Assessment (NCEA) headed the reassessment efforts with participation of scientific experts in EPA, the National Institutes of Health’s (NIH) National Institute of Environmental Health Sciences (NIEHS), and other federal agencies and scientific experts in the private sector and academia. EPA sponsored open meetings in 1991 and 1992 to inform the public about the assessment, receive public comments on plans and activities of the reassessment process, and obtain additional relevant scientific information. Peer-review workshops were convened in 1992 and 1993 to review initial drafts of all background chapters. The workshops were followed by extensive revision and additional review of some chapters. In 1994, EPA released for public review all the chapters plus the first draft of a summary risk characterization chapter, received public comments on the drafts, and submitted the documents to the SAB for review.

In 1995, the SAB, commenting on the 1994 draft assessment, proposed several substantive and contingent recommendations, including revision of the chapter on dose-response modeling for TCDD, development of a chapter on dioxin toxic equivalency factors (TEFs), and an external peer review of redrafted or new chapters, including the chapter on risk characterization. The SAB also recommended that EPA involve outside scientists from the public and private sectors to help determine approaches for revising what was then called Chapter 9: “Risk Characterization of TCDD and Related Compounds.”

In 1996, EPA initiated interaction with a group of 40 stakeholders from the public and private sectors to gather input on approaches for conducting the risk characterization revision. EPA met regularly with the group to ensure ongoing input as recommended by the SAB and shared with them the initial post-SAB revision of the draft risk characterization.

EPA, with NIEHS, revised Chapter 8, developed a new Chapter 9 on TEFs, and revised the former Chapter 9 and renamed it as a free-standing report, “Part III—Integrated Summary and Risk Characterization for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds.” The dioxin report consisted of two other parts: “Part I—Estimating Exposure to Dioxin-Like Compounds” and “Part II—Health Assessment for 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds.” All three parts are collectively referred to as the Reassessment.

On February 24, 1997, the Federal Register announced the public external peer review and 60-day comment period of the revised Chapter 8, “Dose-Response Modeling for 2,3,7,8-TCDD.” On June 12, 2000, the Federal Register announced a similar peer review and public comment period on the revised Part III—Integrated Summary and Risk Characterization and the revised TEFs Chapter 9 in Part II.

Recognizing the broad policy implications of the dioxin reassessment, the National Science and Technology Council established an interagency



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