Asbestos (pronounced /æsˈbɛstəs/ or /æzˈbɛstəs/) is a set of six naturally occurring silicate minerals used commercially for their desirable physical properties.^[1] They all have in common their eponymous asbestiform habit: long (ca. 1:20 aspect ratio), thin fibrous crystals. The prolonged inhalation of asbestos fibers can cause serious illnesses^[2] including malignant lung cancer, mesothelioma, and asbestosis (a type of pneumoconiosis).^[3] The trade and use of asbestos have been restricted or banned in many jurisdictions.

Asbestos became increasingly popular among manufacturers and builders in the late 19th century because of its sound absorption, average tensile strength, its resistance to fire, heat, electrical and chemical damage, and affordability. It was used in such applications as electrical insulation for hotplate wiring and in building insulation. When asbestos is used for its resistance to fire or heat, the fibers are often mixed with cement (resulting in fiber cement) or woven into fabric or mats.

Asbestos mining began more than 4,000 years ago, but did not start large-scale until the end of the 19th century. For a long time, the world's largest asbestos mine was the Jeffrey mine in the town of Asbestos, Quebec.^[4]

Types and associated fibers

Six minerals types are defined by the United States Environmental Protection Agency as "asbestos" including those belonging to the serpentine class and those belonging to the amphibole class. All six asbestos mineral types are known to be human carcinogens.^[5][6]

Serpentine

Serpentine class fibers are curly. Chrysotile is the only member of the serpentine class.

Chrysotile

Chrysotile, CAS No. 12001-29-5, is obtained from serpentinite rocks which are common throughout the world. Its idealized chemical formula is Mg₃(Si₂O₅)(OH)₄.^[7] Chrysotile appears under the microscope as a white fiber.

Chrysotile has been used more than any other type and accounts for about 95% of the asbestos found in buildings in America.^[8] Chrysotile is more flexible than amphibole types of asbestos, and can be spun and woven into fabric. Its most common use has been in corrugated asbestos cement roof sheets typically used for outbuildings, warehouses and garages. It may also be found in sheets or panels used for ceilings and sometimes for walls and floors. Chrysotile has been a component in joint compound and some plasters. Numerous other items have been made containing chrysotile, including brake linings, fire barriers in fuseboxes, pipe insulation, floor tiles, and rope seals for boilers.^{[citation needed]} .

Amphibole

Amphibole class fibers are needle-like. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of the amphibole class.

Amosite

Amosite, CAS No. 12172-73-5, often referred to as brown asbestos, is a trade name for the amphiboles belonging to the cummingtonite-grunerite solid solution series, commonly from South Africa, named as an acronym for "Asbestos Mines of South Africa". One formula given for amosite is Fe₇Si₈O₂₂(OH)₂. Amosite is seen under a microscope as a grey-white vitreous fiber. It is found most frequently as a fire retardant in thermal insulation products, asbestos insulating board and ceiling tiles.^[8]

Crocidolite

Crocidolite, CAS No. 12001-28-4, is the fibrous form of the amphibole riebeckite, found primarily in southern Africa, but also in Australia and Bolivia. One formula given for crocidolite is Na₂Fe²⁺₃Fe³⁺₂Si₈O₂₂(OH)₂. Crocidolite is seen under a microscope as a blue fiber.

Crocidolite 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 breadths less than 1 micrometer that occur in bundles and have very great widths. Asbestos with particularly fine fibers is also referred to as "amianthus".

Other materials

Other regulated asbestos minerals, such as tremolite asbestos, CAS No. 77536-68-6, Ca₂Mg₅Si₈O₂₂(OH)₂; actinolite asbestos, 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, are thought by some to be no less harmful than tremolite, amosite, or crocidolite.^[9] They are referred to as "asbestiform" rather than asbestos. Although the U.S. OSHA has not included them in the asbestos standard, NIOSH and the American Thoracic Society have recommended that they be included as regulated materials. As such, they may still be related to diseases and hazardous.^[9]

Producing nations

In 2009, 2 million tonnes of asbestos were mined worldwide. The Russian Federation was the largest producer with about 50% world share followed by China (14%), Brazil (12.5%), Kazakhstan (10.5%) and Canada (9%).^[10]

In late 2011, Canada's remaining two asbestos mines, both located in the Province of Quebec, halted operations.^[11] In September 2012, the newly elected government in the Province of Quebec followed through with an election promise to halt asbestos mining.^[12]

History

Early uses

Asbestos use in human culture dates back at least 4,500 years, when evidence shows that inhabitants of the Lake Juojärvi region in East Finland strengthened earthenware pots and cooking utensils with the asbestos mineral anthophyllite.^[13] The word asbestos comes from the ancient Greek ἄσβεστος, meaning "unquenchable" or "inextinguishable".^[1][14] One of the first descriptions of a material that may have been asbestos is in Theophrastus, On Stones, from around 300 BC, although this identification has been questioned.^[15] The naming of minerals was not very consistent in ancient times.^{[citation needed]} In both modern and ancient Greek, the usual name for the material known in English as "asbestos" is amiantos ("undefiled", "pure") whence the term for it in, e.g., French amiante. In modern Greek, the word ἀσβεστος or ασβέστης stands consistently and solely for lime.^{[citation needed]}

The term asbestos is traceable to Roman naturalist Pliny the Elder's manuscript Natural History, and his use of the term asbestinon, meaning "unquenchable".^[1][13][14] While Pliny is popularly credited with recognising the detrimental effects of asbestos on human beings,^[16] examination of the primary sources reveals no support for that claim.^[17]

Wealthy Persians amazed guests by cleaning a cloth by exposing it to fire.^[when?] For example, according to Tabari, one of the curious items belonging to Khosrow II Parviz, the great Sassanian king (r. 531–579), was a napkin that he cleaned simply by throwing it into fire. Such cloth is believed to have been made of asbestos imported over the Hindu Kush.^[18] According to Biruni in his book, Gems, any cloths made of asbestos (Persian: آذرشست‎, āzarshost) were called shostakeh (Persian: شستكه‎).^[19] Some Persians^{[who?][when?]} believed the fiber was the fur of an animal, called the samandar (Persian: سمندر‎), which lived in fire and died when exposed to water,^{[20][better source needed][21]} whence the former belief^{[by whom?]} that the salamander could tolerate fire.^{[citation needed]}

Charlemagne, the first Holy Roman Emperor (800–814), is said^{[by whom?]} to have had a tablecloth made of asbestos.^[22]

Marco Polo recounts having been shown, in a place he calls Ghinghin talas, "a good vein from which the cloth which we call of salamander, which cannot be burnt if it is thrown into the fire, is made ..."^[23]

Some archeologists^[who?] 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.^{[24][page needed][unreliable source?]} Others^[who?] assert that the ancients used asbestos to make perpetual wicks for sepulchral or other lamps.^{[20][better source needed]} 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^[who?] used the term asbestos for soapstone, because the two terms have often been confused throughout history.^{[24][page needed][unreliable source?]}

Industrial era

The U.S. asbestos industry began in 1858 when fibrous anthophyllite was mined for use as asbestos insulation by the Johns Company, a predecessor to the current Johns Manville at a quarry at Ward's Hill on Staten Island, New York.^[25] Asbestos became more widespread during the industrial revolution; in 1866 it was used as insulation in the U.S. and Canada. Development of the first commercial asbestos mine began in 1874 in the Appalachian foothills of Quebec.^[26] 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.

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.^[27]

Discovery of toxicity

For additional chronological citations, see also, List of asbestos disease medical articles

The first documented death related to asbestos was in 1906.^{[citation needed]} 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 the UK in 1924. By the 1930s, the UK regulated ventilation and made asbestosis an excusable work-related disease, followed by the U.S about ten years later.^[7] The term mesothelioma was first used in medical literature in 1931; its association with asbestos was first noted sometime in the 1940s.

Approximately 100,000 people in the United States have died, or are terminally ill, from asbestos exposure related to ship building. In the Hampton Roads area, a shipbuilding center, mesothelioma occurrence is seven times the national rate.^[28] Thousands of 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 fourteen died of mesothelioma and an unknown number died from asbestosis.^[29]

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 since the 1930s and had concealed them from the public.^[29]

In Australia, asbestos was widely used in construction and other industries between 1945 and 1980. From the 1970s there was increasing concern about the dangers of asbestos, and its use was phased out. Mining ceased in 1983. The use of asbestos was phased out in 1989 and banned entirely in December 2003. The dangers of asbestos are now well known in Australia and there is help and support for sufferers from asbestosis or mesothelioma.^[30]

Specific products

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.^{[citation needed]} Chrysotile is often present in a wide variety of products and materials, including:

• Chlor Alkali diaphragm membranes used to make chlorine (currently in the USA) [1]
• Drywall and joint compound
• Plaster
• Gas mask filters pre 1960s
• Mud and texture coats
• Vinyl floor tiles, sheeting, adhesives
• Roofing tars, felts, siding, and shingles^[31]
• "Transite" panels, siding, countertops, and pipes
• Popcorn ceilings, also known as acoustic ceilings
• Fireproofing
• Caulk
• Industrial and Marine Gaskets, including those made by Garlock Sealing Technologies
• Packing, a system for sealing a rotating shaft
• Brake pads and shoes
• Stage curtains
• Fire blankets
• Interior fire doors
• Fireproof clothing for firefighters
• Thermal pipe insulation
• Filters for removing fine particulates from chemicals, liquids and wine
• Dental cast linings
• HVAC flexible duct connectors
• Drilling fluid additives

In the European Union and Australia it has recently been banned as a potential health hazard^[32] and is not used at all. Japan is moving in the same direction, but more slowly.

Amphibole group

Amphiboles including amosite (brown asbestos) and crocidolite (blue asbestos) were formerly used in many products until the early 1980s.^{[citation needed]} Tremolite asbestos constituted a contaminant of many if not all naturally occurring chrysotile deposits. The use of all types of asbestos in the amphibole group was banned in much of the Western world by the mid-1980s, and in Japan by 1995.^{[citation needed]} Some products that included amphibole types of asbestos included the following:

• Low density insulating board (often referred to as AIB or asbestos insulating board) and ceiling tiles;
• Asbestos-cement pipe (made until the early 1990s by at least one manufacturer);
• Asbestos-cement sheets and pipes for construction, casing for water and electrical/telecommunication services;
• Thermal and chemical insulation (e.g., fire rated doors, limpet spray, lagging and gaskets).

Cigarette manufacturer Lorillard (Kent's filtered cigarette) used crocidolite asbestos in its "Micronite" filter from 1952 to 1956.^[33]

While mostly chrysotile asbestos fibers were once used in automobile brake pads, shoes, and clutch discs, contaminants of amphiboles were present. Since approximately the mid-1990s, 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).

Artificial Christmas snow, known as flocking, was previously made with asbestos.^[34]

Health problems

All types of asbestos fibers are known to cause serious health hazards in humans.^[35][36][37] While it is agreed that amosite and crocidolite are the most hazardous asbestos fiber types, chrysotile asbestos has produced tumors in animals and is a recognized cause of asbestosis and malignant mesothelioma in humans.^[38]

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.^[39] According to the NCI, "A history of asbestos exposure at work is reported in about 70 percent to 80 percent of all cases. However, mesothelioma has been reported in some individuals without any known exposure to asbestos."^[40] The most common diseases associated with chronic exposure to asbestos include: asbestosis and pleural abnormalities (mesothelioma, lung cancer).^[41] Asbestosis has been reported primarily in asbestos workers, and appears to require long-term exposure, high concentration for the development of the clinical disease. There is also a long latency period (incubation period of an infectious disease, before symptoms appear) of about 12 to 20 years.^[42]

Studies have shown an increased risk of lung cancer among smokers who are exposed to asbestos compared to nonsmokers.^[43]

Asbestos exposure becomes a health concern when high concentrations of asbestos fibers are inhaled over a long time period.^[44] People who become ill from inhaling asbestos are often those who are exposed on a day-to-day basis in a job where they worked directly with the material. As a person's exposure to fibers increases, because of being exposed to higher concentrations of fibers and/or by being exposed for a longer time, then 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.^[44]

Possible mechanisms of carcinogenicity

Stanton and Layard hypothesized in 1977–78 that toxicity of fibrous materials is not initiated by chemical effects;^[45] that is, any trigger-effects of asbestos must presumably be physical, such as (A) mechanical damage or (B) unwanted signal channels (a plausible property for slender transparent fibres) which might disrupt normal cell activity—especially mitosis.

(A) Mechanical Damage. There is experimental evidence that very slim fibers (<60 nm, <0.06 μm in breadth) do tangle destructively with chromosomes (being of comparable size).^[46][47] This is likely to cause the sort of mitosis disruption expected in cancer.

(B) Unwanted Signal channels. This has recently been explored theoretically, but not yet experimentally. The theory argues that this effect would only be feasible for asbestos fibers >100 nm in breadth (>150 nm in the case of chrysotile), which suggests that we should be on the look-out for a possible mixture of different mechanisms for the different fiber-diameter-ranges.^[48][49]

One popular idea of the causal chain is (1) Asbestos fiber → → (3) inflammation → (4) other pathology. While that may be true, it does not explain "(2), the actual trigger":

"What is the physical property of asbestos which initiates any such inflammation?" (After all, inflammation is usually seen as caused by chemical-based processes: immunological &/or bacterial). So inflammation (&/or oxidation etc.) may well be part of the causal chain, but not the crucial first step.^[48]

Other asbestos-related diseases

• It is important to consult a doctor, particularly if the following symptoms develop: shortness of breath, wheezing or hoarseness, persistent cough that worsens over time, blood in fluid coughed up, pain or tightening in chest, difficulty swallowing, swelling of neck or face, decreased appetite, weight loss, fatigue or anemia.^[50]

• Asbestosis: Progressive fibrosis of the lungs of varying severity, progressing to bilateral fibrosis, honeycombing of the lungs on radiological view with symptoms including rales and wheezing. Individuals who have been exposed to asbestos via home, environment, work should notify their doctors about exposure history.
• 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. Although pleural plaques are themselves asymptomatic, in some patients this develops into pleural thickening.
• Diffuse pleural thickening: similar to above and can sometimes be associated with asbestosis. Usually no symptoms shown but if exposure is extensive, it can cause lung impairment.
• Pneumothorax: Some reports have also linked the condition of pneumothorax to asbestos related diseases.

Chemistry

Individual asbestos fibers are invisible to the unaided human eye because their size is about 3–20 µm wide and can be as slim as 0.01 µm. Human hair ranges in size from 17 to 181 µm in breadth.^[51] 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, and in this case, there are two cleavage planes which are much weaker than the third. 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.

When fibers or asbestos structures from asbestos containing materials(ACM) become airborne, the process is called primary release. Primary release mechanisms include abrasion, impaction, fallout, air erosion, vibration, and fire damage. Secondary release occurs when settled asbestos fibers and structures are resuspended as a result of human activities. In unoccupied buildings or during unoccupied periods, fiber release typically occurs by fallout or is induced by vibration or air erosion.^[52]

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 because of 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.

Identification and assessment

A fiber cannot be identified or ruled out as asbestos, either using the naked eye or by simply looking at a fiber under a regular microscope. The most common methods of identifying asbestos fibers are by using polarized light microscopy (PLM) or transmission electron microscopy (TEM). PLM is less expensive, but TEM is more precise and can be used at lower concentrations of asbestos.

If asbestos abatement is performed, completion of the abatement is verified using visual confirmation and may also involve air sampling. Air samples are typically analyzed using phase contrast microscopy (PCM). PCM involves counting fibers on a filter using a microscope. Airborne occupational exposure limits for asbestos are based on using the PCM method.

The American Conference of Governmental Industrial Hygienists has a recommended Threshold Limit Value (TLV) for asbestos of 0.1 fibers/mL over an 8 hour shift. OSHA in the United States and occupational health and safety regulatory jurisdictions in Canada use 0.1 fibers/mL over an 8 hour shift as their exposure limits.^[53]

Common building materials containing asbestos

Most products manufactured today do not contain asbestos. In the industrialized world, asbestos was phased out of building products mostly in the 1970s with most of the remainder phased out by the 1980s. Asbestos containing building materials in residences includes a variety of products, such as: stiple used in textured walls and ceilings; drywall joint filler compound; asbestos contaminated vermiculite, vinyl floor tile; vinyl sheet flooring; window putty; mastic; cement board; furnace tape; and stucco. Asbestos was used a lot in roofing materials, mainly corrugated asbestos cement roof sheets and asbestos shingles. Other sources of asbestos containing materials include fireproofing and acoustic materials.^[54]

Exposure

Asbestos exposure becomes an issue if asbestos containing materials become airborne, such as due to deterioration or damage. Building occupants may be exposed to asbestos, but those most at risk are persons who purposely disturb materials, such as maintenance or construction workers. Housekeeping or custodial employees may be at an increased risk as they may potentially clean up damaged or deteriorated asbestos containing materials without knowing that the material contains asbestos. Asbestos abatement or remediation workers and emergency personnel such as firefighters may also become exposed.^[55] Asbestos-related diseases have been diagnosed in asbestos workers' family members, and in residents who live close to asbestos mines or processing plants.^[56]

Environmental asbestos

Asbestos can be found naturally in the air outdoors and in some drinkable water, including water from natural sources.^[57] Studies have shown that members of the general (non-occupationally exposed) population have 10,000-999,999 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.^[58]

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% for every 10 km that an individual had lived away from a likely asbestos source.^[59]

Portions of El Dorado County, California are known to contain natural amphibole asbestos formations at the surface.^[59][60] 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 EPA study was refuted by its own peer reviewers and never completed or published. 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."

However, the main criticism pointed at EPA was that their testing was conducted in small isolated areas of El Dorado where there were no amphibole asbestos deposits, thus the language regarding amphibole, nonfibrous "particles". Actual surface amphibole deposits in residential areas were ignored for testing purposes. Because of this, no final findings were published by ATSDR.^[61]

A great deal of Fairfax County, Virginia was also found to be underlaid 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.^[59]

Globally, collected samples from Antarctic ice indicate chrysotile asbestos has been a ubiquitous contaminant of the environment for at least 10,000 years. Snow samples in Japan have shown ambient background levels are one to two orders of magnitude higher in urban than in rural areas. Higher concentrations of airborne asbestos fibers are reported in urban areas where there is more ACM (asbestos containing materials) and mechanisms of release (vehicles braking and weathering of asbestos cement materials); concentrations in the range of 1–20 ng/m^3 have been reported. Fibers longer than 5μm are rarely found in rural areas. Ambient concentrations using TEM analysis have been based on mass measurements.^[52]

History of health concerns and regulation

For additional chronological citations, see also, List of asbestos disease medical articles

Until 1900

By the first century AD, Greeks and Romans are claimed to have observed that slaves involved in the weaving of asbestos cloth were afflicted with a sickness of the lungs,^[62] although this is not confirmed by examination of primary sources.^[17]

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.^[63]

At about the same time, what was probably the first study of mortality among asbestos workers was reported in France.^[64] 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.

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.^[65]

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.^[66]

1920s–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, Nellie Kershaw, 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 ..."^[67] 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".^[68]

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.^[69] 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.^[70]

The first known U.S. workers' compensation claim for asbestos disease was in 1927.^[71] 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.^[72]

In 1930, the major asbestos company Johns-Manville produced a report, for internal company use only, about medical reports of asbestos worker fatalities.^[73] 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."^[74]

In 1933, Metropolitan Life Insurance Co. doctors found that 29% of workers in a Johns-Manville plant had asbestosis.^[73] 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."^[74] 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.^[74] In 1935, officials of Johns-Manville and Raybestos-Manhattan instructed the editor of Asbestos magazine to publish nothing about asbestosis.^[74] 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.^[73]

1940s

In 1942, an internal Owens-Corning corporate memo referred to "medical literature on asbestosis ... scores of publications in which the lung and skin hazards of asbestos are discussed."^[73] Testimony given in a federal court in 1984 by Charles H. Roemer, formerly an employee of Unarco, described a meeting in the early 1940s between Unarco officials, J-M President Lewis H. Brown and J-M attorney Vandiver Brown. Roemer stated, "I'll never forget, I turned to Mr. Brown, one of the Browns made this crack (that Unarco managers were a bunch of fools for notifying employees who had asbestosis), and I said, 'Mr. Brown, do you mean to tell me you would let them work until they dropped dead?' He said, 'Yes. We save a lot of money that way.'"^[75] In 1944, a Metropolitan Life Insurance Company report found 42 cases of asbestosis among 195 asbestos miners.^[73]

1950s

In 1951, asbestos companies removed all references to cancer before allowing publication of research they sponsored.^[76] In 1952, Dr. Kenneth Smith, Johns-Manville medical director, recommended (unsuccessfully) that warning labels be attached to products containing asbestos. Later, Smith testified: "It was a business decision as far as I could understand ... the corporation is in business to provide jobs for people and make money for stockholders and they had to take into consideration the effects of everything they did and if the application of a caution label identifying a product as hazardous would cut into sales, there would be serious financial implications."^[77]

In 1953, National Gypsum's safety director wrote to the Indiana Division of Industrial Hygiene, recommending that acoustic plaster mixers wear respirators "because of the asbestos used in the product." Another company official noted that the letter was "full of dynamite" and urged that it be retrieved before reaching its destination. A memo in the files noted that the company "succeeded in stopping" the letter, which "will be modified."^[78]

1960s–1980s

Through the 1970s, asbestos was used to fireproof roofing and flooring, for heat insulation, and for a variety of other purposes. The material was used in fire-check partitioning and doors on North Sea Oil Production Platforms and Rigs.

During mid-to late 1980s, public health concern focused on potential asbestos fiber exposures of building occupants and workers in buildings containing asbestos containing building materials (ACBM) and their risks of developing lung cancer or mesothelioma. As a consequence, the Health Effects Institute (Cambridge, MA) convened a panel to evaluate the lifetime cancer risk of general building occupants as well as service workers.^[79]

Modern regulation

United States

This section uses abbreviations that may be confusing or ambiguous. Specific concerns may be found on the Talk page. Please improve this section if you can. (February 2013)

In 1981, the United States Environmental Protection Agency (EPA) requested information from American companies regarding the asbestos content of their products.^[80]

In 1989 the EPA issued the Asbestos Ban and Phase Out Rule which was subsequently overturned in the case of Corrosion Proof Fittings v. EPA, 947 F.2d 1201 (5th Cir. 1991). This ruling leaves many consumer products that can still legally contain trace amounts of asbestos. For a clarification of products which legally contain asbestos, read the EPA's clarification statement.^[81]

In 2010, Washington State banned asbestos in automotive brakes starting in 2014.^[82]

The EPA has proposed a concentration limit of seven million fibers per liter of drinking water for long fibers (lengths greater than or equal to 5 µm). The Occupational Safety and Health Administration (OSHA), has set limits of 100,000 fibers with lengths greater than or equal to 5 µm per cubic meter of workplace air for eight-hour shifts and 40-hour work weeks.^[83]

OSHA regulations regarding asbestos are covered in 29 C.F.R. 1926.1101. Such work is divided into four categories.

Class I asbestos work means activities involving the removal of TSI and surfacing asbestos containing materials (ACM) and presumed asbestos containing materials (PACM).

Class II asbestos work means activities involving the removal of ACM which is not thermal system insulation or surfacing material. This includes, but is not limited to, the removal of asbestos-containing wallboard, floor tile and sheeting, roofing and siding shingles, and construction mastics.

Class III asbestos work means repair and maintenance operations, where "ACM", including TSI and surfacing ACM and PACM, is likely to be disturbed.

Class IV asbestos work means maintenance and custodial activities during which employees contact but do not disturb ACM or PACM and activities to clean up dust, waste and debris resulting from Class I, II, and III activities.^[84]

United Kingdom

In the United Kingdom, blue and brown asbestos materials were banned outright in 1985 while the import, sale and second hand reuse of white asbestos was outlawed in 1999. The 2012 Control of Asbestos Regulations state that owners of non-domestic buildings (e.g., factories and offices) have a "duty to manage" asbestos on the premises by making themselves aware of its presence and ensuring the material does not deteriorate, removing it if necessary. Employers, e.g. construction companies, whose operatives may come into contact with asbestos must also provide annual asbestos training to their workers^[85]

New Zealand

In 1984, the import of raw amphibole (blue and brown) asbestos into New Zealand was banned. In 2002 the import of chrysotile (white) asbestos was banned.^[86]

Australia

The use of crocidolite (blue) asbestos was banned in 1967, while the use of amosite (brown) asbestos continued in the construction industry until the mid-1980s. It was finally banned from building products in 1989, though it remained in gaskets and brake linings until 31 December 2003, and cannot be imported, used or recycled.^[87][88]

Asbestos continues to be a problem. Two out of three homes in Australia built between World War II and the early 1980s still contain asbestos.^[89]

The union that represents workers tasked with modifying electrical meter boxes at residences stated that workers should refuse to do this work until the boxes have been inspected for asbestos^[90] and the head of an Australian Consortium of Trade Unions has called on the government to protect its citizens by ridding the country of asbestos by 2030.^[91]

Handlers of asbestos materials must have a B-Class license for bonded asbestos and an A-Class license for friable asbestos.

The town of Wittenoom, in Western Australia was built around a (blue) asbestos mine. The entire town continues to be contaminated, and has been disincorporated, allowing local authorities to remove references to Wittenoom from maps and roadsigns.

Turkey

A complete ban on asbestos in Turkey went into effect in 2011.^[92]

Japan

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.^[93] 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.^[93]

South Korea

In May 1997, the manufacture and use of crocidolite and amosite, commonly known as blue and brown asbestos, were fully banned in South Korea.^[94] In January 2009, a full-fledged ban on all types of asbestos occurred when the government banned the manufacture, import, sale, storage, transport or use of asbestos or any substance containing more than 0.1% of asbestos.^[95] In 2011, South Korea became the world's sixth country to enact an asbestos harm aid act, which entitles any Korean citizen to free lifetime medical care as well as monthly income from the government if he or she is diagnosed with an asbestos-related disease.^[96]

Singapore

Use of all types of asbestos has been banned in Singapore since 1989.

Contamination of other products

Asbestos and vermiculite

Vermiculite is a hydrated laminar magnesium-aluminum-iron silicate which resembles mica. It can be used for many industrial applications and has been used as insulation. Some deposits of vermiculite have been found to be contaminated with small amounts of asbestos.^[97]

One vermiculite mine operated by W. R. Grace and Company in Libby, Montana exposed workers and community residents to danger by mining vermiculite contaminated with asbestos, typically actinolite or tremolite. Vermiculite contaminated with asbestos from the Libby mine was used as insulation in residential and commercial buildings through Canada and the United States. W. R. Grace and Company's vermiculite was marketed as Zonolite.

In 1999 the EPA began cleanup efforts in Libby and now the area is a Superfund cleanup area.^[98] The EPA has determined that harmful asbestos is released from the mine as well as through other activities that disturb soil in the area.^[99]

Asbestos and talc

Talc is sometimes contaminated with asbestos.^[100] In 2000, tests in a certified asbestos-testing laboratory found the tremolite form of amphibole asbestos in three out of eight bigger brands of children's crayons that are made partly from talc: Crayola, Prang, and RoseArt.^[101] In Crayola crayons, the tests found asbestos levels from 0.05% in Carnation Pink to 2.86% in Orchid; in Prang crayons, the range was from 0.3% in Periwinkle to 0.54% in Yellow; in Rose Art crayons, it was from 0.03% in Brown to 1.20% in Orange. Overall, 32 different types of crayons from these brands contained more than trace amounts of asbestos, and eight others contained trace amounts. The Art and Creative Materials Institute, a trade association which tests the safety of crayons on behalf of the makers, initially insisted the test results must be incorrect, although they later said they do not test for asbestos.^[101] In May 2000, Crayola said tests by a materials analyst, Richard Lee, whose testimony has been accepted in lawsuits over 250 times on behalf of the asbestos industry, showed two of its crayons were negative for asbestos.^[102] In June 2000, Binney & Smith, the maker of Crayola, and the other makers agreed to stop using talc in their products, and changed their product formulations in the United States.^[102] The mining company, R T Vanderbilt Co of Gouverneur, New York, which supplied the talc to the crayon makers, insists there is no asbestos in its talc "to the best of our knowledge and belief",^[103] but a news article claimed that the United States Mine Safety and Health Administration (MSHA) did find asbestos in four talc samples that it tested in 2000.^[101] At the time, however, the Assistant Secretary for Mine Safety and Health informed the news reporter that his article was in error and that the reporter had misquoted him stating that "In fact, the abbreviation ND (non detect) in the laboratory report – indicates no asbestos fibers actually were found in the samples."^[104] Further supporting the claim of Vanderbilt that asbestos is not found in this industrial grade talc (composed of a very complex mineral mixture) is a decades old record of analytical work that does not find asbestos in this talc by mineral scientists in academia, government and contract laboratories.^{[105][106][107][108][109][110][111][112][113]}

Human, animal and cell health studies conducted on Vanderbilt's controversial talc also lend no support for the presence of asbestos in this talc.^{[114][115][116]} Several non fully peer-reviewed health reports concerning Vanderbilt talc do exist and suggest a "same as" asbestos risk, some of which were referenced in the previously cited news articles.^[117][118]

Asbestos in construction

Asbestos construction in developed countries

The use of asbestos in new construction projects has been banned for health and safety reasons in many developed countries or regions, including the European Union, Australia, Hong Kong, Japan, and New Zealand. A notable exception is the United States, where asbestos continues to be used in construction such as cement asbestos pipes. The 5th Circuit Court prevented the EPA from banning asbestos in 1991 because EPA research showed the ban would cost between $450 and 800 million while only saving around 200 lives in a 13-year timeframe, and that the EPA did not provide adequate evidence for the safety of alternative products.^[119] Until the mid-1980s, small amounts of white asbestos were used in the manufacture of Artex, a decorative stipple finish,^[120] however, some of the lesser-known suppliers of Artex were still adding white asbestos until 1999.^[121] Removing or disturbing Artex is not recommended, as it may contain white asbestos.

Prior to the ban, asbestos was widely used in the construction industry in thousands of materials, some are judged to be more dangerous than others due to the amount of asbestos and a materials friable nature. Sprayed coatings, pipe insulation and Asbestos Insulating Board (AIB) are thought to be the most dangerous due to their high content of asbestos and friable nature. Many older buildings built before the late 1990s contain asbestos. In the United States, there is a minimum standard for asbestos surveys as described by ASTM Standard E 2356–04. The U.S. Environmental Protection Agency includes some but not all asbestos-contaminated facilities on the Superfund National Priorities list (NPL). Renovation and demolition of asbestos contaminated buildings is subject to EPA NESHAP and OSHA Regulations. Asbestos is not a material covered under CERCLA's innocent purchaser defense. In the UK, the removal and disposal of asbestos and of substances containing it are covered by the Control of Asbestos Regulations 2006.^[122]

In older buildings (e.g. those built prior to 1999 in the UK, before white asbestos was finally banned), asbestos may still be present in some areas e.g. old bath panels, concrete water tanks and many other places. Being aware of asbestos locations reduces the risk of disturbing asbestos.^[123] See the asbestos image gallery (external link) to see some common asbestos locations.

Removal of asbestos building components can also remove the fire protection they provide, therefore fire protection substitutes are required for proper fire protection that the asbestos originally provided.^[123][124]

Asbestos construction in developing countries

Some countries, such as India, Indonesia, China, Russia and Brazil have continued widespread use of asbestos. The most common is corrugated asbestos-cement sheets or "A/C Sheets" for roofing and for side walls. Millions of homes, factories, schools or sheds and shelters continue to use asbestos. Cutting these sheets to size and drilling holes to receive 'J' bolts to help secure the sheets to roof framing is done on-site. There has been no significant change in production and use of A/C Sheets in developing countries following the widespread restrictions in developed nations^{[citation needed]}.

Asbestos and 9/11

As the towers collapsed, Lower Manhattan was blanketed in a mixture of building debris and combustible materials. This complex mixture gave rise to the concern that thousands of residents and workers in the area would be exposed to known hazards in the air and in the dust, such as asbestos, lead, glass fibers, and pulverized concrete.^[125] More than 1,000 tons of asbestos are thought to have been released into the air during the destruction of the World Trade Center in New York on 9/11.^[126] Inhalation of a mixture of asbestos and other toxicants is thought to be linked to the unusually high death rate of emergency service workers from cancer since the disaster.^[126] Many thousands more are now thought to be at risk of developing cancer due to this exposure with those who have died so far being only the 'tip of the iceberg'.^[126] Some commentators have criticised authorities for using asbestos in the Towers' construction (see 'Other criticism' below).

In May 2002, after numerous cleanup, dust collection, and air monitoring activities were conducted outdoors by EPA, other federal agencies, New York City and New York State, New York City formally requested federal assistance to clean and/or test residences in the vicinity of the WTC site for airborne asbestos.^[125]

Litigation

The examples and perspective in this section may not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (February 2010)

Asbestos litigation is the longest, most expensive mass tort in U.S. history, involving more than 8,400 defendants and 730,000 claimants as of 2002 according to the RAND Corporation,^[127] and at least one defendant reported claim counts in excess of $800,000 in 2006.^[128]

As of 1999, trends indicate that the worldwide rate at which people are diagnosed with asbestos-related diseases will likely increase through the next decade.^[129][130] Analysts have estimated that the total costs of asbestos litigation in the USA alone is over $250 billion.^[131]

The federal legal system in the United States has dealt with numerous counts of asbestos related suits, which often included multiple plaintiffs with similar symptoms. In 1999 there were 200,000 related cases pending in the federal court system of the United States.^[132] Further, it is estimated that within the next 40 years, the number of cases may increase to 700,000. These numbers help explain how there are thousands of current pending cases.

Litigation of asbestos materials has been slow. Companies sometimes counter saying that health issues do not currently appear in their worker or workers, or sometimes are settled out of court.^[133]

In 1999 the United States enacted the Fairness in Asbestos Compensation Act.^[134] Between 1981 and the present, many asbestos companies have filed for bankruptcy.^[135] While companies filed for bankruptcy, this limited payouts to those who were actually affected by the material. Professor Christopher Edley said what the 1999 Act ultimately would have done if passed would be to "limit punitive damages that seek retribution for the decisions of long-dead executives for conduct that took place decades ago (Professor Christopher Edley, Jr.)."^[134]

In Australia a significant and controversial case was brought against the industrial building materials company James Hardie, which had mined and sold asbestos related products for many years.

Litigation exists outside the United States in England, Scotland, Ireland, the Netherlands, France, Italy, and Japan among other nations (though the amounts awarded in these countries are not as large as in the US). See the companion article for further information.

The volume of the asbestos liability has concerned manufacturers and insurers and reinsurers.^[136] The amounts and method of allocating compensation have been the source of many court cases, and government attempts at resolution of existing and future cases.

Other criticism

Asbestos regulation critics include the asbestos industry^[137] and JunkScience.com owner Steven Milloy. Critics argue that the outright banning of dangerous products, due to government regulation, is inferior to keeping the products while innovating ways to prevent the lethal effects. They argue that the product benefits are too important to ignore, and instead of banning the products, find ways to eliminate risks to those who work with the products. An example is the suggestion by Dixy Lee Ray and others that the shuttle Challenger disintegrated because the maker of O-ring putty was pressured by the EPA into ceasing production of asbestos-laden putty.^[138][139] However, the putty used in Challenger's final flight did contain asbestos, and failures in the putty were not responsible for the failure of the O-ring that led to loss of the shuttle.^[139][140]

Asbestos was used in the first forty floors of the World Trade Center north tower causing an airborne contamination among lower Manhattan after the towers collapsed in the attacks on 11 September 2001. Steven Milloy of the Cato Institute suggested that the World Trade Center towers could still be standing or at least would have stood longer had a 1971 ban not stopped the completion of the asbestos coating above the 64th floor.^[141][142] This was not considered in the National Institute of Standards and Technology's report on the towers' collapse. All fireproofing materials, regardless of what they are made of, are required to obtain a fire-resistance rating prior to installation. All fiber-based lightweight commercial spray fireproofing materials are vulnerable to kinetic energy impacts that are outside of the fire testing upon which their ratings are based, including asbestos-based materials, and may have been removed in large areas by the impact of the planes.^{[143][144][145]}

Substitutes for asbestos in construction

Fiberglass insulation was invented in 1938 and is now the most commonly used type of insulation material. The safety of this material is also being called into question due to similarities in material structure.^[146] However, the International Agency for Research on Cancer removed fiberglass from its list of possible human carcinogens in 2001.^[147]

In 1978, a highly texturized fiberglass fabric was invented by Bal Dixit, called Zetex. This fabric is lighter than asbestos, but offers the same bulk, thickness, hand, feel, and abrasion resistance as asbestos. The fiberglass was texturized to eliminate some of the problems that arise with fiberglass, such as poor abrasion resistance and poor seam strength^[148]

In Europe mineral wool and glass wool are the main insulators in houses.

Many companies that produced asbestos-cement products that were reinforced with asbestos fibers have developed products incorporating organic fibers. One such product was known as "Eternit" and another "Everite" now use "Nutec" fibers which consist of organic fibers, portland cement and silica. Cement-bonded wood fiber is another substitute. Stone fibers are used in gaskets and friction materials.

Another potential fiber is polybenzimidazole or PBI fiber. Polybenzimidazole fiber is a synthetic fiber with high melting point of 760 °C that also does not ignite. Because of its exceptional thermal and chemical stability, it is often used by fire departments and space agencies.

Asbestos alternatives for industrial use include sleeves, rope, tape, fabric, textiles and insulation batt materials made from fiberglass and silica.

Recycling and disposal

In most developed countries, asbestos is typically disposed of as hazardous waste in landfill sites.

The demolition of buildings containing large amounts of asbestos based materials pose particular problems for builders and property developers - such buildings often have to be deconstructed piece by piece, or the asbestos has to be painstakingly removed before the structure can be razed by mechanical or explosive means. One such example is the Red Road high-rise housing development in Glasgow, Scotland which used huge amounts of asbestos cement board for wall panelling - here British health and safety regulations stipulate that asbestos material has to be removed to a landfill site via an approved route at certain times of the day in specially adapted vehicles.

Asbestos can be recycled by transforming it into harmless silicate glass. A process of thermal decomposition at 1000–1250 °C produces a mixture of non-hazardous silicate phases, and at temperatures above 1250 °C it produces silicate glass.^[149] Microwave thermal treatment can be used in an industrial manufacturing process to transform asbestos and asbestos-containing waste into porcelain stoneware tiles, porous single-fired wall tiles, and ceramic bricks.^[150]

See also

Mineralogy

• Asbestine
• List of minerals

Other asbestos-related topics

References

Bibliography

• Castleman, Barry I. Asbestos: Medical and Legal Aspects, 5th edition, Aspen Publishers, Englewood Cliffs, NJ, 1996, ISBN 978-0-7355-5260-9.

Further reading

• George B. Guthrie and Brooke T. Mossman, editors, Health Effects of Mineral Dusts, Mineralogical Society of America Reviews in Mineralogy v. 28, 584 pages (1993) ISBN 0-939950-33-2.
• Deaths and major morbidity from asbestos-related diseases in Asia likely to surge in next 20 years
• Asbestos: an introduction by JW Cherrie
• Tweedale, Geoffrey (2000). Magic Mineral to Killer Dust Turner & Newall and the Asbestos Hazard. Oxford Univ. Press. p. 336. ISBN 978-0-19-829690-4.

External links

Find more about Asbestos at Wikipedia's sister projects
	Definitions and translations from Wiktionary
	Media from Commons
	Learning resources from Wikiversity
	News stories from Wikinews
	Quotations from Wikiquote
	Source texts from Wikisource
	Textbooks from Wikibooks

Independent links

• The Asbestos Information Centre Independent site with information about asbestos and its use in buildings

Regulatory and government links

• U.S. EPA Asbestos Home Page
• ATSDR Case Studies in Environmental Medicine: Asbestos Toxicity U.S. Department of Health and Human Services
• British Government Health and Safety Executive (HSE)
• National Institute for Occupational Safety and Health: Asbestos
• World Health Organization – Asbestos page

Mineral and mining links

• Parachrysotile (asbestos) at the webmineral.com Mineral Database
• Univ. of Minn.: Asbestos
• White Gold Pioneers: Asbestos Mining—The origins of asbestos mining, illustrated with many early photographs

Health and the environment

• About Your House – General Series – Asbestos
• British Government Health and Safety Executive (HSE) essential guides
• Hazards magazine's comprehensive asbestos resource pages
• The Miracle Mineral Fiber – Asbestos
• Asbestos: Magic mineral or deadly dust?, CBC Digital Archives
• About Asbestos (2006), European Agency for Safety and Health at Work (OSHA)
• A USGS map of "Naturally Occurring Asbestos" in Eastern America
• Occupational exposure to asbestos and man-made vitreous fibres and risk of lung cancer: a multicenter case-control study in Europe, Rafael Carel et al.