Delayed effects of environmentally relevant concentrations of 3,3′,4,4′-tetrachlorobiphenyl (PCB-77) and non-polar sediment extracts detected in the prolonged-FETAX

In the prolonged-FETAX (prolonged-Frog Embryo Teratogenic Assay- Xenopus) tadpoles are allowed to develop until metamorphosis after an initial 4 day early life-stage exposure (FETAX). PCB 77 (3,4,3′,4′-tetrachlorobiphenyl) and sediment extracts were used in the presented experiments. Concentrations of PCB 77 (0.03 nM = 8.55 ng/L; 3 nM = 855 ng/L; 300 nM = 85.5 μg/L, 30,000 nM = 8.55 mg/L) were derived on the basis of dioxin-like toxic equivalency concentrations known to be present in pore-water. The results were compared to those obtained with the standard FETAX. In the prolonged-FETAX the percentage of animals passing metamorphosis within 115 days was significantly decreased in the groups exposed to 300 or 30,000 nM PCB 77. Significantly increased percentages of tadpoles were halted in thyroid hormone dependent early metamorphic NF stages ≤ 55 (3 nM PCB 77) and metamorphic stages 56–60 tadpoles (300 nM PCB 77 and 30,000 nM PCB 77). Non-polar sediment extracts from two contaminated Dutch sites significantly decreased, and one significantly increased the percentage of animals that passed metamorphosis. These results were in accordance with earlier in vitro results in a thyroid hormone dependent assay and strongly suggest the presence of thyroid hormone disrupting compounds in the aquatic environment. In the classical FETAX neither PCB 77 nor non-polar sediment extracts induced any effects. The results of the present study indicate that the prolonged-FETAX is an important in vivo tool in addition to the in vitro T-screen to assess long-term effects of early life-stage exposure to environmentally relevant concentrations of (mixtures of) compounds and that affect thyroid hormone dependent physiology.