Health risk of chrysotile revisited

Abstract

This review provides a basis for substantiating both kinetically and pathologically the differences between chrysotile and amphibole asbestos. Chrysotile, which is rapidly attacked by the acid environment of the macrophage, falls apart in the lung into short fibers and particles, while the amphibole asbestos persist creating a response to the fibrous structure of this mineral. Inhalation toxicity studies of chrysotile at non-lung overload conditions demonstrate that the long (>20 µm) fibers are rapidly cleared from the lung, are not translocated to the pleural cavity and do not initiate fibrogenic response. In contrast, long amphibole asbestos fibers persist, are quickly (within 7 d) translocated to the pleural cavity and result in interstitial fibrosis and pleural inflammation. Quantitative reviews of epidemiological studies of mineral fibers have determined the potency of chrysotile and amphibole asbestos for causing lung cancer and mesothelioma in relation to fiber type and have also differentiated between these two minerals. These studies have been reviewed in light of the frequent use of amphibole asbestos. As with other respirable particulates, there is evidence that heavy and prolonged exposure to chrysotile can produce lung cancer. The importance of the present and other similar reviews is that the studies they report show that low exposures to chrysotile do not present a detectable risk to health. Since total dose over time decides the likelihood of disease occurrence and progression, they also suggest that the risk of an adverse outcome may be low with even high exposures experienced over a short duration.

• Amphibole asbestos
• cement products
• chrysotile
• epidemiology
• health risk
• inhalation toxicology
• mining

Declaration of interests

The preparation of this review was supported by a grant from the International Chrysotile Association, Washington, DC, USA, in cooperation with The Canadian Chrysotile Association, Montréal, QC, Canada. The affiliation of the authors is as shown on the cover page and includes university, government institute, hospital and corporate affiliations as well as independent toxicology consultants. The review is the professional work product of the authors and may not necessarily represent the views of the corporate sponsors. Two of the authors, David Bernstein and Allen Gibbs have appeared as expert witnesses in litigation concerned with alleged health effects of exposure to chrysotile. Jacques Dunnigan has served as an expert witness on the health effects of chrysotile before the Commission de la santé et sécurité du travail du Quebec/Workers Compensation Board of Québec.

Notes

*WHO fibres: defined as fibers >5 μm long, <3 μm wide and with length:width ratios >3:1; WHO (1985).

*Total fibers: all objects with a length:diameter aspect ratio greater than 3:1

*OSHA 29 CFR Part 1915: coal tar pitch volatile, 4-nitrobiphenyl, alpha-naphthylamine, methyl chloromethyl ether, 3,3′-dichlorobenzidine (and its salts), bis-chloromethyl ether, beta-naphthylamine, benzidine, 4-aminodiphenyl, ethyleneimine, beta-propiolactone, 2-actylaminofluorene, 4-dimethylaminoazobenzene, nitrosodimethylamine, vinyl chloride, inorganic arsenic, lead, benzene, acrylonitrile, ethylene oxide, formaldehyde, asbestos.

*Odds Ratio (OR): The odds ratio is a relative measure of risk, telling us how much more likely it is that someone who is exposed to the factor under study will develop the outcome as compared to someone who is not exposed; an OR of 1 or less indicates no effect. Even if the OR is greater than 1, if the lower bound of the 95 % confidence interval (CI) is 1 or less then the OR is not different statistically from 1.