.S.
Department of Health and Human Services |
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For Release on Delivery
Expected at 9:30 PM
on Thursday, June 20, 2002
Mr. Chairman and
members of the Subcommittee, I am Dr. Gregory Wagner, an occupational health
expert at the National Institute for Occupational Safety and Health (NIOSH),
Centers for Disease Control and Prevention (CDC). I am pleased to appear before you today to provide this testimony
on behalf of NIOSH.
NIOSH is a
research institute within CDC, a part of the Department of Health and Human
Services. CDC, through NIOSH, is the
federal agency responsible for conducting research and making recommendations
to identify and prevent work-related illness and injury.
Asbestos
is a term that is generally used to refer to a group of fibrous minerals with
exceptional resistance to degradation by heat, acids, bases, or solvents. The minerals are not combustible and have a
high melting point and low thermal and electrical conductivity. These and other useful properties had resulted
in the development of thousands of commercial uses for asbestos-containing materials
by the early 1970s. However, as the use
of asbestos dramatically increased, the lethal effects of airborne asbestos
became clear. Regulatory action and
liability concerns related to the now well-established connection between
inhalation of asbestos fibers and a variety of serious and often fatal diseases
have reduced or eliminated the use of asbestos in many commercial
products. However, asbestos and
asbestos-containing materials are still found in many residential and
commercial settings and pose a risk of exposure to workers and others.
Asbestos
is defined in Federal regulations as the minerals chrysotile, crocidolite,
amosite, tremolite, actinolite, and anthophyllite. The Occupational Safety and Health Administration (OSHA), the
Mine Safety and Health Administration (MSHA) and the Environmental Protection
Agency (EPA) regulate these six minerals.
All of the minerals, except for actinolite, have been used commercially.
The results from epidemiologic studies of workers exposed to these minerals
provide the scientific evidence of a causal relationship between exposure and
adverse health effects in humans.
Exposure
to asbestos significantly increases the risk of contracting several
diseases. These include:
1.) AsbestosisCa disease characterized by scarring
of the air-exchange regions of the lungs;
2). Lung cancerCfor which
asbestos is one of the leading causes among nonsmokers, and which occurs at
dramatically high rates among asbestos-exposed smokers;
3.) Malignant mesotheliomaCan almost
invariably fatal cancer of the tissue lining the chest or abdomen for which
asbestos and similar fibers are the only known cause; and
4.) Nonmalignant
pleural diseaseCwhich can
appear as a painful accumulation of bloody fluid surrounding the lungs, but
which more commonly is seen as thick and sometimes constricting scarring of the
tissue surrounding the lungs.
In
addition, asbestos exposure is associated with excess mortality due to cancer
of the larynx and cancer of the gastrointestinal tract. The malignant diseasesCthe cancers
including mesotheliomaCare often fatal within a year or a few years
of initial diagnosis. In contrast,
asbestosis deaths typically occur only after many years of suffering from
impaired breathing.
We
do not know exactly how asbestos fibers cause disease. We do know that microscopic fibers can
become airborne during various industrial processes or from handling of
asbestos-containing materials and can then be inhaled and/or swallowed. As much as 50 percent or more of inhaled
asbestos fibers can remain lodged in the lungs, where it is almost impossible
for the body to eliminate them.
Asbestos fibers are extremely resistant to destruction in body fluids,
and many of these fibers are too long to be engulfed and removed by the cells
that normally scavenge and remove particles that happen to deposit in the
lungs. Generally, as the burden of
retained fibers increases in the body, so does the likelihood of disease. Most asbestos-related diseases, particularly
the malignant ones, have long latency periods often extending 10-40 years from
initial exposure to onset of illness. While asbestos-related lung cancer and
mesothelioma are frequently not curable, they and other asbestos-related
diseases are clearly preventable by eliminating or limiting exposures to
asbestos. The amount and duration of
exposure are factors that can determine the risk of adverse health effects.
In 1990 testimony before
OSHA, NIOSH broadened its science-based definition of "asbestos" as a
result of concerns about the microscopic identification of the six regulated
asbestos minerals. The six minerals can
also occur in a non-fibrous (so-called Amassive@) form.
The non-fibrous mineral forms of the six asbestos minerals can be found
geologically in the same ore deposits in which the fibrous asbestos minerals
occur or in deposits where other commercially exploited minerals are mined
(e.g., industrial grade talc).
"Cleavage fragments" can be generated from the non-fibrous
forms of the asbestos minerals during their handling, crushing, or processing,
and these Acleavage fragments@ are often microscopically indistinguishable
from typical asbestos fibers of the (fibrous) minerals.
The elemental composition
of the six asbestos minerals can vary slightly as a result of geological
conditions such as pressure, temperature, or proximity of other minerals. Recognizing these variations in elemental
composition, NIOSH believes that the six asbestos minerals can be defined by
their "solid-solution" mineral series. For example, the mineral series
tremolite-ferroactinolite contains the asbestos mineral actinolite. These mineral series are considered
solid-solutions in which cations (i.e., sodium, calcium, magnesium, iron, etc.)
are replaced by other cations which can affect the elemental composition of the
mineral without significantly altering the structure.
NIOSH bases this expanded
"asbestos" definitionCencompassing the entire solid-solution mineral series for each of
the six currently regulated asbestos minerals and including cleavage fragments
from the non-fibrous forms of these mineralsCon scientific evidence from cellular and animal studies suggesting that
dimension, specifically length and diameter, as well as durability, may be more
critical factors in causing disease than chemical or elemental
composition.
In
June 1980, OSHA asked NIOSH to provide technical assistance to investigate lung
problems in workers at a plant using vermiculite that had been mined in
Libby. Shortly thereafter, MSHA also
requested technical assistance from NIOSH to investigate the magnitude of
health hazards in vermiculite mines.
MSHA was particularly concerned about two reported cases of Adust-related lung disease@ in workers
at the Libby mine.
In
response to these requests, NIOSH initiated epidemiological studies in Libby,
Montana. The epidemiological studies carried out by NIOSH between 1980
and 1985 showed that occupational exposure to mineral fibers that contaminate
Libby vermiculite caused high rates of asbestos-related diseases among exposed
workers at the Libby mine complex. The
fibers these workers were exposed to included tremolite, one of the minerals
within the definition of asbestos as currently regulated. Some recent evidence indicates that only 10
to 20% of the fibrous mineral content of the Libby vermiculite was
tremolite. A much higher proportionC80 to 90%Cof the fiber contaminant
in this vermiculite has been characterized as several other similar fibers that
are not currently regulated as asbestos, such as richterite and winchite.
Richterite and winchite are fibrous minerals that are not classified as
asbestos by mineralogists.
NIOSH played a pivotal role in documenting the health hazard
associated with occupational exposure to asbestos-contaminated vermiculite at
the mine in Libby, Montana. NIOSH made
its findings available beginning in 1985 through meetings in Libby with workers
and their representatives, employer representatives, and members of the
community. NIOSH also published its
findings in several scientific papers to alert the occupational health
community about the identified problem.
It is clear in hindsight that further work remained to be done, in
particular, with respect to further studies of downstream users of Libby
vermiculite products. NIOSH is applying what we learned from our Libby
investigations to our current and future activities both in Libby and
throughout our program.
At present, NIOSH is following up on potential exposures of
workers who use or process vermiculite from other sources. Since closure of the
Libby mine in 1990, most of the vermiculite now being produced for domestic use
is obtained from one of four mines, three of them domestic and one located in
South Africa. The degree to which the vermiculite from these other sources is
contaminated with asbestos is not clear. At OSHA=s
request, NIOSH is conducting environmental sampling at expansion plants and
horticultural operations where vermiculite is used. NIOSH will complete asbestos exposure assessments at two
expansion plants for each vermiculite ore supplier, along with a number of
horticultural sites. We expect the
field data collection to be completed by the end of 2002. At present, field sampling has been
completed at four expansion plants and three horticultural operations. From
these studies we expect to learn the degree to which an asbestos exposure
hazard exists in vermiculite from sources other than Libby, Montana. Once these
studies are completed, we plan to produce and disseminate a technical report
that describes the extent to which newly mined or imported vermiculite presents
an asbestos risk to current vermiculite worker. Based on the findings, we may
issue further guidance for protective measures to be taken.
Additional research possibilities that NIOSH is considering
include efforts to better determine physical and/or chemical characteristics
affecting toxicity of fibers including those occurring naturally and those
manufactured. Direct evidence by which
to attribute particular health effects to each possible fiber type is not
currently available. Epidemiological studies of people exposed to naturally
occurring or manufactured fibers would provide important new information, and
studies conducted with animals could provide mechanistic and other toxicologic
data.
Asbestos fibers have many different lengths and diameters. Additional work to improve and standardize
the methods for asbestos fiber measurement is being considered because it would
help advance prevention and control efforts to protect exposed workers. Human assessment of risk and occupational
exposure limits is based on airborne fiber concentrations determined by the use
of phase contrast microscopy (PCM).
This analytical method leaves an undetermined number of asbestos fibers
collected on each sample uncounted because many fibers are too small in
diameter to be detected and because the standard procedure for counting fibers
using PCM takes into account only fibers longer than 5 micrometers in
length. Current asbestos exposure risk
assessment is based only on a subset of fibers that can be detected using PCM
techniques. More sensitive analytical methods are currently available, but
these methods could benefit from better standardization.
In summary, we know much about the adverse health effects caused by the inhalation of asbestos fibers. Increased understanding of the health effects of fibrous minerals that fall outside the existing definitions of asbestos will help us find ways to provide appropriate protection for workers exposed to those materials. Further identification of workplace sources of vermiculite exposure and the tracking of persons potentially exposed to fiber-contaminated vermiculite and other contaminated materials will help us develop appropriate public health strategies for preventing exposure to these materials. While information continues to be gathered, public health prudence requires that vermiculite from the Libby mine or products containing vermiculite originating in Libby be considered potentially dangerous and that proper precautions be taken to minimize the generation and inhalation of any dust during the handling of these materials until analysis of the particular vermiculite or vermiculite-containing product shows that it does not produce an asbestos hazard.