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The Importance of Exposure Levels Regarding Asbestos Related Mortality

by

Mont Wrobleski

Some research has shown a correlation between high exposure rates to asbestos with a significant excess of cancer related deaths. Just how much impact do exposure levels really have on mortality?

One interesting study is called, Lung cancer among asbestos cement workers. A Swedish cohort study and a review. By C G Ohlson, C Hogstedt – Br J Ind Med 1985;42:397-402. Here is an excerpt: Abstract – A cohort study of 1176 Swedish asbestos cement workers did not indicate any asbestos related excess mortality. Possible explanations of the negative outcome are relatively low exposure levels and the predominant use of chrysotile in production. Such a tentative conclusion is supported by a review of five mortality studies of workers exposed to asbestos cement that report considerable differences in relative risks for lung cancer. These differences could be explained by various degrees of cumulative exposure, the amount of amphiboles in the production, and methodological shortcomings. A median exposure of 10-20 fibre-years does not seem to cause an increased risk of lung cancer, particularly when only chrysotile is used.

A second study is called, A study of the mortality of workers in an asbestos factory by M. L. Newhouse Br J Ind Med 1969;26:294-301. Here is an excerpt: Abstract – A study of the mortality of workers in an asbestos factory. A cohort study of over 4,500 male workers employed at an asbestos factory making both textiles and insulation materials is described. The main analysis of the mortality of workers employed between April 1, 1933, the date of the implementation of the Asbestos Regulations, and May 1, 1964. The analysis was made in relation to job, length of exposure, and length of follow-up after first exposure. There was no significant difference between the number of deaths occurring in the factory population and the national figures, until an interval of 16 years or longer had elapsed from first exposure in the factory. There were 1,160 men who fulfilled this criterion. In this group there was no excess mortality among those who worked in jobs where exposure was low or moderate, but among those with jobs which entailed heavy exposure there was a significant excess of deaths from cancer of the lung and pleura, and cancer of other sites, in men with a total period of employment in the factory of less than two years, as well as with those who worked for longer. Excess mortality from respiratory disease was observed only among severely exposed workers with long service.

A third study is called, The effects of long-term ingestion of asbestos on the colon of F344 rats by Kelley J. Donham, MS, DVM, John W. Berg, MD, Loren A. Will, DVM, MPh, Joel R. Leininger, DVM, PhD, – Department of Preventive Medicine and Environmental Health, College of Medicine, University of Iowa, Iowa City, Iowa – National Large Bowel Cancer Project Here is an excerpt: Abstract – Weanling F344 rats, which were fed a diet containing 10% chrysotile (B), were studied over their lifetime to determine the effects of ingested asbestos on the colon. Control groups consisted of rats fed a diet containing a 10% nonnutritive cellulose or a standard laboratory rat diet. The pathological findings in the colons of 501 rats (189 on asbestos diet, 197 on fiber control diet, and 115 on standard control diet), are reported here. Epithelial tumors of the colon (eight adenocarcinomas and one adenoma) were found in nine of the rats on study. Four of the tumors were in asbestos-fed rats, two tumors were found in the non-nutritive cellulose controls, and three tumors were found in the standard laboratory rat diet controls. The probability (based on actuarial analysis) of developing adenoma or adenocarcinomas during the 32 months of the study were 7.4% for the asbestos-fed group, 3.5% for the fiber control diet and 4.0% on the standard control diet. In addition, one malignant mesothelioma of the type induced by intraperitoneally administered asbestos was found in the asbestos-fed group. Non-neoplastic lesions of the colon were also evaluated. The cumulative risk for development of any colon-associated lesion (non-neoplastic plus neoplastic lesions) was greatest for asbestos-fed rats (17.9%), compared to 13.6% for those fed the fiber control diet and 8.2% for those fed the standard control diet. The colon tissue levels of adenosine, 3-5-cyclic monophosphate (cAMP) were significantly lower in the animals fed asbestos compared to the control diets. Chrysotile fibers were seen by electronmicroscopy (e.m.) in six of ten ashed colon specimens of rats fed the asbestos diet. Although the differences in numbers of tumors between the animals fed asbestos and the controls were not statistically significant at the 5% level, we felt that the combination of observations including 1) evidence of increased probability of asbestos-fed animals to develop colon lesions in general; 2) evidence of a special type of mesothelioma in rats fed asbestos; 3) evidence for a cell regulator defect (lowered cAMP levels) in colon tissues of animals fed asbestos; and 4) evidence for asbestos fiber penetration of the colonic mucosa (e.m. studies) suggest that ingested asbestos is not inert in the colon.

If you found any of these excerpts interesting, please read the studies in their entirety. We all owe a debt of gratitude to these researchers.

Monty Wrobleski is the author of this article on

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