Obstructive airflow limitation in tunnel workers exposed to crystalline silica

Background: Development of obstructive airflow limitation is a major problem among tunnel workers. Little is known about the relationship between exposure to crystalline silica and pulmonary function among workers using tunnel boring machines (TBM). Such workers are primarily exposed to stone dust containing crystalline silica. Other relevant exposures are known to be low. Aims: To assess exposure to respirable α-quartz and to determine the relationship between exposure and pulmonary function in TBM workers. Methods: In total 414 male tunnel workers (mean (range) age 40 (18-62) years) and a reference group of 83 non-exposed age-matched male subjects were included in the health examinations and spirometry was performed. The referents were recruited among other heavy construction workers and administrative personnel. Altogether 249 air samples were collected by personal sampling for determination of respirable α-quartz. Job tasks in tunneling and years of exposure were classified using interviews and questionnaires. Results: The geometric mean exposure to α-quartz among the TBM workers was 0.052 mg m-3 (GSD 3.0). The tunnel workers had been exposed for 9 years on average (range 1-41 years). Compared to the referents, the tunnel workers had significantly lower FEV1/FVC (78.0 vs 80.1, p=0.007) and MMEF % of predicted (80.2 vs 88.7 %, p=0.005). Adjusted for ever- smoking, FEV1/FVC and MMEF % of predicted were negatively associated with years of exposure in TBM work (p=0.01 and p=0.004, respectively). Conclusions: TBM workers may be exposed to high levels of crystalline silica. These results indicate that the exposure may cause obstructive airflow limitation, primarily affecting the small airways.