Characterization of dioxin-like activity of sediments from a Czech river basin

Synthetic organic chemicals are present in environmental compartments as co mplex mixtures and therefore their potential effects are difficult to predi ct. In this study, in vitro bioassays using wild-type fish and rat hepatoma cell lines and their corresponding recombinant cell systems were used to e valuate 2,3.7,8-tetrachlorodibenzo-p-dioxin (TCDD)-like activity in extract s of sediments collected from rivers of the Czech Republic. All the sedimen t extracts elicited statistically significant responses in all the cell lin es tested. For most sediment extracts, a complete dose-response relationshi p was obtained. The maximal efficacy of the samples was between 57 and 143% of the maximal induction elicited by TCDD. Greater responsiveness, sensiti vity, and reproducibility were observed for recombinant than wild-type cell s. Cell line-specific differences in the sensitivity to compounds present i n the complex sediment extracts were observed. The TCDD equivalents (TCDD-E Qs) determined from the different cell bioassays were correlated. Greater c oncentrations of TCDD-EQs were obtained with fish cell lines. The TCDD-EQs calculated from the results of chemical analysis of toxic equivalents (TEQs ) were in good agreement with those determined by bioassays; the arty hydro caron receptor (AhR)-effects of the identified chemicals appear to be gener ally additive. This indicates that most of the TCDD-like activity was accou nted for by the compounds identified and quantified by instrumental analysi s. Fractionation along with mass-balance calculations allowed identificatio n of the active fractions and classes of compounds. Polycyclic aromatic hyd rocarbons (PAHs) were found to be responsible for most of the AhR-mediated activity in sediments.