title: Relative potency of PCB126 to TCDD for sublethal embryotoxicity in the mummichog (Fundulus heteroclitus).
abstract: The relative potency (ReP) of 3,3',4,4',5-pentachlorobiphenyl (PCB126) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) for sublethal responses was assessed in Fundulus heteroclitus embryos. Eggs were treated with intravitelline injections of graded sublethal doses of PCB126 (312-5000 pg g(-1) wet weight, ww) or TCDD (5-1280 pg g(-1) ww). At 16 days post-fertilization (DPF), craniofacial deformities were observed in larvae hatched from eggs treated with the two highest doses of PCB126 (2500-5000 pg g(-1) ww). Both compounds caused a dose-responsive reduction of larval growth and prey capture ability (at ≥1250 pg g(-1) ww), and induction of ethoxyresorufin-O-deethylase (EROD) activity (at ≥80 pg g(-1) ww). The dose-response relationships for EROD activity for PCB126 and TCDD had similar slopes and the ReP of PCB126 to TCDD for EROD activity was estimated at 0.71. This is 140-fold higher than the World Health Organization (WHO) TCDD equivalency factor (TEF) of PCB126 for fish (0.005), which is based on rainbow trout (Oncorhynchus mykiss) embryolethality data. The slope of the dose-response relationship for prey capture ability for PCB126 was steeper than for TCDD, suggesting different mechanisms of action. Expression levels of several genes were also studied by quantitative real-time polymerase chain reaction (qPCR) following exposure to single doses of TCDD or PCB126 (1280 and 1250 pg g(-1) ww, respectively) causing similar EROD induction. A different pattern of responses was observed between PCB126 and TCDD: PCB126 appeared to induce antioxidant responses by inducing sod2 expression, while TCDD did not. These results suggest that relative potencies are species-specific and that the current ReP for PCB126 underestimates its toxicity for some fish species. It is recommended to develop species-specific RePs for a variety of sublethal endpoints and at environmentally relevant doses.
authors: Institut des Sciences de la Mer, Université du Québec à Rimouski, Rimouski, Québec, Canada.
authors: Cyril
authors: C
authors: Rigaud
authors: Catherine M
authors: CM
authors: Couillard
authors: Jocelyne
authors: J
authors: Pellerin
authors: Benoît
authors: B
authors: Légaré
authors: Patrice
authors: P
authors: Gonzalez
authors: Peter V
authors: PV
authors: Hodson
mesh_terms: D000818:Animals; D049628:Body Size / Q000187:drug effects; D019363:Cytochrome P-450 CYP1A1 / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D029941:Fish Proteins / Q000235:genetics / Q000378:metabolism; D023781:Fundulidae / Q000196:embryology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D009043:Motor Activity / Q000187:drug effects; D011078:Polychlorinated Biphenyls / Q000633:toxicity*; D000072317:Polychlorinated Dibenzodioxins / Q000633:toxicity*; D011235:Predatory Behavior / Q000187:drug effects; D014874:Water Pollutants, Chemical / Q000633:toxicity*
chemical_list: D029941:Fish Proteins; D000072317:Polychlorinated Dibenzodioxins; D014874:Water Pollutants, Chemical; D011078:Polychlorinated Biphenyls; D019363:Cytochrome P-450 CYP1A1; C023035:3,4,5,3',4'-pentachlorobiphenyl