We’ve heard that asbestos is a carcinogen and thus dangerous for use.
Yes, asbestos has been classified by the International Agency for Research on Cancer (IARC-WHO) as Group 1 carcinogen (Carcinogenic to humans). This classification does not take into account carcinogenic potency of different types of asbestos, even though it has been proved that the carcinogenic potency of amphiboles is 100-500 times higher than that of chrysotile.
If you consider carefully the whole list of chemicals referred to this group, you will be surprised. The list includes chromium and nickel compounds, quartz, solar radiation, vinyl chloride, alcoholic beverages, salted fish, tobacco, wood dust, oral contraceptives, passive smoking, shoe manufacture and repair, production of furniture, combustion of coal, iron and steel founding, paints, rubber manufacturing industry, etc.
The classification of the World Health Organization (WHO) establishes hazard of a substance rather than risk. Almost four hundred other products and industrial processes are considered carcinogenic to human, probably or possible carcinogenic to humans, but this does not mean that we must ban their use. This means that we need a strict control over their use.
Is there evidence for a difference in biological potency between chrysotile and amphibole fibers?
Yes, there is an overwhelming body of evidence based on epidemiological studies on clinical findings, and on lung tissue mineral analysis in humans showing a definite difference in potency between chrysotile and amphiboles.
Recently published data show that the morbidity and mortality experience of workers handling chrysotile is much less severe than that of workers exposed to amphiboles (or to mixtures containing them). The results of analyzing mineral contents of lung tissue show large residual amounts of amphibole fibers.
References for Question 2:
Wagner JC, Moncrieff CF, Coles R,GriffithsDM andMunday,DE(1986). British Journal of Industrial Medicine 43:391-395
A study among naval dockyard workers showing increasing amounts of amphiboles in lung tissue and increasing severity of asbestosis, but no increase of chrysotile.
Wagner JC, Newhouse ML, Corrin B, Rossiter CER and Griffiths DM (1988). British Journal of Industrial Medicine 45(5):301-308
The lungs from 36 past workers of an asbestos factory using chrysotile, crocidolite and amosite were examined. Crocidolite and amosite lung contents were strongly associated with asbestosis and with mesothelioma, whereas no such correlation was evident with chrysotile and mullite.
McConnell EE, Chevalier HJ, Hesterberg TW, Hadley JG, Mast RW (1994). ILSI Monograph - Toxic and Carcinogenic Effects of Solid Particles in the Respiratory Tract. Eds. DL Dungworth, JL Mauderly and G. Oberdorster. ILSI Press,Washington,DC(pp. 461-467)
Following an inhalation study where the effects of crocidolite and chrysotile were compared, the authors conclude: crocidolite causes more inflammatory disease and at an earlier time than chrysotile asbestos.
Is there evidence for a difference in potency of fibers according to fiber length?
There is evidence from experimental studies that while long (thin and durable) fibers are associated with ill-health effects in animals, no such association is found with asbestos fibers shorter than 5 microns. The great majority of fibers found in the general environment are shorter than 5 microns. Thus, while the presence of long fibers, such as may be found in the workplace, may be associated with adverse health effects in workers, the presence of short asbestos fibers in the general environment should not be of concern, at least for chrysotile asbestos.
References for Question 3:
Doll R, (1989). In Non-Occupational Exposure to Mineral Fibers, Eds. J. Bignon, J. Peto and R. Saracci. WHO/IARC Scientific Publications No. 90,Lyon: 511-518.
"Properly speaking, no particle should be described as a fiber unless it is at least 5 µm long and the diameter is less than one third of its length"
"There is increasing evidence that short fibers (properly described as elongated particles) are much less carcinogenic, if they are carcinogenic at all"
DavisJMG, Addison, J,BoltonRE, Donaldson K, Jones AD, and Smith T (1986). British Journal of Experimental Pathology 67(3): 415-430.
The effects of long vs short (100% shorter than 5µ) amosite fibers were compared. At the end of 12 months of dust inhalation (10 mg/m") long fibers caused development of widespread pulmonary fibrosis, and a third of the animals developed pulmonary tumors or mesotheliomas. No fibrosis at all, and no pulmonary neoplasms were found in animals treated with short fiber dust.
Chatfield EJ (1983). Short mineral fibers in airborne dust. Proceedings from a Symposium,Stockholm, September 28, 1982, Government of Sweden, Arbete och Halsa (publisher) 19: 9-93.
In rural areas the level of asbestos fibers longer than 5 microns are less than 1 fiber/liter (0.001 f/cc). In urban environments higher levels, up to 40 f/l (0.04 f/cc) were observed. Most fibers in general atmosphere are shorter than 5 microns (95-98%).
What is the risk associated with the presence of asbestos at concentration levels found in the general environmental air?
Asbestos fibers in the general environmental air have been present long before commercial exploitation of the mineral. This phenomenon is due to the natural erosion from geological formations quite common throughout the world, and the total amount of asbestos emitted from natural sources is much greater than that emitted from industrial sources. In general, the ambient air concentrations rarely exceed 0.001 f/cc. At these low levels, the risk is undetectably low, indeed much lower than other risks, such as natural background radiation. Such a low risk has been labeled: "acceptable" by the WHO, or "not significant", by the Ontario Royal Commission on Asbestos.
References for Question 4:
Churg A (1986). American Review of Respiratory Disease, 134 (1):125-127.
Study comparing health effects in residents of chrysotile mining towns, where levels are from 200 to 500 times higher than in most North American cities, to those seen in urban residents. In spite of higher levels in these mining towns, no evidence of higher asbestos-related diseases were found. The author concludes: "These observations should provide reassurance that exposure to chrysotile asbestos from urban air or in public buildings will not produce detectable disease".
This is in agreement with other reports on residents of chrysotile mining towns in Québec, which have consistently failed to demonstrate excess respiratory disease incidence. These are:
McDonald AD, and McDonald JC (1980). Cancer 46(7): 1650-1656.
Siemiatycki J. (1982). Health effects on the general population (mortality in the general population in asbestos mining areas). Proceedings, World Symposium on Asbestos,Montreal, 25-27 May, pp.337-348.
Pampalon R, Siemiatycki J, et Blanchet M, (1982). Pollution environnementale par l'amiante et santé publique au Québec. Union Médicale du Canada 111(5): 475-489.
McDonald JC, (1985). Health implications of environmental exposure to asbestos. Environmental Health Perspectives 62:319-328.
Report of the Royal Commission on Matters of Health and Safety Arising from the Use of Asbestos inOntario(1984). Eds. JS Dupré, JF Mustard, RJ Uffen. Published by the Ontario Ministry of the Attorney General 2:666.
"Considering all of the above data together, we conclude that asbestos fiber concentrations in the ambient air are extremely low. Counts of fibers longer than 5 microns taken by electron microscope are often less than 0.001 f/cc".
Chrysotile asbestos in the workplace: Can chrysotile be handled without undue risk to the workers? What is the risk to workers handling chrysotile asbestos at today's controlled exposure levels?
Lung fibrosis, lung cancer and mesothelioma have been definitely correlated with exposure to airborne respirable fibers of asbestos. This correlation has been ascertained for both intensity (dose) and duration of exposure. The correlation is especially strong for mesothelioma and exposure to the amphibole varieties of asbestos.
With regard to intensity (or exposure levels) of exposure, this aspect has been examined more recently, especially with regard to the very low exposure levels to chrysotile only.
Results of recently reported cohort surveys, where the health experience at very low exposure levels to chrysotile only was examined, support the following statements:
References for Question 5:
Berry G, and Newhouse ML (1983). British Journal of Industrial Medicine 40(1):1-7
A mortality (1942-1980) study carried out in a factory producing friction materials, using almost exclusively chrysotile. Compared with national death rates, there were no detectable excess deaths due to lung cancer, gastrointestinal cancer, or other cancers. The exposure levels were low, with only 5% of men accumulating 100 fiber-years/ml. The authors state: "The experience at this factory over a 40-year period showed that chrysotile asbestos was processed with no detectable excess mortality".
Newhouse ML, and Sullivan KR (1989). British Journal of Industrial Medicine 46(3):176-179.
The 1983 study (referred to above), has been extended by seven years. The authors confirm that there was no excess of deaths from lung cancer or other asbestos related tumors, or from chronic respiratory disease. After 1950, hygienic control was progressively improved at this factory, and from 1970, levels of asbestos have not exceeded 0.5-1.0 f/ml. The authors conclude: "It is concluded that with good environmental control, chrysotile asbestos may be used in manufacture without causing excess mortality".
Thomas HF, Benjamin IT, Elwood PC, and Sweetnam PM (1982). British Journal of Industrial Medicine 39(3):273-276.
In an asbestos-cement factory using chrysotile only, 1,970 workers were traced, and their mortality experience was examined. There was no appreciably raised standardized mortality ration (SMR) for the causes of death investigated, including all causes, all neoplasms, cancer of the lung and pleura, and cancers of the gastrointestinal tract. The authors indicate: "Thus the general results of this mortality survey suggest that the population of the chrysotile asbestos-cement factory studied are not at any excess risk in terms of total mortality, all cancer mortality, cancers of the lung and the bronchus, or gastrointestinal cancers".
McDonald JC, Liddell DK, Dufresne A, and McDonald AD (1993). British Journal of Industrial Medicine 50:1073-1081.
This study is undoubtedly the largest cohort of asbestos workers ever studied and followed for the longest period is that of the miners and millers of the chrysotile mines in Québec. The cohort, which was established in 1966, comprises some 11,000 workers born between 1891-1920 and has been followed ever since. Optimal use was made of all available dust measurements to evaluate for each cohort member his exposure in terms of duration, intensity and timing. The accumulated mortality data showed that the mortality rate in the cohort was not significantly different from that for the general population.
Can one single asbestos fiber damage health when inhaled?
Of course not, even though asbestos opponents claim that “one fiber kills”.
Let us give you a simple example. Every 60 seconds, the lungs of a normal person handle some10 litersof air. In the general environmental air of cities and rural areas, concentrations of approximately 1 fiber per liter (possibly a little more or a little less, depending on circumstances of location, weather conditions, etc.) are found around the world. It follows from these two observations that every day,14,400 litersof air (10 litersx 60 min. x 24 hrs), each one containing 1 fiber, transit through the lungs of a "normal" non-occupationally exposed person posing no health risk
Asbestos in Water: Does the use of asbestos-cement pipes contribute significantly to the presence of asbestos in water? Is there a risk associated with the presence of asbestos in drinking water?
The use of asbestos-cement (A/C) pipes dates back to the early 1920s, and it is estimated that by the end of the 1980's, close to 3 million kilometers of pipes have been laid worldwide to convey potable water.
The results of most studies published so far indicate that the source waters already contain asbestos fibers (mostly shorter than 1 u in length) before passing through the A/C pipe systems, often in numbers reaching several millions per liter, and it is generally agreed that A/C pipes do not appreciably raise the asbestos fiber content of water, and that the quantities found are within those which occur naturally. As to the risk of health resulting from the presence of asbestos in potable water, results of several years of laboratory investigation in animals fed for their entire lifespan with very large (several billions of fibers every day) quantities of asbestos incorporated into their diet have consistently failed to indicate any raised incidence of gastrointestinal tumors, or of any other pathological changes in the gastrointestinal tract. Epidemiological studies on human health effects related to asbestos levels in drinking water have failed to indicate any increased risk of alimentary tract tumors following the direct ingestion of asbestos fibers.
References for Question 7:
Hallenbeck WH, Chen EH,HesseCS, Patel-Mandlik K, and Wolff AH (1978). Journal of American Water Works Association. 70(2):97-102
A study of 15 water supply systems in the State of Illinois (U.S.A.) where some asbestos cement pipes were up to 50 years old, and where the water was non-aggressive to moderately aggressive, showing no significant differences before and after passing through the asbestos-cement pipe network.
Millette JR, Craun GF, Stober JA, Kraemer DF, Tousignant HG, Hidalgo E, Duboise RL, and Benedict J (1983. Environmental Health Perspectives. 53:91-98
Some areas inFloridahave been receiving drinking water through asbestos-cement pipes for 30-40 years. The authors mention: "No evidence for an association between the use of A/C pipes for carrying drinking water and deaths due to gastrointestinal and related cancers was found in this study".
Asbestos substitutes: Non-asbestos fibrous materials are used extensively, and are often proposed as environmentally friendly substitutes for asbestos. In which areas of application are these materials used? Is there evidence available indicating biological activity of non-asbestos fibrous materials?
Non-asbestos fibrous materials, both man-made (PVA, fiberglass, ceramic fibers) and extracted from natural deposits (cellulose, basalt fibers), are used and/or proposed as substitutes for asbestos. In industrialized countries, they can be found in practically all the major areas of applications of chrysotile. There are wide variations in competitiveness according to price, availability, technical performance, ease of handling and mixing, compatibility with other materials in composites, durability, etc.
Yet, there is no single fibrous alternative that could replace asbestos in all of its many varied applications. On the other hand, some fibrous materials are really not alternatives for asbestos, as they are used in areas where asbestos cannot be used (example: very high temperature refractory materials).
Compared to asbestos, evidence of biological activity of non-asbestos fibrous materials has been reported only recently. Except for a very limited number of materials (example: mineral wools), epidemiological scrutiny has yet to be undertaken in order to substantiate possible human health hazards.
On the other hand, recently published results from cell, tissue and animal experimentation indicate that all the materials reviewed in this section display some degree of biological activity, i.e. have adverse health effects.
These results suggest that their widespread production and use should be governed by appropriate monitoring and control of dust exposure, especially so for materials which are long.
References for Question 8:
U.S.Dept. Of Labor (OSHA) Synthetic Mineral Fibers: Hazard Description:
The American Occupational Safety and Health Administration (OSHA) has declared that glass fibers are "reasonably anticipated to be a carcinogen". The OSHA report states that "Several epidemiological studies have demonstrated statistically significant elevations in the risk of lung cancer and other respiratory system cancers among workers employed in fibrous glass and mineral wool manufacturing facilities".
International Agency for Research on Cancer (IARC) 1988. Man-Made Mineral Fibers: In IARC Monographs on the Evaluation of the Carcinogenic Risk of Chemicals to Man, 43:39-171,Lyon,France, WHO.
The WHO's IARC has classified glasswool, rockwool, slagwool and refractory ceramic fibers as "possibly carcinogenic to humans."
INSERM (French medical research council) Expert Council, Health effects of Substitute Fibers,Paris, June 1998: Quote from the Executive Summary:
Given the present uncertainties concerning the effects of asbestos substitute fibers in humans, it is important to ensure that exposure levels in users of products containing asbestos substitute fibers are as low as possible.
The biopersistence of Canadian chrysotile asbestos following inhalation, David M. Bernstein, Consultant in Toxicology, Geneva, Switzerland
Results of studies conducted by three leading toxicological laboratories from Switzerland, Germany and the United States demonstrate that the clearance half-time of chrysotile, i.e. the number of days necessary to clear 50% of fibers remaining in lungs following the exposure period, is 15 days.
Chrysotile was also compared to most popular substitute fibers. The researchers found strong evidence of hazards posed by those substitutes, even though their manufacturers propose them as environmentally friendly: the clearance half-time of the ceramic fiber was 60 days, aramid fibers – up to 90 days, cellulose fibers – over 1,000 days; the clearance half-time of amphibole asbestos (amosite) was almost 466 days.
Asbestos friction materials: What is the contribution to the general environment resulting from the use of chrysotile in friction materials?
Asbestos has been a major constituent of automotive friction materials for more than 70 years, where the presence of mostly chrysotile asbestos imparts strength, flexibility, heat resistance to brake linings, in addition to friction and wear properties.
Comprehensive investigations conducted with the support of the U.S. EPA have shown that on the average, more than 99.7% of the asbestos emitted as a result of wear and abrasion has been converted into other products such as forsterite, a material which has been found non-carcinogenic in animals. Furthermore, it has been determined that such asbestos (less than 1%) as may be present in wear debris consists predominantly of very short (0.3 µ) fibers.
Thus, the emission of free fibers resulting from brake lining wear is a negligible health factor in urban air pollution. Exhaust fumes and fine particles emitted from tires due to friction prove more dangerous.
References for Question 9:
Lynch JR (1968). Journal of the Air Pollution Control Association. 18(12):824-826
This study by investigators of the U.S. Department of Health, Education and Welfare, Public Health Service (Cincinnati) provides evidence from analysis of dust obtained from inside brake drums removed for brake relining, and also from laboratory experiments devised to permit sampling decomposition products of the lining under operating conditions. The authors conclude: "Only a very small proportion of the asbestos worn from brake linings is released as free fiber; the remainder is converted into some other mineral as a result of the extreme temperatures generated at small spots on the lining surface. Thus, although urban air contains a few free fibers as a result of brake lining wear, they represent a very small proportion of the total asbestos used in the manufacture of brakes".
Jacko MG, DuCharme RT, and Somers JH (1973). Society of Automotive Engineers, Reprint # 730548:1813-1831
In this report by scientists from the Bendix Corporation and the U.S. EPA, the authors state that on the average, more than 99.7% of the asbestos during vehicle operation is trapped or emitted as olivine or forsterite particles.
Jaffrey S (1990). Annals of Occupational Health. 34:529-534
Data in theU.K.have been obtained from situations of highly intensive vehicular traffic (City ofLondon), indicating that the use of asbestos in such applications causes no measurable contribution to urban environmental asbestos air concentrations. The asbestos fiber counts presumably released from vehicular traffic at two very busy road junctions in the Greater London Area (Motorway #1 - North Circular Roadand Euston Underpass) were from 0.0002 to 0.0004 f/ml.
Chrysotile cement construction materials: What is the contribution to the environment resulting from the use of chrysotile in fiber cement materials (slate, asbestos cement pipes)?
Chrysotile cement was invented inAustria in 1901 and has been widely used every since worldwide. By mixing chrysotile fiber with cement, this chemical and physical links allows the manufacture of a lighter and stronger slate, sheets, pipes, etc. Thus, this strong link between the fiber and the matrix does not allow the fiber to become airborne, even in areas of heavy water and wind erosion.
Studies undertaken in areas where chrysotile cement materials are widely used show that their contribution to the presence of chrysotile fibers in the environment is not significant.
References for Question 10:
Teichert U (1986). Staub Reinhaltung der Luft. 46:432-434
Data pertinent to the extent of possible emissions from A/C construction products and the air concentrations in various countries have been obtained at different times from 1980 to 1997.
InGermany, the study of emission on coated and uncoated and coated roofing materials revealed low asbestos fiber concentrations, even though severe corrosion was observed on uncoated asbestos cement roofs and a considerable quantity of materials containing asbestos could be removed by blowing and suction. Yet, asbestos fiber concentrations that were measured in populated areas were well below the level considered acceptable by German health authorities, i.e.: clearly below 1000 fibers per cubic meter.
Felbermayer W, andUssarMB(1980). Research Report: Airborne asbestos fibers eroded from asbestos cement sheets. Institute fur Umweltschutz and Emissionsfragen,Leoben,Austria.
InAustria, a comparison of the asbestos fiber concentrations in those areas with and without asbestos cement roofing (< 0.0001 f/ml) led to the conclusion that there is no statistically significant connection between the use of asbestos cement materials and the asbestos fiber concentrations found in the various measurement areas.
Safety & Welfare ofWestern Australia(1990). Report of the Working Party on Asbestos Cement Products
InAustralia, possible contribution from asbestos cement roofing materials of school buildings to the air concentrations in the vicinity of these buildings was studied. It was found that measurements were mostly < 0.0002 f/ml.