Effects of volcanic activity on the mortality figures for respiratory diseases.

By concentric circles with radiuses of 10km, 20km and 30km centered on Mt. Sakurajima, 25 cities, towns, and villages in the area surrounding this volcano were classified into three regional groups on the basis of human settlements. Utilizing data from the vital statistics issued by the Kagoshima prefectural government, the mortality figures for selected respiratory diseases covering an 11-year period 1975 to 1985 were compared among these regional groups. Patterns for the year-by-year variation of the age-adjusted mortality rates for these respiratory diseases were also examined in relation to some of the air pollution indices for correlation with the volcanic activity of Mt. Sakurajima. Results were as follows:1) In the regional groups within 20km of Mt. Sakurajima, the observed number of deaths from bronchitis significantly exceeded the expected one for the standard population, and a clear declining gradient in the SMR (standardized mortality ratio) was observed with increased distance from this volcano. On a year-by-year basis for the 11-year period, the positive correlation coefficient obtained between the age-adjusted mortality rate and the atmospheric concentration of sulfur dioxide was statistically significant.2) For asthma, the observed number of deaths was not significantly different from the expected one in the two regional groups within 20km of Mt. Sakurajima, but it exceeded the expected one in another regional group, 20km to 30km from the volcano. On a year-by-year basis, the age-adjusted rate for mortality due to asthma did not correlate with any of the air pollution indices for the volcanic activity of Mt. Sakurajima.3) For emphysema, the observed number of deaths exceeded the expected one in the study area as a whole but no evidence for increased or decreased mortality was found in association with the distance from Mt. Sakurajima.4) The observed number of deaths from pneumonia significantly exceeded the expected one in the regional group within 10km of Mt. Sakurajima. On a year-by-year basis, the age-adjusted mortality rate for pneumonia correlated with the number of eruptions of this volcano but correlated inversely with the atmospheric concentrations of sulfur dioxide and total suspended particles.5) For acute bronchitis, no differences between the observed and expected numbers of deaths were found in any of the three regional groups but its age-adjusted mortality rate correlated with the atmospheric concentration of sulfur dioxide on a year-by-year basis.From the above, it is considered possible that volcanic air pollution may have a causal association with the mortality figure for bronchitis but not with those for other respiratory diseases.