Notice of Public Comment/Workshop on Proposed Revised Toxicity Equivalency Factors (TEF WHO-97) for PCDDs, PCDFs, and Dioxin-Like PCBs

The Office of Environmental Health Hazard Assessment (OEHHA) is releasing a draft document, Proposal for the Adoption of the Revised Toxicity Equivalency Factor (TEFWHO-97) Scheme to solicit public comment. This draft document has been developed by OEHHA for use in implementing the programs for Toxic Air Contaminants (Health and Safety Code Section 39650 et seq.) and Air Toxics Hot Spots (Health and Safety Code Section 44300 et seq.).

Chlorinated dioxin-like compounds are widespread and persistent environmental contaminants, emitted by various combustion processes, which are suspected of causing cancer and other adverse health impacts. In 1986, the California Air Resources Board identified chlorinated dibenzo-p-dioxins and dibenzofurans as toxic air contaminants, and OEHHA determined a cancer potency value for 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The cancer potency for other dioxin-like congeners varies according to their chemical structure. Toxicity Equivalency Factors (TEFs) are numerical factors that express the toxicity of an individual dioxin-like compound relative to the toxicity of TCDD. The original International TEFs were developed by a group of scientists convened by the World Health Organization (WHO). These are used in the Air Toxics Hot Spots Program to evaluate the cancer risk due to exposure to mixtures of chlorinated dibenzo-p-dioxins and dibenzofurans. More recently, WHO has sponsored revisions of the original TEF table, in order to reflect new data and improved understanding of the nature and mechanisms of toxicity of dioxin-like compounds. Chlorinated dioxins and dibenzofurans were recently identified as priority chemicals for evaluation of their impact on children's health under the Children's Environmental Health Protection Act (SB25, 1999).

OEHHA proposes that the revised version of the TEF scheme (TEFWHO-97) should be adopted for use by the Toxic Air Contaminants Program. A document has been prepared which describes the revised scheme, reviews the technical basis for the TEF methodology in its latest form, and illustrates the effects of the revisions on some typical calculations of total dioxin equivalents. We are seeking comments on the document, including its clarity, and the appropriateness of the methodology and data on which the TEF scheme is based. Following this public comment period, the document and any comments received, along with OEHHA's response to these comments, will undergo review by the state's Scientific Review Panel on Toxic Air Contaminants.

The draft document Proposal for the Adoption of the Revised Toxicity Equivalency Factor (TEFWHO-97) Scheme becomes available on the OEHHA Home Page at on January 6, 2003. The availability of the document on this site will commence a 30-day public review period that will end on February 5, 2003.

A public workshop will be held at 1.00 pm - 4.00 p.m. on Friday, January 24, 2003 in Oakland. Location information is as follows:
Training Room 1
Elihu Harris Building
1515 Clay St., 2nd Floor
Oakland, CA 94612

Please direct any inquiries concerning technical matters or availability of this document to:

Dr. John Budroe
Chief, Air Toxicology and Risk Assessment Section
Air, Community, and Environmental Research Branch
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA, 94612

E–mail: (link sends e-mail)

Telephone: (510) 622-3145

Information about dates and agenda for meetings of the Scientific Review Panel can be obtained from the ARB web page at