11 August 2000

The US Environmental Protection Agency (EPA) has released a Science Advisory Board (SAB) review draft of the Health Assessment Document for Diesel Exhaust (EPA/600/8-90/057E), dated July 2000. The document was prepared by the National Center for Environmental Assessment (NCEA) within EPA’s Office of Research and Development.

Effective today, the EPA begins a public review process of the document. Written comments from stakeholders must be submitted by 29 September 2000.

The current document follows three earlier drafts of the EPA Diesel Health Assessment, which were published in 1994, 1998 and in November 1999. In all cases, the Clean Air Scientific Advisory Committee (CASAC), a panel of experts within the SAB, found that the document was not scientifically adequate for making regulatory decisions concerning the use of diesel powered engines. The current draft incorporates comments provided by the CASAC in February 2000. The document will undergo another CASAC review in the Fall of 2000.

The most controversial issues include carcinogenic classification of diesel particulates and cancer risk factors. In its last review, the CASAC panel did not find sufficient scientific explanation for the cancer risk guidelines in the EPA draft, which classified diesel exhaust as “highly likely” to be carcinogenic.

Diesel exhaust is characterized as “likely to be carcinogenic to humans by inhalation at any exposure condition” in the current draft. Neither the current nor the previous drafts, however, adopt a quantified cancer unit risk factor for diesel exhaust. Existing exposure-response data in animal studies have been deemed inappropriate for the estimation of human cancer risk. Exposure-response data in available human studies are considered by the EPA too uncertain to derive a confident quantitative estimate of cancer unit risk. In this respect, the EPA position is different from that of the California Air Resources Board, which has adopted an official cancer unit risk factor for diesel particulates.

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 a solid scientific foundation.

For more information contact: Technical Information Staff, NCEA-W (8623D), US Environmental Protection Agency, 1200 Pennsylvania Avenue, NW., Washington, DC 20460; telephone: 202-564-3261; facsimile: 202-565-0050; e-mail: nceadc.comment@epa.gov.

Download the document from the EPA server