|Biological Potency||Fibre Length||Concentration Level||Exposure Levels||Single Asbestos Fibre|
|Asbestos in Water||Asbestos Substitutes||Asbestos Friction Materials||Chrysotile Cement|
Is there evidence for a difference in biological potency between chrysotile asbestos and the amphibole fibres types?
Answer to Question 1
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 the amphiboles.
Recently published data show that:
1. The morbidity and mortality experience of workers handling chrysotile only is much less severe than that of workers exposed to amphiboles (or to mixtures containing them).
2. The results of mineral contents of lung tissue by fibre type show that large amounts (100-fold) of amphiboles are found in the lungs of cases compared to controls. This is not so for chrysotile.
References for Question 1
Wagner JC, Moncrieff CF, Coles R, Griffiths DM and Munday, 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.
Albin A, Pooley FD, Stromberg U, Attewell R, Mitha R and Welinder H (1994).
Occup. Environ. Med. 51: 205-211
Retention patterns of asbestos fibres in lung tissue among asbestos cement workers. A study showing different kinetics for amphibole and chrysotile fibres in human lung tissue. Amphibole fibre concentrations increase with duration of exposure, whereas chrysotile concentrations do not. The authors indicate that their study supports a former finding of a possible adaptive clearance of chrysotile and conclude that their findings support the hypothesis that adverse effects are associated rather with the fibres that are retained (amphiboles), than with the ones being cleared (largely chrysotile).
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 fibres according to fibre length?
Answer to Question 2
Two different sets of data are pertinent to this question:
There is evidence from experimental studies that while long (thin and durable) fibres are associated with ill-health effects in animals, no such association is found with asbestos fibres shorter than ~ 5 microns. The great majority of fibres found in the general environment are shorter than 5 microns. Thus, while the presence of long fibres, such as may be found in the workplace, may be associated with ill-health effects in workers, the presence of short asbestos fibres in the general environment should not be of concern, at least for chrysotile asbestos.
References to Question 2
Doll R, (1989). In Non-Occupational Exposure to Mineral Fibres, 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 fibre 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 fibres (properly described as elongated particles) are much less carcinogenic, if they are carcinogenic at all”.
Davis JMG, Addison, J, Bolton RE, 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 fibres were compared. At the end of 12 months of dust inhalation (10 mg/m„) long fibres caused development of widespread pulmonary fibrosis, and a third of the animals developed pulmonary tumours or mesotheliomas. No fibrosis at all, and no pulmonary neoplasms were found in animals treated with short fibre dust.
Chatfield EJ (1983). Short mineral fibres 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 fibres longer than 5 microns are less than 1 fibre/litre (0.001 f/cc). In urban environments higher levels, up to 40 f/l (0.04 f/cc) were observed. Most fibres 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?
Answer to Question 3
Asbestos fibres in the general environmental air have been present long before manís 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 labelled: “acceptable” by the WHO, or “not significant”, by the Ontario Royal Commission on Asbestos or “further control not justified”, by the Royal Society, London.
References to Question 3
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 in Ontario (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 fibre concentrations in the ambient air are extremely low. Counts of fibres longer than 5 microns taken by electron microscope are often less than 0.001 f/cc. If we consider the fibres that would be seen by an optical microscope, it is extremely rate in Ontario to have concentrations greater than 0.001 f/cc. The recent Ontario data suggest that fibre levels are lowest where population density is lowest, although the earlier Ontario data did not reveal this relationship. In Chapter 9 we conclude that the health risks presented to building occupants from exposure to 0.001 optically visible fibres per cubic centimetre is not significant. It follows that the fibre levels discussed in this section present a clearly insignificant health risk. We see no reason to worry about the health effects of the prevalent level of asbestos fibres in the outdoor air in Ontario”.
Asbestos in the workplace: Can asbestos be handled without undue risk to the workers? What is the risk to workers handling chrysotile asbestos at today's controlled exposure levels?
Answers to Question 4
Lung fibrosis, lung cancer and mesothelioma have been definitely correlated with exposure to airborne respirable fibres 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 cohorts surveys, where the health experience at very low exposure levels to chrysotile only was examined, support the following statements:
There are low levels of exposure to chrysotile asbestos in the workplace, where no excess morbidity (disease) and mortality have been detected. There is no undue risk to workers handling chrysotile asbestos, at today's controlled exposure levels (~ 1 f/cc).
References for Question 4
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 fibre-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 tumours, 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
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
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. Findings on mortality have been published on five occasions, and the most recent report provides an update of the results of analysis of mortality for the period 1976-1988 inclusive. One of the central findings of this update is that over several narrow categories of exposure up to 300 mpcf.y, the SMRs for lung cancer fluctuated around unity, with no evidence of trend and increased steeply above that exposure level. Still more recently, the same authors confirmed their original findings with a mortality update up to 1992: Liddell FDK, McDonald AD and McDonald JC. Ann. Occup. Hyg. 41:13-35 (1997).
Can exposure to one single asbestos fibre kill?
Answers to Question 5
It should be realized that it is almost physically impossible to test this proposition experimentally. It is virtually impossible to challenge cells, tissues or whole animals to one single fibre, because of the ubiquity of asbestos fibres; it should be realized that one milligram of asbestos may contain several hundred million respirable fibres. Furthermore, it is a universally acknowledged fact that experimental protocols call for a minimum dose of several hundreds of thousands of fibres in order to induce observable effects.
On the other hand, the following facts may help in reaching sensible judgement:
1. Every 60 seconds, the lungs of a normal person handle some 10 liters of air.
2. In the general environmental air of cities and rural areas, concentrations of approximately l fibre per liter (possibly a little more or a little less, depending on circumstances of location, weather conditions, etc.) are found around the world.
3. It follows from these two observations that every day, 14,400 liters of air (10 liters x 60 min. x 24 hrs), each one containing 1 fibre, transit through the lungs of a “normal” non-occupationally exposed person.
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?
Answers to Question 6
The use of asbestos-cement (A/C) pipes dates back to the early 1920's, and it is estimated that by the end of the 1980ís, close to 3 million kilometres of pipes will have been laid worldwide to convey potable water.
Highly aggressive waters may attack the cement matrix, and consequently lead to the release of fibres into the water circulating through the pipes, and A/C pipes are not recommended for use under such highly corrosive conditions, unless protected with specially designed internal protective lining.
The results of most studies published so far indicate that the source waters already contain asbestos fibres (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 fibre 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 fibres every day) quantities of asbestos incorporated into their diet have consistently failed to indicate any raised incidence of gastrointestinal tumours, 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 tumours following the direct ingestion of asbestos fibres.
References for Question 6
Hallenbeck WH, Chen EH, Hesse CS, 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.
MacRae KD (1988). Journal of the Royal College of Physicians of London 22(1):7-10
In this review article, the author concludes: “It would thus seem highly unlikely that the asbestos-cement pipe distribution system makes any biologically significant contribution to the asbestos content of water passing through it”. “It is highly improbable that asbestos release from asbestos cement pipes is relevant to the development of cancer.”
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 in Florida have 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”.
Polissar L, Severson RK, Boatman ES and Thomas DB (1982). American Journal of Epidemiology 116(2):314-328
The site of the study was Puget Sound region of Western Washington, and the state's three largest metropolitan areas (Everett, Seattle and Tacoma) were used for comparison. Everett was the “high exposure municipality”, where asbestos levels ranged from 37.2 to 556 million fibres per liter. Seattle and Tacoma had relatively low concentrations, averaging 7.3 million fibres per liter. The three metropolitan areas were subdivided into census tracts grouped by asbestos concentration. Data on cancer incidence were obtained from a surveillance registry; cancer mortality information came from death certificates. Duration of exposure to asbestos in drinking water was estimated and divided into long term (greater than 30 years) versus short term (less than 30 years) groups. Following the analysis of the results, the principal investigator, Dr Lincoln Pollisar of the Fred Hutchinson Cancer Research Center, concluded that: “Results of this study and prior studies of cancer in relation to waterborne asbestos are inconsistent, and provide little evidence that asbestos in community water supplies has altered the risk of any cancer”.
Asbestos substitutes: Non-asbestos fibrous materials are used extensively, and are often proposed as substitutes for asbestos. In which areas of application are these materials used? Is there evidence available indicating biological activity of non-asbestos fibrous materials?
Answers to Question 7
Non-Asbestos fibrous materials, both man-made and extracted from natural deposits, 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 asbestos.
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.
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.
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 and thin and which display long “in vivo” durability.
References for Question 7
U.S. Dept. Of Labor (OSHA) Synthetic Mineral Fibers: Hazard Description:
The American Occupational Safety and Health Administration (OSHA) has declared that glass fibres 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 fibres as “possibly carcinogenic to humans.”
INSERM (French medical research council) Expert Council, Health effects of Substitute Fibres, Paris, June 1998: Quote from the Executive Summary:
Given the present uncertainties concerning the effects of asbestos substitute fibres in humans, it is important to ensure that exposure levels in users of products containing asbestos substitute fibres are as low as possible.
Looking at the conclusions of the various chapters in the report, questions recur about the possibility of risk involving rock wool and ceramic fibres in particular.
Once again, there is little or no sound toxicological data for materials such as cellulose (whose proinflammatory nature is known) and polyvinyl alcohol fibres which are in widespread use today.
Asbestos friction materials: What is the contribution to the general environment resulting from the use of asbestos in friction materials?
Answers to Question 8
Asbestos has been a major constituent of automotive friction materials for more than 70 years, where the presence of mostly chrysotile asbestos (from 25% to 65% by weight) 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) fibres.
Thus, the emission of free fibres resulting from brake lining wear is a negligible health factor in urban air pollution. Indeed, recent estimates of air concentrations of asbestos resulting from vehicular brakes in large U.S. cities range from 0.051 ng/m³ (Rochester, NY) to 0.258 ng/m³ (Los Angeles, CA). If a conversion factor of 30 fibres measured optically per nanogram of asbestos used, the values for Los Angeles would be 7.74f/M³ or 0.000007 f/cc.
References for Question 8
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 fibre; 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 fibres 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 the U.K. have been obtained from situations of highly intensive vehicular traffic (City of London), indicating that the use of asbestos in such applications causes no measurable contribution to urban environmental asbestos air concentrations. The asbestos fibre counts presumably released from vehicular traffic at two very busy road junctions in the Greater London Area (Motorway #1 - North Circular Road and Euston Underpass) were from 0.0002 to 0.0004 f/ml.
Fibre-Cement construction materials: What is the contribution to the environment resulting from the use of chrysotile in fibre cement materials?
Answers to Question 9
Chrysotile cement was invented in Austria in 1901 and has been widely used every since worldwide. By mixing chrysotile fibre with cement, this chemical and physical links allows the manufacture of a lighter and stronger slate. Thus, this strong link between the fibre and the matrix does not allow the fibre 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 fibres in the environment is not significant.
References to Question 9
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.
In Germany, the study of emission on coated and uncoated and coated roofing materials revealed low asbestos fibre 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 fibre concentrations that were measured in populated areas were well below the level considered acceptable by German health authorities, i.e.: clearly below 1000 fibres per cubic metre.
Felbermayer W, and Ussar MB (1980). Research Report: Airborne asbestos fibres eroded from asbestos cement sheets. Institute fur Umweltschutz and Emissionsfragen, Leoben, Austria
In Austria, a comparison of the asbestos fibre 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 fibre concentrations found in the various measurement areas.
Safety & Welfare of Western Australia (1990). Report of the Working Party on Asbestos Cement Products
In Australia, 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.
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