Exposure to Particulate Matter and Respirable Crystalline Silica in Tunnel Construction Workers Using Tunnel Boring Machines

OBJECTIVES: This study aimed to assess the exposure to a selection of aerosols and gases in the work environment for workers performing tunnel construction using tunnel boring machines (TBMs), to identify determinants of exposure based on the information available and to calculate robust estimates of exposure using a statistical model. The focus was particulate matter (PM) and respirable crystalline silica (RCS). In addition, concentrations of nitrogen dioxide (NO(2)), elemental carbon (EC), and oil mist were assessed. METHODS: Personal sampling was conducted from February 2017 to February 2019. PM in the thoracic and the respirable aerosol fractions was collected, and RCS was determined in the respirable aerosol fraction. Context information was collected on questionnaires. Because the workers could participate in the sampling more than once and multiple measurements were performed on the same date a mixed model was used in the analysis. Concentrations of PM and RCS are presented as estimated and measured geometric means (GM(est) and GM(mea)) and estimated arithmetic mean (AM(est)) in addition to the median. Measured concentrations of NO(2), EC, and oil mist are presented as geometric means. RESULTS: A total of 290 and 289 personal samples of PM in the thoracic and respirable aerosol fractions were available for analysis, respectively. Work title/work location, type of work (production, maintenance, or a combination of the two), and date of sampling were identified as determinants of exposure. Workers in the front of the TBMs had the highest exposure to PM and RCS. The GM(est) of RCS exposure varied from 35 to 413 μg m(–3) depending on the work title. The geometric standard deviations for measured RCS concentrations by work title ranged from 1.6 to 3.5. A total of 16 samples of NO(2) and EC and 12 samples of oil mist were collected. Maximum values of NO(2) and EC were 54 µg m(–3) and 23 µg m(–3), respectively. The maximum measured value of oil mist was 0.08 mg m(–3). CONCLUSIONS: All TBM workers were exposed to PM and RCS. Exposure to RCS may be substantial, and workers in front of the TBM were exposed to the highest concentrations of both PM and RCS. A day-to-day variation was found, probably caused by differences in drilling activities. Preventive measures are warranted to keep the exposure to PM and consequently the exposure to RCS as low as possible to protect the health of workers in tunnel construction.