In Libby, Montana, historical occupational exposures to asbestos fibers were as high as 130 fibers/cc; the current occupational permissible exposure limit (PEL) is 0.1 fibers/cc. Exposure to these asbestos fibers among Libby-area workers and residents has been conclusively linked to the development of asbestos-related diseases (ARD). These diseases include asbestosis, bronchogenic carcinoma, mesothelioma and pleural plaque fibrosis of the pleural lining. Pleural plaques, caused by scarring of the pleural lining, are indicative of asbestos exposure, but usually do not confer physiologic compromise. Asbestosis is defined as bilateral diffuse interstitial fibrosis of the lungs due to inhalation of asbestos fibers (American Thoracic Society 1986). Patients with asbestosis present with shortness of breath and a dry cough, and pulmonary function tests consistent with a restrictive defect and reduced oxygen-diffusing capacity. Typical radiographic findings include evidence of interstitial fibrosis, with the disease most severe at the lung bases, often accompanied by pleural plaques. These findings of lung fibrosis are not specific, and can be seen in interstitial fibrosis from other causes. The occurrence of pleural disease and pulmonary fibrosis, as well as a history of asbestos exposure, leads to the diagnosis of asbestosis. In addition to fibrosis, the presence of asbestos bodies (asbestos fibers coated with protein by the lung) in microscopic sections of the lung is definitive (though not required) for the diagnosis of asbestosis (Hinson 1973; Craighead, Abraham et al. 1982).
Malignant mesothelioma is a rare tumor of the mesothelial lining of the pleural and peritoneal spaces that is almost exclusively associated with asbestos exposure (Knudson 1995). Mesotheliomas often present with recurrent serous effusions that are sent for cytological examination. The disease is more common now than it was in the past, and while the incidence before was due to occupational asbestos exposure, the increase in incidence over the last ten years has more often been associated with secondary industry and environmental asbestos exposure (Whitaker 2000). Asbestos exposure combined with cigarette smoking results in a synergistically high incidence of bronchogenic lung cancer, but smoking does not appear to significantly increase the incidence of mesothelioma (Selikoff, Hammond et al. 1968). These illnesses typically have long latency periods (20-30 years) and in the case of asbestosis and mesothelioma, are considered to be incurable at this time.
In November of 1999, the Region 8, Environmental Protection Agency (EPA) and US Public Health Service offices, and the Agency for Toxic Substance Disease Registry (ATSDR) began community-wide testing in the Libby area. The EPA began testing for asbestos at the mine site, the loading sites, and the Libby expansion plant, homes, playgrounds and baseball fields. Data indicated hundreds of workers were exposed to asbestos and family members of the workers were exposed when the workers wore their contaminated clothes home. Others in the community were exposed to asbestos when they, as children, played in piles of vermiculite, or when they used it as a soil conditioner in their gardens or as insulation in their homes. Further, there is growing evidence that residents living in certain areas of Libby may have been exposed to dangerous ambient air concentrations of asbestos associated with mine operations that took place in and around the town.
Description of Health Problem:
The amphibole asbestos (actinolite-tremolite series) found in Libby has some unique physical characteristics. The fiber is a thin, long, rigid, "needle like" fiber that, once respired into the alveolar sacs of the lung, is retained. The fiber penetrates into the walls of these air sacks with migration of fibers to the pleural lining. An inflammatory process ensues, resulting in fibrosis of pleural tissues primarily, with a lesser amount of interstitial fibrosis. While health effects seen to date in the Libby area are characteristic of other asbestos exposure, they have been observed to have predominantly affected the pleural lining, causing a progressive fibrosis in a significant number of people. As fibrosis progresses, it leads to restriction of the lungs from normal expansion, resulting in respiratory and cardiac failure in a significant number of those with asbestos related changes. There tends to be a latency of approximately 20-30 years before fibrosis presents clinically.
In individuals with asbestos-related changes, the risk of bronchogenic cancer rises to 5-10 times that of a non-exposed, nonsmoking population. The National Cancer Institute indicates that if a person has asbestos-related disease, and smokes, the risk of lung cancer goes up 90 times. Unfortunately, there has been a high incidence of smoking in Libby's asbestos-exposed population, and significant numbers of lung cancers. Data from the Montana Department of Public Health and Human Services, Bureau of Vital Statistics show that deaths from respiratory neoplasm between 1979 and 1990 represented 7.20% of total deaths, 2% higher than for other Montana counties. An additional risk for those with asbestos related disease is the occurrence of malignant mesothelioma. This frequency of mesothelioma per capita, in Libby, is considered unusually high.
American Thoracic Society, Diagnosis of nonmalignant diseases related to asbestos. Am Rev Respir Dis, 1986. 134: p. 363-368.
Hinson, K.F.W., Otto, H., Webster, I., Rossiter, C.E., Criteria for the diagnosis and grading of asbestosis., in Biological effects of asbestos, J.C. Gilson, Timbress, V., Wagner, J.C., Eds. 1973, Pergamon Press: Oxford. p. 54-57.
Craighead, J.E., et al., The pathology of asbestos-associated diseases of the lungs and pleural cavities: diagnostic criteria and proposed grading schema. Report of the Pneumoconiosis Committee of the College of American Pathologists and the National Institute for Occupational Safety and Health. Arch Pathol Lab Med, 1982. 106(11): p. 544-96.
Knudson, A., Asbestos and mesothelioma: genetic lessons from a tragedy. Proc Natl Acad Sci U S A, 1995. 92(24): p. 10819-20.
Whitaker, D., The cytology of malignant mesothelioma. Cytopathology, 2000. 11(3): p. 139-51.
Selikoff, I.J., E.C. Hammond, and J. Churg, Asbestos exposure, smoking, and neoplasia. JAMA, 1968. 204(2): p. 106-12.
Photos courtesy of Dudley Dana, Dana Gallery