Although the dominant cause of COPD is cigarette smoking, occupational exposure to mineral dusts, organic dusts and irritant gases or vapours contributes significantly to the incidence and severity of chronic airways disease, including COPD. The most common respiratory manifestation of exposure to dusts or fumes is a chronic cough productive of sputum (chronic bronchitis). This may or may not be associated with airflow limitation, as determined by a decrease in forced expiratory volume in 1 second (FEV1). Several longitudinal studies have shown that exposure to coal dust is associated with a loss of respiratory function, even in the absence of pneumoconiosis. The average loss of function can be comparable to the changes attributable to smoking, with some individuals suffering substantial and clinically significant impairment. In addition to underground mining, workers in other occupations with exposure to mineral dusts (such as building work) or fumes (such as welding) may be at risk of occupationally induced COPD, although the epidemiological evidence is generally less strong for these categories of workers. It is also underappreciated that exposure to agricultural dusts (such as grain dust, vegetable fibres or animal feed) is a significant cause of chronic airway disease and accelerated decline in lung function. Thus, the prevalence of chronic bronchitis in farmers, particularly swine confinement farmers, is high, even among nonsmokers.
In general, population-based studies have supported the findings of workplace-based studies, particularly with regard to dusty jobs or jobs involving mixed exposure to dusts and gases. The population-attributable fraction of occupational factors to the burden of COPD morbidity has been estimated to range from 15–20% and may reach 40% among nonsmokers. In Europe, it was estimated that a total of 39 300 deaths from COPD in 2000 were a result of work-related exposures to dusts and fumes.