Possible synergism of exposure to airborne manganese and smoking habit in occurrence of respiratory symptoms.

The possible combined action of manganese exposure and smoking on the rate of respiratory symptoms was studied in three groups of male workers at various levels of exposure to manganese: occupational exposure (369 workers), relatively high ambient exposure (190 workers) and low ambient exposure (204 workers). The study was carried out by means of the standard epidemiological method. Between non-smokers in the different groups there was no difference in the prevalence of respiratory symptoms. In smokers the prevalence was significantly higher in workers occupationally exposed to manganese than in those with a low ambient exposure. The tendency of the prevalence of respiratory symptoms to increase with the extent of the smoking habit was also most pronounced in the groups of occupationally exposed workers. Since other relevant factors under control in the compared groups were more or less uniform, the results indicate that managanese exposure and smoking might have a possible synergistic effect on the occurrence and rate of respiratory symptoms.