Research Lung Cancer and Elemental Carbon Exposure in Trucking Industry Workers Eric Garshick,1,2 Francine Laden,2,3,4 Jaime E. Hart,2 Mary E. Davis,3,5 Ellen A. Eisen,6,7 and Thomas J. Smith 3 1Pulmonary and Critical Care Medicine Section, VA Boston Healthcare System, Boston, Massachusetts, USA; 2Channing Division of Network Medicine, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA; 3Exposure, Epidemiology and Risk Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; 4Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA; 5 Department of Urban and Environmental Policy and Planning, Tufts University, Medford, Massachusetts, USA; 6Environmental and Occupational Medicine and Epidemiology Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA; 7Environmental Health Sciences Division, School of Public Health, University of California, Berkeley, California, USA Background : Diesel exhaust has been considered to be a probable lung carcinogen based on studies of occupationally exposed workers. Efforts to define lung cancer risk in these studies have been limited in part by lack of quantitative exposure estimates. o Bjectiv : We conducted a retrospective cohort study to assess lung cancer mortality risk among U.S. trucking industry workers. Elemental carbon (EC) was used as a surrogate of exposure to engine exhaust from diesel vehicles, traffic, and loading dock operations. Methods : Work records were available for 31,135 male workers employed in the unionized U.S. trucking industry in 1985. A statistical model based on a national exposure assessment was used to estimate historical work-related exposures to EC. Lung cancer mortality was ascertained through the year 2000, and associations with cumulative and average EC were estimated using proportional hazards models. r esult : Duration of employment was inversely associated with lung cancer risk consistent with a healthy worker survivor effect and a cohort composed of prevalent hires. After adjusting for employment duration, we noted a suggestion of a linear exposure–response relationship. For each 1,000-µg/m3 months of cumulative EC, based on a 5-year exposure lag, the hazard ratio (HR) was 1.07 [95% confidence interval (CI): 0.99, 1.15] with a similar association for a 10-year exposure lag [HR = 1.09 (95% CI: 0.99, 1.20)]. Average exposure was not associated with relative risk. c onclusi : Lung cancer mortality in trucking industry workers increased in association with cumulative exposure to EC after adjusting for negative confounding by employment duration. k ey words : diesel exhaust, elemental carbon, lung cancer, occupational exposure, particulate matter, traffic. Environ Health Perspect 120:1301–1306 (2012). http://dx.doi.org/10.1289/ ehp.1204989 [Online 1 June 2012] Concern has been raised for > 40 years that exposure to diesel exhaust results in lung can- cer in humans (National Research Council 1981). Diesel exhaust has included a mix- ture of elemental carbon (EC) particles with adsorbed mutagenic and carcinogenic poly- cyclic aromatic hydrocarbons (PAH), con- densed engine oil, other organic compounds, and exhaust gases. Previous epidemiologic studies have reported a positive association between lung cancer risk and work in occupa- tions with some degree of diesel exhaust expo- sure [e.g., Bhatia et al. 1998; Diesel Working Group 1995; Garshick et al. 2004; Lipsett and Campleman 1999; Steenland et al. 1990; U.S. Environmental Protection Agency (EPA) 2002]. Previous evaluations by administrative and regulatory authorities have judged diesel exhaust to be a probable lung carcinogen (International Agency for Research on Cancer 1989) likely capable of causing lung cancer at ambient levels [California Environmental Protection Agency 1998; U.S. EPA 2002]. The main criticisms have been that few studies have included exposure measurements, and those studies that have included such measures have been limited in their ability to credibly extrapolate changes in exposure over time, to link exposure to personal work records, or to provide quantitative risk estimates (Health Effects Institute Air Toxics Review Panel 2007). In the United States increasingly stringent emission standards have been implemented for new on-road and off- road diesel engines (U.S. EPA 2001, 2007). However, older diesel engines have remained in service for several decades in the United States and for even longer in other parts of the world. Therefore, understanding the quantitative assessment of lung cancer risk remains important. Accurate linkage between work history and quantitative or semiquantitative estimates or exposure categories requires knowledge of current and historical exposure scenarios and estimates of intensity. To address this issue, we designed a retrospective cohort study and a current and historical exposure assessment of workers employed by four large union- ized (Teamsters) carriers in the United States. Our approach takes advantage of three key characteristics: a) the large number of detailed work records available, b) stable relation- ships between union job titles and duties over time, and c) known dates of diesel equipment use (Garshick et al. 2002). We conducted a national exposure assessment in this industry Environmental Health Perspectives • volume 120 | number 9 | September 2012 between 2001 and 2006 to characterize expo- sures to EC as a marker of exposure to die- sel and other traffic-related particulate matter (PM) (Davis et al. 2006, 2007, 2009; Smith et al. 2006) including a source apportion- ment assessment for components of exposure (Sheesley et al. 2008a, 2008b). EC was cho- sen as our exposure marker because it is an exhaust constituent that may serve as a tracer for diesel emissions when the source is close to the subject, as it is in trucking operations. Exposure models were used to estimate job- and location-specific exposures to EC in the United States between 1971 and 2000, taking into account spatial and temporal determinants (Davis et al. 2006). We have previously reported elevated stan- dardized mortality ratios (Laden et al. 2007) and an elevated risk of lung cancer mortal- ity with increasing years of work as a driver or dockworker in this cohort (Garshick et al. 2008). For the present analysis we linked a his- torical EC exposure model to work records to estimate personal EC exposures and examine their association with lung cancer mortality. Methods Population and work history. Computerized work records were obtained for 58,326 union- ized trucking industry employees (54,319 men and 4,007 women) employed in 1985 in four large national trucking companies. Job titles and duties were common among all companies, and records included dates of hire Address correspondence to E. Garshick, Pulmonary and Critical Care Medicine Section, VA Boston Healthcare System, 1400 VFW Parkway, West Roxbury, MA 02132 USA. Telephone: (617) 323- 7700, ext 35536. Fax: (857) 203-5670. E-mail: eric. garshick@va.gov We thank M.J. Canner for statistical programming assistance; F.E. Speizer for suggestions on the manu- script and the study design; L. Byrd, International Brotherhood of Teamsters Safety and Health Department; B. Schaefer, Central States Pension Fund; and the participating companies and the workers who participated in this study. The study was supported by grants from the National Institute of Health, National Cancer Institute (R01 CA90792), the National Institute of Environmental Health Sciences (ES 00002), and the Health Effects Institute (4705-RFA03-1/04-1). The authors declare they have no actual or potential competing financial interests. Received 19 January 2012; accepted 31 May 2012. 1301