Nomination Summary for Dioxin toxic equivalence factor studies (N95036)

Nominated Substances: 2,2'-4,4',5,5'-Hexachlorobiphenyl (PCB 153), 2,3',4,4',5-Pentachlorobiphenyl, 3,3,4,4,5-Pentachlorobiphenyl (PCB 126), 1,2,3,7,8-Pentachlorodibenzo-p-dioxin, 2,3,4,7,8-Pentachlorodibenzofuran, Toxic equivalency factor evaluation (Binary mixture; PCB 126/PCB 153), 2,3,7,8-Tetrachlorodibenzo-p-dioxin, Toxic equivalency factor evaluation (Dioxin mixture)

Nomination Date: 03/27/1995

Nominator: NIEHS, EPA

Rationale: Scientists from NIEHS and EPA formed a committee to address issues concerning Dioxins and Toxic Equivalency Factors (TEFs). The activity of some members of this class of compounds is generally expressed relative to the prototypical 2,3, 7,8-tetrachlordibenzo-p-dioxin due to the existence of a common mechanism of action, i.e., binding to the Ah receptor. The use of TEFs to predict carcinogenicity remains an unresolved concept because of the limited database on carcinogenicity of this class of compounds. The purpose of this study is to expand the database on the applicability of TEFs in predicting carcinogenicity.

NTP Principles: not specified