Diesel engine exhaust exposure in underground mines: Comparison between different surrogates of particulate exposure

ABSTRACT

Exposure to diesel particulate matter (DPM) is frequently assessed by measuring indicators of carbon speciation, but these measurements may be affected by organic carbon (OC) interference. Furthermore, there are still questions regarding the reliability of direct-reading instruments (DRI) for measuring DPM, since these instruments are not specific and may be interfered by other aerosol sources. This study aimed to assess DPM exposure in 2 underground mines by filter-based methods and DRI and to assess the relationship between the measures of elemental carbon (EC) and the DRI to verify the association of these instruments to DPM. Filter-based methods of respirable combustible dust (RCD), EC, and total carbon (TC) were used to measure levels of personal and ambient DPM. For ambient measurements, DRI were used to monitor particle number concentration (PNC; PTrak), particle mass concentration (DustTrak DRX and DustTrak 8520), and the submicron fraction of EC (EC_1;Airtec). The association between ambient EC and the DRI was assessed by Spearman correlation. Geometric mean concentrations of RCD, respirable TC (TC_R) and respirable elemental EC (EC_R) were 170 µg/m³, 148 µg/m³, and 83 µg/m³ for personal samples, and 197 µg/m³, 151 µg/m³, and 100 µg/m³ for ambient samples. Personal measurements had higher TC_R:EC_R ratios compared to ambient samples (1.8 vs. 1.50) and weaker association between EC_R and TC_R. Among the DRI, the measures of EC₁ by the Airtec (ρ = 0.86; P < 0.001) and the respirable particles by the DustTrak 8520 (ρ = 0.74; P < 0.001) showed the strongest association with EC, while PNC showed a weak and non-significant association with EC. In conclusion, this study provided important information about the concentrations of DPM in underground mines by measuring several indicators using filter-based methods and DRI. Among the DRI, the Airtec proved to be a good tool for estimating EC concentrations and, although the DustTrak showed good association with EC, interferences from other aerosol sources should be considered when using this instrument to assess DPM.

KEYWORDS:

• Diesel exposure
• direct-reading instrument
• DPM
• elemental carbon
• ultrafine particles

Conflicts of interest

G.L and H.C currently work on the project for Agnico Eagle Mines and IAMGold, respectively, companies that were investigated in the study. The authors declare no other conflicts of interest relating to the material presented in this article.

Acknowledgments

The authors would like to thank all the workers who participated in the study, and François Couture, Benoît Gaulin, Yves Lapointe, and Sébastien Roy for their technical support.

Additional information

Funding

This project was financially supported by the Fonds de Recherche du Québec Nature et Technologies (FRQNT #CF133003) and the Institut de Recherche Robert-Sauve en Santé et en Sécurité du Travail (IRSST #2015-0008). A.S.F received a scholarship from the FRQNT and the Institut de Recherche en Santé Publique de l'Université de Montréal (IRSPUM).