Yokkaichi Asthma: Health Effects of Air Pollutants in Japan

Yokkaichi asthma from the 1960s to the early 1980s involved the onset and exacerbation of asthma, chronic bronchitis, and chronic obstructive lung disease, which was attributed to sulfur dioxide (SO2). Inhaled SO2 easily dissolves in the epithelial lung lining fluid of the nose and upper airways and generates secondary reactive compounds, such as sulfurous acid and sulfuric acid. These derivatives increase the level of prostaglandin D2, inducing the constriction of airway smooth muscle, inflammatory responses, and oxidative stress. As a result, exposure to SO2 causes bronchoconstriction in asthmatic subjects and exacerbates asthma. Many epidemiological studies found that exposure to SO2 was associated with mortality and incidence of asthma and chronic obstructive pulmonary diseases for adult, and prevalence of persistent cough/phlegm, asthma-like attack for schoolchildren. These scientific evidences played an important role to support the causal relationship between ambient SO2 and chronic obstructive pulmonary disease in individual patients who filed a lawsuit against the petroleum industry group.