Evaluation of 1-Nitropyrene as a Surrogate Measure for Diesel Exhaust: Assessment of Personal Air Monitoring Data from an Underground Mine

Abstract

Objectives We investigate the hypothesis that 1-Nitropyrene (1-NP) concentration in air is a viable surrogate measure of diesel exhaust exposure, as compared with industry-standard elemental carbon (EC) and total carbon (TC) measurements. 1-NP content in personal air samples was measured for a cohort of underground miners and compared with measures of Elemental Carbon (EC), Organic Carbon (OC), and Total Carbon (TC) in the same samples. Additionally, data from surveys was assessed as potential modifiers of these comparisons, and used to form a predictive model for 1-NP. Methods Personal exposure data were collected on a cohort of 20 employees at a large underground metal mine during 4 different sample campaigns. Full-shift personal sampling was conducted using an MSHA compliant SKC DPM impactor downstream of a GS-1 cyclone pre-filter. Each DPM filter element was analyzed for EC and OC using NIOSH method 5040. After EC and OC analysis each DPM filter was extracted with methylene chloride and analyzed for 1-NP using an LC/MS/MS method. Results Regression analysis of 1-NP vs. EC yields a 5.3% increase in geometric mean (GM) 1-NP for each 10% increase in GM EC (p<0.001). Associations between 1-NP and OC or TC were not found to be statistically significant. Survey data variables for location in the mine, fuel type, and cigarettes smoked were investigated for effect modification upon the 1-NP/EC association and none were found statistically significant. Out of ten survey variable combinations examined as predictive models for 1-NP, a model predicting 1-NP from primary tasks conducted alone was found to yield the best model performance (cross-validated r2=0.254). Conclusions 1-NP was found to be associated with EC in personal air samples. 1-NP was not found to be associated with OC or TC with statistical significance, due to a large number of OC samples below the limit of detection. Location within the mine, fuel type, and cigarette use as examined in this study were not found to significantly affect the 1-NP/EC association. Information on primary job tasks can be used to predict personal air concentrations of 1-NP.