Effects of SO₂ on respiratory system of adult miyakejima resident 2 years after returning to the Island

Background: Mt. Oyama in Miyakejima Island erupted in June, 2000. All Miyake villagers were forced to evacuate from the island in September, 2000, due to continuous eruptions and emissions of unsafe amounts of volcanic gas, mainly SO₂. From February, 2005, Miyake villagers returned to the island despite volcanic gas still being emitted. Objectives: This study examines the 2-yr changes in Miyake residents' respiratory systems from autumn 2004 to November 2006. Methods: The study population was 823 Miyake adult residents who participated in the health check-up in 2006. Respiratory effects were evaluated by a questionnaire for respiratory symptoms and spirometry. SO₂ has been continuously monitored at 7 sampling points of the inhabited area. The mean SO₂ concentration from February 2005 to November 2006 was 0.031 ppm. The area was categorized into 4 areas by SO₂ concentration, namely, areas L, H-1, H-2 and H-3, where average SO₂ concentrations were 0.019, 0.026, 0.032, and 0.045 ppm, respectively. Results: The study subjects showed no deterioration in lung function. Prevalence of cough and phlegm among all participants were significantly higher in 2006 than in 2004, and age-, sex- and smoking-adjusted odds ratios of cough and phlegm were 1.75 (95%CI 1.33- 2.30) and 1.44 (1.12-1.87). Prevalence of chronic bronchitis-like symptoms among normosusceptive subjects in 2006 was 4.1% which was significantly higher than that of 2.1% in 2004 (p=0.035). Compared to area L, the frequencies of phlegm and irritation of the nose were significantly increased in areas H-2 and H-3. Conclusion: SO₂ exposure-related respiratory symptoms were observed in adult Miyakejima residents after returning to the island.