Increased risk of chronic obstructive pulmonary diseases in coke oven workers: interaction between occupational exposure and smoking.

BACKGROUND Coke oven workers are regularly exposed to coke oven emissions (COE) and may be at risk of developing lung diseases. There is limited evidence for the link between exposure to COE and chronic obstructive pulmonary diseases (COPD). The aim of this study was to explore the dose-response relationship between COE exposure and COPD and to assess the interaction with cigarette smoking. METHODS Seven hundred and twelve coke oven workers and 211 controls were investigated in southern China. Benzene soluble fraction (BSF) concentrations as a surrogate of COE were measured in representative personal samples and the individual cumulative COE exposure level was quantitatively estimated. Detailed information on smoking habits and respiratory symptoms was collected and spirometric tests were performed. RESULTS The mean BSF levels at the top of two coking plants were 743.8 and 190.5 microg/m3, respectively, which exceed the OSHA standard (150 microg/m3). After adjusting for cigarette smoking and other risk factors, there was a significant dose-dependent reduction in lung function and increased risks of chronic cough/phlegm and COPD in coke oven workers. The odds ratio for COPD was 5.80 (95% confidence interval 3.13 to 10.76) for high level cumulative COE exposure (> or =1714.0 microg/m3-years) compared with controls. The interaction between COE exposure and smoking in COPD was significant. The risk of COPD in those with the highest cumulative exposure to COE and cigarette smoking was 58-fold compared with non-smokers not exposed to COE. CONCLUSION Long term exposure to COE increases the risk of an interaction between COPD and cigarette smoking.