[show abstract][hide abstract] ABSTRACT: A decline in brown trout (Salmo trutta fario) catches has been reported in Switzerland, but at present the causative factors have not been clearly identified. Estrogen-active endocrine disrupters (EEDs) have been suggested as one possible explanation, since they are widespread in the aquatic environment and often found at elevated concentrations. In the present study the effects of long-term estrogenic exposure on the reproductive capability of brown trout were investigated. Adult fish were continuously exposed to an environmentally relevant mixture of the natural estrogens estrone (E1), 17beta-estradiol (E2) and the xenoestrogen 4-nonylphenol (NP); the average measured concentrations over the entire exposure time (n=9) were 14.0 ng/l (Min 8.1 and Max 20.6) for E1, 2.1 ng/l (Min 1.3 and Max 4.1) for E2 and 111.0 ng/l (Min 106.7 and Max 115.9) for NP. A solvent control served as negative control, and up to 10-fold higher mixture concentration than the environmentally relevant concentration served as positive control. The fish were exposed for 150 days from the onset of gonadal recrudescence until sexual maturation. Plasma vitellogenin (Vtg) was significantly induced by both concentrations of the estrogenic mixture, whereas effects on growth and fertility were only observed in fish exposed to the high mixture treatment. Fertilization success and offspring hatchability in brown trout exposed to the high mixture treatment were significantly reduced to 9% and 6%, respectively. Developmental time from fertilization until hatching, the percentage of larvae with malformations and survival of larvae, however, were not affected. The results suggest that a combination of estrogen-active compounds at environmentally relevant concentrations would not adversely affect those parameters of brown trout reproductive capability measured in this study. Plasma Vtg in male brown trout appeared to be more sensitive to (xeno)estrogen exposure than the measured reproductive effects.
[show abstract][hide abstract] ABSTRACT: Estrogenic exposure has been reported to occur in Swiss rivers, and there is concern that reduced reproductive health, caused by disturbances of the endocrine system, may contribute to the observed decline in brown trout catch. Consequently, we aimed to determine if disturbances of the endocrine system do occur in wild brown trout (Salmo trutta) in Switzerland and, in the affirmative case, if these might affect trout population status. Our first task was to characterize the estrogenicity of Swiss midland rivers that receive effluents from sewage treatment plants (STP). Next, we performed a set of laboratory and field exposure experiments aimed at elucidating how estrogens affect sexual development and reproductive parameters as estrogen-sensitive targets in the life cycle of brown trout. Subsequently, we assessed the demographic status of brown trout populations in the field which were exposed to the cumulative impact of estrogen-active compounds and other stressors. Finally, we integrated the data into a life-cycle model to predict potential population-level consequences of the (xeno)estrogenic exposure. The estrogenicity of 18 Swiss midland rivers was characterized bioanalytically by applying the YES bioassay to water samples and by measuring plasma vitellogenin (VTG) levels in resident brown trout. Generally, estrogenic contamination of the rivers appears to occur only locally and at comparatively low levels (0.2-2 ng/l 17β-estradiol equivalents). In laboratory experiments, potential disruptive effects of estrogens on gonadal differentiation and reproduction of brown trout were investigated. The estrogen-sensitive window of brown trout gonad differentiation was found to differ from other salmonid species. Feminisation of the developing gonads occurred only after exposure to rather high estrogen concentrations. Analysis of VTG mRNA levels indicated that the yolk may accumulate environmental estrogens and act as a long-term reservoir. The experiments to study the effects of prolonged estrogen exposure on reproduction of mature brown trout showed that, while VTG was induced at low concentrations (20 ng/l estrone (E1), 2 ng/l 17β-estradiol (E2) and 400 ng/l 4-nonylphenol (NP)), effects on reproductive parameters such as fertility became evident only at the higher dose (100 ng/l estrone, 10 ng/l 17β-estradiol and 4000 ng/l 4-nonylphenol). For the field study, the river Lützelmurg (Canton Thurgau) was selected as our study site. This river is impacted by the estrogen-active effluents of one sewage treatment plant (STP). Estrogenic levels in the river were found to be highly variable over time, but showed a distinct difference between sites upstream and downstream from the STP effluent - a difference which was also reflected by the VTG levels of caged and resident brown trout. From the brown trout demographic data, it is evident that factors other than estrogen exposure, including habitat quality, strongly influence population structure. The results from the modelling supported this finding and showed that the trout population in the Lützelmurg is likely to be more sensitive to changes of survival rates in the first winter and beyond than to changes in early life stage survival or reproductive parameters. From the overall results of our project, we conclude that a significant influence of estrogenic contamination on brown trout population densities in the majority of Swiss rivers appears not to be likely.
CHIMIA International Journal for Chemistry 04/2008; 62(5):376-382. · 1.05 Impact Factor