Definition of Asbestos

Asbestosis is defined as diffuse interstitial fibrosis of the lung that has been caused by inhalation of asbestos fibers. Clinically evident and radiologic changes of asbestosis are usually associated with prolonged heavy exposures to asbestos, which are far higher than necessary  to produce mesothelioma.


Changes of asbestosis are frequently absent in cases of mesothelioma. If they are present, then there is usually a strong and convincing history of asbestos exposure.


The main histopathologic evidence for asbestos exposure is dependent on the finding of asbestos bodies in light microscopic sections of lung tissue either by conventional or iron stains. Asbestos bodies are golden, brown, club-shaped, often beaded structures that contain a clear pale transparent straight needle-like core. 


They are formed by the coating of the asbestos fiber with ferritin and protein and take months or years to develop after deposition of the fiber in the lung. If the morphologic criteria are carefully adhered to the majority (greater then 95%) of the asbestos bodies are found on examination by electron microscopy with energy dispersive x-ray spectrometry to contain commercial amphibole (crocidolite or amosite) cores. 


In some areas of the world with environmental exposures to asbestos they contain tremolite or anthophyllite. Asbestos bodies formed from chrysotile are rare. The finding of one convincing asbestos body by light microscopy in a standard histologic section nearly always signifies an above-background exposure. However, ferruginous bodies that are not formed on asbestos fibers can occur, for example, on talc, mica, kaolin, coal, carbon, rutile, and iron. 


These are distinguished by having cores that are yellow or black or platy rather than fibrous. Particular care has to be exercised by the histopathologist when evaluating cases with mixed dust exposures where substantial amounts of sheet silicates (talc, mica, kaolin, etc.) are present; these silicates can be coated to form ferruginous bodies and although these are platy, they can be cut at such an angle as to appear to be fibrous and can be incorrectly identified as asbestos.


If the histopathologist finds clusters of asbestos bodies, this usually signifies very high levels of commercial asbestos fibers.


Definition of Asbestos
Identification of Asbestos
Asbestos Mineralogy and Health Effects
Asbestos

Mesothelioma and Asbestos Exposure

Mesothelioma and Asbestos Exposure
It was the Conference on the Biological Effects of Asbestos at the New York Academy of Sciences, organized by Irving Selikoff in November 1964 , that put both mesothelioma and asbestos on the map. Before that meeting, few people in the scientific or general community had much knowledge of either subject. 


There they learned the nature and numerous essential industrial uses of a group of naturally occurring mineral fibers, collectively known as asbestos, although in fact comprising at least five distinct materials, chemically, physically, and geologically. Of these, chrysotile, a serpentine mineral mined mainly in Quebec and the Ural mountains of Russia, made up over 90%. 


Of the remainder the two most important were crocidolite and amosite, produced mainly in South Africa and Australia, both amphibole minerals with distinctive qualities valuable for heat insulation, naval marine use, and the production of large-bore cement pipes. 


Two other amphibole mineral fibers were anthophyllite, of limited production in Finland, and tremolite, little used, though by far the most widespread geologically. 


Presenters at the conference stated that within some 20 years of the first industrial exploitation of asbestos in the 1880s, workers heavily exposed to airborne fiber and dust developed a distinctive, seriously disabling and sometimes fatal diffuse pulmonary fibrosis, later termed asbestosis. 


Little was done to limit exposure until the late 1930s, when after a well-conducted survey of four asbestos textile plants in North Carolina, Dreessen et al (2) and others of the U.S. Public Health Service recommended in 1938 that a workplace dust concentration of 5 million particles per cubic foot (about 15 fibers/mL) should not be exceeded. 


Mainly because of the Second World War, this recommendation was not implemented; and probably for the same reason it went unnoticed that there were case reports by some German pathologists of malignant tumors of the pleura and peritoneum in men with asbestosis. Thus it was only in the 1950s that the causal association of asbestos exposure with lung cancer in the United Kingdom, and later with mesothelioma in South Africa , was recognized.

Until that time even the very existence of primary malignancies of the mesotheleum was questioned by reputable pathologists. Looking back, however, a review by Saccone and Coblenz in 1943 had included the identification of over 40 cases in autopsies published since 1870, and referred to two cases of “endothelioma” reported in 1767 by Lieutaud in France among 3000 autopsies. 


That mesothelial cancers in low frequency probably occurred well before the industrial use of asbestos is discussed more fully later. Indeed, a low background incidence of unknown etiology has almost certainly continued, affecting both children and adults.


Mesothelioma and Asbestos Exposure

• Diagnosing Mesothelioma is Difficult
• The Stigma of Lung Cancer Why Are Lung Cancer
• Identification of Asbestos

Asbestos Mineralogy and Health Effects

Asbestos Mineralogy and Health Effects

Fibers and fibrous minerals, for example, the asbestos minerals, erionite (one of the many natural and synthetic zeolite species), fiberglass, or other silica forms (diatoms) have been shown to be extremely hazardous. Their airborne character is paramount, and the specific gravity of the species, the size, and an appropriate morphology that permits suspension are of primary consideration. 

Asbestos as a ubiquitous natural resource refers to several types of fibrous minerals formed by earth processes and made up of microscopic bundles of fibers. The dangers associated with inhalation of asbestos fibers haveeen known for more than 30 years. Asbestos is known as a group A human carcinogen. The potential hazards of exposure to asbestos materials are of concern worldwide. 

There are several modes of exposure to airborne fibers including occupational exposure and the erosion of natural deposits in asbestos-bearing rocks. Asbestos may also be dispersed in water from a number of sources, including erosion of natural deposits, corrosion, and disintegration of asbestos materials. Governments and industries have introduced regulatory measures requiring safety controls throughout the product life cycle to limit asbestos exposure to the general public and workers. 

Although asbestos materials have been well documented as to their physical and chemical characteristics, they remain under investigation both by mineralogists studying geologic aspects and by pathologists/epidemiologists studying medical aspects. The term asbestos may be well known, but the precise definition, safe level of exposure, duration of exposure, and asbestos types of these fibrous materials still raise questions and often lead to differences of opinions and arguments as well as legal disputes.

Asbestos Mineralogy and Health Effects

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• Mesothelioma Doctors
• Mesothelioma is an Incurable Asbestos Cancer

Asbestos

Asbestos  from Greek ἄσβεστος, "unquenchable" or "inextinguishable") is a set of six naturally occurring silicate minerals exploited commercially for their desirable physical properties. They all have in common their asbestiform habit, long, (1:20) thin fibrous crystals. 

The inhalation of asbestos fibers can cause serious illnesses, including malignant lung cancer, mesothelioma (a formerly rare cancer strongly associated with exposure to amphibole asbestos), and asbestosis (a type of pneumoconiosis). Long exposure to high concentrations of asbestos fibers is more likely to cause health problems. The European Union has banned all use of asbestos and extraction, manufacture and processing of asbestos products.

Asbestos became increasingly popular among manufacturers and builders in the late 19th century because of its sound absorption, averagetensile strength, and its resistance to fire, heat, electrical and chemical damage. 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. Commercial asbestos mining began in the Eastern Townships of Quebec, Canada and the world's largest asbestos mine is located in the town of Asbestos, Quebec.

Asbestos

• Identification of Asbestos
• Asbestos Mineralogy and Health Effects