Background: Mt. Oyama, Miyakejima, began to erupt in June 2000, and the island was evacuated. Volcanic gas emissions, composed primarily of sulfur dioxide (SO2), gradually decreased, and residents returned to the island after the evacuation order was lifted in February 2005. Aims: In this study, the effects on residents' health from the exposure environment following lifting of the evacuation order in February 2005 were investigated first in February 2006 and then in each November from 2006 to 2011. The relationship between the amount of exposure to SO2 and the health effects was studied in adult Miyakejima residents. Methods: The subjects of this study were registered residents aged 18 and above at the time of each medical checkup. A total of 4,089 checkups were conducted. The mean values and percentage of 0.10 ppm or more hourly values were sought from 81 months of exposure concentration data. Health effects were evaluated through pulmonary function tests and the self-administered questionnaire. Results: There were significant differences in %FVC and %FEV1 observed in a comparison of pulmonary function by area. However, there was no significant difference observed in the same comparison over time. In the context of exposure concentration, a significantly higher proportion of persons with an increased frequency of cough and phlegm symptoms was observed in areas with an annual mean SO2 concentration of around 40 ppb or above when compared with residents in areas with a minimal exposure concentration. In addition, there was a significant increase in throat, nose, eye and skin symptoms in areas where the annual mean SO2 concentration exceeded about 10 ppb. Conclusions: Follow-up observation should be continued, with a focus on the relationship between the amount of exposure to SO2 and health effects.
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