OAK CREEK Toxicology & Risk Assessment Consulting An Evaluation of the Use of Toxic Equivalency Factors to Assess Reproductive Hazards of PCBs to Wildlife Polycyclic Aromatic Hydrocarbons or PAHs are a large group of compounds consisting of three or more fused aromatic rings formed during the incomplete combustion of man-made and natural organic materials. According to the Environmental Protection Agency or EPA, PAHs are found in all environmental media and as a class of compounds, PAHs are among some of the most abundant at hazardous waste sites. As such, mixtures of PAHs at hazardous waste sites are thought to pose potential health risk to potentially exposed individuals. The critical effect or the adverse effect to which animals are most sensitive is thought to be the ability of PAHs to cause cancer. Is exposure PAHs at hazardous waste sites causing an increase in cancer incidence? OR ARE WE OVER-REGULATING PAHs? James S. Smith, Jr.

Adverse Reproductive Effects Associated With PCBs Decreased reproductive success Neurotoxic effects Changes in reproductive behavior Teratogenic effects Reduced survivability OAK CREEK

PCBs Cause Toxicity Through A Dioxin-Like Mechanism Bind the aryl hydrocarbon receptor (AhR) PCB-AhR complexes bind DNA regulatory elements to induce gene expression Induce 3-methylcholanthrene-like enzyme activity Species and tissue specific enzyme profile Liver: CYP1A1 gene Aryl hydrocarbon hydroxylase (AHH) Ethoxyresorufin-O-deethylase (EROD) OAK CREEK

Induction of CYP1A1 and EROD Dioxin-Like Compounds Induce CYP1A1 Increase EROD activity ? ? Adverse Reproductive Effects OAK CREEK

Dioxin-Like PCBs Non-ortho substituted or coplanar congeners 126 (3,3’,4,4’,5-pentaCB) 169 (3,3’,4,4’,5,5’-hexaCB) Mono-ortho substituted analogues 123 (2’,3,4,4’,5-pentCB) 114 (2,3,4,4’,5-pentaCB) 105 (2,3,3’,4,4’-pentaCB) 118 (2,3’,4,4’,5-pentaCB) 156 (2,3,3’,4,4’,5-hexaCB) 167 (2,3’,4,4’,5,5’-hexaCB) 157 (2,3,3’,4,4’,5’-hexaCB) 189 (2,3,3’,4,4’,5,5’-heptaCB). OAK CREEK

1997 WHO TEFs Mammals Fish Birds Compound OAK CREEK 2,3,7,8-TCDD 1 3,4,4',5-TCB 81 0.0001 a,b,c,e 0.0005 0.1 e 3,3',4,4'-TCB 77 0.05 3,3',4,4',5-PeCB 126 0.005 3,3',4,4',5,5'-HxCB 169 0.01 0.00005 0.001 2,3,3',4,4'-PeCB 105 <0.000005 2,3,4,4',5-PeCB 114 a,b,c,d b f 2,3',4,4',5-PeCB 118 0.00001 2',3,4,4',5-PeCB 123 a,c,d 2,3,3',4,4',5-HxCB 156 b,c 2,3,3',4,4',5'-HxCB 157 b,c,d 2,3',4,4',5,5'-HxCB 167 a,d 2,3,3',4,4',5,5'-HpCB 189 a,c a Limited data set b Structural similarity c QSAR modeling prediction from CYP1A induction (monkey, pig, chicken, or fish) d No new data from 1993 review e In vivo CYP1A induction f QSAR modeling prediction from class specific TEFs Compound 1997 WHO TEFs OAK CREEK

TEFs Used to Estimate Exposure to Dioxin-Like Compounds Assumed that PCBs have dioxin-like toxicity PCB “toxic” potency is determined relative to that of 2,3,7,8-TCDD Dioxin equivalent exposure is therefore:  (TEFi x Ci)n OAK CREEK

Some Problems With the Use of TEFs TEFs do not address Non-dioxin-like toxicity Some PCBs are antagonistic of dioxin-like toxicity Biological relevance ? OAK CREEK

Non-Dioxin-Like PCBs Di-ortho PCBs Do not bind AhR Do not induce AHH/EROD Induce phenobarbital-like enzyme activity Associated with adverse effects: CYP2B induction Hypovitaminosis A Hypothyroidism Carcinogenic effects Neurotoxic effects OAK CREEK

Biological Relevance Induction of CYP1A1 or EROD correlated with adverse reproductive effect? Sure What does it mean? There is no mechanistic evidence that AhR binding or induction of CYP1A1 or EROD is linked to the occurrence or severity of any adverse effects. (US EPA (1995) OAK CREEK

Effects of PCB Congeners OAK CREEK

Dioxin-Inducible P-450s P-450 Subclass Activity Humans Rodents Birds CYP1A1 EROD/AHH +/- ++ ++ 6 B -testosterone hydroxylase ? + ? CYP1A2 MROD + + ? ACOH ? + ? Caffeine Metabolism + ? ? CYP2A1 PROD ? + ? CYP1B1 4 a -estradiol hydroxylase + + ? CYP2B1 PROD + + ? CYP2B2 PROD ? + ? CYP2H 16a-testosterone hydroxylase ? ? + 16 B -testosterone hydroxylase ? ? + CYP3A 2 B -testosterone hydroxylase ? ? + 6 B -testosterone hydroxylase ? +++ + 15 a -testosterone hydroxylase ? ? + CYP3A1 PROD ? + ? OAK CREEK

Reproductive Effects Linked to Other Enzymes? Phenobarbital is known to alter testosterone profiles and testicular function (Wani et al. 1996). Do inducers of phenobarbital-type enzyme activity have similar effects? Enzymes that act on estrogen may also be a potential mechanism for reproductive effect. Effects of estrogen metabolites OAK CREEK

Relative Potency of Dioxin for Reproductive Effects OAK CREEK

Relative Potency for Induction OAK CREEK

TEF Use Likely to Over-Estimate Reproductive Risk to Wildlife EROD induction has not been mechanistically linked to adverse reproductive effect. Other dioxin-induced enzyme activities may be more plausibly linked to the occurrence of adverse reproductive effect These other enzymes are induced at dioxin concentrations that are orders of magnitude higher than required for EROD induction OAK CREEK

Conclusion Identify PCB congeners of concern for adverse reproductive effects in wildlife Use TEFs cautiously with the knowledge that adverse reproductive effects have not been mechanistically linked to EROD induction Explore the use of other plausible biologically-based PCB-induced enzyme activities as potential markers of exposure. OAK CREEK