Research Confirms that Indirect and Intermittent Exposure to Asbestos Increases Risk of Mesothelioma

Posted by Janice Pennington

An eighteen-year study by some of the nation’s foremost experts on asbestos disease has confirmed that workers who are exposed to asbestos indirectly and intermittently are at a significantly increased risk for developing mesothelioma and cancers of the pleura (the lining of the lung). The results of the study by Dr. John Dement, of Duke University, and other scientists were recently published in the prestigious American Journal of Industrial Medicine.

The article was based on an asbestos disease screening program initiated by the Sheet Metal Health Occupational Institute Trust, which was formed in 1985 to study the health hazards to U.S. and Canadian sheet metal workers. Over 17,000 sheet metal workers with over 20 years in the trade were followed by researchers from 1986 to 2004 to determine the workers’ cause of death and other vital statistics. Sheet metal workers are known to experience significant exposure to asbestos in their work, even though they do not work with asbestos directly and are not exposed on an everyday basis. Sheet metal tradesmen traditionally work in the construction, railroad and shipbuilding industries. The workers make industrial metal products such as air conditioning units, refrigerators, ventilation systems, metal roofing and facades. Fabricating the metal itself involves no exposure to asbestos, but sheet metal tradesmen often encountered the dangerous substance while working on industrial sites in close proximity to insulators, in areas that were being sprayed with asbestos fireproofing material, or when renovating ventilation systems that previously had been insulated with asbestos. The spraying of asbestos insulation was banned in 1973 because it released such high levels of asbestos. Still, sheet metal workers may be exposed to asbestos today when working on older ventilation systems previously insulated with asbestos.

Dr. Dement’s study analyzed the sheet metal workers’ chest X-ray results according to International Labour Office criteria, their smoking history and other vital information. The scientists also analyzed the cause of death for workers who died during the eighteen-year period of the study.

The investigation revealed that the participating sheet metal workers had a significantly reduced mortality rate for several types of disease such as diabetes, heart disease and alcoholism. Plus, there was no overall increased risk for cancer generally. There was, however, a significant increase in the rates of mesothelioma, pleural cancer and asbestosis over the general population. In addition, the risk for mesothelioma and pleural cancer was increased even when the workers’ chest X-rays did not demonstrate the presence of asbestosis. The study confirmed that workers whose exposure to asbestos was indirect and intermittent are at an increased risk for asbestos disease, including mesothelioma.

This important research leaves no doubt that the dangers of asbestos exposure are not limited to those who worked directly with asbestos or were exposed to it every day. What is true for the sheet metal workers studied by Dr. Dement and his colleagues is undoubtedly true for other workers and workers’ family members as well.

The entire study is published at: Dement J, et al., Mortality among sheet metal workers participating in a medical screening program. Am. J. Ind. Med. 2009 Aug;52(8):603-13.

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