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Association minéralogique du Canada
Read the following reviews on Special Publication 5
REVIEW PUBLISHED IN GEOSCIENCE CANADA, VOL. 29, NO. 3, P. 132-134
Health Effects of Chrysotile Asbestos: Contribution of Science to Risk-Management Decisions
Edited by R.P. Nolan, A.M. Langer,
M. Ross, F.J. Wicks and R.F. Martin
The Canadian Mineralogist
Special Publication 5
Mineralogical Association of Canada
PO Box 78087
Ottawa, Ontario K2E 1B1
2001, 304 p., $38.00 paperback
Reviewed by Pat E. Rasmussen
Environmental and Occupational
Environmental Health Science Bureau
Tunney's Pasture, Address Locator 0803C
Ottawa, Ontario K1A 0L2
An international workshop entitled "Health Effects of Chrysotile Asbestos: Contribution of Science to Risk-Management Decisions" was held in Montreal in September 1997, sponsored by the Mineralogical Association of Canada. The purpose of the workshop was to review the biological data available for the various types of asbestos fibre, to compare the health effects of chrysotile asbestos with other types of asbestos, and to calculate the risks associated with current levels of exposure to chrysotile.
The workshop proceedings were published in 2001 as a five-part monograph, with each part containing three to eight peer-reviewed articles, a Discussion, and a Rapporteur's Report. In a single volume, Health Effects of Chrysotile Asbestos provides the perspectives of a wide range of experts, including epidemiologists, toxicologists, occupational hygienists, medical researchers, clinicians, mineralogists, economic geologists, environmental chemists, and engineers. The proceedings are framed with an Introduction by Dr. Robert Nolan, a General Discussion facilitated by Drs. Robert Murray and Kevin Browne, and a Summary of the Symposium by Dr. Arthur Langer. The Preamble by Dr. Robert Martin, Editor of The Canadian Mineralogist, is followed by an obituary to Dr. Murray, who was a leading expert on the health effects of asbestos and an active participant in the Montreal workshop.
Advancing science beyond traditional barriers requires, as a first step, grasping the foreign terminology of other disciplines. Biologists need help with the language of geology, geoscientists need help with the language of the medical community, and researchers everywhere need help with the language of the regulators. The editors and authors of Health Effects of Chrysotile Asbestos deserve a lot of credit for getting this right. The articles are clearly written with concise and interesting explanations of the basic concepts underlying each discipline, using minimal specialized jargon. The short but excellent Glossary of Terms serves as a bridge linking the many health sciences and earth sciences disciplines covered in the proceedings.
A significant glitch in communication arises from the nomenclature of the asbestos minerals. Current regulations are based on the generic term "asbestos." Most dictionaries define "asbestos" simply as a fibrous mineral that doesn't burn, which is what it meant in the original Greek. In the regulatory world, the fibres of six minerals are defined as "asbestos": chrysotile, amosite, crocidolite, actinolite, tremolite, and anthophyllite. These are also the terms used in commerce, although chrysotile is the only asbestos mineral still of commercial importance. Health scientists and clinicians who study asbestos-related diseases define the asbestos minerals in terms of their varying potencies, the most potent being the amphibole minerals (amosite, crocidolite, actinolite, tremolite, and anthophyllite) and the least potent being the serpentine mineral chrysotile.
In 1978 the Commission on New Minerals and Mineral Names (CNMMN) examined these mineral names with the aim of "eliminating redundancies and cleaning up the nomenclature" and determined that the terms crocidolite and amosite were no longer valid. In his Preamble, Dr. Martin explains that the CNMMN does not approve of the use of special names to refer to the habit of a mineral. It was ruled that riebeckite and grunerite (respectively) are the correct names and must be used exclusively. Thus, even before the fibrous minerals crocidolite and amosite were banned from the world market, their commercial names were banned from the pages of The Canadian Mineralogist.
The epidemiologists and toxicologists tasked with reviewing a century of complex lung disease and exposure data for this book either missed or ignored the 1978 CNMMN ban, and continued to refer to crocidolite and amosite in their manuscripts. In his Summary of the Symposium, Dr. Langer presents compelling arguments in their defense. After all, these are the names that evoke the key physical property of asbestos minerals: their fibrous habit. It is this property that allows asbestos fibres to be woven into fireproof textiles, to become airborne and remain airborne, and to penetrate deeply into the lungs and stay there until they do serious damage. Crocidolite and amosite are terms with historical meaning and significance: they have an important place in medical literature and regulatory documents spanning a hundred years.
Apparently these arguments do not wash with the CNMMN. Just as the Canada Post cannot accept two names for a street, we are told the CNMMN cannot accept separate names for the fibrous versus chunky forms of the same mineral. To accommodate the biologists' preference and still abide by the rules of mineral nomenclature, the editors fashioned a compromise. Throughout the book, the mineral formerly known as crocidolite is termed riebeckite-asbestos ("crocidolite"). The mineral formerly known as amosite is termed grunerite-asbestos ("amosite"). Some readers may find these bulky constructions of hyphenated words, brackets, and quotation marks a bit daunting, like trying to keep track of the characters' names in a 19th century Russian novel. It is well worth the effort: understanding the nomenclature is key to understanding the discussions and debates about the data sources underlying asbestos epidemiology and risk assessments.
In Part 1, Exposure to Amphibole-Asbestos and Mixed Fibers, a collection of six papers provides an overview of the health hazards associated with the inhalation of asbestos minerals, and introduces the methodologies used for exposure assessments, epidemiological studies, and risk assessments. The first paper by Dr. Langer examines the approach used for risk assessments carried out in the United States, which are based primarily on the experience of insulation workers in the New York-New Jersey area in the mid- to late-1900s. These data are considered reliable for risk assessments because the fates of all the workers are known and their exposure histories are known. Excess lung disease in the insulation workers was caused by chronic exposures to high levels of potent amphibole fibres (amosite and crocidolite) or to mixtures of amphibole and chrysotile fibres. Dr. Langer clarifies that these workers do not represent a single population exposed to a single substance. He concludes that the group consists of multiple subpopulations, each having different exposure histories and exposures to different types of fibres, and that the controlling risk factors are type of fibre and intensity of exposure. Existing regulations are based on past experiences with amphibole-asbestos and mixed asbestos fibres and do not differentiate between more and less biologically active asbestos minerals. In short, the asbestos minerals vary widely in their potency, and current regulations were designed to protect against the worst of them. These observations set the stage for much discussion throughout the remainder of the book.
Part 2, Exposure to Commercial Chrysotile - Mineralogy, Modern Products and Exposures, consists of six papers describing the major deposits of chrysotile around the world, production and consumption trends, regulations to control occupational exposures currently in place worldwide, successes and limitations of workplace monitoring techniques, and exposures of the general population. Of particular interest is the paper by Dr. Anthony Williams-Jones and colleagues from McGill University, which examines the distribution of tremolite in the vicinity of chrysotile ore of the Jeffrey mine in Asbestos, Quebec. Studies of chrysotile mine and mill workers in Quebec have determined that the amphibole mineral tremolite is the principal fibre in their lung tissues, rather than chrysotile as might be expected. The chrysotile ores in the Jeffrey mine are essentially amphibole free. However, if mining staff are unaware of the distribution of the tremolite-bearing zones, there is a high probability that tremolite-bearing rock will be included in the ore and find its way to the mill, leading to exposures of people in the mill environment. To ensure that the chrysotile ores are produced with minimal tremolite contamination, the authors recommend a lithogeochemical screening method to identify and avoid potential amphibole-rich zones.
In Part 3, Mechanisms of Mesothelioma and Lung Cancer, Drs. Neil Johnson and Brooke Mossman review current knowledge of factors influencing dose-effect relationships for chrysotile, including level of exposure, physical dimensions of the fibres, and biopersistence of the retained fibres in the lung. Chrysotile is considered the least potent of the asbestos minerals for the reason that chrysotile fibres are cleared from the lungs more rapidly than amphibole fibres. Studies of biopersistence are made through examination of fibres in autopsy lung samples, and measurement of fibre levels in broncho-alveolar fluid. Chronic exposure to high levels of airborne fibres of any type of asbestos, including chrysotile, causes the extensive scarring of the lung tissue called asbestosis. Among those with asbestosis, the risk of developing lung cancer is greatest for people who also smoke cigarettes. Mesothelioma is another type of asbestos-related tumor, which usually develops 30-40 years after exposure, and is most commonly associated with past exposures to crocidolite and amosite. Chrysotile on its own may or may not cause human mesotheliomas (the evidence is uncertain), but chrysotile is commonly contaminated with tremolite which does cause them. The two other articles in Part 3 describe emerging information about a possible viral agent that may be contributing to the increase in incidence of mesothelioma in a number of industrialized countries.
The eight articles in Part 4, Exposure to Commercial Chrysotile - Historical Perspectives of the Health Effects, document a wide range of international perspectives, experiences, and regulatory trends. The topics include occupational and environmental exposures to asbestos in mining and milling operations in Canada, Italy, and Russia, and in the asbestos-cement industry in India. An article by Drs. Toshiaki Hagashi and Ken Takahashi provides an overview of commercial use, exposures, health effects, and regulatory trends in Japan, and describes the release of asbestos fibre during demolition of buildings following the 1995 Kobe earthquake. Canadian epidemiologist Dr. Michel Camus emphasizes the need for risk assessments of the fibrous materials proposed as substitutes for asbestos, which include ceramics, glass, and rockwool products. A key paper by Dr. Stanislav Domnin and colleagues examines effects of exposure to low concentrations of asbestos-containing dust on children's health. The authors report a relationship between the concentration of asbestos in ambient air in Asbest City, a chrysotile mining and milling area in the Urals, and peak figures of bronchitis, acute respiratory infection and inflammatory diseases in children. The exposures of these children are low compared to the occupational setting, but high compared to other non-occupational settings such as inside buildings containing asbestos. Their study departs from the traditional focus of the literature, which is mainly on the carcinogenic properties of chrysotile at high levels of exposure, and represents an important new direction of research into the potential for non-malignant respiratory disease among children.
Part 5, Exposure to Commercial Chrysotile - Modern Perspectives of the Health Effects, describes the difficulties in identifying health hazards associated with the current low levels of exposure to chrysotile experienced by modern workers and by the general population. In the first article Dr. John Hoskins provides perspectives on the toxicological data and its interpretation. In the second article Dr. Bernard Gee describes problems with the clinical diagnosis of early signs of pulmonary disease. In the final paper Drs. Richard Wilson and Bertram Price continue to examine the assumptions underlying USA risk assessments, in keeping with themes introduced in Part 1, and outline areas where the science conflicts with the regulations. In contrast with the large body of evidence for disease potential at high levels of exposure, there is a lack of evidence for health effects at current levels of urban exposure. This lack of evidence forces regulators to make assumptions about cause and effect at low levels of exposure. The result is a debate about the key assumption: that is, whether it should be assumed that there is a linear dose-response relationship or whether it should be assumed that there is a threshold effect. We recognize this as the place where the science has reached its limits, and where there is a clear need for further research, because it is the place where the experts start to disagree.
Apart from the clumsy mineral names - grunerite-asbestos ("amosite") is as distracting as an ant carting its dead companion across the page - my only complaint is that the table of contents is buried inside the back cover. Nothing at the front or on the cover indicates that there are five parts to this book. Someone in the habit of reading books from back to front might be quite satisfied to find the full table of contents on pages 303 and 304. The rest of us are likely to flip to the first table of contents that we encounter, which is on page 7 and covers Part 1 only, and mistakenly believe it to represent the contents of the whole book.
A highlight of the book is the remarkably candid nature of the discussion sections. The participating scientists, who are leaders in their respective fields, openly discuss the strengths and weaknesses of their methods, problems caused by historical changes in diagnostic and analytical techniques, the inevitable disagreements in interpretation, and their concerns with the limitations of current knowledge. These informal exchanges nicely complement the formal peer-reviewed contributions, and provide useful insights into areas of controversy and data gaps.
Although this was a scientific workshop, not a policy workshop, the contributors often express opinions on social and ethical aspects of the asbestos issue. The workshop participants all appear to agree that current regulations are protective, but there is general acknowledgment that these regulations are not applied equally everywhere around the world. The participants speak of the moral obligation on the part of exporting nations to provide training in the handling and use of chrysotile products and implementation of good work practices, and endorse the view that export of control technologies should accompany any export of chrysotile asbestos to consumer nations. It is on this appropriate note that Arthur Langer closes the final chapter.
|© 2006 Mineralogical Association of Canada||Last update 2012-11-15|