Influence of sulfur dioxide on the respiratory system of Miyakejima adult residents 6 years after returning to the island

BACKGROUND: Mount Oyama, on the Japanese island of Miyakejima, began erupting in June 2000, necessitating the evacuation of 3,000 island residents. Volcanic gas emissions, primarily consisting of sulfur dioxide (SO(2)), gradually decreased and residents returned to the island after the evacuation order was lifted in February 2005. OBJECTIVES: To assess the exposure-effect and exposure-response relationships between SO(2) exposure and effects on respiratory system in adult Miyakejima residents. METHOD: Health checkups focusing on pulmonary function and respiratory/irritative symptoms were conducted six times every November from 2006 to 2011. The study population comprised 168 subjects who underwent all health checkups. SO(2) concentrations were measured at six fixed monitoring stations in inhabitable areas. RESULT: Based on the annual mean SO(2) concentration, inhabitable areas were classified into three categories; namely, lower (L), higher (H-1), and highest (H-2) areas. Average SO(2) concentrations (ppb) during 3 months prior to each health checkup dropped from 11.3 to 3.29, 32.2 to 13.4 and 75.1 to 12.6 from 2006 to 2010/2011 in L, H-1, and H-2. No significant declines in pulmonary function were observed in all areas. However, prevalence of subjective symptoms such as "Cough," "Irritation and/or pain in throat," "Irritation, runny nose, and/or nasal sniffles," and "Irritation and/or pain in the eyes," dependently increased on SO(2) concentration. Odds ratios were statistically significant at approximately 70 ppb of SO(2) or above. CONCLUSION: Adult residents of Miyakejima island showed no deterioration in pulmonary function at SO(2) levels, but complained of respiratory/irritative symptoms in an SO(2) concentration-dependent manner.