But a diesel industry group says it's a different story for modern engines in the U.S.
"The scientific evidence was compelling and the Working Group's conclusion was unanimous: Diesel engine exhaust causes lung cancer in humans," says Dr Christopher Portier, chairman of the IARC Working Group. "Given the additional health impacts from diesel particulates, exposure to this mixture of chemicals should be reduced worldwide."
The Diesel Technology Forum responded to the WHO's findings, noting that in the U.S., diesel engines today are subject to stringent emissions regulations. It pointed to a study released in April, the Advanced Collaborative Emissions Study by the Health Effects Institute, testing the effect of EPA-2007 engines on mice, which found "few biologic effects to diesel exhaust exposure." The study was sponsored by U.S. Environmental Protection Agency, the California Air Resources Board, industry and HEI.
In 1988, IARC classified diesel exhaust as "probably carcinogenic" to humans. An Advisory Group that reviews and recommends future priorities for the IARC Monographs Program had recommended diesel exhaust as a high priority for re-evaluation since 1998.
There has been mounting concern about the cancer-causing potential of diesel exhaust, particularly based on findings in epidemiological studies of workers exposed in various settings. A March 2012 publication of the results of a large U.S. National Cancer Institute/National Institute for Occupational Safety and Health study of occupational exposure to such emissions in underground miners showed an increased risk of death from lung cancer in exposed workers.
IARC also concluded that gasoline exhaust was possibly carcinogenic to humans, a finding unchanged from the previous evaluation in 1989.
The Diesel Technology Forum noted that diesel engine and equipment makers, fuel refiners and emissions control technology manufacturers have invested billions of dollars in research in an ongoing effort to reduce emissions to meet the increasingly diverse and stringent clean air standards throughout the world.
"The results of these long-term commitments are very clear," said Allen Schaeffer, DTF executive director, in a statement. "New technology diesel engines, which use ultra-low sulfur diesel fuel, advanced engines and emissions control systems, are near zero emissions for nitrogen oxides, hydrocarbons and particulate matter.
"In the U.S. for example, diesel exhaust is only a very small contributor to air pollution. EPA's most recent data indicates that diesel accounts for less than 6% of all particulate matter in the air. And today in Southern California, more fine particles come from brake and tire wear than from diesel engines."
3/5/2012 Heavy Exposure to Diesel Exhaust Linked to Lung Cancer Death in Miners
4/13/2012 Study Finds Few Effects from Diesel Exhaust from EPA-07 Engines