br We restricted the mortality
We restricted the mortality analysis timeframe to 2001–2011, which reduced the total number of deaths from 847 deaths, confirmed through death records search (1988–2011), to 526 deaths. We confirmed through death records that one mesothelioma, one cancer of the pleura, and two asbestosis deaths occurred prior to 2001. Excluding deaths prior to 2001 from the analysis removed older, long-term residents and former WM/WRG workers from our study population and may have caused an underestimation of the death rates. This exclusion was ne-cessary to eliminate possible recall and ascertainment bias due to the enrollment of deceased persons by proxy interviews with relatives
f/cc, fibers per cubic centimeter. ICD, International Classification of Diseases. SMR, Standard mortality ratios.
∗Statistically significant. aNatural log of asbestos exposure in f/cc x month. bCut points are based on the 50th and 75th percentile of those with a calculated total exposure metric (N = 5161). cFollow-up period 2001–2011.
living in the study area in 2001. It also eliminates the limitations of using ICD-9 to identify mesothelioma deaths; the ICD-10 coding system has a unique code for mesothelioma beginning in 1999.
Since mesothelioma is a rare cancer, the number of cases in this analysis are very small with seven incident cases between 1988 and 2010 and four deaths from 2001 to 2011. Whitehouse and colleagues reported on nine mesothelioma cases from Libby in non-occupationally exposed people, appearing to have resulted from exposure to con-tamination of the PD98059 (Whitehouse et al., 2008). The authors note that this number is likely an undercount given out-migration of the community and the long latency of the disease delaying the peak of the epidemic. Similarly, there is a need for continued public health sur-veillance to fully assess the impact of this historical exposure in Min-neapolis, since processing operations ceased in 1989 and community and site remediation was not completed until 2002. Continued follow-up via linkage with the state cancer registry is likely to identify newly diagnosed cases of respiratory cancers associated with this exposure. Given the recent findings of pleural changes and pulmonary deficits associated with low-level occupational exposure to Libby asbestos in a 30-year follow up (Lockey et al., 2015), repeat clinical follow-up for pulmonary deficits among NMCVI participants with prior radiographic evidence of exposure (Alexander et al., 2012) is also recommended to further our understanding of these latent effects.
Finally, there are important implications for ongoing public health practice suggested by these findings. Among the many uses for Libby vermiculite was as attic insulation, a product known commercially as Zonolite. While it is not known how many homes in the U.S. have vermiculite attic insulation, one estimate suggested up to 35 million homes (Loushin, 2010). When disturbed through remodeling, or other activities, this and other residential sources of asbestos exposure, re-presents ongoing health risks (Noonan, 2017; Spear et al., 2012). These ongoing exposures in homes may account for the observation that mesothelioma rates have not declined among females in the U.S. as they have among males (reflecting reduced workplace exposures). In fact, among white females, there was a statistically significant average an-nual increase of 0.6% in the rate of mesothelioma between 1975 and 2015 in the U.S. (U.S. National Cancer Institute (NCI) SEER Program).
In 2001, the U.S. EPA began a program for removal of vermiculite insulation from homes in Libby, Montana. This was based, in part, on a determination of imminent and substantial endangerment from as-bestos contaminated source materials in residential and commercial areas of Libby. As part of a 2014 settlement of a nationwide class action lawsuit, W.R. Grace, has more recently established the Zonolite Attic Insulation Trust, a fund for reimbursing costs to remove Zonolite brand vermiculite insulation from homes and commercial properties (Zonolite Attic Insulation Trust, 2014).
Mounting evidence of the health impacts of Libby asbestos in ex-posed communities such as Libby, Montana and Northeast Minneapolis, MN, makes a case for active intervention by public health practitioners to educate the public and promote safe removal of vermiculite attic insulation by asbestos abatement contractors in all communities.
Our analysis provides further evidence that low-dose community exposure to Libby amphibole asbestos from a neighborhood vermiculite processing plant is associated with increased asbestos-related disease and mortality. Even when accounting for possible occupational asbestos exposure, we observed significant excess mesothelioma and lung cancer deaths in females. Lung cancer incidence was significantly elevated in both genders, even after adjusting for an overall cancer deficit, and deaths from all respiratory cancers combined were elevated in both genders.