TEFs for dioxins and furans as MFO inducers in fish: Where do we compare potencies?
- Environment Canada, Burlington, Ontario (Canada). National Water Research Inst.
Dose-response relationships were examined in detail for the abilities of 5 polychlorinated dibenzo-p-dioxins (PCDDs) and 4 polychlorinated dibenzofurans (PCDFs) to induce EROD activity in rainbow trout. For some congeners, slopes of EROD activity versus exposure to PCDD or PCDF were not parallel to slopes for TCDD; for PCDDs, slopes usually decreased with increasing chlorination. Because of the different slopes, the potencies of PCDDs and PCDFs relative to TCDD decreased with increasing dosages; hence, toxic equivalent factors (TEFs) will vary with the endpoint selected. TEFs were usually largest (congeners were closer in potency to 2,3,7,8-TCDD) when potencies were compared at threshold PCDD/F concentrations, where EROD activity first increased above control levels. These concentrations are typical of those in wild fish. TEFs derived from conventional ED50s were smaller because non-parallel curves diverged. Because EROD activity increases logarithmically in response to doses of PCDD/Fs, the midpoint of the regression where confidence limits are smallest was the log ED50. Comparisons of log ED50s gave TEFs between the threshold and ED50-derived TEFs. The conventional TEF system was developed largely for the protection of humans from PCDDs and PCDFs. These conventional TEFs, derived by comparisons of ED50s, can underestimate the potencies of these compounds in fish at low doses, where the nonparallel dose-response lines are closest to that of TCDD.
- OSTI ID:
- 203622
- Report Number(s):
- CONF-9511137-; ISBN 1-880611-03-1; TRN: IM9614%%134
- Resource Relation:
- Conference: 2. Society of Environmental Toxicology and Chemistry (SETAC) world conference, Vancouver (Canada), 5-9 Nov 1995; Other Information: PBD: 1995; Related Information: Is Part Of Second SETAC world congress (16. annual meeting): Abstract book. Global environmental protection: Science, politics, and common sense; PB: 378 p.
- Country of Publication:
- United States
- Language:
- English
Similar Records
Potency of 3,3{prime},4,4{prime},5-pentachlorobiphenyl (PCB 126) and 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD), to produce lake trout early life stage mortality
Ethoxyresorufin O-deethylase induction of polychlorinated diphenyl ethers in H4IIE cells