The causative relationship between asbestos exposure and mesothelioma has been clearly established for almost a century. While scientists are still working out the precise biological mechanisms responsible for the development of the malignancy, there is no question that workers who’ve been exposed to asbestos are candidates for pleural mesothelioma, peritoneal mesothelioma or the rarer forms of the disease. Even as no safe exposure limit has been established, studies have shown that workers with a significant lung burden of asbestos fibers are more likely to be diagnosed with mesothelioma than are others workers. This means that workers from industries which featured greater uses of the mineral have an elevated risk for disease development as well.

One such industry that has been investigated for the risk that employment posed to its workers is the field of automotive brake mechanics. Vehicle brakes featured a significant amount of asbestos and workers in the field have definitely developed mesothelioma. However, the issue of general causation due to work exposure has become controversial due to the publication of some recent studies that have raised questions regarding the exposure that individual mechanics had to asbestos dust. These studies indicated that the sample of brake workers they investigated did not show higher lung burden counts than a control sample of workers who did not have occupational exposure to asbestos. Thus, these studies concluded that brake mechanics were no more likely to develop mesothelioma than were those other workers.

However, an article has recently been published in the Annals of Occupational Hygiene that calls these studies and their conclusions into question. The author, Murray M. Finkelstein of the Mount Sinai Hospital in Toronto, Canada, has identified a number of methodological problems in the previous studies that limit their conclusions. Mr. Finkelstein has deployed a statistical apparatus that overcomes these methodological problems and he has concluded that brake mechanics are more likely to develop an asbestos-related disease, such as mesothelioma, because of their occupational exposures to asbestos.

Overview of the Article

The author quotes two articles published in 2004 that individually concluded that brake mechanics were not of a higher risk for developing mesothelioma due to their occupational exposures to asbestos. He then identified the common sources of data between the two articles, which included a comparative analysis of asbestos fiber burden between 10 brake mechanics who developed mesothelioma and 19 control subjects who did not work in asbestos-exposed occupations. The analysis conducted by the original researchers indicated that the brake mechanics in their study did not have a significantly higher burden of asbestos fibers in their lungs when compared to workers from fields without occupational asbestos exposure, so it was concluded that brake mechanics are not more likely to develop asbestos-related illness because of their exposures.

It is at this interpretation of the original researchers’ data that the author’s article is directed at.

The author’s analysis and interpretation of the data is based on the same published dataset as the previous articles. In his analysis of their methods, he concluded that a different statistical apparatus was necessary for a proper investigation of the question, so his study is based on a combination of methods that each parsed the data in specific ways. It is through the analysis of these individual methods that he draws his conclusions from.

His study specifically compared the counts and distributions of two different asbestos fiber types, chrysotile and tremolite, in the lungs of the control and case groups. Along with the general carcinogenicity of asbestos, the incidence rate of mesothelioma, and other asbestos-related diseases, increases based on the type of asbestos fiber that a person has been exposed to. There are two main classes of asbestos fibers and the fibers identified in this study are representative of each class: tremolite is an amphibole fiber, while chrysotile is a serpentine fiber. The individual classes are distinguished by their shape and structure. Amphibole fibers have a needle-like shape and a rigid structure that make them quite durable. Once amphibole fibers lodge into a person’s tissue structures, they are very difficult for the body to remove. Serpentine fibers have a curved shape (hence their name) and are more pliable than the amphiboles, which means they are slightly easier for the body to breakdown. Even though both fiber classes have been shown to be carcinogenic, the amphibole fibers are known to be more dangerous than the serpentine fibers.

Conclusion

When the author compared the datasets using the modified statistical apparatus, he found that brake workers did, in fact, have a higher general concentration of these fibers than did the control group. More importantly though, he found that they had significantly higher count of tremolite fibers, which means they would be even more at risk for mesothelioma than if they “only” had a higher count of the chrysotile fibers.

Labels: asbestos