What Is Asbestos?
Asbestos is the name of a group of highly fibrous minerals with
separable, long, and thin fibers. Separated asbestos fibers are strong
enough and flexible enough to be spun and woven. Asbestos fibers are heat
resistant, making them useful for many industrial purposes. Because of
their durability, asbestos fibers that get into lung tissue will remain
for long periods of time.
For more information on asbestos, see ATSDR's Toxicological Profile on
Asbestos. Other ATSDR resources include the Public Health Statement on
Asbestos, which is the summary chapter from the Toxicological Profile, and
the ToxFAQs for Asbestos, which is a shorter question and answer version.
There are two general types of asbestos, amphibole and chrysotile.
Some studies show that amphibole fibers stay in the lungs longer than
crystotile, and this tendency may account for their increased toxicity
(harmfulness to the body).
Scanning electron micrograph of asbestiform
amphibole from a former vermiculite mining site near Libby,
Montana. Source: U.S. Geological Survey and U.S. Environmental
Protection Agency, Region 8, Denver, Colorado.
Regulatory agencies such as the U.S. Environmental Protection Agency
(EPA) and Occupational Safety and Health Administration (OSHA) recognize
six asbestos minerals: chrysotile, a serpentine mineral with long and
flexible fibers; and five amphibole (with relatively brittle crystalline
fibers) minerals, actinolite asbestos, tremolite asbestos, anthophyllite
asbestos, crocidolite asbestos, and amosite asbestos.
We are all exposed to low levels of asbestos in the air. These
"ambient" - or typical - air concentrations of asbestos fibers
are 0.00001 to 0.0001 fibers per milliliter (fiber/mL). Much more
concentrated levels of exposure are known to cause health
effects in humans. For more information on asbestos exposure, see the
Public Health Statement on Asbestos, "How might I be exposed to
Asbestos Exposure and Your Work
Asbestos exposure can occur in the workplace, particularly if you work
or have worked as a(n):
- Pipe or Steam Fitter
- Brake Repair Mechanic
- Insulation Installer
- Dry Wall Finisher
- Shipyard Worker
Individuals who have worked in the above industries should consult with
a physician with expertise in the evaluation and management of
asbestos-related lung disease.
Chrysotile Asbestos Exposure
The asbestos fibers detected in the samples taken at the World Trade
Center sites were chrysotile asbestos.
Amphibole Asbestos Exposure
- Mining activities
Exposure to tremolite asbestos
(a type of amphibole asbestos) can occur in workers involved
in mining, milling, and handling of other ores and rocks
containing tremolite asbestos (such as vermiculite or talc).
Residents who live near mining, milling, or manufacturing
sites that involve tremolite asbestos-containing material may
be exposed to higher levels of airborne asbestos.
A vermiculite mine in Libby,
Montana. Asbestos has been detected in vermiculite from this mine.
Insulation and Building Materials
asbestos can be found in a variety of building materials, such
as insulation, ceiling or floor tiles, and cement pipes.
Amphibole asbestos has been found in some vermiculite sources
used as home and building insulation. Much of the
asbestos-contaminated vermiculite mined in Libby, Montana, was
used to produce attic insulation products.
Bagged asbestos awaits
disposal in a landfill.
Workers or homeowners involved in demolition work, maintenance,
repair, or remodeling of buildings containing these products can be
exposed to higher airborne fibrous amphibole levels than levels in
ambient air. However, exposure can occur only when materials
containing asbestos are disturbed in some way to release fibers into
the air. When asbestos-containing materials are solidly embedded or
contained, exposure risk will be minimal.
ATSDR, in conjunction with the EPA recently published a brochure which
identifies potential health hazards posed by asbestos in certain
building insulation products. The brochure provides information on how
to identify these products and steps individuals can take to reduce
exposure. Also, see ATSDRs Vermiculite Consumer Products Fact Sheet.
- Consumer Products
Vermiculite was also commonly sold in
gardening and hardware stores. It was used as a soil amendment
(conditioner to improve soil quality) or fertilizer carrier, and it
was an ingredient in many potting soil mixtures.
In addition, small amounts of amphibole asbestos have been found in
some talc-containing crayons. The Consumer Product Safety Commission (CPSC)
concluded that the risk is extremely low that children would be
exposed to asbestos fibers in crayons. The U.S. manufacturers of these
crayons, however, have agreed to eliminate talc from their products.
The combined use of detection methods called light microscopy, electron
microscopy, and energy dispersive X-ray analysis offer the most accurate
approach to identify asbestos and to estimate concentrations that may
become airborne upon disturbance. For the purposes of counting asbestos
fibers in these samples, regulatory agencies commonly count as fibers
those particles of asbestos minerals at least 5 micrometers in length and
with length: width ratios of 3:1. For other purposes, such as detecting
fibers in bulk building materials, asbestos particles with length: width
ratios of 5:1 are counted. Air concentrations of asbestos fibers in
ambient (typical) air are 0.00001 to 0.0001 fibers per milliliter (fiber/mL).
The recently established exposure limit for U.S. workplaces is 0.1 fiber/mL.
For your convenience, we have prepared a list of
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