After a 10-year-long risk assessment, the Washington, D.C.-based U.S. Environmental Protection Agency's (EPA) Office of Research and Development has found evidence to suggest that long-term exposure to diesel engine exhaust may cause cancer, while simultaneously admitting insufficient scientific proof exists to support its findings.
“It is reasonable to presume that the [diesel exhaust] hazard extends to environmental exposure levels … [and] the potential human health effects of diesel exhausts is persuasive, even though assumptions and uncertainties are involved,” the EPA's Diesel Health Assessment Document says.
The agency has concluded that current scientific evidence is insufficient to define any risk levels between diesel exhaust exposure and lung cancer, as well as asthma and other respiratory disorders. The report also shows that scientific evidence does not confirm that diesel emissions are a known human carcinogen.
Nevertheless, the report confirms conclusions made previously in documents from several world health agencies and studies in California, and is significant because the EPA regulates diesel emissions under the Clean Air Act.
“This will underscore that diesel exhaust is a health hazard and should be controlled,” the Clean Air Trust's Frank O'Donnell says. Furthermore, he adds, the report is “the most in-depth assessment to-date” on diesel fumes.
But with insufficient evidence, some are skeptical about the assessment. “EPA's review of the cancer issue is significant because it states that the actual risk from exposure to diesel particulates, the primary health risk concern, may be zero,” Chicago-based Engine Manufacturers Association (EMA) spokesman Jed Mandel said in an EMA press release.
According to the Washington, D.C.-based Diesel Technology Forum, the report is based on past diesel technology rather than today's clean diesel technology. “While the report focused on the past, the future is clean diesel — diesel trucks and buses built today are more than eight times cleaner than just a dozen years ago,” says Forum Executive Director Allen Schaeffer.
The EPA admits that its findings are based on exposure from diesel engines built prior to the mid-1990s, but contends that the results continue to be valid because many of those trucks remain in service today. The agency also admits that as new diesel engines with cleaner exhaust emissions replace existing engines, it will have to update its assessment.
The report, however insufficient, should help support the agency's October diesel engine regulations, which require certain diesel engines be retrofitted with cleaner-burning fuels. In fact, a draft of the assessment was part of the scientific basis that supported recently established EPA exhaust emission standards for heavy duty highway engines that will take effect with 2007 model year trucks. The 2007 standards are designed to reduce emissions by as much as 95 percent.
The EPA's voluntary Diesel Retrofit Program also is helping states and local agencies retrofit older engines to make them run cleaner and to develop model programs to reduce emissions from idling engines. Additionally, the agency is developing a proposal to address pollution from diesel-powered non-road vehicles and equipment. The agency says that it will publish a rule early next year dealing with diesel exhaust sources, such as construction equipment and hauler trucks.
Based on several categories of how carcinogenic a substance or chemical is, diesel was rated a 2 out of 4 during the assessment, with 1 signifying a definite carcinogen, according to the EPA's Suzanne Ackerman. “Additional studies are currently underway,” she adds. “That is why there is not sufficient evidence yet.”
To view the assessment, visit cfpub.epa.gov/ncea and click on the “diesel” link.