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
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.
CDC. Follow-up on Mount St. Helens. MMWR 1980;29:263-4.
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.
Green FH, Vallyathan V, Mentnech MS, et al. Is volcanic ash a
pneumoconiosis risk? Nature 1981;293:216-7.
Vallyathan V, Mentnech MS, Stettler LE, Dollberg DD, Green FH.
Mount St. Helens' volcanic ash: hemolytic activity. Environ
Res
1983;30:349-60.
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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