Volcanic sulfur dioxide and acute respiratory symptoms on Miyakejima island

Objectives: Following a volcanic eruption in 2000, high concentrations of ambient sulfur dioxide (SO₂) are still observed on Miyakejima, Japan despite the reversal 2 years ago of the ban on residents living on the island. This study examines the association between current levels of volcanic SO ₂ and the incidence of acute subjective symptoms in volunteers on Miyakejima. Methods: The authors conducted a follow-up study on 611 healthy volunteers, on a person-hour basis (28 413 person-hours), who visited the island to provide support to residents from February to July 2005. Adverse health symptoms were measured by self-administered diary and exposure was approximated using monitoring data across 14 sites. Associations between incidence rates and increasing SO₂ levels (reference (the lowest), very low, low, middle and high) were examined using Poisson regression. Results: Hourly incidence of cough, scratchy throat, sore throat and breathlessness showed clear exposureresponse relationships with SO₂ concentrations. There were statistically significant risks of those symptoms at relatively low SO ₂ levels. Thus, rate ratios in the 0.6-2.0 ppm exposure band (vs <0.01 ppm) were: for cough, 3.4 (95% Cl 1.8 to 6.6) in men and 9.8 (3.9 to 24.9) in women; for sore throat, 3.2 (1.7 to 6.2) in men and 5.8 (2.0 to 16.5) in women; and for breathlessness, 10.5 (4.2 to 26.6) in men and 18.5 (4.6 to 74.3) in women. Little evidence of SO₂ effects on sputum and nasal discharge/congestion was observed in this study. Eye and skin irritations showed inconsistent results between hourly maximal and hourly mean SO₂ concentrations. Conclusion: The authors observed strong evidence of an exposure-response relationship between volcanic SO₂ and subjective acute respiratory symptoms among a healthy population on Miyakejima. The results are consistent with reports that females and non-smokers are more sensitive to irritant gas than males and smokers, respectively.