[Effects of volcanic sulfur dioxide on reconstruction workers and residents returning to Miyake Island]

Four and half years have passed since Mt. Oyama in Miyake Island erupted. Ambient sulfur dioxide (SO2) is still above the environmental air standard in parts of the island, even though emission of the volcanic gas has diminished. Reconstruction of life-support infrastructure in the island and safety measures started in July 2002, and a short-term trial stay project for former residents was completed in April 2003 for the total rehabilitation of the island. We conducted health examinations, and questionnaires on clinical symptoms among the reconstruction workers in January 2003, as well as questionnaires on respiratory symptoms among former residents who joined the trial stay, in late fall of 2003. The peak expiratory flow rate and symptoms of the workers and the symptoms of the short-term residents were not correlated to SO2 concentrations. In addition, we investigated the medical histories of outpatients at Miyake-mura National Insurance Center Clinic. We could not recognize any cases directly connected with higher ambient SO2 concentration in the area of the island, but there was a male worker, in his thirties, who suffered an initial attack of bronchial asthma, which required intensive care and treatment. As a general rule, all the workers and the residents are asked to wear gas masks for SO2 when its concentration is above 2.0 ppm and to stay in the house with desulfuration facilities as a precautionary measure at night. The residents are now well informed about the risks of volcanic gas and preventive measures for adverse health effects. We could not evaluate correlations between SO2 exposure indices and health effects sufficiently due to the limitation of the field study, but this study presents useful pieces of information as a risk communication for reconstruction workers and former inhabitants to the island.