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.