What is
asbestos?
Asbestos is the name given to a group of minerals that
occur naturally in the environment as bundles of fibers that can be separated
into thin, durable threads. These fibers are resistant to heat, fire, and
chemicals and do not conduct electricity. For these reasons, asbestos has been
used widely in many industries.
Chemically, asbestos minerals are silicate compounds,
meaning they contain atoms of silicon and oxygen in their molecular structure.
Asbestos minerals are divided into two major groups:
Serpentine asbestos and amphibole asbestos. Serpentine asbestos includes the
mineral chrysotile, which has long, curly fibers that can be woven. Chrysotile
asbestos is the form that has been used most widely in commercial applications.
Amphibole asbestos includes the minerals actinolite, tremolite, anthophyllite,
crocidolite, and amosite. Amphibole asbestos has straight, needle-like fibers
that are more brittle than those of serpentine asbestos and are more limited in
their ability to be fabricated .
How is
asbestos used?
Asbestos has been mined and used commercially in North
America since the late 1800s. Its use increased greatly during World War II
.Since then, asbestos has been used in many industries. For example, the
building and construction industries have used it for strengthening cement and plastics
as well as for insulation, roofing, fireproofing, and sound absorption. The
shipbuilding industry has used asbestos to insulate boilers, steam pipes, and
hot water pipes. The automotive industry uses asbestos in vehicle brake shoes
and clutch pads. Asbestos has also been used in ceiling and floor tiles;
paints, coatings, and adhesives; and plastics. In addition, asbestos has been
found in vermiculite-containing garden products and some talc-containing
crayons.
In the late 1970s, the U.S. Consumer Product Safety
Commission (CPSC) banned the use of asbestos in wallboard patching compounds
and gas fireplaces because the asbestos fibers in these products could be
released into the environment during use. In addition, manufacturers of
electric hairdryers voluntarily stopped using asbestos in their products in
1979. In 1989, the U.S. Environmental Protection Agency (EPA) banned all new
uses of asbestos; however, uses developed before 1989 are still allowed. The
EPA also established regulations that require school systems to inspect
buildings for the presence of damaged asbestos and to eliminate or reduce
asbestos exposure to occupants by removing the asbestos or encasing it
In June 2000, the CPSC concluded that the risk of
children’s exposure to asbestos fibers in crayons was extremely low . However,
U.S. manufacturers of these crayons agreed to eliminate talc from their
products.
In August 2000, the EPA conducted a series of tests to
evaluate the risk for consumers of adverse health effects associated with
exposure to asbestos-contaminated vermiculite. The EPA concluded that exposure
to asbestos from some vermiculite products poses only a minimal health risk.
The EPA recommended that consumers reduce the low risk associated with the
occasional use of vermiculite during gardening activities by limiting the
amount of dust produced during vermiculite use. Specifically, the EPA suggested
that consumers use vermiculite outdoors or in a well-ventilated area; keep
vermiculite damp while using it; avoid bringing dust from vermiculite into the
home on clothing; and use premixed potting soil, which is less likely to
generate dust
The regulations described above and other actions,
coupled with widespread public concern about the health hazards of asbestos,
have resulted in a significant annual decline in the U.S. use of asbestos.
Domestic consumption of asbestos amounted to about 803,000 metric tons in 1973,
but it had dropped to about 2,400 metric tons by 2005
What are the health hazards of exposure to
asbestos?
People may be exposed to asbestos in their workplace,
their communities, or their homes. If products containing asbestos are
disturbed, tiny asbestos fibers are released into the air. When asbestos fibers
are breathed in, they may get trapped in the lungs and remain there for a long
time. Over time, these fibers can accumulate and cause scarring and
inflammation, which can affect breathing and lead to serious health problems
Asbestos has been classified as a known human
carcinogen (a substance that causes cancer) by the U.S. Department of Health
and Human Services, the EPA, and the International Agency for Research on
Cancer . Studies have shown that exposure to asbestos may increase the risk of
lung cancer and mesothelioma (a relatively rare cancer of the thin membranes that
line the chest and abdomen). Although rare, mesothelioma is the most common
form of cancer associated with asbestos exposure. In addition to lung cancer
and mesothelioma, some studies have suggested an association between asbestos
exposure and gastrointestinal and colorectal cancers, as well as an elevated
risk for cancers of the throat, kidney, esophagus and gallbladder. However, the
evidence is inconclusive.
Asbestos exposure may also increase the risk of
asbestosis (an inflammatory condition affecting the lungs that can cause
shortness of breath, coughing, and permanent lung damage) and other
nonmalignant lung and pleural disorders, including pleural plaques (changes in
the membranes surrounding the lung), pleural thickening, and benign pleural
effusions (abnormal collections of fluid between the thin layers of tissue lining
the lungs and the wall of the chest cavity). Although pleural plaques are not
precursors to lung cancer, evidence suggests that people with pleural disease
caused by exposure to asbestos may be at increased risk for lung cancer.
Who is at risk
for an asbestos-related disease?
Everyone is exposed to asbestos at some time during
their life. Low levels of asbestos are present in the air, water, and soil.
However, most people do not become ill from their exposure. People who become
ill from asbestos are usually those who are exposed to it on a regular basis,
most often in a job where they work directly with the material or through
substantial environmental contact.
Since the early 1940s, millions of American workers
have been exposed to asbestos. Health hazards from asbestos fibers have been
recognized in workers exposed in the shipbuilding trades, asbestos mining and
milling, manufacturing of asbestos textiles and other asbestos products, insulation
work in the construction and building trades, and a variety of other trades.
Demolition workers, drywall removers, asbestos removal workers, firefighters,
and automobile workers also may be exposed to asbestos fibers. Studies
evaluating the cancer risk experienced by automobile mechanics exposed to
asbestos through brake repair are limited, but the overall evidence suggests
there is no safe level of asbestos exposure . As a result of Government
regulations and improved work practices, today’s workers (those without
previous exposure) are likely to face smaller risks than did those exposed in
the past.
Individuals involved in the rescue, recovery, and
cleanup at the site of the September 11, 2001, attacks on the World Trade
Center (WTC) in New York City are another group at risk of developing an
asbestos-related disease. Because asbestos was used in the construction of the
North Tower of the WTC, when the building was attacked, hundreds of tons of
asbestos were released into the atmosphere. Those at greatest risk include
firefighters, police officers, paramedics, construction workers, and volunteers
who worked in the rubble at Ground Zero. Others at risk include residents in
close proximity to the WTC towers and those who attended schools nearby. These
individuals will need to be followed to determine the long-term health
consequences of their exposure
One study found that nearly 70 percent of WTC rescue
and recovery workers suffered new or worsened respiratory symptoms while
performing work at the WTC site. The study describes the results of the WTC
Worker and Volunteer Medical Screening Program, which was established to
identify and characterize possible WTC-related health effects in responders.
The study found that about 28 percent of those tested had abnormal lung
function tests, and 61 percent of those without previous health problems
developed respiratory symptoms . However, it is important to note that these
symptoms may be related to exposure to debris components other than asbestos.
Although it is clear that the health risks from
asbestos exposure increase with heavier exposure and longer exposure time,
investigators have found asbestos-related diseases in individuals with only
brief exposures. Generally, those who develop asbestos-related diseases show no
signs of illness for a long time after their first exposure. It can take from
10 to 40 years or more for symptoms of an asbestos-related condition to appear.
There is some evidence that family members of workers
heavily exposed to asbestos face an increased risk of developing mesothelioma.
This risk is thought to result from exposure to asbestos fibers brought into
the home on the shoes, clothing, skin, and hair of workers. To decrease these
exposures, Federal law regulates workplace practices to limit the possibility
of asbestos being brought home in this way. Some employees may be required to
shower and change their clothes before they leave work, store their street
clothes in a separate area of the workplace, or wash their work clothes at home
separately from other clothes.
Cases of mesothelioma have also been seen in
individuals without occupational asbestos exposure who live close to asbestos
mines.
What factors
affect the risk of developing an asbestos-related disease?
Several factors can help to determine how asbestos
exposure affects an individual, including :
- Dose (how much asbestos an individual was exposed to).
- Duration (how long an individual was exposed).
- Size, shape, and chemical makeup of the asbestos fibers.
- Source of the exposure.
- Individual risk factors, such as smoking and pre-existing lung
disease.
Although all forms of asbestos are considered
hazardous, different types of asbestos fibers may be associated with different
health risks. For example, the results of several studies suggest that
amphibole forms of asbestos may be more harmful than chrysotile, particularly
for mesothelioma risk, because they tend to stay in the lungs for a longer
period of time.
How does
smoking affect risk?
Many studies have shown that the combination of
smoking and asbestos exposure is particularly hazardous. Smokers who are also
exposed to asbestos have a risk of developing lung cancer that is greater than
the individual risks from asbestos and smoking added together . There is
evidence that quitting smoking will reduce the risk of lung cancer among
asbestos-exposed workers .Smoking combined with asbestos exposure does not
appear to increase the risk of mesothelioma .However, people who were exposed
to asbestos on the job at any time during their life or who suspect they may
have been exposed should not smoke.
How are
asbestos-related diseases detected?
Individuals who have been exposed (or suspect they
have been exposed) to asbestos fibers on the job, through the environment, or
at home via a family contact should inform their doctor about their exposure
history and whether or not they experience any symptoms. The symptoms of
asbestos-related diseases may not become apparent for many decades after the
exposure. It is particularly important to check with a doctor if any of the
following symptoms develop:
- Shortness of breath, wheezing, or hoarseness.
- A persistent cough that gets worse over time.
- Blood in the sputum (fluid) coughed up from the lungs.
- Pain or tightening in the chest.
- Difficulty swallowing.
- Swelling of the neck or face.
- Loss of appetite.
- Weight loss.
- Fatigue or anemia.
A thought physical examination, including a chest X-Ray
and lung function tests, may be
recommended. The chest x-ray is currently the most common tool used to detect
asbestos-related diseases. However, it is important to note that chest x-rays
cannot detect asbestos fibers in the lungs, but they can help identify any
early signs of lung disease resulting from asbestos exposure
Studies have shown that computed tomography ( CT) (a
series of detailed pictures of areas inside the body taken from different
angles; the pictures are created by a computer linked to an x-ray machine) may
be more effective than conventional chest x-rays at detecting asbestos-related
lung abnormalities in individuals who have been exposed to asbestos .
A lung biopsy, which detects microscopic asbestos fibers
in pieces of lung tissue removed by surgery, is the most reliable test to
confirm the presence of asbestos-related abnormalities. A bronchoscopy is a
less invasive test than a biopsy and detects asbestos fibers in material that
is rinsed out of the lungs. It is important to note that these tests cannot
determine how much asbestos an individual may have been exposed to or whether
disease will develop .
Asbestos fibers can also be detected in urine, mucus,
or feces, but these tests are not reliable for determining how much asbestos
may be in an individual’s lungs
How can workers
protect themselves from asbestos exposure?
The Occupational Safety and Health Administration
(OSHA) is a component of the U.S. Department of Labor (DOL) and is the
Federal agency responsible for health and safety regulations in maritime,
construction, manufacturing, and service workplaces. OSHA established
regulations dealing with asbestos exposure on the job, specifically in
construction work, shipyards, and general industry, that employers are required
to follow. In addition, the Mine Safety and Health Administration (MSHA),
another component of the DOL, enforces regulations related to mine safety.
Workers should use all protective equipment provided by their employers and
follow recommended workplace practices and safety procedures. For example,
National Institute for Occupational Safety and Health (NIOSH)-approved
respirators that fit properly should be worn by workers when required.
(national cancer institute)