Ultrastructural study of the effect of air pollution by SO2 on the respiratory air-ways

Sulfur dioxide (SO₂) has been associated with excessive mortality during air pollution disasters such as that which occurred in Meuse Valley, Belgium in 1930, Donora Pennsylvania, in 1948and London in 1952. The SO₂ particulate complex results chiefly from the burning of fossil fuels. Exposure can cause irritant and toxic effects on the human airways and result in broncho- constriction. It also can aggravate existing pulmonary or cardiac problems. A positive interaction between particles and SO₂ to produce morphologic changes in airways has been suggested by smog incidents, but has not been evaluated by experiments. So, this study was done to answer the following questions: (1) What morphologic changes are produced by repeated injury to airway epithelial cells by SO₂? (2) What is the time course of these morphologic features? (3) Can a model of acute bronchitis be created which is not due to infection? Ultrastructural changes occurring in the epithelial cells lining the airways of the experimental rats were studied. A sequence of epithelial changes was seen with exposure to 100, 200 or 400 p.p.m. for up to 4 weeks. For example: loss of cilia, vacuolation, pyknosis, goblet cell hyperplasia and the development of stratified squamous epithelium after 2 to 7 days at 200 p.p.m Higher doses (400 p.p.m.) produced squamous cell metaplasia after 2 weeks. Exposure to 40 p.p.m. SO₂ alone for 4 hours per day for 6 weeks produced no changes, but 24 hours after a 4 hours exposure to 40 p.p.m. SO₂ plus 0.74 gm of carbon dust per cu.m. of air, neutrophils were recruited into airway epithelium. It is suggested that this synergistic effect is due to the carbon particles adsorbing SO₂, which leaches off slowly, perhaps within macrophages, to recruit Leucocytes in airways.