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Risk FactorsWorking with asbestos is the major risk factor for mesothelioma. A history
of asbestos exposure exists in almost all cases. However, mesothelioma has been reported in some individuals without any
known exposure to asbestos. In rare cases, mesothelioma has also been associated with irradiation, intrapleural thorium
dioxide (Thorotrast), and inhalation of other fibrous silicates, such as erionite.
Asbestos is the name of a group
of minerals that occur naturally as masses of strong, flexible fibers that can be separated into thin threads and woven.
Asbestos has been widely used in many industrial products, including cement, brake linings, roof shingles, flooring products,
textiles, and insulation. If tiny asbestos particles float in the air, especially during the manufacturing process, they may
be inhaled or swallowed, and can cause serious health problems. In addition to mesothelioma, exposure to asbestos increases
the risk of lung cancer, asbestosis (a noncancerous, chronic lung ailment), and other cancers, such as those of the larynx
and kidney.
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ExsposureAsbestos was known in antiquity, but it wasn't mined and widely used commercially
until the late 1800s. Its use greatly increased during World War II. Since the early 1940s, millions of American workers have
been exposed to asbestos dust. Initially, the risks associated with asbestos exposure were not publicly known. However, an
increased risk of developing mesothelioma was later found among shipyard workers, people who work in asbestos mines and mills,
producers of asbestos products, workers in the heating and construction industries, and other tradespeople. Today, the U.S.
Occupational Safety and Health Administration (OSHA) sets limits for acceptable levels of asbestos exposure in the workplace,
and created guidelines for engineering controls and respirators, protective clothing, exposure monitoring, hygiene facilities
and practices, warning signs, labeling, recordkeeping, and medical exams. By contrast, the British Government's Health and
Safety Executive (HSE) states formally that any threshold for mesothelioma must be at a very low level and it is widely agreed
that if any such threshold does exist at all, then it cannot currently be quantified. For practical purposes, therefore, HSE
does not assume that any such threshold exists. People who work with asbestos wear personal protective equipment to lower their
risk of exposure.
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OccupationalExposure to asbestos fibres has been recognised as an occupational health hazard
since the early 1900s. Several epidemiological studies have associated exposure to asbestos with the development of lesions
such as asbestos bodies in the sputum, pleural plaques, diffuse pleural thickening, asbestosis, carcinoma of the lung and larynx,
gastrointestinal tumours, and diffuse mesothelioma of the pleura and peritoneum.
The documented presence of asbestos fibres
in water supplies and food products has fostered concerns about the possible impact of long-term and, as yet, unknown exposure of
the general population to these fibres. Although many authorities consider brief or transient exposure to asbestos fibres as
inconsequential and an unlikely risk factor, some epidemiologists claim that there is no risk threshold. Cases of mesothelioma
have been found in people whose only exposure was breathing the air through ventilation systems. Other cases had very minimal
(3 months or less) direct exposure.
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Paraoccupational Secondary ExposureFamily members and others living with asbestos workers have
an increased risk of developing mesothelioma, and possibly other asbestos related diseases. This risk may be the result of exposure
to asbestos dust brought home on the clothing and hair of asbestos workers. To reduce the chance of exposing family members to
asbestos fibres, asbestos workers are usually required to shower and change their clothing before leaving the workplace.
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Asbestos In BuildingsMany building materials used in both public and domestic premises prior to
the banning of asbestos may contain asbestos. Those performing renovation works or diy activities may expose themselves to asbestos
dust. In the UK use of Chrysotile asbestos was banned at the end of 1999. Brown and blue asbestos was banned in the UK around 1985.
Buildings built or renovated prior to these dates may contain asbestos materials.
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Environmental ExposuresIncidence of mesothelioma had been found to be higher in populations living
near naturally occuring asbestos. For example, in Cappadocia, Turkey, an unprecedented mesothelioma epidemic caused 50% of all
deaths in three small villages. Initially, this was attributed to erionite, however, recently, it has been shown that erionite
causes mesothelioma mostly in families with a genetic predisposition.
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