Background: Mt. Oyama on Miyakejima Island, Tokyo, erupted in June, 2000. All Miyake village citizens were forced to evacuate from the island in September, 2000, due to continuous eruptions and emissions of unsafe amounts of volcanic gas, mainly sulfur dioxide (SO2). Beginning in February, 2005, citizens began to return to live on the island despite the fact that volcanic gas was still being emitted. Aims: In this study, the health effects of exposure to the environment on Miyakejima Island following the 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 health effects was studied in child residents of Miyakejima.Methods: The subjects of this study were registered residents of Miyakejima aged 17 or under at the time of each medical check-up. A total of 1,005 check-ups were conducted. The mean values and the percentage of hourly values that were 0.10 ppm or more were obtained from 81 months of exposure concentration data obtained from fixed-point monitoring. Health effects were evaluated through the self-administered ATS-DLS questionnaire. Results: A significantly higher proportion of persons with an increased frequency of "throat" symptoms was observed in areas with an annual mean SO2 concentration of 20.7 ppb or above when compared with residents in areas with a minimal exposure concentration. In addition, there was a significant increase in "cough", "eye" and "skin" symptoms in areas where the annual mean SO2 concentration exceeded 28.0 ppb. Conclusions: We observed minor health effects on the respiratory system due to 7-year exposure to SO2 on Miyakejima Island. Follow-up observation should be continued with a focus on the relationship between the amount of exposure to SO2 and health effects until the volcanic gas emissions have ceased.
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