The Diesel Exhaust in Miners Study: III. Interrelations between respirable elemental carbon and gaseous and particulate components of diesel exhaust derived from area sampling in underground non-metal mining facilities

Abstract

Diesel exhaust (DE) has been implicated as a potential lung carcinogen. However, the exact components of DE that might be involved have not been clearly identified. In the past, nitrogen oxides (NO(x)) and carbon oxides (CO(x)) were measured most frequently to estimate DE, but since the 1990s, the most commonly accepted surrogate for DE has been elemental carbon (EC). We developed quantitative estimates of historical exposure levels of respirable elemental carbon (REC) for an epidemiologic study of mortality, particularly lung cancer, among diesel-exposed miners by back-extrapolating 1998-2001 REC exposure levels using historical measurements of carbon monoxide (CO). The choice of CO was based on the availability of historical measurement data. Here, we evaluated the relationship of REC with CO and other current and historical components of DE from side-by-side area measurements taken in underground operations of seven non-metal mining facilities. The Pearson correlation coefficient of the natural log-transformed (Ln)REC measurements with the Ln(CO) measurements was 0.4. The correlation of REC with the other gaseous, organic carbon (OC), and particulate measurements ranged from 0.3 to 0.8. Factor analyses indicated that the gaseous components, including CO, together with REC, loaded most strongly on a presumed 'Diesel exhaust' factor, while the OC and particulate agents loaded predominantly on other factors. In addition, the relationship between Ln(REC) and Ln(CO) was approximately linear over a wide range of REC concentrations. The fact that CO correlated with REC, loaded on the same factor, and increased linearly in log-log space supported the use of CO in estimating historical exposure levels to DE.

Fig. 1.

Scatter plots of REC and TEC (left panel) and of REC and SEC (right panel), by mining facility (A–I = facilities). Solid line depicts the x = y line.

Fig. 2.

Scatter plots and regression analyses between natural log-transformed (Ln) CO and REC measurements for all mining facilities combined (Overall) and by facility (A-I). Analysis of the data from all facilities is presented in the upper left panel where the solid line depicts the fitted regression line Ln(REC) = α + β × Ln(CO) and the shaded area, the 95% CI. The facility-specific panels depict two models: one fixed-effects model allowing for facility-specific intercepts and a common slope (solid line) and one mixed-effects model with fixed facility-specific intercepts and facility-specific random slopes (dashed line).

Fig. 3.

Scatter plots and regression analyses between natural log-transformed (Ln) NO₂ and REC measurements for all mining facilities combined (Overall) and by facility (A-I). Analysis of the data from all facilities is presented in the upper left panel where the solid line depicts the fitted regression line Ln(REC) = α + β × Ln(NO₂) and the shaded area, the 95% CI. The facility-specific panels depict two models: one fixed-effects model allowing for facility-specific intercepts and a common slope (solid line) and one mixed-effects model with fixed facility-specific intercepts and facility-specific random slopes (dashed line).