A novel contact assay for testing aryl hydrocarbon receptor (AhR)-mediated toxicity of chemicals and whole sediments in zebrafish (Danio rerio) embryos

The European Water Framework Directive aims to achieve a good ecological and chemical status in surface waters until 2015. Sediment toxicology plays a major role in this intention as sediments can act as a secondary source of pollution. In order to fulfill this legal obligation, there is an urgent need to develop whole-sediment exposure protocols, since sediment contact assays represent the most realistic scenario to simulate in situ exposure conditions. Therefore, in the present study, a vertebrate sediment contact assay to determine aryl hydrocarbon receptor (AhR)-mediated activity of particle-bound pollutants was developed. Furthermore, the activity and the expression of the CYP1 family in early life stages of zebrafish after exposure to freeze-dried sediment samples were investigated. In order to validate the developed protocol, effects of beta-naphthoflavone and three selected sediment on zebrafish embryos were investigated. Results documented clearly AhR-mediated toxicity after exposure to beta-naphthoflavone (beta-NF) and to the sediment from the Vering canal. Upregulation of mRNA levels was observed for all investigated sediment samples. The highest levels of all investigated cyp genes (cyp1a, cyp1b1, cyp1c1, and cyp1c2) were recorded after exposure to the sediment sample of the Vering canal. In conclusion, the newly developed sediment contact assay can be recommended for the investigation of dioxin-like activities of single substances and the bioavailable fraction of complex environmental samples. Moreover, the exposure of whole zebrafish embryos to native (freeze-dried) sediment samples represents a highly realistic and ecologically relevant exposure scenario.