Effects of sulfur dioxide on fractional exhaled nitric oxide concentration in the child residents of Miyakejima Island

The island of Miyakejima in Japan is subject to ongoing emissions of volcanic gases, including high concentrations of sulfur dioxide (SO₂). Annual health checkups on the island, therefore, include the examination of respiratory system parameters. Here, we aimed to investigate the relationship between SO₂ exposure and fractional exhaled nitric oxide (FeNO) concentration among children who received health checkups from 2008 to 2014. The subjects were 83 and 31 second-year junior high school students aged 13-14 years who resided on Miyakejima island and an SO₂-free reference island, respectively. SO₂ concentration in the air was measured at 6 fixed-point monitoring stations. FeNO was examined according to the American Thoracic Society guideline and European Respiratory Society recommendations for standardized procedures. Average concentrations of SO₂ on Miyakejima over a period of 3 months prior to each health checkup from 2008 to 2014 were 22.2, 20.6, 8.9, 10.5, 10.7, 4.4 and 8.0 ppb, respectively. Among the Miyakejima students, geometric mean (GM) FeNO concentrations measured at each health checkup from 2008 to 2014 were 28.2, 18.2, 23.6, 35.5, 36.9, 28.1, and 32.1 ppb. The GM FeNO concentration measured from all Miyakejima students across the study period was 28.3 ppb. No clear dose-response relationship was observed. The GM FeNO concentration among the students from the reference island was 27.7 ppb in 2017. No significant difference was observed between the two populations, even when the data was stratified by sex and sensitivity. There was no clear significant difference in GM of FeNO concentration between Miyakejima and control students, when the average concentration of SO₂ over a period of 3 months was 22 ppb or less.