U.N. Agency Calls Diesel Exhaust Human Carcinogen; Industry Questions Conclusion

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By Rick Mitchell and Pat Rizzuto (Washington, D.C.)  

PARIS--The International Agency for Research on Cancer (IARC) has classified diesel exhaust as a known cause of cancer in humans based on “sufficient” evidence that exposure is associated with an increased risk for lung cancer.

The Lyon-based agency, which is linked to the World Health Organization, said June 12 that diesel engine exhaust is a group 1 carcinogen under the IARC classification system.

The new designation modifies IARC's classification of diesel exhaust made more than 20 years ago. IARC in 1988 characterized diesel engine exhaust as “probably carcinogenic to humans,” and it has been a high priority for review for more than a decade.

The announcement came after a week of meetings by IARC's Working Group on Diesel Engine Exhaust and Gasoline Engine Exhaust.

“The scientific evidence was reviewed thoroughly by the working group and, overall, unanimously it was concluded that there was sufficient evidence in humans for the carcinogenicity of diesel exhaust,” working group Chairman Christopher Portier told reporters in a telephone news conference.

“The working group believes very strongly in [this conclusion],” he added.

Portier, director of the Agency for Toxic Substances and Disease Registry under the U.S. Centers for Disease Control and Prevention, said the working group also “noted a positive association [for diesel exhaust], limited evidence, with an increased risk for bladder cancer.”

He said the working group also examined evidence for gasoline exhaust and classified it as a possible carcinogen, group 2B in its classification system. That was the same conclusion reached by the group in 1989.

Conclusion Called 'Premature.'

The U.S.-based Diesel Technology Forum issued a statement on its website questioning the new IARC conclusions, citing what it identified as a study by the U.S. Environmental Protection Agency and other government organizations that found “few biologic effects to diesel exhaust exposure.”

“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., EPA indicates that diesel accounts for less than 6 percent of all particulate matter in the air,” the forum said.

Howard Feldman, director of regulatory and scientific affairs for the American Petroleum Institute, described IARC's decision as “premature.”

“The agency should have reserved judgment on the carcinogenicity of exhaust from newer fuels and engines until the extensive research currently under way is completed,” Feldman said in a statement provided to BNA.

He referred to ultralow-sulfur diesel that began to be used June 1, 2006; new-technology engines that can meet EPA's 2007 emission standards; and an Advanced Collaborative Engine Study (ACES) being conducted by the Health Effects Institute.

Environmental Group Sees 'Confirmation.'

In contrast, Peter Lehner, executive director of the Natural Resources Defense Council, issued a statement saying IARC's announcement “confirms what we've known for decades--diesel pollution is deadly and threatens our health.”

“Adding to years of studies showing links between diesel pollution and asthma, heart, and other respiratory ailments, we now have confirmation that diesel pollution can cause cancer,” Lehner said.

IARC Director Christopher Wild said the agency's role is to summarize available scientific evidence and put it into the public domain so that governments can decide on permissible levels of exposure, both in the workplace and in the general population.

“It's now up to national and international regulatory authorities to weigh [this evidence] with other factors, such as effects on other health endpoints, because these compounds don't only lead to lung cancer but also lead to other chronic diseases, cardiovascular diseases, chronic respiratory illnesses,” Wild said.

But he said governments will also weigh the benefits of diesel technology and alternatives to it.

Kurt Straif, head of IARC's Monographs program, said the program's task is to identify hazards. The next step is a risk assessment, conducted by regulatory authorities, that should aim to better characterize exposure and “the exposure-response relationship,” he said.

Portier said the working group did not address what levels of exposure to diesel exhaust could be safe, but he said the United States and European Union have set “stringent” exhaust standards, phased in over a number of years, “that are very likely to reduce exposure to these carcinogens in the environment.”

No Specific Exposure Singled Out.

Straif said the subgroup on evidence on cancer in humans considered all pertinent epidemiological studies and published evidence related to diesel exhaust.

As part of its work, the subgroup considered studies on occupational exposure in well-defined groups with relatively high exposure levels, such as underground miners, railroad workers, truckers, and bus company workers.

These studies identified various exposure levels and risks, including a study of underground miners that found a two- to threefold relative risk and one of railroad workers that found a relative risk of about 1.4, “or a risk increase of about 40 percent,” he said.

However, he noted that the working group concluded, along with the subgroup, that all occupational and other exposures to diesel engine exhaust, including in traffic, can cause lung cancer without focusing on one type of exposure.

Inconclusive on Childhood Effects.

Portier noted that the group reviewed epidemiological evidence and a wide array of toxicological evidence, including laboratory studies.

“We had a little bit of epidemiological evidence on children and whether or not exposure during development in early life made a big difference in overall risk. There really wasn't enough evidence there for us to make any evaluations,” he said.

But he said laboratory animal evidence indicated that individual nitroarenes, a component of diesel exhaust, showed “some patterns that suggest vulnerability during early stages of life. …”

“So there are periods that might make a difference, but that's just from laboratory experiments, not epidemiological evidence,” he said.

The U.S. National Toxicology Program's 12th Report on Carcinogens, issued in June 2011, classifies diesel exhaust particulates as reasonably anticipated human carcinogens “based on limited evidence of carcinogenicity from studies in humans and supporting evidence from studies in experimental animals and mechanistic studies.”

By Rick Mitchell and Pat Rizzuto (Washington, D.C.)  

More information on the IARC's conclusions is available at http://press.iarc.fr/pr213_E.pdf.