19 October 2000 | updated 15 November 2000

On its meeting on October 12-13, the EPA Science Advisory Board’s (SAB) Clean Air Scientific Advisory Committee (CASAC), Diesel Review Panel has approved the EPA’s most recent draft Health Assessment Document for Diesel Exhaust (EPA/600/8-90/057E, dated July 2000). The document has been approved with some changes, as outlined in a CASAC review report (the report is expected to be posted in the SAB web site in November—follow the links below). As a result of this decision, which follows a 6-year long review process, the US EPA will finally adopt its formal position on the health effects of diesel emissions.

The July 2000 version of the EPA’s Health Assessment Document follows three earlier drafts, which were published in 1994, 1998 and in November 1999. In all these cases, the CASAC panel found that the document was not scientifically adequate for making regulatory decisions concerning the use of diesel powered engines.

Two classes of possible health effects are discussed in the adopted Health Assessment Document: (1) nonmalignant respiratory effects and (2) carcinogenic effects. The EPA confirmed its earlier findings on the non-cancer effects of ambient PM, such as increased mortality and morbidity. The recommended chronic exposure level without appreciable hazard (inhalation Reference Concentration, RfC) for diesel particulates has been adopted at 5 µg/m3.

A number of conclusions has been drawn on the cancer effects of diesel exhaust particulates, as follows:

  • Diesel exhaust is classified as “likely to be carcinogenic” (down-graded from “highly likely to be carcinogenic”, as described in the November 1999 draft). 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.
  • 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.
  • As a result, no specific cancer unit risk estimate for diesel exhaust is adopted or recommended in the EPA assessment.

The EPA’s position on quantitative cancer risk assessment is in contradiction to the findings of the California Air Resources Board (ARB), which has established unit risk estimates for cancer from diesel exhaust particulates. The ARB estimates are based on some old railroad worker studies, which were later found unsuitable for such purpose by the EPA.

The adopted document is considered by many the most comprehensive, scientifically accurate, and objective summary of current human knowledge on the health effects of diesel emissions. The document will be updated as more information is available in the future, specifically in the area of quantitative cancer risk assessment.

The SAB is an advisory body reporting to the EPA Administrator. The function of the SAB is to provide credible technical advice to the EPA to ensure that EPA regulations are based on solid scientific foundations.

For further information contact Robert Flaak, Clean Air Scientific Advisory Committee, Science Advisory Board, tel (202) 564-4546; fax (202) 501-0582; e-mail flaak.robert@epa.gov.

Source: EPA SAB (EPA draft diesel health assessment | SAB Reports Page)

Preliminary reviewers comments