Garshick et al. and change in employment status, job, and trucking terminal assignment. In one com- pany (18.5% of the cohort) complete records were only available for workers still employed in 1993, so that company’s workers were only included if they were continuously employed from 1985 to 1993. Records for another com- pany were not available before 1972, and work history before that date was based on job and terminal in 1972. Approval was obtained from the institutional review boards of Brigham and Women’s Hospital, Harvard School of Public Health, and VA Boston Healthcare System. Individual consent to participate was not required. Mortality. Date of death and cause-spe- cific mortality from 1985 through 2000 was obtained from the National Death Index using social security number, name, and date of birth as matching criteria. Because prolonged sur- vival is rare, we included deaths with primary lung cancer, according to the International Classification of Diseases, 9th Revision (ICD-9) code 162 (World Health Organization 1978) and 10th Revision (ICD-10) codes C33-C34 (World Health Organization 1993) as cases even if not the underlying cause of death. Men were included in the analysis if they worked for at least 1 year for one of the study com- panies. In addition, analyses were limited to men ≥ 40 years of age in 1985 because most lung cancer deaths (96%) occurred in this age group (n = 31,135). Current exposure. Major jobs, diesel use, and numbers of workers in each job in 1985 are presented in Table 1. An exposure assess- ment was conducted from 2001 through 2006. This assessment included 5-day sampling trips to 36 trucking terminals randomly chosen to be representative of the 139 large terminals (> 100 workers) in these companies (Davis et al. 2006; Smith et al. 2006). We measured cross-shift (8–12 hr) EC in particulate matter ≤ 1.0 μm in aerodynamic diameter (PM the using the 5040 method from the National Institute for Occupational Safety and Health (1998). We collected > 4,000 EC measure- ments, including personal samples from dock 1.0) workers and mechanics, and area measure- ments in loading docks, offices, and truck cabs. Ambient background conditions were mea- sured at the periphery of the upwind terminal. Area measurements, including 214 loading dock samples, were collected at 44 smaller terminals (1–2 per trip) within 75 miles. Separate exposure models were con- structed for drivers and terminal workers. Drivers included pick-up and delivery (P&D) drivers, long-haul (LH) drivers, and hostlers (Davis et al. 2007) and terminal-based work- ers included dockworkers and mechanics (Davis et al. 2006). Models were validated with six repeat trips (Davis et al. 2009). Using structural equation modeling (SEM) for the terminal workers, personal EC expo- sure was a function of work area EC, and in turn, work area EC was a function of job, terminal characteristics related to size and ven- tilation, and upwind ambient (background) EC. Background EC was a function of local weather, distance from an interstate highway, land use, and U.S. census region. For P&D and LH drivers, home terminal ambient EC was a significant determinant of truck cab EC. In contrast to LH drivers who had air con- ditioned cabs, temperature was also a deter- minant of exposure for P&D drivers because cab EC was higher when the windows were predicted to be open. For drivers and hostlers, we determined factors scaling exposure based on ambient terminal EC. Office workers were assumed to have background exposures. Historical exposure. Details of our histori- cal model are presented elsewhere (Davis et al. 2011). Historical trends in ambient terminal EC were modeled based on historical trends in the coefficient of haze (COH) available for 1971 through 2000, a measurement of par- ticulate matter based on optical density, highly predictive of ambient EC (R2 = 0.94) (Cass et al. 1984). We validated this approach using data from a 1988 through 1989 assessment of EC in the same industry that used the same methodology as our current assessment (Zaebst et al. 1991). The ratio of ambient EC from 1988–1989 compared with 2001–2006 was Job in 1985 Long-haul driver (LH) Pick-up/delivery (P&D) Dockworker Combination worker Mechanic Hostler Clerk Other jobs 1302 Table 1. Distribution of jobs in 1985 among men ≥ 40 years of age with ≥ 1 year of work (n = 31,135). Job duties Drives heavy-duty trucks between large terminals. Diesel first used 1951–1957; transition complete 1954–1965, depending on company Drives trucks locally; picks up and delivers cargo. Diesel first used 1972–1978; transition complete 1980–1992, depending on company Loads/unloads cargo on dock using forklifts Diesel forklifts in three companies starting in 1979–1986 through 1994–1996 in large terminals Duties include P&D driver and dockworker Maintains trucks in large terminal shops Drives a tractor or a specialized tractor to move trailers to and from freight dock and in yard Cashiers, dock clerks, dispatchers, customer service representatives, and others in terminal offices Janitor, unionized manger, trainee, or not defined n (%) 10,825 (35) 5,866 (19) 5,710 (18) 4,938 (16) 1,741 (6) 666 (2) 843 (3) 546 (2) identical to the ratio of COH data over the same time periods; this finding demonstrates that historical trends in COH and ambient EC were similar (Davis et al. 2011). Monthly ambient background EC estimates were deter- mined for the 139 large terminals between 1971–2000 using location specific tempera- ture, windspeed, and other terminal-specific data as input into the SEM exposure model. In addition to changes in ambient expo- sure, our historical model accounted for changes in job-related exposures based on com- parison of 1988 through 1989 to 2001 through 2006 measured values. For dockworkers who drove propane forklifts, the geometric mean of predicted EC in terminals that were sampled in 1988–1989 and adjusted for background EC was 1.36 gμ/m 3 (Davis et al. 2011; Zaebst et al. 1991). The value measured by Zaebst et al. (1991) was nearly identical (1.30 gμ/m 3), sup- porting the validity of our approach. The data reported by Zaebst et al. (1991) were also used to account for changes in the type of fuel used for forklifts, which included diesel in large ter- minals operated by three companies during the 1980s through the mid-1990s, as well as gaso- line and propane (Table 1). This approach pro- vided multipliers that reflect historical changes in exposure for each job, including fuel type for dockworkers. We used these multipliers to estimate exposures for 1971 through 1989; we applied linear extrapolation for exposures that occurred from 1990 through 2000. Personal exposure. Data on historical job and terminal-specific monthly EC con- centrations, which were determined by the exposure model, were summed by year to estimate an individual’s cumulative exposure (μg/m 3-months). Because workers may have had more than one job in a year, job-specific EC was weighted by the fraction of time spent in each job. Job-specific EC values before 1971 (8% of total exposure time) were assigned 1971 exposures because COH data were not avail- able to estimate background. Combination workers (Table 1) were assumed to spend 50% of their time as a P&D driver and 50% as a dockworker. Fifty percent of exposure time was accounted for by work at the 139 larger terminals for which we had directly modeled exposure. EC predictions at one terminal were an order of magnitude higher than in others due to extreme weather values and other model input characteristics. Therefore, this terminal was assigned exposure values from another terminal in the same city. Based on available information, it is likely that nearly all terminals not directly modeled were smaller terminals (≤ 100 workers). From our exposure assess- ment, the mean difference between large and smaller terminal loading dock area EC mea- sured during the same trip was 0, indicating no meaningful bias in applying our terminal expo- sure model. For exposure time without directly ovlume 120 | number 9 | September 2012 • Environmental Health Perspectives