Asbestos as a Contaminant
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. 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. 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]
Diseases caused by asbestos include:
- 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.
Other asbestos-related diseases
- 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.
Asbestos (a misapplication of Latin: asbestos “quicklime” from Greek; a, “not” and sbestos, “extinguishable”) describes any of a group of minerals that can be fibrous, many of which are metamorphic and are hydrous magnesium silicates. These minerals, together with their occurrences, uses, and associated hazards, have been discussed in detail by Guthrie and Mossman (1993).
The name is derived for its historical use in lamp wicks; the resistance of asbestos to fire has long been exploited for a variety of purposes. Asbestos was used in fabrics such as Egyptian burial cloths and Charlemagne’s tablecloth (which according to legend, he threw in a fire to clean). Asbestos occurs naturally in many forms (see below); it is mined from metamorphic rocks.
When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement or woven into fabric or mats. Asbestos is used in brake shoes and gaskets for its heat resistance, and in the past was used on electric oven and hotplate wiring for its electrical insulation at elevated temperature, and in buildings for its flame-retardant and insulating properties, tensile strength, flexibility, and resistance to chemicals. The inhalation of some kinds of asbestos fibers, however, can cause a number of serious illnesses, including cancer. Many uses of asbestos are banned in many countries.
Types of asbestos and associated fibres
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks. Chrysotile is the type most often used industrially. It is more flexible than other types of asbestos; it can be spun and woven into fabric. This is the kind of asbestos of which theatre curtains are made, as well as firefifgters’ suits, and possibly Charlemagne’s tablecloth. There is evidence that this type of asbestos is harmful, although not perhaps as harmful as other forms(refer to UK Health & Safety Commission report Asbestos: Effects on health of exposure to asbestos, 1985). One formula given for Chrysotile is Mg3(Si2O5)(OH)4.
Amosite, CAS No. 12172-73-5, is a trade name for the amphiboles belonging to the Cummingtonite – Grunerite solid solution series, commonly from Africa, named as an acronym from Asbestos Mines of South Africa. One formula given for Amosite is Fe7Si8O22(OH)2. This type of asbestos is highly biohazardous.
Riebeckite, CAS No. 12001-28-4, also known under the variety name of Crocidolite, is an amphibole from Africa and Australia. It is the fibrous form of the amphibole riebeckite. Blue asbestos is commonly thought of as the most dangerous type of asbestos (see above and below). One formula given for Crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2. This type of asbestos is highly biohazardous.
Notes: chrysotile commonly occurs as soft friable fibers. Asbestiform amphibole may also occur as soft friable fibers but some varieties such as amosite are commonly straighter. All forms of asbestos are fibrillar in that they are composed of fibers with widths less than 1 micrometer that occur in bundles and have very long lengths. Amphiboles most commonly occur in nature in a safer nonfibrous form. Asbestos with particularly fine fibers is also referred to as “amianthus”.
Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca2Mg5Si8O22(OH)2; actinolite asbestos (or smaragdite), CAS No. 77536-66-4, Ca2(Mg, Fe)5Si8O22(OH)2; and anthophyllite asbestos, CAS No. 77536-67-5, (Mg, Fe)7Si8O22(OH)2; are less commonly used industrially but can still be found in a variety of construction materials and insulation materials and have been reported in the past to occur in a few consumer products. Other natural and not currently regulated asbestos minerals, such as richterite, Na(CaNa)(Mg,Fe++)5[Si8O22](OH)2, and winchite, [ ](CaNa)Mg4(Al,Fe3+)Si8O22(OH)2, may be found as a contaminate in products such as the vermiculite containing Zonolite insulation manufactured by W.R. Grace and Company. These forms of asbestos are no less harmful than chrysotile, amosite, or crocidolite.