California Air Resources Board

SACRAMENTO – The California Air Resources Board (ARB) and the Office of Environmental Health Hazard Assessment (OEHHA) have released the document, Draft Health Risk Assessment of Diesel Exhaust, for public and scientific peer review. Diesel exhaust is being considered for identification as a toxic air contaminant (TAC) under California's Air Toxics Law (Assembly Bill 1807).

        After the release of this document there will be a 90 day public review period, which extends through August 8. A public workshop has been scheduled for July 1 to solicit comments and recommendations. This version of the report, along with the comments received and any revisions resulting from the comments, will be reviewed and discussed with the Scientific Review Panel (SRP) at a public meeting. The SRP is an independent body of scientists appointed by the Secretary for Environmental Protection, the state Senate and the Assembly with backgrounds in atmospheric science, toxicology, biostatistics, occupational health and cancer research. Following SRP approval, the report will be submitted to the ARB at a public hearing for possible identification as a toxic air contaminant.

        Under the AB 1807 air toxics identification program, staff from both the ARB and OEHHA have prepared this draft report for public review that will be the basis for the proposed identification of diesel exhaust as a TAC. The SRP has been responsible for reviewing the exposure and health assessment reports produced by ARB and OEHHA staff before they are rendered to the Air Resources Board for formal adoption. Under this program, the ARB is responsible for establishing regulations if needed to ensure cleaner air for Californians, and OEHHA assists in protecting public health by providing objective scientific evaluation of health risks.

        Unlike an assessment of a single chemical, diesel exhaust is a complex mixture of thousands of gases, vapors and fine particles, and in turn, makes the evaluation of health effects of diesel a complex scientific issue. Sorting out the contributions between the chemicals and particles is scientifically challenging. Some of the chemicals, such as benzene and formaldehyde, have been previously identified as TACs by the ARB and are listed as carcinogens either under the state's Proposition 65 or under the federal Hazardous Air Pollutants (HAPS) programs.