Fixed-effect-level toxicity equivalents—a suitable parameter for assessing ethoxyresorufin-O-deethylase induction potency in complex environmental samples

Within the scope of bioassay-directed identification of dioxin-like toxicants in complex environmental samples, EC50-based and fixed-effect-level-based 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity equivalents (TEQs) were compared to assess 7-ethoxyresorufin-O-deethylase (EROD) inducing potency of sediment fractions using the rainbow trout liver cell line RTL-W1 as bioassay system. Toxicity equivalents on the basis of fixed effect levels are suggested in order to minimize interpretation problems due to the superposition of enzyme-inducing and enzyme-inhibiting effects. Bioassay-directed fractionation of a contaminated sediment extract in the industrial region of Bitterfeld (Germany) based on fixed-effect-level TEQs indicated high dioxin-like activity in the lipophilic sediment fractions containing the prototypic arylhydrocarbon receptor (AhR) agonists polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs). However, only a small part of the EROD induction could be attributed to the PCBs and PAHs that were analyzed. Significant EROD induction occurred also with some of the more polar fractions.