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Low levels of asbestos are in the air we breathe and some of the water we drink,
including water from natural sources.Studies have shown that members of the
general (nonoccupationally exposed) population have tens of thousands to
hundreds of thousands of asbestos fibers in each gram of dry lung tissue, which
translates into millions of fibers and tens of thousands of asbestos bodies in
every person's lungs.
The EPA has proposed a concentration limit of 7 million fibers per liter of
drinking water for long fibers (lengths greater than or equal to 5 µm). OSHA
(Occupational Safety and Health Administration) has set limits of 100,000
fibers with lengths greater than or equal to 5 µm per cubic meter of workplace
air for 8-hour shifts and 40-hour work weeks.
Most respirable asbestos fibers are invisible to the unaided human eye because
their size is about 3.0-20.0 µm in length and can be as thin as 0.01 µm. Human
hair ranges in size from 17 to 181 µm in width.[7] Fibers ultimately form
because when these minerals originally cooled and crystallized, they formed by
the polymeric molecules lining up parallel with each other and forming oriented
crystal lattices. These crystals thus have three cleavage planes, just as other
minerals and gemstones have. But in their case, there are two cleavage planes
that are much weaker than the third direction. When sufficient force is
applied, they tend to break along their weakest directions, resulting in a
linear fragmentation pattern and hence a fibrous form. This fracture process
can keep occurring and one larger asbestos fiber can ultimately become the
source of hundreds of much thinner and smaller fibers.
As asbestos fibers get smaller and lighter, they more easily become airborne and
human respiratory exposures can result. Fibers will eventually settle but may
be re-suspended by air currents or other movement.
Friability of an asbestos containing product means that it is so soft and weak
in structure that it can be broken with simple finger crushing pressure.
Friable materials are of the most initial concern due to their ease of damage.
The forces or conditions of usage that come into intimate contact with most
non-friable asbestos containing materials are substantially higher than finger
pressure. Non-friable asbestos products can release substantial quantities of
asbestos fibers into their environments as well.
As early as 1898 the Chief Inspector of Factories of the United Kingdom reported
to Parliament in his Annual Report about the "evil effects of asbestos dust".
He reported the "sharp, glass like nature of the particles" when allowed to
remain in the air in any quantity, "have been found to be injurious, as might
have been expected" (Report of the Select Committee 1994). In 1906 a British
Parliamentary Commission confirmed the first cases of asbestos deaths in
factories in Britain and recommended better ventilation and other safety
measures. In 1918 a US insurance company produced a study showing premature
deaths in the asbestos industry in the United States. In 1926 the Massachusetts
Industrial Accidents Board processed the first successful compensation claim by
a sick asbestos worker.[citation needed] Many American injuries from asbestos
exposure came from shipbuilders working during World War II.
The problem with asbestos arises when the fibers become airborne and are
inhaled. Because of the size of the fibers, the lungs cannot expel them.
[Casarrett & Doull's Toxicology (2001), pp 520-522]
* Asbestosis – A lung disease first found in naval shipyard workers, asbestosis
is a scarring of the lung tissue from an acid produced by the body's attempt to
dissolve the fibers. The scarring may eventually become so severe that the
lungs can no longer function. The latency period (the time it takes for the
disease to develop) is often 10-20 years.
* Mesothelioma – A cancer of the mesothelial lining of the lungs and the chest
cavity, the peritoneum (abdominal cavity) or the pericardium (a sac surrounding
the heart). It is believed that mesothelioma is caused by generation of
reactive oxygen species (ROS) by the asbestos fibers. There is also some
evidence to suggest that simian virus 40 (SV40) works together with asbestos in
the development of malignant mesothelioma. Asbestos exposure is linked to at
least 50% of patients developing malignant mesothelioma. Malignant mesothelioma
has a peak incidence 35-45 years after asbestos exposure. Median survival for
patients with malignant mesothelioma is 11 months. Asbestos has a synergistic
effect with tobacco smoking in the causation of pleural mesothelioma.
* Cancer – Lung cancer has been linked to asbestos. Asbestos exposure alone can
cause lung cancer, but asbestos exposure and tobacco smoking have a synergistic
effect, greatly increasing the chances of contracting lung cancer. Cancer of
the larynx has been linked to asbestos. Some studies suggest that asbestos
exposure is linked to a slightly increased risk of stomach, pharyngeal, and
colorectal cancer.
EWG Action Fund estimates that in the United States, about 9,900 people die each
year of asbestos-related diseases, such as mesothelioma, asbestosis, lung
cancer, and gastrointestinal cancer.
* asbestos warts – caused when the sharp fibres lodge in the skin and are
overgrown causing benign callus-like growths.
* pleural plaques – discrete fibrous or partially calcified thickened area
which can be seen on X-rays of individuals exposed to asbestos. They do not
become malignant or cause other lung impairment.
* diffuse pleural thickening – similar to above and can sometimes be associated
with asbestosis. Usually no symptoms shown but if extensive can cause lung
impairment.
Source: http://en.wikipedia.org/wiki