Diesel engine exhaust exposures in two underground mines

Exposure to diesel engine exhaust (DE) is a major concern in underground mines. It has been linked to cardiopulmonary diseases and is classified as a human carcinogen. The goal of this study is to assess DE exposures in workers at two underground gold mines, to compare exposure levels within and between the mines, and to compare different methods of measuring DE exposures, namely respirable combustible dust (RCD), elemental carbon (EC) and total carbon (TC). Ambient and personal breathing zone (PBZ) measurements were taken. Side-by-side monitoring of RCD and of the respirable fraction of EC and TC (ECR and TCR) was carried out in the workers' breathing zone during full-shift work. Regarding ambient measurements, in addition to ECR, TCR and RCD, a submicron aerosol fraction (less than 1 µm) of EC and TC was also sampled (EC1 and TC1). Average ambient results of 240 µg/m3 in RCD, 150 µg/m3 in ECR and 210 µg/m3 in TCR are obtained. Average PBZ results of 190 µg/m3 in RCD, 84 µg/m3 in ECR and 150 µg/m3 in TCR are obtained. Very good correlation is found between ECR and EC1 with a Pearson correlation coefficient of 0.99 (p < 0.01) calculated between the two log-transformed concentrations. No differences are reported between ECR and EC1, nor between TCR and TC1, since ratios are equal to 1.04, close to 1, in both cases. Highest exposures are reported for load-haul-dump (LHD) and jumbo drill operators and conventional miners. Significant exposure differences are reported between mines for truck and LHD operators (p < 0.01). The average TCR/ECR ratio is 1.6 for PBZ results, and 1.3 for ambient results. The variability observed in the TCR/ECR ratio shows that interferences from non-diesel related organic carbon can skew the interpretation of results when relying only on TC data.