Garshick et al. exposures are equivalent to effects of short- er-term high-intensity exposure resulting in a comparable estimate of cumulative exposure 3-month. The overlap in esti- in terms of gμ/m mated lung cancer risks in the current trucking industry cohort and the underground miner cohort study reported by Attfield et al. (2012) supports this assertion. Although we obtained detailed work records and carefully assessed exposure, an additional limitation is a lack of informa- tion on personal risk factors for lung cancer. Although cigarette smoking is a major risk fac- tor, the degree that it is a confounder depends on its differential association with exposure (Blair et al. 2007). Since workers in the study cohort were all unionized trucking industry employees, they were generally similar with regards to socioeconomic status which is a known correlate of smoking habits. Smoking rates also vary by age and birth cohort and all analyses were adjusted for these factors. In a 2003 questionnaire survey, we obtained information regarding smoking habits. In our previous assessment of lung cancer risk in this cohort based on job title (Garshick et al. 2008), indirect adjustment (Axelson and Steenland 1988) for smoking did not mean- ingfully influence estimated relative risks for lung cancer. Adjustment for differences in smoking habits based on job title increased relative risk estimates among P&D drivers, dockworkers, and combination workers by 4–8% and decreased relative risks among LH drivers by 15%. In addition, if short-term workers have different behaviors (e.g., smoke more heavily) than longer-term workers, this could contribute to negative confounding in analyses unadjusted for duration. Drivers have a commercial license and undergo medi- cal certification that could also indicate that healthier workers continue working. To conclude, our results suggest lung can- cer mortality increases with cumulative EC exposures in trucking industry workers in jobs with regular exposures to particulates from pre-2007 diesel exhaust and other mobile sources. Our exposure assessment indicates that there has been substantial success in reducing trucking industry EC exposures and therefore we predict a reduction in future lung cancer risk in this industry. Ref Rencs Applebaum KM, Malloy EJ, Eisen EA. 2007. Reducing healthy worker survivor bias by restricting date of hire in a cohort study of Vermont granite workers. Occup Environ Med 64:681–687. Applebaum KM, Malloy EJ, Eisen EA. 2011. Left truncation, susceptibility, and bias in occupational cohort studies. Epidemiology 22:599–606. Arrighi HM, Hertz-Picciotto I. 1996. Controlling the healthy worker survivor effect: an example of arsenic exposure and respiratory cancer. Occup Environ Med 53:455–462. Attfield MD, Schleiff PL, Lubin JH, Blair A, Stewart PA, 1306 Med 13:105–118. 1950–1990. AIHA J (Fairfax, Va) 64:472–479. and lung cancer. Epidemiology 9:84–91. Blair A, Stewart P, Lubin JH, Forastiere F. 2007. Methodological issues regarding confounding and exposure misclassifica- tion in epidemiological studies of occupational exposures. Am J Ind Med 50:199–207. Brown SC, Schonbeck MF, McClure D, Baron AE, Navidi WC, Byers T, et al. 2004. Lung cancer and internal lung doses among plutonium workers at the Rocky Flats Plant: a case–control study. Am J Epidemiol 160:163–172. California Environmental Protection Agency. 1998. Air Resources Board. Rulemaking Identification of Particulate Emissions from Diesel-Fueled Engines as a Toxic Air Contaminant. Available: http://www.arb.ca.gov/regact/diesltac/diesltac. htm [accessed 5 August 2012]. Cardis E, Vrijheid M, Blettner M, Gilbert E, Hakama M, Hill C, et al. 2007. The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks. Radiat Res 167:396–416. Cass GR, Conklin MH, Shah J, Huntzicker J, Macias ES. 1984. Elemental carbon concentrations: estimation of an historical database. Atmos Environ 18:153–162. Chevrier J, Picciotto S, Eisen EA. 2012. A comparison of stan- dard methods with g-estimation of accelerated failure- time models to address the healthy-worker survivor effect: application in a cohort of autoworkers exposed to metal- working fluids. Epidemiology 23:212–219. Davis ME, Hart JE, Laden F, Garshick E, Smith TJ. 2011. A retrospective assessment of occupational exposure to elemental carbon in the U.S. trucking industry. Environ Health Perspect 119:997–1002. Davis ME, Laden F, Hart JE, Garshick E, Blicharz A, Smith TJ. 2009. Predicting changes in PM exposure over time at U.S. trucking terminals using structural equation modeling techniques. J Occup Environ Hyg 6:396–403. Davis ME, Smith TJ, Laden F, Hart JE, Blicharz AP, Reaser P, et al. 2007. Driver exposure to combustion particles in the U.S. trucking industry. J Occup Environ Hyg 4:848–854. Mauderly JL. 2011. Engine-operating load influences diesel exhaust composition and cardiopulmonary and immune responses. Environ Health Perspect 119:1136–1141. National Institute for Occupational Safety and Health. 1998. Elemental Carbon (Diesel Particulate) 5040. In: NIOSH Mannual of Analytical Methods (Cassinelli ME, O’Connor PF, eds). 4th ed. Atlanta GA:National Institute for Occupational Safety and Health. National Research Council. 1981. Health Effects of Exposure to Diesel Exhaust: The Report of the Health Effects Panel of the Diesel Impacts Study Committee. Washington, DC:National Academy Press. Neumeyer-Gromen A, Razum O, Kersten N, Seidler A, Zeeb H. 2009. Diesel motor emissions and lung cancer mortality— results of the second follow-up of a cohort study in potash miners. Int J Cancer 124:1900–1906. Office of Research and Development. 2002. Health Assessment Document for Diesel Engine Exhaust. EPA/600/8-90/057F. Washington, DC:National Center for Environmental Assessment, U.S. Environmental Protection Agency. Pope CA III, Burnett RT, Turner MC, Cohen A, Krewski D, Jerrett M, et al. 2011. Lung cancer and cardiovascular disease mortality associated with ambient air pollution and cigarette smoke: shape of the exposure–response relationships. Environ Health Perspect 119:1616–1621. Schauer JJ. 2003. Evaluation of elemental carbon as a marker for diesel particulate matter. J Expo Anal Environ Epidemiol 13:443–453. Sheesley RJ, Schauer JJ, Garshick E, Laden F, Smith TJ, Blicharz AP, et al. 2008a. Tracking personal exposure to particulate diesel exhaust in a diesel freight terminal using organic tracer analysis. J Expo Sci Environ Epidemiol Sheesley RJ, Schauer JJ, Smith TJ, Garshick E, Laden F, Marr LC, et al. 2008b. Assessment of diesel particulate matter expo- sure in the workplace: freight terminals. J Environ Monit 19:172–186. 10:305–314. Vermeulen R, et al. 2012. The Diesel Exhaust in Miners Study: a cohort mortality study with emphasis on lung cancer. J Natl Cancer Inst 104:869–883. Axelson O, Steenland K. 1988. Indirect methods of assessing the effects of tobacco use in occupational studies. Am J Ind Cause- specific mortality in the unionized U.S. trucking industry. Environ Health Perspect 115:1192–1196. Li N, Sioutas C, Cho A, Schmitz D, Misra C, Sempf J, et al. 2003. Ultrafine particulate pollutants induce oxidative stress and mitochondrial damage. Environ Health Perspect Bailey CR, Somers JH, Steenland K. 2003. Exposures to diesel Lipsett M, Campleman S. 1999. Occupational exposure to diesel exhaust in the International Brotherhood of Teamsters, exhaust and lung cancer: a meta-analysis. Am J Public Bhatia R, Lopipero P, Smith AH. 1998. Diesel exhaust exposure McDonald JD, Campen MJ, Harrod KS, Seagrave J, Seilkop SK, 111:455–460. Health 89:1009–1017. Davis ME, Smith TJ, Laden F, Hart JE, Ryan LM, Garshick E. Smith TJ, Davis ME, Reaser P, Natkin J, Hart JE, Laden F, et al. 2006. Modeling particle exposure in U.S. trucking terminals. 2006. Overview of particulate exposures in the U.S. trucking Environ Sci Technol 40:4226–4232. industry. J Environ Monit 8:711–720. de Kok TM, Driece HA, Hogervorst JG, Briedé JJ. 2006. Steenland K, Deddens J, Stayner L. 1998. Diesel exhaust and Toxicological assessment of ambient and traffic-related particulate matter: a review of recent studies. Mutat Res 613:103–122. Diesel Working Group. 1995. Diesel Exhaust: A Critical Analysis of Emissions, Exposure, and Health Effects. Special Report. Cambridge, MA:Health Effects Institute. Garshick E, Laden F, Hart JE, Rosner B, Davis ME, Eisen EA, et al. 2008. Lung cancer and vehicle exhaust in trucking industry workers. Environ Health Perspect 116:1327–1332. Garshick E, Laden F, Hart JE, Rosner B, Smith TJ, Dockery DW, et al. 2004. Lung cancer in railroad workers exposed to diesel exhaust. Environ Health Perspect 112:1539–1543. Garshick E, Smith TJ, Laden F. 2002. Investigators’ Report. Quantitative assessment of lung cancer risk from diesel exhaust exposure in the U.S. trucking industry: a feasibil- ity study. In: Research Directions to Improve Estimate of Human Exposure and Risk from Diesel Exhaust. A Special Report of the Institute’s Diesel Epidemiology Working Group (Diesel Epidemiology Working Group, ed). Boston, MA:Health Effects Institute, 113–150. lung cancer in the trucking industry: exposure–response analyses and risk assessment. Am J Ind Med 34:220–228. Steenland NK, Silverman DT, Hornung RW. 1990. Case–control study of lung cancer and truck driving in the Teamsters Union. Am J Pub Health 80:670–674. U.S. EPA (U.S. Environmental Protection Agency). 2001. Heavy- Duty Highway Diesel Program. Regulations and Standards. Available: http://www.epa.gov/otaq/highway-diesel/regs. htm#emer-vehi (accessed 5 August 2012). U.S. EPA (U.S. Environmental Protection Agency). 2002. Health Asessment Document for Diesel Engine Exhaust. Available: http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=29060 [accessed 1 August 2012]. U.S. EPA (U.S. Environmental Protection Agency). 2007. Nonroad Diesel Equiment. Regulations and Standards. Available: http://epa.gov/nonroad-diesel/regulations.htm#1 [accessed 5 August 2012]. Wittmaack K. 2007. In search of the most relevant parameter for quantifying lung inflammatory response to nanoparticle exposure: particle number, surface area, or what? Environ Health Effects Institute Air Toxics Review Panel. 2007. Summary Health Perspect 115:187–194. of diesel exhaust. In: Mobile-Source Air Toxics: A Critical Review of the Literature on Exposure and Health Effects. HEI Special Report 16. Boston, MA:Health Effects Institute, 135–148. Organization. World Health Organization. 1978. International Classification of Diseases, 9th Revision. Vol 1. Geneva:World Health World Health Organization. 1993. International Classification International Agency for Research on Cancer. 1989. Diesel and of Diseases, 10th Revision. Vol 1. Geneva:World Health gasoline engine exhausts. IARC Monogr Eval Carcinog Organization. Risks Hum 46:41–188. 49:1013–1020. Jain N, Hart JE, Smith TJ, Garshick E, Laden F. 2006. Smoking behavior in trucking industry workers. Am J Ind Med Laden F, Hart JE, Smith TJ, Davis ME, Garshick E. 2007. Zaebst DD, Clapp DE, Blade LM, Marlow DA, Steenland K, Hornung RW, et al. 1991. Quantitative determination of trucking industry workers’ exposures to diesel exhaust particles. Am Ind Hyg Assoc J 52:529–541. ovlume 120 | number 9 | September 2012 • Environmental Health Perspectives