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Epidemiologic Notes and Reports Cytotoxicity of Volcanic Ash: Assessing the Risk for Pneumoconiosis

The recent eruptions of the Mount Augustine volcano in Alaska, which began March 27, 1986, have again raised concerns about the possible adverse health effects of exposure to volcanic dusts (1). Following similar eruptions at Mount St. Helens in Washington State, beginning May 18, 1980 (2); El Chichon, south of Mexico City, Mexico, March 29, 1982; and Galunggung in West Java, Indonesia, May 5, 1983, immediate, acute, and nonspecific irritant effects were reported in the eyes and upper airways of persons exposed to volcanic dusts over wide geographic areas. Moreover, repeated exposures to high concentrations of volcanic ash can pose a potential risk for the development of pneumoconiosis, especially if the particle-size distribution of volcanic ash includes an appreciable proportion of respirable-sized particles ( less than or equal to 10 um in median mass aerodynamic diameter (MMAD)) which contain the toxic mineral, free crystalline silica (SiO((2))). Because such exposures may involve workers who are regularly employed outdoors, as well as workers specifically assigned to clean up after volcanic eruptions, the National Institute for Occupational Safety and Health (NIOSH) has conducted laboratory-based studies to provide indices of the cytotoxicity and fibrogenicity of various substances possibly present in volcanic ash. These indirect evaluations indicated that certain respirable fractions of volcanic ash were moderately cytotoxic in vitro and mildly fibrogenic in vivo (3-6).

To determine whether these results are representative of other types of volcanic ash, NIOSH compared the cytotoxicity of samples from the eruptions of Mount St. Helens, El Chichon, and Galunggung with those of a mineral of known cytotoxicity, quartz, and a relatively inert mineral, barite. Assays for cytotoxicity were based on the hemolysis of the red cells of sheep and the release of the enzymes, lactate dehydrogenase, B-N-acetylglucosaminidase, and B-glucuronidase, from alveolar macrophages (Table 3). The ash samples were all similar in quartz content and elemental composition. However, the sample of volcanic ash from Galunggung was significantly more cytotoxic than the other ash samples and approximated the cytotoxicity of quartz. The samples of volcanic ash from Mount St. Helens and El Chichon had cytotoxicities about midway between those of quartz and barite. Differences in the cytotoxicities of volcanic ash were related more to differences in the particle-size distributions in each ash sample than to differences in minerologic composition; those samples having the greater proportions of small particles (i.e., more surface area per given weight of ash sample) exhibited more cytotoxic activity. Reported by University of West Virginia, Morgantown; Pathology Section, Laboratory Investigations Br, Div of Respiratory Disease Studies, Applied Biology and Physics Br, Div of Behavioral and Biomedical Science, National Institute for Occupational Safety and Health, CDC.

Editorial Note

Editorial Note: Exposure to airborne mineral dusts has been associated with the subsequent development of chronic bronchitis (mucous hypersecretion or obstructive-airways disease) and/or pneumoconiosis in humans. Pulmonary fibrosis usually results from cumulative exposure to dust, and may not become manifest until several decades after initial exposure. The type and severity of disease resulting from exposure to mineral dusts depends to a large extent on the size, shape, surface characteristics, chemistry, and crystallinity of the dust particles.

Several methods have been developed to measure the cytotoxicity of mineral dusts in vitro. The two methods reported here use the hemolysis of bovine red cells and the release of lysosomal enzymes from alveolar macrophages as end points. Although many minerals show good correlation between the values obtained in these tests and in vivo fibrogenicity, the occurrence of false-positive and false-negative results may weaken the predictive value of the tests. Further study is needed to determine the causes of these discrepancies and the exact relationship between cytotoxicity and fibrogenicity.

Volcanic ash is a good example of an environmental hazard with unknown potential to cause pneumoconiosis in human populations (1). The results of these studies show that ash from all three volcanoes was cytotoxic in vitro, and exposure studies conducted in animals indicate that volcanic ash is mildly fibrogenic in vivo (1,5). However, the results of a 5-year longitudinal follow-up of loggers exposed to volcanic ash from Mount St. Helens suggest that risks of chronic bronchitis or pneumoconiosis are probably negligible in humans under the usual conditions of such occupational exposure, i.e., initially high and decreasing over time. Following an explosive volcanic eruption, with significant potential for chronic human exposure to volcanic ash, it would be appropriate to evaluate the size distribution of the sedimented ash and the percentage of free crystalline silica in the respirable-sized ash particles. Based on such an evaluation and a consideration of the intensity, frequency, and duration of exposure, it would be possible to provide appropriate advice to occupational and community groups about the need for limiting or avoiding exposures.

References

  1. Buist AS, Bernstein RS. Health effects of volcanoes: an approach to evaluating the health effects of an environmental hazard. Am J Public Health 1986;76(suppl):1-90.

  2. CDC. Follow-up on Mount St. Helens. MMWR 1980;29:263-4.

  3. Green FH, Bowman L, Castranova V, et al. Health implications of the Mount St. Helens eruption: laboratory investigation. Ann Occupational Hyg 1982;26:921-33.

  4. Green FH, Vallyathan V, Mentnech MS, et al. Is volcanic ash a pneumoconiosis risk? Nature 1981;293:216-7.

  5. Vallyathan V, Mentnech MS, Stettler LE, Dollberg DD, Green FH. Mount St. Helens' volcanic ash: hemolytic activity. Environ Res 1983;30:349-60.

  6. Vallyathan V, Mentnech MS, Tucker JH, Green FH. Pulmonary response to Mount St. Helens' volcanic ash. Environ Res 1983;30:361-71.



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