asbestos

Asbestos is a group of minerals with long, thin fibrous crystals. The word "asbestos" is derived from a Greek adjective meaning inextinguishable. The Greeks termed asbestos the "miracle mineral" because of its soft and pliant properties, as well as its ability to withstand heat.

Asbestos became increasingly popular among manufacturers and builders in the late 19th century due to its resistance to heat, electricity and chemical damage, its sound absorption and tensile strength. 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.

This "miracle material" is now known to be highly toxic. The inhalation of asbestos fibers can cause serious illnesses, including mesothelioma and asbestosis. Since the mid 1980s, many uses of asbestos have been banned in many countries.

Contents [hide]
1 Types and associated fibres
1.1 White
1.2 Brown
1.3 Blue
1.4 Other materials
2 Production trends
3 Uses
3.1 Historic usage
3.2 Specific products
3.2.1 Serpentine group
3.2.2 Amphibole group
4 Health issues
4.1 Other asbestos-related diseases
4.2 Asbestos as a contaminant
4.3 Environmental asbestos
5 History of health concerns and regulation
5.1 Prior to 1900
5.2 1900s - 1910s
5.3 1920s and 1930s
5.4 1940s
5.5 1950s
5.6 1960s-early 80s
5.7 Modern regulation
5.7.1 United States
5.7.2 New Zealand
6 Contamination of other products
6.1 Asbestos and vermiculite
6.2 Asbestos and talc
7 Asbestos in construction
7.1 Asbestos construction in developed countries
7.2 Asbestos construction in developing countries
8 Litigation
9 Critics of safety regulations
10 Substitutes for asbestos in construction
11 Recycling and disposal
12 See also
12.1 Mineralogy
12.2 Other internal links
13 References
14 Additional reading
15 External links
15.1 Regulatory and government links
15.2 Mineral and mining links
15.3 Health and the environment



[edit] Types and associated fibres

Chrysotile asbestos
Asbestos fibersSix minerals are defined as "asbestos" including: chrysotile, amosite, crocidolite, tremolite, anthophyllite and actinolite.


[edit] White
Chrysotile, CAS No. 12001-29-5, is obtained from serpentine rocks which are common throughout the world. Chrysotile fibers are curly as opposed to fibers from amosite, crocidolite, tremolite, actinolite, and anthophyllite which are needlelike.[1] Chrysotile, along with other types of asbestos, has been banned in dozens of countries and is only allowed in the United States and Europe in very limited circumstances. Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America.[2] Applications where chrysotile might be used include the use of joint compound. It is more flexible than amphibole types of asbestos; it can be spun and woven into fabric. The most common use is within corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It is also found as flat sheets used for ceilings and sometimes for walls. Numerous other items have been made containing chrysotile including brake linings, cloth behind fuses (for fire protection), pipe insulation, in floor tiles and in rope seals to boilers.[citation needed]

Mg3[Si2O5](OH)4


[edit] Brown
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. It is found most frequently as a fire retardant in thermal insulation products and ceiling tiles.[2]


[edit] Blue
Crocidolite, CAS No. 12001-28-4 is an amphibole found primarily in southern Africa, but also in Australia. It is the fibrous form of the amphibole riebeckite. One formula given for crocidolite is Na2Fe2+3Fe3+2Si8O22(OH)2. 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 micrometre that occur in bundles and have very long lengths. Asbestos with particularly fine fibers is also referred to as "amianthus". Amphiboles such as tremolite have a crystal structure containing strongly bonded ribbonlike silicate anion polymers that extend the length of the crystal. Serpentine (chrysotile) has a sheetlike silicate anion which is curved and which rolls up like a carpet to form the fiber.[3]


[edit] Other materials
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)5(Si8O22)(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 asbestiform 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 contaminant in products such as the vermiculite containing zonolite insulation manufactured by W.R. Grace and Company. These minerals are thought to be no less harmful than tremolite, amosite, or crocidolite, but since they are not regulated, they are referred to as "asbestiform" rather than asbestos although may still be related to diseases and hazardous.


[edit] Production trends

Asbestos output in 2005In 2005, 2.2 million tons of asbestos were mined worldwide. Russia was the largest producer with about 40% world share followed by China and Kazakhstan.[4]


[edit] Uses

[edit] Historic usage
Asbestos was named by the ancient Greeks who also recognized certain hazards of the material. The Greek geographer Strabo and the Roman naturalist Pliny the Elder noted that the material damaged lungs of slaves who wove it into cloth.[5][6] Charlemagne, the first Holy Roman Emperor, is said to have had a tablecloth made of asbestos.[7][8]

Wealthy Persians, who bought asbestos imported over the Hindu Kush, amazed guests by cleaning the cloth by simply exposing it to fire. According to Biruni in his book of Gems, any cloths made of asbestos (Persian: آذرشست, āzarshast or Persian: آذرشب, āzarshab) were called (Persian: شستكه) shastakeh[9]. Some of the Persians believed the fiber was fur from an animal (named samandar, Persian: سمندر) that lived in fire and died when exposed to water.[10][11]

Some archeologists believe that ancients made shrouds of asbestos, wherein they burned the bodies of their kings, in order to preserve only their ashes, and prevent their being mixed with those of wood or other combustible materials commonly used in funeral pyres.[12] Others assert that the ancients used asbestos to make perpetual wicks for sepulchral or other lamps.[8][10] In more recent centuries, asbestos was indeed used for this purpose. Although asbestos causes skin to itch upon contact, ancient literature indicates that it was prescribed for diseases of the skin, and particularly for the itch. It is possible that they used the term asbestos for alumen plumosum, because the two terms have often been confused throughout history.[12]

Asbestos became more widespread during the industrial revolution; in the 1860s it was used as insulation in the U.S. and Canada. Development of the first commercial asbestos mine began in 1879 in the Appalachian foothills of Quebec.[13] By the mid 20th century uses included fire retardant coatings, concrete, bricks, pipes and fireplace cement, heat, fire, and acid resistant gaskets, pipe insulation, ceiling insulation, fireproof drywall, flooring, roofing, lawn furniture, and drywall joint compound.[8]

Approximately 100,000 people in the United States have died, or will die, from asbestos exposure related to ship building. In the Hampton Roads area, a shipbuilding center, mesothelioma occurrence is seven times the national rate.[14] Thousands of metric tons of asbestos were used in World War II ships to wrap the pipes, line the boilers, and cover engine and turbine parts. There were approximately 4.3 million shipyard workers in the United States during WWII; for every thousand workers about 14 died of mesothelioma and an unknown number died from asbestosis.[13]

Asbestos fibers were once used in automobile brake pads and shoes. Since the mid-1990s, a majority of brake pads, new or replacement, have been manufactured instead with linings made of ceramic, carbon, metallic and Aramid fiber (Twaron or Kevlar—the same material used in bulletproof vests).

Kent, the first filtered cigarette on the market, used crocidolite asbestos in its "Micronite" filter from 1952 to 1956.[15]

The first documented death related to asbestos was in 1906.[16] In the early 1900s researchers began to notice a large number of early deaths and lung problems in asbestos mining towns. The first diagnosis of asbestosis was made in England in 1924.[6] By the 1930s, England regulated ventilation and made asbestosis an excusable work related disease, about ten years sooner than the U.S.[6][17] The term Mesothelioma was not used in medical literature until 1931, and was not associated with asbestos until sometime in the 1940s.[16]

The United States government and asbestos industry have been criticized for not acting quickly enough to inform the public of dangers, and to reduce public exposure. In the late 1970s court documents proved that asbestos industry officials knew of asbestos dangers and tried to conceal them.[13]

In Japan, particularly after World War II, asbestos was used in the manufacture of ammonium sulfate for purposes of rice production, sprayed upon the ceilings, iron skeletons, and walls of railroad cars and buildings (during the 1960s), and used for energy efficiency reasons as well. Production of asbestos in Japan peaked in 1974 and went through ups and downs until about 1990, when production began to drop severely.[18]


[edit] Specific products

[edit] Serpentine group
Serpentine minerals have a sheet or layered structure. Chrysotile is the only asbestos mineral in the serpentine group. In the United States, chrysotile has been the most commonly used type of asbestos. According to the U.S. EPA Asbestos Building Inspectors Manual, chrysotile accounts for approximately 95% of asbestos found in buildings in the United States. Chrysotile is often present in a wide variety of materials, including:

joint compound
mud and texture coats
vinyl floor tiles, sheeting, adhesives
roofing tars, felts, siding, and shingles
"transite" panels, siding, countertops, and pipes
fireproofing
caulk
gaskets
brake pads and shoes
clutch plates
stage curtains
fire blankets
interior fire doors
fireproof clothing for firefighters
thermal pipe insulation
In the European Union and Australia it has recently been banned as a potential health hazard[19] and is not used at all. Japan is moving in the same direction, but more slowly. Revelations that hundreds of workers had died in Japan over the previous few decades from diseases related to asbestos sparked a scandal in mid-2005.[20] Tokyo had, in 1971, ordered companies handling asbestos to install ventilators and check health on a regular basis; however, the Japanese government did not ban crocidolite and amosite until 1995, and a full-fledged ban on asbestos was implemented in October 2004.[20]


[edit] Amphibole group
Five types of asbestos are found in the amphibole group: amosite, crocidolite, anthophyllite, tremolite, and actinolite. Amosite, the second most likely type to be found in buildings, according to the U.S. EPA Asbestos Building Inspectors Guide, is the "brown" asbestos.

Amosite and crocidolite were formerly used in many products until the early 1980s. The use of all types of asbestos in the amphibole group was banned (in much of the Western world) by the mid-1980s, and by Japan in 1995. These products were mainly:

Low density insulation board and ceiling tiles
Asbestos-cement sheets and pipes for construction, casing for water and electrical/telecommunication services
Thermal and chemical insulation (i.e., fire rated doors, limpet spray, lagging and gaskets)

[edit] Health issues
Chrysotile asbestos, like all other forms of industrial asbestos, has produced tumors in animals. Mesotheliomas have been observed in people who were occupationally exposed to chrysotile, family members of the occupationally exposed, and residents who lived close to asbestos factories and mines.[1] Brown asbestos, like all asbestos, is hazardous. Blue asbestos is commonly thought of as the most dangerous type of asbestos. Tremolite often contaminates chrysotile asbestos, thus creating an additional hazard.

Asbestos exposure becomes a health concern when high concentrations of asbestos fibers are inhaled over a long time period.[21] People who become ill from asbestos are almost always those who are exposed on a day-to-day basis in a job where they work directly with the material. As a person's exposure to fibers increases, either by breathing more fibers or by breathing fibers for a longer time, that person's risk of disease also increases. Disease is very unlikely to result from a single, high-level exposure, or from a short period of exposure to lower levels.[22]


[edit] Other asbestos-related diseases
Asbestos warts – caused when the sharp fibers 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.

[edit] Asbestos as a contaminant

Asbestos fibres (SEM picture)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.[23] 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 a product containing asbestos 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 materials containing asbestos are substantially higher than finger pressure.


[edit] Environmental asbestos
This article or section deals primarily with North America and does not represent a worldwide view of the subject.
Please improve this article or discuss the issue on the talk page.

Asbestos can be found naturally in the air outdoors and in some drinkable water, including water from natural sources.[24] Studies have shown that members of general (non-occupationally 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.[25]

Asbestos from natural geologic deposits is known as "Naturally Occurring Asbestos" (NOA). Health risks associated with exposure to NOA are not yet fully understood, and current US federal regulations do not address exposure from NOA. Many populated areas are in proximity to shallow, natural deposits which occur in 50 of 58 California counties and in 19 other U.S. states. In one study, data was collected from 3,000 mesothelioma patients in California and 890 men with prostate cancer, a malignancy not known to be related to asbestos. The study found a correlation between the incidence of mesotheliomas and the distance a patient lived from known deposits of rock likely to include asbestos, the correlation was not present when the incidence of prostate cancer was compared with the same distances. According to the study, risk of mesothelioma declined by 6 percent for every 10 kilometers that an individual had lived from a likely asbestos source.[26]

Portions of El Dorado County, California are known to contain natural asbestos formations near the surface.[27][26] The USGS studied amphiboles in rock and soil in the area in response to an EPA sampling study and subsequent criticism of the EPA study. The study found that many amphibole particles in the area meet the counting rule criteria used by the EPA for chemical and morphological limits, but do not meet morphological requirements for commercial-grade-asbestos. The executive summary pointed out that even particles that do not meet requirements for commercial-grade-asbestos may be a health threat and suggested a collaborative research effort to assess health risks associated with "Naturally Occurring Asbestos".[28]

Large portions of Fairfax County, Virginia were also found to be underlain with tremolite. The county monitored air quality at construction sites, controlled soil taken from affected areas, and required freshly developed sites to lay 6 inches (150 mm) of clean, stable material over the ground.[26]


[edit] History of health concerns and regulation
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Discussion of this nomination can be found on the talk page. (January 2008)


[edit] Prior to 1900
By the first century AD, Greeks and Romans had already observed, at least in passing, that slaves involved in the weaving of asbestos cloth were afflicted with a sickness of the lungs. [29]

Early concern in the modern era on the health effects of asbestos exposure can be found in several sources. Among the earliest were reports in Britain. The annual reports of the Chief Inspector of Factories reported as early as 1898 that asbestos had 'easily demonstrated' health risks.[30]

At about the same time, what was probably the first study of mortality among asbestos workers was reported in France. [31] While the study describes the cause of death as chalicosis, a generalized pneumoconiosis, the circumstances of the employment of the fifty workers whose death prompted the study suggest that the root cause was asbestos or mixed asbestos-cotton dust exposure.


[edit] 1900s - 1910s
Further awareness of asbestos-related diseases can be found in the early 1900s, when London doctor H. Montague Murray conducted a post mortem exam on a young asbestos factory worker who died in 1899. Dr. Murray gave testimony on this death in connection with an industrial disease compensation hearing. The post-mortem confirmed the presence of asbestos in the lung tissue, prompting Dr. Murray to express as an expert opinion his belief that the inhalation of asbestos dust had at least contributed to, if not actually caused, the death of the worker[32].

The record in the United States was similar. Early observations were largely anecdotal in nature and did not definitively link the occupation with the disease, followed by more compelling and larger studies that strengthened the association. One such study, published in 1918, noted:

All of these processes unquestionably involve a considerable dust hazard, but the hygienic aspects of the industry have not been reported upon. It may be said, in conclusion, that in the practice of American and Canadian life insurance companies asbestos workers are generally declined on account of the assumed health-injurious conditions of the industry [33].

[edit] 1920s and 1930s
Widespread recognition of the occupational risks of asbestos in Britain was reported in 1924 by a Dr. Cooke, a pathologist, who introduced a case description of a 33-year old female asbestos worker with the following: 'Medical men in areas where asbestos is manufactured have long suspected the dust to be the cause of chronic bronchitis and fibrosis...[34]." Dr. Cooke then went on to report on a case in 1927 involving a 33-year old male worker who was the only survivor out of ten workers in an asbestos carding room. In the report he named the disease "asbestosis[35]."

Dr. Cooke's second case report was followed, in the late 1920s, by a large public health investigation (now known as the Merewether report after one of its two authors) that examined some 360 asbestos-textile workers (reported to be about 15% of the total comparable employment in Britain at the time) and found that about a quarter of them suffered from pulmonary fibrosis [36]. This investigation resulted in improved regulation of the manufacturing of asbestos-containing products in the early 1930s. Regulations included industrial hygiene standards, medical examinations, and inclusion of the asbestos industry into the British Workers' Compensation Act [37].

The first known US workers' compensation claim for asbestos disease was in 1927[38]. In 1930, the first reported autopsy of an asbestosis sufferer was conducted in the United states and later presented by a doctor at the Mayo Clinic, although in this case the exposure involved mining activities somewhere in South America[39].

In 1930, the major asbestos company Johns-Manville produced a report, for internal company use only, about medical reports of asbestos worker fatalities.[40] In 1932, A letter from U.S. Bureau of Mines to asbestos manufacturer Eagle-Picher stated, in relevant part, "It is now known that asbestos dust is one of the most dangerous dusts to which man is exposed".[41] In 1933, Metropolitan Life Insurance Co. doctors found that 29% of workers in a Johns-Manville plant had asbestosis.[40] Likewise, in 1933, Johns-Manville officials settled lawsuits by 11 employees with asbestosis on the condition that the employees' lawyer agree to never again "directly or indirectly participate in the bringing of new actions against the Corporation."[41] In 1934, officials of two large asbestos companies, Johns-Manville and Raybestos-Manhattan, edited an article about the diseases of asbestos workers written by a Metropolitan Life Insurance Company doctor. The changes downplayed the danger of asbestos dust.[41] In 1935, officials of Johns-Manville and Raybestos-Manhattan instructed the editor of Asbestos magazine to publish nothing about asbestosis.[41] In 1936, a group of asbestos companies agreed to sponsor research on the health effects of asbestos dust, but required that the companies maintain complete control over the disclosure of the results.[40]


[edit] 1940s