Scientific Evidence on Chrysotile Asbestos and Health*

Asbestos in drinking water

"Generally, it has been concluded that the concentrations of asbestos in drinking water resulting from the use of asbestos-cement pipes do not present a hazard to human health." (Letter addressed to Mr. Nickos Kouinis, Municipality of Corinth, from Mr. Ivanildo Hespanhol Community Water Supply & Sanitation Unit, Division of Environmental Health World Health Organization, April 12, 1990)

Environmental risk

Fibre type differences

"It is also recommended that countries should move quickly to lower the occupational exposure limit for an individual worker to 1 f/ml or below, if they have not already done so. For crocidolite and amosite asbestos, on the basis of health, it is recommended that their use should be prohibited as soon as possible. (Occupational Exposure Limit for Asbestos. Report prepared by a WHO meeting, Oxford, UK, 10-11 April, 1989.)

Asbestos insulation in buildings

"Intact and undisturbed asbestos materials do not pose a health risk. The mere presence of asbestos in a building does not mean that the health of building occupants is endangered. Asbestos-containing material which is in good condition, and is not somehow damaged or disturbed, is not likely to release asbestos fibres into the air. Removal is often not a building owner's best course of action to reduce asbestos exposure. In fact, an improper removal can create a dangerous situation where none previously existed". (Managing Asbestos in Place: A Building Owner's Guide to Operations and Maintenance Programs for Asbestos-Containing Materials. United States Environmental Protection Agency, July 1990.)

Product risks

"The use of asbestos-containing friction materials does not pose a detectable risk to the general population." (Report of an IPCS Group meeting on The reduction of asbestos in the environment, 12-16 December 1988, Rome, Italy. Published under the joint sponsorship of UNEP, ILO and WHO, 1989.)

Evidence of threshold

"In our judgement, asbestosis can be deemed a disease of past high exposure levels and will not occur in workers exposed to the regulated levels of occupational exposure now in force in Ontario (e.g. 1.0 f/ml)." (Dupré J S, Mustard J F & Uffen R J. Report of the Royal Commission on Matters of Health and Safety Arising from the Use of Asbestos in Ontario. Ontario Ministry of the Attorney General, 1984:94-97.)

€  asbestosis as a precursor to lung cancer

"To me the available data indicate that the only scientifically established association of lung cancer and asbestos exposure is the association of asbestosis and lung cancer; thus, only the presence of asbestosis can be used to incriminate asbestos as a cause of lung cancer." (Churg A. Asbestos, Asbestosis and Lung Cancer, Modern Pathology 6, 1993; 6:509-511)

€  lung cancer

(i) Mining
"There is no statistically significant evidence of increased lung cancer risk at ¾ 300 mpcf x years [i.e. 50 f/cc for 20 years] in the chrysotile mine and mill workers of Quebec." (McDonald JC, Liddell FDK, Dufresne A, and McDonald AD, The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 Br Jr Ind Med 1993; 50:1073-1081.)

"The significance of this study is that at current levels of occupational exposure any deaths from asbestosis or lung cancer are most unlikely." (study co-author J.C McDonald)

(ii) Friction materials
"It is concluded that with good environmental control (0.5 - 1.0 f/ml), chrysotile asbestos may be used in manufacture without causing excess mortality." (Berry G, Newhouse ML. Mortality of workers manufacturing friction materials using asbestos. Brit. Jr. of Ind. Med., 1983; 40(1):1-7.)

(iii) Asbestos-cement
"median exposure of 10-20 fibre€years does not seem to cause an increased risk of lung cancer" (Olsen CG and Hogstedt C, Lung Cancer among asbestos cement workers: A Swedish cohort sudy and review, Brit J. Ind. Med. 1985; 42(6):397-402.)

"Measured airborne fibre concentrations available since 1970 from personal samplers showed mean levels below 1 f/ml, although higher levels had probably occurred previously in certain area of the factory. No excess of lung cancer was observed in the mortality follow up by comparison with either national or local death rates." (Gardner MJ, Winter PD, Pannett B & Powell CA, Follow up study of workers manufacturing chrysotile asbestos cement products, Br J Ind. Med, 1986; 43:726-732.)

"Studies of three groups of workers manufacturing asbestos cement products containing almost exclusively chrysotile fibre show little indication of raised levels of asbestos-related diseases. This is in contrast to most studies of workers making similar products from mixed fibres containing mainly chrysotile but also the amphiboles crocidolite and amosite." (Gardner MJ & Powell CA. Mortality of asbestos cement workers using almost exclusively chrysotile fibre, J. Soc. Occup. Med., 1986; 36:124-126.)

A follow-up study of 1,970 workers in an asbestos-cement factory using chrysotile only, at low levels of exposure, showed no significant Standard Mortality Ratio (SMR) excesses. The causes of death investigated included neoplasms and cancers of the lung, pleura and gastrointestinal tract. (Thomas HF, Benjamin LT, Elwood PC & Sweetnam PM. Further follow-up study of workers from an asbestos cement factory. Br J Ind Med, 1982; 39(3):273-276.)

An investigation of 5,645 asbestos-cement manufacturing workers found no increased mortality resulting from chrysotile exposures of approximately 15 f/ml years. (Weill H, Hughes J & Waggespack C. Influence of dose and fibre type of respiratory malignancy risk in asbestos-cement manufacturing, Am. Rev. Resp. Dis., 1979; 120(2):345-354.)

(iv) General public
This study of environmentally and domestically exposed women demonstrates that the general population exposed to chrysotile is not at a detectably increased risk of lung cancer, even when exposures have been very high (25-30 f/ml/years). It should be noted that the exposure of women in Quebec was at least 16 times those applied in the INSERM report and approaches levels found in well-controlled chrysotile mines, mills and factories. (Camus & Siemiatycki, 1996 - In Press)

€ mesothelioma

"...at present levels of environmental control, any mesothelioma risk from exposure in either area A or B [of Quebec's chrysotile mines] would be far below the limits of epidemiological detection." (McDonald JC & McDonald AD. Chrysotile, tremolite and mesothelioma - Editorial. Science, 1995, January 10.)

"As a practical matter, the data indicate that chrysotile will not produce mesothelioma in those exposed to any current or recent regulated numbers of fibres, and certainly not in those exposed to chrysotile encountered at environmental levels." (Churg A. Chrysotile, tremolite and malignant mesothelioma in man. Chest. 1988; 93(3):621-628)

* A more comprehensive list of scientific references is available from The Asbestos Institute.

                                                                 July 22, 1996