Comparison between personal sampling methodologies for evaluating diesel particulate matter exposures in mines: submicron total carbon corrected for the adsorption of vapor-phase organic carbon vs. respirable total carbon

Abstract

In the mining industry, personal measurements of elemental and total carbon are frequently used as surrogates of diesel particulate matter (DPM) exposure, and the respirable or submicron fractions are usually measured. However, vapor-phase organic carbon (OC) can be adsorbed in the filters, interfering with total carbon results. This study presents a comparative evaluation between the submicron fraction of DPM concentrations corrected for the adsorption of the vapor-phase OC (dynamic blank), and the respirable fraction of DPM corrected for a field blank. Respirable and submicron fractions of total carbon (TC_R and TC₁) and elemental carbon (EC_R and EC₁) concentrations were sampled in parallel, in the workers’ breathing zone, in an underground gold mine. A total of 20 full-shift personal samples were taken for each size fraction. Field blanks were collected each day for both the submicron and respirable fractions, while dynamic blank correction was also applied for the submicron fraction. TC_R presented a larger and statistically different geometric mean concentration compared to TC₁ (98 µg/m³ vs. 72 µg/m³; p = 0.01), while the concentrations of EC_R and EC₁ were not statistically different (58 µg/m³ vs. 54 µg/m³; p = 0.74). Average TC_R/EC_R ratio was 1.7, while the TC₁/EC₁ ratio was 1.3. In addition, 93% of EC had an aerodynamic size lower than 1 µm, while the proportion of TC particles in the submicron fraction was lower (73%). Finally, a similar quantity of OC was found when analyzing the dynamic and field blanks of the filters with the submicron fraction selective size (24 µg and 22 µg, respectively). In conclusion, the correction for the vapor phase OC by the dynamic blank was not a significant correction in our study design compared to the field blank samples. This study suggests that the differences in TC may be explained by the different aerodynamic fractions of DPM collected. In addition, elemental carbon measurements did not seem to be extensively affected by the aerodynamic size of the particles collected.

Keywords:

• Diesel exposure
• DPM
• elemental carbon
• mining industry
• total carbon

Additional information

Funding

Funding was provided by Fonds de Recherche du Québec - Nature et Technologies. No conflicts of interest were reported by the author(s).