A new study by researchers at UC Berkeley and Harvard claims that trucking industry workers who have been regularly exposed to diesel vehicle exhaust have an elevated risk of lung cancer with each increasing year of work.

Although an elevated risk of lung cancer has long been attributed to diesel exhaust exposure, previous studies specifically implicating diesel exhaust as a carcinogen were limited due to a lack of exposure measurements and work records relating job title to exposure-related job duties, the study’s authors said.

“Our results suggest that lung cancer mortality in workers with a previous history of regular exposures to particulate from diesel exhaust and other mobile sources is elevated and increases with increasing exposure duration,” the report said. “The increase in lung cancer risk suggests a contribution from diesel exhaust and a mix of vehicle emissions from other sources because each group of workers had different patterns of current and historical exposures. These results along with previous studies support current efforts to reduce emissions from both diesel vehicles and other sources of vehicle and traffic-related emissions.”

The study collected work records for 31,135 male workers employed in the unionized U.S. trucking industry in 1985, examining lung cancer mortality through 2000 for jobs associated with current and historical use of diesel-, gas- and propane-powered vehicles using the National Death Index, indirectly adjusting for cigarette smoking.

The eight categories of workers studied were long-haul driver, pickup and delivery, dockworker, combination worker in the truck cab or loading dock, mechanic, hostler in a terminal yard, clerks in a terminal office, and other jobs.

According to the report, long-haul drivers (LH), P&D drivers, dockworkers, and combination workers all had significantly elevated hazard ratios (HR) compared to the other four categories that did not have regular exposure to exhaust. Combination workers were rated as the most endangered, followed by dockworkers, P&D and LH drivers.

“Adjusting for age and a healthy-worker survivor effect, lung cancer hazard ratios were elevated in workers with jobs associated with regular exposure to vehicle exhaust,” the report said. “Mortality risk increased linearly with years of employment and was similar across job categories despite different current and historical patterns of exhaust-related particulate matter from diesel trucks, city and highway traffic, and loading dock operations. Smoking behavior did not explain variations in lung cancer risk.”

“HRs were statistically significantly elevated for dockworkers and combination workers and were elevated but of borderline significance for LH and P&D drivers,” the report stated. “HRs were not elevated for work as a hostler or mechanic or for other jobs, and the HR for clerks was statistically significantly reduced.”

However, the American Trucking Assns. (ATA) responded to the report by pointing out that conditions and regulations have dramatically improved since 1985, noting that exhaust gas recirculation and other emission-control technologies have reduced NOx emissions by nearly half and diesel particulate filters (DPF) have reduced tailpipe emissions of particulate matter by 90%.

“Today, on-road diesel engines contribute just 1% of the nation's total emissions of volatile organic compounds, carbon monoxide and sulfur dioxide and less than 1.5% of the nation's total emissions of fine particulate matter,” Glen Kedzie, vp & environmental affairs counsel for ATA, told FleetOwner. “Fine particulate emissions from on-road diesel engines have been cut by more than half over the past decade. On-road heavy-duty diesel trucks produce half as much fine particulates as off-road sources, including bulldozers, tractors, railroad locomotives and ships.”

On average, the workers studied were hired in their mid-30s and were predominantly Caucasian, lived in the South or Midwest, and worked in the trucking industry for an average of 22 years. There were 4,306 deaths and 779 cases of lung cancer from 1985 through 2000, the report said.