Lack of combined effects of exposure and smoking on respiratory health in aluminium potroom workers

Objective-To investigate the combined influence on respiratory health of sm oking and exposure in an aluminium potroom. Methods-In a cross sectional study of 75 potroom workers (23 never smokers, 38 current smokers, 14 ex-smokers) and 56 controls in the same plant (watc hmen, craftsmen, office workers, laboratory employees; 18 non-smokers, 21 c urrent smokers, 17 ex-smokers), prevalences of respiratory symptoms and spi rometric indices were compared. Results-Smokers in the potroom group had a lower prevalence of respiratory symptoms than never smokers or ex-smokers, which was significant for wheezi ng (2.6% v 17.4% and 28.6% respectively, both p<0.01), whereas respiratory symptoms in controls tended to be highest in smokers (NS). No effects of po troom work on the prevalence of respiratory symptoms could be detected. In potroom workers, impairment of lung function due to occupational exposure w as found only in non-smokers, with lower results for forced vital capacity (FVC) (98.8% predicted), forced expiratory volume in one second (FEV,) (96. 1% predicted) and peak expiratory flow (PEF) (80.2% predicted) compared wit h controls (114.2, 109.9, and 105.9% predicted; each p<0.001). Conversely, effects of smoking on lung function were only detectable in non-exposed con trols (current smokers v non-smokers: FVC 98.8% v 114.2% predicted; p<0.01; FEV, 95.5 v 109.9% predicted; p<0.05). Conclusions-In a cross sectional survey such as this, the effects of both s moking and occupational exposure on respiratory health may be masked in sub jects with both risk factors. This is probably due to strong selection proc esses which result in least susceptible subjects continuing to smoke and wo rking in an atmosphere with respiratory irritants.