Effects of sulfur dioxide on the respiratory system of Miyakejima child residents 6 years after returning to the island.

Objectives: This study investigated the health effects of volcanic gas, mainly sulfur dioxide (SO2), exposure on the children of Miyakejima Island.

Methods: Health checkups were conducted in November from 2006 to 2011. Health effects were evaluated through a self-administered questionnaire on respiratory and irritative symptoms, and spirometry. SO2 was measured continuously from February 2005 onward at six fixed monitoring stations in inhabitable areas. Based on mean SO2 concentration during 3 months before each health checkup, inhabitable areas were classified into three categories: (1) lower (area L); (2) higher (area H-1); and (3) highest (area H-2).

Results: Average concentrations (ppb) of SO2 decreased year-by-year and ranged from 11.3 to 2.47 in area L, from 32.2 to 12.2 in area H-1, and from 75.1 to 12.1 in area H-2, respectively. In general, prevalence of respiratory and irritative symptoms was higher in area H-2, and the prevalence decreased year-by-year in all three areas by Cochran-Armitage test for trend. We defined a study population in area L in 2008 as a reference population because we had no unexposed population. Applying a logistic regression model, age-, sex-, and hypersusceptibility-adjusted prevalence odds ratios to the reference population showed clear exposure-dependent increases in some irritative symptoms such as "Irritation and/or pain in throat" and "in eyes," and approximately 30 ppb seemed to be the threshold concentration. Spirometry did not show any significant differences.

Conclusions: Though no pulmonary functions were affected, some subjective symptoms were detected dose-dependently by SO2 exposure concentration in child residents during the 6 years after the eruption.