Black Carbon Exposure Characteristics in Diesel Engine Vehicle-related Jobs

ABSTRACT This study aimed to assess the black carbon (BC) exposure characteristics of eight jobs including machinery operators, forklift operators, automobile assemblers, garbage collectors, garbage truck drivers, deliverers, toll operators, and crane operators in seven industries. BC exposure measurements were taken every minute by workers (N=106) using an AE51 microaethelometer affixed with a microcyclone while keeping detailed records of their time-activity patterns and whereabouts during working hours. A total of 71,987 observations on a 1-min timescale were categorized and analyzed based on four potential BC exposure determinants: operation of diesel engine vehicle (yes or no), proximity to source of BC (near or far), workplace (indoor or outdoor), and work type (moving or stationary). Among the eight jobs, the highest geometric mean (GM) BC exposure level was 9.5 µg m-3 for forklift operators in indoor workplaces, followed by toll operators (GM=7.4 µg m-3), machinery operators (GM=7.4 µg m-3), and garbage collectors (GM=5.5 µg m-3). BC exposure levels for each of the four determinants showed significant differences considering the random effect of workers and dates nested within a job and with fixed effects of four determinants and their pairwise interaction terms (p<0.001). In particular, the average exposure level of BC was approximately twice as high when working near diesel engine equipment than when working at a far distance. In comparing the BC exposure level according to the combination of the four exposure determinants, proximity to the diesel exhaust sources and indoor work were identified as the main factors that increase the BC exposure level. Diesel particulate filter installation on diesel engine vehicles was effective in reducing BC exposure. Our findings on the main exposure determinants could help develop a model that predicts BC exposure levels in different job groups.