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 toxican ts in complex environmental samples, EC50-based and fixed-effect-level-base d 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity equivalents (TEQs) we re compared to assess 7-ethoxyresorufin-O-deethylase (EROD) inducing potenc y of sediment fractions using the rainbow trout liver cell line RTLW1 as bi oassay system. Toxicity equivalents on the basis of fixed effect levels are suggested in order to minimize interpretation problems due to the superpos ition of enzyme-inducing and enzyme-inhibiting effects. Bioassay-directed f ractionation of a contaminated sediment extract in the industrial region of Bitterfeld (Germany) based on fixed-effect-level TEQs indicated high dioxi n-like activity in the lipophilic sediment fractions containing the prototy pic arylhydrocarbon receptor (AhR) agonists polychlorinated biphenyls (PCBs ) and polycyclic aromatic hydrocarbons (PAHs). However, only a small part o f the EROD induction could be attributed to the PCBs and PAHs that were ana lyzed. Significant EROD induction occurred also with some of the more polar fractions.