In our study, we aim to characterize the estrogenicity of 18 independent rivers that receive effluent from sewage treatment works. During the winter and summer of 2003, we collected multiple water samples and measured environmental estrogens with an in vitro yeast-based reporter gene assay; estrogenicity was expressed as ng 17beta-estradiol equivalents (EEQ) per L of water. Estradiol equivalents values in winter ranged from 0.3 to 2.0 ng/L and, in summer, from 0.4 to 7.0 ng/L. Winter and summer EEQ values were not correlated with each other or with the dilution factor of the effluent in the river. Variation in EEQ values was large and correlated from winter to summer. Part of this variation in estrogenicity is explained by water flow rates; variation is larger at reduced flow rates. We measured plasma vitellogenin concentrations in immature male brown trout. At five sites, vitellogenin concentrations exceeded 1 microg/ml; however, at the majority of the sites, plasma vitellogenin concentrations were below 0.5 microg/ml. Our data indicate that the exposure of brown trout to environmental estrogens in Swiss midland rivers is low. However, some sites show reoccurring higher EEQ values and, at some sites, plasma vitellogenin concentrations in male fish clearly are elevated.

This field study examined the vitellogenin (VTG) biomarker response under conditions of low and fluctuating activities of environmental estrogenicity. The present study was performed on immature brown trout (Salmo trutta) exposed to the small river Luetzelmurg, which is located in the prealpine Swiss midland region and receives effluents from a single sewage treatment plant (STP). To understand better factors influencing the relationship between estrogenic exposure and VTG induction, we compared VTG levels in caged (stationary) and feral (free-ranging) fish, VTG levels in fish from up- and downstream of the STP, and two different methods for quantifying VTG (enzyme-linked immunosorbent assay vs real-time reverse transcription-polymerase chain reaction), and we used passive samplers (polar organic chemical integrative sampler [POCIS]) to integrate the variable, bioaccumulative estrogenic load in the river water over time. The POCIS from the downstream site contained approximately 20-fold higher levels of bioassay-derived estrogen equivalents than the POCIS from the upstream site. In feral fish, this site difference in estrogenic exposure was reflected in VTG protein levels but not in VTG mRNA. In contrast, in caged fish, the site difference was evident only for VTG mRNA but not for VTG protein. Thus, the outcome of VTG biomarker measurements varied with the analytical detection method (protein vs mRNA) and with the exposure modus (caged vs feral). Our findings suggest that for environmental situations with low and variable estrogenic contamination, a multiple-assessment approach may be necessary for the assessment of estrogenic exposure in fish.