The effect of exposure to SO₂ on the respiratory system of power-station workers

Sulfur dioxide (SO₂) is generally recognized as a respiratory irritant, but its effects if any at low levels of exposure are uncertain. We studied 38 power station technicians exposed to 0.8 ppm (parts per million) 8-h weighted levels of sulfur dioxide, and compared them to workers performing similar tasks without such exposure. Those exposed complained 5.8 times more frequently of cough (95% CI = 1.8-20.6, P < 0.001), and also had significantly more sputum production. There was also a trend for increasing prevalence of dyspnea. On the other hand there was no decrease in pulmonary function test values. In the eight exposed subjects who complained of dyspnea, there was a significant decrease in pulmonary flow values. We conclude that power station workers exposed to low levels of SO₂ have increased respiratory symptoms, and deserve compensation if their symptoms become chronic. The pulmonary function tests were not different from the control subjects, but there may be a small group who are prone to long-term morbidity. Additional studies are warranted to confirm our findings, and to define immediate and long-term morbidity due to low exposure to SO₂.