Follow-up pulmonary function studies in copper smelter workers

Sulfur dioxide, a respiratory irritant, is a common occupational exposure in non-ferrous smelters. Between 1973 and 1974 health and pulmonary function data were collected on 113 copper smelter workers and an accelerate loss of pulmonary function (forced expiratory volume in the first second [FEV1] associated with sulfur dioxide levels of 1 ppm or higher was reported. In the present study, 92 of these workers were relocated and 66 agreed to participate in a follow-up survey which used the same model spirometer and standardized pulmonary function technique employed in the original study. For the 66 subjects studied, pulmonary function test revealed 3 individual with moderate chronic obstructive pulmonary disease (COPD), 5 individual with mild COPD, and 58 individuals with normal spirometry. The mean forced vital capacity (FVC) was 99.6% per cent of predicted. The mean FEV1 was 93.5 per cent of predicted, significantly lower than expected (p<.001). This decrease was found to be significant only for those 41 subjects with a history of cigarette usage (p<.001). The mean FEV1 which had been predicted to decline at a rate of 56 cc per year based on 1973 to 1974 data actually increased by 1 cc per year between 1973 and 1980 (p<.01). The greatest improvement of FEV1 was noted in those individuals who had quite smoking since 1974. The study demonstrated that cigarette smoking is a major contributing factor in accelerated loss of pulmonary function. An effect attributable to low-level sulfur dioxide exposure could not be confirmed.