ENVIRONMENTAL NEWS California moves ahead on diesel exhaust study
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cientists advising California regulators approved a longterm study concluding that diesel exhaust is a probable human carcinogen. The determination, which is expected to be approved by the California Air Resources Board (CARB) in July, puts the state's action ahead of a similar assessment underway at EPA. The California study by the Office of Environmental Health Hazard Assessment study was unanimously approved by the Air Resources Board's science advisory panel in April. It was based on over 30 epidemiological studies of exposed workers, including rail workers and miners. The researchers found that exposure to diesel exhaust in concentrations of 1.54 pg/m 3 over a 70-year lifetime will C3.US6 450 cancer C3SCS for every 1 million Californians. A similar study conducted by EPA's National Center for Environmental Assessment used the same epidemiological studies but also incorporated results from animal studies to estimate human cancer risk. Agency staff found that over a lifetime, daily exposure to diesel exhaust in concentrations of about 2 pg/m 3 , produced a cancer risk that ranged from 2 to 400 cancer cases per 100,000 exposed individuals. EPA's Clean Air Act Science Advisory Committee (CASAC), a group of air experts drawn from business, academia, and medicine, declined to approve the study at their May meeting, said EPA study manager William Pepelko of the National Center for Environmental Assessment. Most significantly, CASAC recommended that EPA collect new ambient diesel exhaust data, to see whether any change might affect the toxicity assessment, said Pepelko. The study's exhaust data was collected in the 1980s when
After a decade of work, EPA and California scientists developed similar reports describing the cancer risk from diesel exhaust.
the study was first underway. "Changes in engine technology and fuels have been moving at a fast pace in the last few years," Pepelko said. However, "this new data probably will not have an effect on the toxicity of diesel," he added. The CASAC members also questioned the study's use of animal studies and human exposure data, but they did not appear to question the risk estimates, Pepelko said. The panel is expected to provide the study authors with written recommendations in June. The lack of historical occupational exposure data collected before the 1970s explains why EPA included the animal data when calculating its range of estimated cancer risk, said Pepelko. The California study, however, concluded that the uncertainty associated with the historical exposure gap is compensated for. "The greater than usual uncertainty in the exposure estimates is substantially offset by the much smaller than usual range of extrapolation from occupational exposures of interest to the ambient levels of concern," the scien-
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tists wrote. "The availability of human data obviates the need to use animal data, thus avoiding the uncertainties of animal-tohuman extrapolation." California's Air Resources Board has no plans to ban diesel uel or tighten its tough diesel fuel standards, said board spokesperson Jerry Martin. The board is expected to accept the report's recommendation at its July 30 meeting, which will allow the CARB to comply with state law requiring a formal identification of any chemical that Californians are exposed to that could cause cancer, Martin said. Given the length of time these studies have been in development, neither provides any surprises, said Joseph Mauderly of the Lovelace Inhalation Research Institute in Albuquerque, N.M. Mauderly reviewed both studies and is chair of the CASAC. The National Institute of Occupational Health and Safety first recommended that diesel exhaust be considered a potential occupational carcinogen in 1988. "Nobody is really saying, at least in the medical research community, that there is no risk from diesel exhaust," Mauderly said. Diesel exhaust is a complex mixture of gases and fine particles, and contains over 40 substances that EPA considers hazardous, including benzene. But the trucking and diesel fuel industries are opposed to regulatory changes. California's Attorney General and environmentalists have sued four major supermarket chains, claiming their diesel trucks are in violation of state law requiring companies to inform residents of potential health threats. The environmental groups are recommending a switch to liquefied natural gas. CATHERINE M. COONEY
0013-936X/98/0932-250A$15.00/0 © 1998 American Chemical Society
