In nearly every asbestos trial, the plaintiffs’ experts will invariably compare asbestos exposure levels from defendants’ products to airborne concentrations of asbestos in the ambient air. The apparent purpose of such a comparison is to provide a bare semblance of quantitative rigor to otherwise unsupported causation opinions. However, such an argument depends in part on taking a position that the risk from exposure to ambient asbestos levels caries some minute, but unquantifiable, level of risk. The plaintiffs’ experts correctly note that because every living human being has been exposed to some amount of asbestos from ambient asbestos, there is no entirely unexposed control population. However, they are incorrect that this need be the end of the discussion about quantifying the risk posed from ambient exposures. In an ambitious first-of-its-kind study by Glynn et al., the health outcomes of millions of Americans residing in rural and urban environments have been statistically analyzed to demonstrate a lack of observed risk from ambient exposure in urban environments by using rural populations, whose exposure levels were one or more orders of magnitude lower than city dwellers, as the controls. This important finding will make it increasingly difficult for the plaintiffs’ experts to rely on ambient background exposures as a quantitative point of reference for their causation opinions.
Relying on Surveillance, Epidemiology and End Results (SEER) data from 1973-2012, Glynn and colleagues statistically analyzed various urban and rural regions in the United States over time. The paper broke down urban and rural populations by utilizing the Rural-Urban Continuum Code (RUUC) previously developed by the U.S. Department of Agriculture. For female incident rates, the paper cited 1380 cases of pleural mesothelioma reported to SEER from 1973-2010. Notably, as would be expected if there was no detectable increase in risk from ambient exposures, there was no “clear trend” in annual urban rates for females compared to rural incident rates. In fact, the paper noted that for 19 of the 40 years reviewed, urban rates were actually lower than the rural rates for women.
Urban male incident rates were greater than rural incident rates, which came as no surprise due to an increased chance that males would experience occupational exposure at worksites found only in urban environments, such as shipyards. Accordingly, the urban rates were “elevated” over rural rates 39 out of 40 years.
The paper has garnered an interesting letter to the editor by Dr. Murray Finkelstein, who regularly testifies on behalf of the plaintiffs in asbestos litigation. He has proposed a hypothesis that female usage of cosmetic talc products could have carried a level of risk, which may have drowned out the otherwise detectable risk from ambient exposure levels. However, a comprehensive response from the authors amply demonstrated various reasons for why such a hypothesis is implausible.
You can obtain a copy of the paper by Glynn et al. here, and the related letter to the editor and the response, here and here. You are also invited to share your thoughts in the comments section.