br In the U S Environmental Protection
2001). In 2001, the U.S. Environmental Protection Agency (EPA) in-vestigated the Minneapolis WM/WRG facility as part of a national evaluation of Libby vermiculite processing sites and found up to 95% amphibole asbestos in rock samples taken from nearby residences and on the site (Minnesota Department of Health, 2001). As an emergency action, the EPA identified and subsequently remediated 259 con-taminated residential properties, most located within a 1–2 mile radius of the processing plant.
The Minnesota Department of Health (MDH) assessed the extent of exposure to Libby amphibole asbestos (LAA) among residents and former WM/WRG workers after the discovery of widespread asbestos contamination in the neighborhood, anecdotal reports of health impacts among former workers, and published reports on the occurrence of
☆ This work was supported by the Centers for Disease Control and Prevention, Environmental Public Health Tracking Cooperative Agreement Grant 2U38EH000617. The findings and conclusions are solely those of the authors and do not necessarily reflect the views of the Centers for Disease Control and Prevention. This study was reviewed and approved by the Minnesota Department of Health IRB (#13-303). E-mail address: [email protected] (T. Konen).
asbestos-related diseases in the Libby population. The study, known as the Northeast Minneapolis Community Vermiculite Investigation (NMCVI), identified a cohort of over 6000 PepstatinA members and plant workers, living within a defined study area within one half mile of the facility and characterized the type and extent of community and occupational exposure for health monitoring (Kelly et al., 2006; Minnesota Department of Health, 2005). Combining individual ex-posure histories with available data on ore shipments, industrial hy-giene sampling, air emissions and dispersion modeling, and waste handling, the NMCVI estimated exposure concentrations and duration for several primary exposure pathways. The pathways included occu-pational exposure of former workers, cumulative ambient exposure of Libby asbestos from furnace stacks and fugitive dust emissions, children playing in vermiculite waste piles, and direct handling of vermiculite processing waste. While occupational exposures were the most severe, occasionally 100 times the current U.S. occupational standards, mod-eled airborne plant emissions indicated that the short-term air con-centrations of asbestos fibers in residential areas closest to the plant during processing may have exceeded current occupational standards (Kelly et al., 2006). For children playing in waste piles (see photo (Tillett, 2012)), exposures were estimated to exceed 1.0 fiber/cm3 (f/
cc) per event (Kelly et al., 2006; Minnesota Department of Health, 2005). Further analysis of exposure data showed that, for most mem-bers of the cohort, geometric mean cumulative ambient exposures (which averaged 0.02 fibers/cc x month) obtained from dispersion modeling were the largest source of exposure, while activity-based exposures were substantial contributors to the upper end (90th per-centile) of the distribution (Adgate et al., 2011).
While many types of asbestos have been associated with malignant and non-malignant lung diseases, studies show that amphibole asbestos may pose a greater risk of mesothelioma than commercially used chrysotile asbestos (Anderson et al., 2005; ATSDR, 2001; McDonald and McDonald, 1997; U.S. Environmental Protection Agency, 2014). Excess morbidity and mortality associated with occupational exposure to LAA has been reported among Libby vermiculite miners (Amandus et al., 1987; Amandus and Wheeler, 1987; Antao et al., 2012; McDonald et al., 1986a, 1986b; Sullivan, 2007). Non-occupational exposure in Libby community members has been associated with respiratory symptoms, the development of non-malignant radiographic abnormalities, pleural disease, and elevated mortality (ATSDR, 2002; Larson et al., 2012; Peipins et al., 2003; Vinikoor et al., 2010; Weill et al., 2011).
Although the Libby mine was the major domestic producer of ver-miculite prior to 1990 and shipped asbestos contaminated vermiculite ore to hundreds of processing facilities throughout the United States (U.S. Geological Survey), there is limited evidence of community health impacted by Libby asbestos from exposure in proximity to processing facilities outside of Libby, MT.
In a stratified sample of the NMCVI cohort, Alexander et al. (2012) evaluated chest radiographs for pleural abnormalities consistent with pneumoconiosis, excluding WM/WRG workers and household members of workers (Alexander et al., 2012). Pleural abnormalities represent the most common marker of exposure to asbestos (Myers, 2012) and are risk factors for pulmonary function deficits (Larson et al., 2012; Weill et al., 2011; Whitehouse, 2004). The prevalence of pleural abnormal-ities by B-reader consensus of 461 participant radiographs was 10.8%. A history of direct contact with the waste or playing in vermiculite piles was associated with having pleural abnormalities; however, long-term, ambient exposure in the community was even more strongly associated with pleural abnormalities (Alexander et al., 2012).