US EPA publishes final Health Assessment Document For Diesel Exhaust

4 September 2002

The US Environmental Protection Agency (EPA) published yesterday the final Health Assessment Document for Diesel Engine Exhaust, EPA/600/8-90/057F, dated May 2002. The document is perhaps the most comprehensive, scientifically accurate, and objective summary of current human knowledge on the health effects of diesel emissions. The assessment evaluates (1) the health effects literature to identify the most important exposure hazards to humans and (2) the exposure-response characteristics of the key health effects so that information is available for understanding the possible impact on an exposed population. The document was prepared by the EPA Office of Research and Development’s National Center for Environmental Assessment (NCEA).

The major conclusions of the assessment can be summarized as follows:

• Diesel exhaust is classified as “likely to be carcinogenic” (down-graded from “highly likely to be carcinogenic” in earlier draft versions of the document). Epidemiological studies suggest that occupational exposures to diesel exhaust particulates cause a small increase in the risk of lung cancer, in the range of about 20-50%. The EPA believes the cancer hazard is also applicable to ambient (i.e. environmental) exposures, even though none of the studies examined by the EPA show that lung cancer hazard is indeed present at environmental levels of exposure.
• No specific cancer unit risk estimate for diesel exhaust is adopted or recommended in the EPA assessment. Animal (rat) cancer studies are not clear for human hazard prediction and unsuitable for environmental exposure risk estimate. Quantitative statements on human risk cancer should be based on human epidemiological studies. However, the currently available data, due to a number of uncertainties, is deemed unsuitable for quantitative risk assessment.
• Non-cancer health effects from diesel emissions may include short-term (i.e., acute) exposure effects such as transient irritation and inflammatory reaction, as well as exacerbation of existing allergies and asthma symptoms. The nature and extent of these symptoms, however, are highly variable across the population.
• Diesel emissions, as a mixture of many constituents, also contribute to ambient concentrations of several criteria air pollutants including nitrogen oxides, sulfur oxides, fine particles, as well as other hazardous air pollutants.

The final version of the EPA’s Health Assessment Document follows four earlier drafts, which were published in 1994, 1998, 1999, and in July 2000. All of the draft versions were subject to review by the EPA Science Advisory Board’s (SAB) Clean Air Scientific Advisory Committee (CASAC) Diesel Review Panel. In the case of the 1994-1999 versions, the CASAC panel found that the document was not scientifically adequate for making regulatory decisions concerning the use of diesel powered engines. The draft of July 2000 was approved by the CASAC panel in October 2000. The July 2000 version of the assessment, along with the review comments of the CASAC panel, was part of the scientific basis for EPA’s 2007 emission standards for heavy-duty highway engines completed in December 2000.

The health assessment’s conclusions are based on exposure to exhaust from diesel engines built prior to the mid-1990’s. The emission levels and composition of the diesel particulate matter and the gases change with the engine technology. While EPA believes that the assessment’s conclusions apply to the general use of diesels today, the conclusions in the Health Assessment Document will need to be reevaluated as cleaner diesel engines replace a substantial number of existing engines.

Source: US EPA