Amosite is usually brown or tan, with much straighter
and fibers than chrysotile. Amosite was the second
most commonly used type of asbestos, comprising
approximately 5%of the asbestos placed in buildings
and factories.
Crocidolite is a fairly rare form of asbestos,
unique because of its very obvious blue color.
Crocidolite fibers appear long and straight, much
like Amosite.
The remaining three asbestos types were not extensively
used in commercial products in the United States.
Asbestos Uses
Asbestos fibers have been used in many different
applications in our industrialized society. The
most common uses of asbestos have been:
In the United States, commercial
use of asbestos began in the early 1900’s and
peaked in the period from World War II into
the 1970’s. Under the Clean Air Act of 1970
the Environmental Protection Agency (EPA) began
regulating many asbestos-containing materials
which, by EPA definition, are materials with
more than 1- percent asbestos.
Asbestos
Health Effects
It is now clear that exposure
to airborne asbestos fibers can cause disease.
The risk of developing asbestos-related disease
varies according to the intensity, duration
and nature of the exposure.
Asbestos exposure can cause
a number of disabling and fatal diseases. The
principal route of exposure is by inhalation
through the nose and mouth. Asbestos, traditionally
valued for its indestructibility, is especially
resistant to the internal defenses of the human
body. Once lodged inside the lungs, most fibers
will not break up or dissolve. They can’t be
neutralized or removed.
ASBESTOSIS
is a disease that is characterized by
pulmonary fibrosis, a progressive scarring
of the lung caused by the accumulation
of asbestos fibers. Asbestosis is associated
exclusively with chronic, occupational
exposure. The build up of scar tissue
interferes with oxygen uptake through
the lungs and can lead to respiratory
and heart failure. Often, asbestosis is
a progressive disease, even in the absence
of continued exposure. Symptoms include
shortness of breath, cough, fatigue, and
vague feelings of sickness. When the fibrosis
worsens, shortness of breath occurs even
at rest. |
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LUNG CANCER is a malignant
tumor of the bronchi covering. The tumor grows
through surrounding tissue invading and often
obstructing the air passages. The earliest symptom
is often a persistent cough; a physical exam
may attribute the symptom of chronic bronchitis.
Chest x-rays sometimes show shadows that indicate
tumors and enlarged lymph nodes. However, the
definitive diagnosis of lung cancer is based
upon microscopic examination of lung tissue.
The time between exposure to asbestos and the
occurrence of lung cancer, is 20-30 years. There
is no threshold or limit of exposure below which
the risk of lung cancer is not increased.
MESOTHELIOMA is a cancer
of the mesothelium, the lining of the chest
or the lining of the abdominal wall. Early stages
are associated with few symptoms. By the time
it is diagnosed, it is almost always fatal.
Effective therapy does not exist. There is no
exposure threshold for mesothelioma. This is
suggested by the observation that family members
of asbestos-exposed workers have developed mesothelioma.
Presumably cleaning the clothes of the exposed
worker has exposed these individuals to asbestos
dust and led to the disease. Similar to other
asbestos- related diseases, mesothelioma has
an extended latency period of 30 to 40 years.
PLEURAL PLAQUES and
PLEURAL CALCIFICATION are markers of
exposure and may develop 10 to 20 years after
initial exposure. Plaques are opaque patches
visible on chest x-rays that consist of dense
strands of connective tissue surrounded by cells.
All commercial types of asbestos induce plaques.
Plaques can occur even when fibrosis is absent
and do not seem to reflect the severity of pulmonary
disease.
OTHER DISEASES and
adverse health effects have been noted among
the population exposed to asbestos fibers. Increased
incidences of non-respiratory cancers have been
observed in some recent epidemiological studies.
Cancers of the larynx, esophagus, stomach, colon-rectum,
kidney and pancreas are present at slightly
higher than predicted levels.
Other substances appear to
cooperate with asbestos to multiply the risk
of lung cancer. People who smoke 20 cigarettes
per day increase their risk of developing lung
cancer by ten-fold (10X) when compared to non-smoker.
Workers exposed to the same level of asbestos
as insulation workers historically increase
their risk of developing lung cancer by five-fold
(5X). These two factors working together have
a synergistic effect; the smoker exposed to
asbestos fibers is at least fifty times (50X)
more likely to develop lung cancer than the
general public.
