Estrogenic activities in water and sediment from French rivers using zebrafish-based bioassays

Over the last decade, assessment of exposure of fish to aquatic endocrine disrupting chemicals (EDCs) and their effects on endocrine functions has become a major issue in ecotoxicology. In the present study, we explore the potential use of newly developed zebrafish (zf)-based in vitro and in vivo bioassays to detect estrogenic compounds in aquatic environment. For this purpose we use stable zf-estrogen receptor (zfER) subtypes (zfERa, zfERb1, zfERb2) in the zebrafish liver (ZFL) cell line and transgenic cyp19a1b-GFP zf embryos to screen organic extracts of sediment and water (using polar organic compounds integrative samplers - POCIS) sampled from 19 French river sites. Results showed no detection of estrogenic activities in sediment extracts by zf-based in vitro bioassays. Unlike zfERs in vitro bioassays, human receptor (hERa) in vitro bioassay was able to detect estrogenic activities in sediment extracts. However, POCIS-based bio-monitoring provide much more significant information on zf-based in vitro bioassays as estrogenic activities were mainly detected for most of the river sites. High numbers of POCIS extracts were found to be more active on zfERb2 than on zfERa. The responsiveness of zfERb2 to environmental samples is important as this estrogen receptor subtype is present in fish species but not in humans. In addition, SPE-based fractionation of POCIS extracts allowed distinguishing fractions that were active on zfERb2 from those active on hERa. These results suggest a significant inter-assay difference (human MCF-7 versus zebrafish ZFL cells). Moreover, we found similar estrogenic activities on in vivo bioassay by sediment and POCIS extracts as observed on in vitro bioassays. Complementarily, this in vivo assay will allow taking into account the bioavailability and pharmacodynamics of estrogen mimicking compounds to enhance the efficiency and the accuracy of EDCs testing strategies. In summary, this study reports for the first time the use of fish-based bioassays, supporting the significance of using both in vitro and in vivo fish models to detect species-specific active contaminants in aquatic environment