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.
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.
