Estrogenic potential of the Venice, Italy, lagoon waters

The exposure of the Venice lagoon (Italy) to endocrine-disrupting compounds (EDCs) from different sources was investigated. Spatial and time distribution of EDC concentrations were determined in four sampling sessions (December 2001-May 2002) by solid phase extraction followed by high-performance liquid chromatography separation coupled with mass spectrometry detection via electrospray interface (SPE-HPLC-ESI-MS), which allowed identification of natural (estradiol, estrone) and synthetic estrogenic compounds, both steroidal (ethinylestradiol, mestranol) and nonsteroidal (benzophenone, bisphenol-A, nonylphenol, nonylphenol monoethoxylate carboxylate). No significant differences in the EDC distribution were observed between stations located near selected sources (raw sewage from the historical center of Venice, treated municipal and industrial effluents from sewage treatment plants, and areas undergoing the inflow of rivers). While synthetic nonsteroidal analytes were recorded in the 1 to 1040 ng/L range (average concentration: 34 ng/L), steroidal EDC (estradiol, ethinylestradiol) concentrations were lower (1-125 ng/L; average concentration: 8 ng/L). The estrogenic activity of lagoon waters was estimated in terms of estradiol equivalent concentration (EEQ) by applying the estradiol equivalency factors (EEFs). Steroidal EDCs (estradiol, ethinylestradiol) contributed >97% to the total potential estrogenicity of the waters, which accounted for 4 to 172 ng/L (average: 25 ng/L), as total EEQs. These levels are likely to pose adverse effects on the Venice lagoon aquatic organisms.     

Bioassay-derived androgenic and estrogenic activity in municipal sewage in Australia and New Zealand

Raw sewage and sewage at various stages of treatment were sampled from 15 municipal sewage treatment plants in south Queensland (Australia) and Canterbury (New Zealand). Estrogenic and androgenic activities were determined with sheep estrogen receptor and rainbow trout androgen receptor binding assays, respectively. Selected estrogenic chemicals were also analyzed by gas chromatography-mass spectrometry. The raw sewage influents contained significant levels of both estrogenic (<4-185 ng/L estradiol equivalents) and androgenic (1920-9330 ng/L testosterone equivalents) activity. Subsequent treatment of raw sewage successfully removed most of the activity so that the estrogenicity and androgenicity associated with the final effluents were very low (<1-4.2 ng/L estradiol equivalents and <6.5-736 ng/L testosterone equivalents, respectively). Secondary treatment was the most effective treatment step to remove estrogenic and androgenic activity from sewage water. Activated sludge treatment in particular removed 92% to >99% of the estrogenic activity and 82% to >99% of the androgenic activity in sewage.     

Characterization of the estrogenicity of Swiss midland rivers using a recombinant yeast bioassay and plasma vitellogenin concentrations in feral male brown trout

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.     

Estrogenic potential of halogenated derivatives of nonylphenol ethoxylates and carboxylates

Halogenated derivatives of nonylphenol and of its alkylates are generated during drinking water disinfection and treatment procedures. In this paper we analyze the potential of these compounds to interact with the estrogen receptor and to activate hormone-regulated gene promoters. We used the recombinant yeast assay (RYA) and the human breast cancer cell MCF7 proliferation assay for both estrogenic and antiestrogenic activities and the enzyme-linked receptor assay to examine in vitro binding to the receptor. Many nonylphenol derivatives were very weak estrogens in our functional tests when compared to nonylphenol while retaining a substantial affinity for the estrogen receptor in vitro. Antiestrogenicity tests demonstrated that brominated nonylphenol and most of the carboxylated compounds studied here behaved as estrogenic antagonists in the RYA. We also detected an increased cytotoxicity for the carboxylated derivatives in both yeast and mammalian cells. We conclude that derivatization may mask the apparent estrogenicity of nonylphenol, but the resulting compounds still represent a potential hazard since they are still able to bind the estrogen receptor and to influence the physiological response to estrogens. Our results also illustrate the advantage of combining different methods to assay estrogenicity of unknown substances.     

Changes in estrogenic and androgenic activities at different stages of treatment in wastewater treatment works

Estrogenic and androgenic activities of wastewater were determined during treatment in five wastewater treatment works (WWTWs) in the Untied Kingdom. With one exception, both estrogenic and androgenic activities decreased markedly as wastewater progressed through the plants; removal rates were generally 70% or higher, sometimes reaching 100%. Most of the reduction in activity occurred during secondary (biological) treatment. In both influents and effluents, estrogenic and androgenic activities were appreciably lower in samples collected in August, when the amount of rain had been substantial, compared with samples collected in April and May. Most final effluents contained very low (or nondetectable) estrogenic activity (undetectable to 13 ng/L of estradiol equivalents) and androgenic activity (undetectable to 143 ng/L of dihydrotestosterone [DHT] equivalents), although one (from a WWTW that had only primary treatment) contained relatively high activities (40 ng/L of estradiol equivalents; 4,033 ng/L of DHT equivalents). The type of treatment available at the various WWTWs also affected the activity of the final effluent. The biological significance of these results will depend upon which chemicals contribute to the estrogenic and androgenic activities, because of widely different potencies of different estrogenic chemicals, and on the degree of dilution of the effluents in their receiving waters.     

Comparison of the estrogenic activities of seawater extracts from Suruga Bay, Japan, based on chemical analysis or bioassay

The present study compared estrogenicity measured by in vitro bioassay and estrogenicity estimated by the chemical analysis of seawater from Suruga Bay, Japan. Nonylphenol, bisphenol A, estrone, 17beta-estradiol, nonhydroxy polycyclic aromatic hydrocarbons, and hydroxy polycyclic aromatic hydrocarbons, some of which show estrogenic activity, were selected as the target compounds. The yeast two-hybrid system was used to evaluate the estrogenic activities of seawater and chemicals with or without rat liver S9. Concentrations of estrogenic compounds in seawater were measured by chemical analysis using gas chromatography/ mass spectrometry. The main estrogenic compounds in seawater were estrone (< or = 9.2 ng/L), bisphenol A (< or = 1,070 ng/L), and nonylphenol (< or = 276 ng/L). The highest estrogenic activities in seawater were observed near a sewage treatment plant, but the predicted potencies based on the chemistry data were higher than those observed experimentally for the estrogenic activity in seawater. The estrogenicity measured by bioassay was raised considerably after S9 treatment; this observation was limited to the zone of freshwater immediately adjacent to the wastewater outfall.     

Evaluation of Estrogenic Activity in Surface Water and Municipal Wastewater in Shanghai,China

Estrogenic potency of water samples from various rivers and wastewater treatment plants (WWTPs) in Shanghai was determined to assess the estrogenic pollution in typical Chinese urban regions. While the estrogenic activity, calculated as estradiol equivalents (EEQs), in surface water was found to be 2.48–41.9 ng/L, it was 47.7–80.1 ng/L in the influents from WWTPs. After treatment (removal rate of 62.3%–83.6%), the EEQ level in effluents was 7.82–24.8 ng/L, which was within the range of the corresponding receiving rivers. Our findings suggest that WWTP effluents may not be the predominate source of potential aquatic estrogenic contamination in Shanghai.     

Estrogenicity patterns in the Swiss midland river Lützelmurg in relation to treated domestic sewage effluent discharges and hydrology

Sewage treatment works (STW) discharge estrogenic effluent into rivers, which leads to variable estrogenicity of river water. Here, we characterize how the factors effluent and hydrology influence the estrogenicity of river water. We selected a river for which good hydrological data are available and collected water samples upstream and downstream from a STW discharge; effluent was sampled as well. Sampling took place during four 12-d periods, associated with the seasons, and always occurred in the morning. We also investigated the estrogenicity along the river, both by grab sampling and by passive sampling. Estrogens were analyzed by a recombinant yeast assay (YES); the estrogenicity of a sample was equated to the 17beta-estradiol standard of the YES (ng/L). Estrogenicity upstream from the STW was mostly close to the detection limit of the YES (maximum, 0.4 ng/L). Estrogenicity of effluent ranged between 0.2 and 7.7 ng/L; lower estrogenicity was associated with higher hydraulic retention times. Downstream from the STW, estrogenicity exceeded 1 ng/L on 25% of the days (maximum, 2.1 ng/L). Measured river water estrogenicity correlated positively and significantly with predicted estrogenicity based on effluent estrogenicity and effluent dilution factor. Grab samples taken along the river indicate that no significant sources of estrogens were upstream from the STW; downstream from the STW, the pattern of estrogenicity was highly variable. However, passive sampling showed that the estrogenicity of river water downstream from the STW decreased continuously with increasing distance from the STW, which is largely explained by dilution.     

Horizontal and Vertical Distribution of Estrogenic Activities in Sediments and Waters from Tokyo Bay, Japan

Endocrine-disrupting chemicals with estrogenic activity (e.g., alkylphenols) have been detected in coastal Japan. We aimed to determine estrogenic activity in extracts of river water, seawater, sediments, and sediment cores from Tokyo Bay by in vitro gene expression assay. Fifty-one of 57 extracts had some estrogenic activity. E₂ equivalents (ng E₂ equivalents per gram dry weight or per liter above the limit of detection) in river water samples ranged from 0.70 to 4.01 ng/L; in seawater samples from 0.34 to 2.52 ng/L; and in surface sediments from 2.07 to 12.1 ng/g. The relationship between salinity and estrogenic activity in water samples suggested that fresh water is one source of environmental estrogens in Tokyo Bay. Fractionation of sediment extracts showed that the highest estrogenic activity was observed in the midpolar fraction. The observed activities were compared with activities mediated by known concentrations of nonylphenol, bisphenol-A, estrone, and 17-estradiol. In sediment collected near the sewage treatment plants, the estrogenic activity of the midpolar fraction could be explained about 34% by nonylphenol and estrone contained in this fraction. Core sediment measurements detected estrogenic activity from as far back as the 1960s. The regulations on the industrial wastewater in early 1970s would be one of the main reasons for the lower estrogenic activity in the upper section of the sediment core. The high estrogenic activities as measured in water and sediment samples from Tokyo might be restricted to certain coastal areas.     

Chemical and Biological Characterization of Estrogenicity in Effluents from WWTPs in Ria de Aveiro (NW Portugal)

Effluents from wastewater treatment plants (WWTPs) are responsible for the input of estrogenic contaminants into aquatic ecosystems, leading to widespread effects in wildlife. In the present work, levels of estrone (E1), 17α- and 17β-estradiol (E2), 17α-ethinylestradiol (EE2), bisphenol A (BPA), and nonylphenol (NP) were quantified in effluents from WWTPs located in Ria de Aveiro (NW Portugal), as well as in the final effluent discharged into the Atlantic Ocean through the S. Jacinto submarine outfall. Reference sites, located at the entrance of the estuarine system and at the seaside, were also included. Samples were collected under summer (June 2005) and winter (February 2006) conditions. For the summer survey samples, estrogenicity and androgenicity were evaluated using the yeast estrogen screen (YES) and the yeast androgen screen (YAS) assay. Estrone levels varied from 0.5 to 85 ng/L in the summer survey and between <LOD (limits of detection) and 43 ng/L in winter; estradiol levels ranged from <LOD to 9.2 ng/L in summer and were always <LOD in the winter survey; EE2 levels were always <LOD for both surveys. NP concentrations ranged from 75 ng/L up to 2,350 ng/L in summer and from 10 to 2,410 ng/L in winter; BPA levels varied from 2.8 to 897 ng/L in summer and from 2.6 up to 316 ng/L in winter. Biological assays disclosed estrogenic levels at reference sites lower than the ones reported to pose risk for wildlife. However, the S. Jacinto outfall effluent released high concentrations of NP and BPA into the marine environment.     

Chemical and biological analysis of endocrine-disrupting hormones and estrogenic activity in an advanced sewage treatment plant

The steroid hormones estrone (E(1)), 17beta-estradiol (E(2)), estriol (E(3)), 17alpha-ethinylestradiol (EE(2)), and their conjugated forms were surveyed throughout an advanced sewage treatment plant (STP). The estrogen concentrations in water and sludge samples, collected in October 2004 and April 2005, were determined by gas chromatography-mass spectrometry and liquid chromatography-tandem mass spectrometry. Simultaneously, the estrogenic activity was quantified using estrogen-responsive reporter cell lines (MELN) to investigate the behavior of overall estrogenic compounds. The estrogen concentrations in the inlet ranged from 200 to 500 ng/L, with the contribution of conjugated forms being higher than 50%. The major estrogens in influent were E(1) and E(3). The estrogenic activity was between 25 and 130 ng/L of E(2) equivalents (EEQs). Estrogen concentrations and estrogenicity measured in the inlet and in primary treated sewage were similar, showing a weak impact of primary treatment on hormone removal. In contrast, both estrogen concentration and estrogenicity decreased during biological treatment, with high removal efficiencies (>90%). Estrone, E(2), and EE(2) persisted in the treated water below 10 ng/L, whereas the estrogenicity was lower than 5 ng/L of EEQs. Estrogen mass flux in the effluent and sludge represented less than 2 and 4%, respectively, of the inlet. Consequently, the fraction of estrogens sorbed into the sludge was very small, and biodegradation was the main vehicle for estrogen elimination. This dual approach, comparing chemical and biological analysis, allowed us to confirm that most of the estrogenic activity occurring in this STP, which receives mainly domestic sewage, resulted from sex hormones.     

Comparative analysis of estrogenic activity in sewage treatment plant effluents involving three in vitro assays and chemical analysis of steroids

In this study, we assessed and compared the suitability of three in vitro screening tools for the measurement of estrogenic activity in sewage treatment plant effluents (STPEs). These assays were the yeast estrogen screen (YES), production of zona radiata proteins (ZRPs) in trout hepatocytes, and the induction of reporter gene expression in the transfected rainbow trout gonad cell line RTG-2. Data obtained with the YES were additionally compared with calculated estrogenicity, based on steroid analysis data of the effluents. For comparison purposes, the response of the in vitro systems toward the estrogenic chemicals beta-estradiol, ethinyl estradiol, bisphenol-A, nonylphenol, and octylphenol was assessed. All three assays showed sensitivities in the same order of magnitude in response to the steroid compounds tested, with ZRP production being the least sensitive. Regarding the estrogenic environmental chemicals tested, the RTG-2 assay was more than an order of magnitude more sensitive than the other two assays. Despite their different sensitivities toward selected test chemicals, the three in vitro systems indicated estrogenic activity in the same concentration range for the tested STPEs. Calculated estrogenicity (chemical analysis) and measured estrogenicity (YES) were of the same order of magnitude for the STPEs tested. The present study indicates that all three in vitro systems, with the yeast-based system being the easiest and most robust, are applicable for the screening of estrogenic activity in effluent samples.     

Nonylphenol affects the granulation pattern of epidermal mucous cells in rainbow trout, Oncorhynchus mykiss

Nonylphenol is a biodegradation product of nonionic surfactants and has recently attracted considerable attention due to its estrogenic potential. Sexually mature male rainbow trout were repeatedly exposed (one to four periods of 10 days each) to environmentally relevant concentrations of nonylphenol (1 microg/L, 10 microg/L) and for comparison, trout were injected with estradiol. Since estrogens are known to induce structural changes within the fish skin, a similar effect of xenobiotics with estrogen-like activity was assumed. Samples of skin were evaluated by means of light and electron microscopy and histochemistry. In trout exposed to nonylphenol and to estradiol, the structure of the epidermis was altered: an irregular overall architecture was often accompanied by detached pavement cells, vacuolation of the cytoplasm, and severely deformed cell nuclei. However, the granulation pattern of the mucous cells was influenced exclusively after exposition to nonylphenol. The number of large and irregularly shaped mucosomes depended more on the exposure period than on the concentration of nonylphenol. Furthermore, this alteration has not yet been reported for any other pollutant or stressor and, thus, can be classified as an effect that would strongly indicate exposure to nonylphenol.     

Estrogenicity in bile of juvenile rainbow trout as measure of exposure and potential effects of endocrine disruptors

Estrogenicity in the bile of juvenile rainbow trout exposed to effluents from municipal sewage treatment plants and various industries was assayed by using a recombinant yeast strain containing the human estrogen receptor alpha gene. Estrogenicity in bile also was measured after deconjugation of steroids to provide an estimate of the exposure and as an endpoint for potential effects on the organism. In unexposed fish or fish exposed for three weeks at control localities, 0.5 to 9 ng of estradiol equivalents (EEq) were found per gram of bile (ng EEq/g bile). Fish exposed for three weeks in cages placed in the receiving waters near outlets of municipal effluent had an average activity of 26 ng EEq/g bile. Fish exposed to undiluted sewage water in aquaria had a bile estrogenicity of 51 to 87,000 ng EEq/g bile. Unconjugated estrogens contributed only 8% or less to the estrogenicity in bile of fish exposed to municipal effluents. Municipal sewage effluents were more estrogenic than the industrial effluents that were investigated. Estrogenicity in bile was compared to that in extracts of wastewater by using the same receptor assay, and to vitellogenin induction in the plasma of the same fish. Bile estrogenicity proved to be a useful and sensitive (internal) measure of exposure and indicated its potential for the display of biological effects as a complement or replacement of more laborious assays.     

Endocrine disruptors in sewage treatment plants,receiving river waters,and sediments: integration of chemical analysis and biological effects on feral carp

Occurrence of alkylphenol ethoxylates or their metabolites (alkylphenols and carboxylated derivatives), as well as natural and synthetic steroids in sewage treatment plant (STP) effluents and in their receiving waters, has been related to biological effects, measured as alterations of plasma vitellogenin (VTG) concentration in natural fish populations. Water composites of STP influents, effluents, sludge, river water, sediment, and feral carps (Cyprinus carpio) were analyzed over a seven-month period in two tributaries of the Llobregat River (NE Spain). Solid-phase extraction/liquid chromatography/mass spectrometry (SPE-LC-MS) analysis revealed concentrations of up to 31 microg/L for nonylphenol ethoxylates (NPEOs), 15 microg/L for nonylphenol (NP), and 35 microg/L for nonylphenoxy carboxylate (NPE1C) in river water downstream of STPs. These compounds were also found to accumulate in river sediment with concentrations ranging from 10 to 820 microg/kg of NPEOs and from 22 to 645 microg/kg for NP. Natural and synthetic estrogens and progestogens also occurred in the water and sediments analyzed but in the ng/L and microg/kg range, respectively. Vitellogenin fluctuated among sites and sampling periods, but it was found to be increased in male carp collected downstream of the main STP. A correlation between endocrine-disrupting compounds (EDCs) in water and sediment and plasma VTG concentration in male carp was observed, especially for alkylphenolic compounds in water and sediment samples (r = 0.83-0.84 for n = 24) and for estriol and estrone in water (r = 0.78 and 0.94 for n = 9 and 8, respectively).     

In vivo bioassay-guided fractionation of marine sediment extracts from the Southern California Bight, USA, for estrogenic activity

The exposure and uptake of environmental estrogenic compounds have been reported in previous studies of demersal flatfish species in the central Southern California Bight (SCB), USA. The objective of this study was to evaluate the estrogenic or feminizing activity of marine sediments from the SCB by using in vivo vitellogenin (VTG) assays in male or juvenile fish. In 2003, sediments were collected near wastewater outfalls serving the counties of Los Angeles (LACSD) and Orange (OCSD), and the city of San Diego (SD), California, USA. Cultured male California halibut (CH; Paralichthys californicus) were either directly exposed to sediments for 7 d or treated with two intraperitoneal injections of sediment extract over 7 d. The 17beta-estradiol (E2) equivalent values ranged from 1 to 90 microg/kg with LACSD > SD > OCSD. Measurable concentrations of E2 were observed in all sediment extracts and ranged from 0.16 to 0.45 ng/g. Estrone (El) was only observed in sediments near the LACSD outfall (0.6 ng/g). Alkylphenols and alkylphenol ethoxylates were observed in all sediment samples, but were highest near the OCSD outfall, where concentrations of nonylphenol were 3,200 ng/g. Fractionation studies of the LACSD sediment extract collected in 2004 failed to demonstrate relationships between VTG expression and 62 analytes, including E2, which was observed in the whole extract (2.9 ng/g). Oxybenzone (1.6 ng/g) was identified in bioactive fractions as well as unknown compounds of relatively high polarity. These results indicate that estrogen receptor-based assays may underestimate environmental estrogenic activity and estrogenic compounds other than classic natural and xenoestrogens may contribute to estrogenic activity of sediments from the SCB.     

In vitro and in vivo estrogenicity and toxicity of o-, m-, and p-dichlorobenzene

The estrogenicity of o-, m-, and p-dichlorobenzene (DCB) was evaluated with a yeast estrogen screen (YES) and zebrafish (Danio rerio) vitellogenin (VTG) assays. With the YES, p-DCB and m-DCB were found to be estrogenic in a concentration-responsive manner. The relative potency measured with the YES (relative to 17beta-estradiol) was 2.2 x 10(-7) for p-DCB and 1.04 x 10(-8) for m-DCB. Following acute toxicity tests with the zebrafish, plasma VTG production was measured to examine the in vivo estrogenic activity of the three compounds after a 14-d exposure. Adult zebrafish were exposed to different concentrations of o-, m- and p-DCB, ranging from 0.1 to 32 mg/L; ethynylestradiol ([EE2]; 5 ng/L, 10 ng/L, 50 ng/L, and 100 ng/L) was used as a positive control. After exposure, blood samples were taken and protein electrophoresis was performed to determine the relative VTG content. Gonadosomatic indices (GSI) and condition factors (CF) were also calculated. Elevated VTG levels and decreased female GSIs were found in fish exposed to > or = 5 ng EE2/L and in fish exposed to > or = 10 mg p-DCB/L. Low GSIs coincided with high levels of VTG in the blood of female zebrafish. This relation was not only found in fish exposed to EE2 but also in controls and fish exposed to DCB. Therefore, a direct or indirect effect of VTG on the GSI is suggested rather than a direct toxic effect of the tested compounds on the gonads.     

Estrogenic Compounds and Estrogenicity in Surface Water,Sediments, and Organisms from Yundang Lagoon in Xiamen,China

Seven estrogenic compounds—estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2), diethylstilbestrol (DES), nonylphenol (NP), octylphenol (OP), and bisphenol A (BPA)—in sediments, surface water, pore water, and organisms were investigated and estrogenic activities were estimated by examining estradiol equivalent (EEQ) concentrations in Yundang Lagoon of Xiamen. The results showed that estrogenic compounds were present in all matrixes of interest: in surface water, ranging from 609.61 to 711.31 ng/l; in pore water, ranging from 562.12 to 1038.15 ng/l; in sediments, ranging from 1433.12 to 2060.41 ng/g; and in biota samples, ranging from 1373.76 to 3199.09 ng/g (lipid weight). NP was the predominant component in all collected samples and the highest concentration was 1964.80 ng/g in sediment. Total EEQ ranged from 4.56 to 13.79 ng/l in surface water, from 2.40 to 17.16 ng/l in pore water, and from 8.66 to 23.95 ng/g in sediments. However, major contributors to total EEQ concentrations were E2, E1, and DES. The EEQ concentrations in surface water samples were at a higher level in comparison to that reported in European countries. To biological sample, the highest level of total estrogenic compounds was found in the short-necked clam. Higher values of the biota–sediment accumulation factor (BSAF) were found in short-necked clam and black seabream, indicating that the living habits of organism and physical–chemical properties of estrogenic compounds might influence the bioavailability of estrogenic compounds in organisms.     

Comparison of vitellogenin responses in zebrafish and rainbow trout following exposure to environmental estrogens

In this comparative study, the suitability of the commonly used in vivo biomarker for estrogenicity, vitellogenin (VTG), upon waterborne exposure to known environmental estrogens is evaluated in both male zebrafish (Danio rerio) and juvenile rainbow trout (Oncorhynchus mykiss). The results from initial experiments in which both species were exposed to 4-tert-octylphenol (OP) or 17 alpha-ethynylestradiol under semistatic conditions for 3 weeks demonstrated a difference in species sensitivity for OP exposure. Additional dose-response studies (semistatic, 3 weeks) with 4-nonylphenol (20, 100, and 500 microg/L), bisphenol A (40, 200, and 1000 microg/L), dibutylphthalate (40, 200, and 1000 microg/L DBP), and 17beta-estradiol (20 and 100 ng/L E2) were conducted. All these compounds, except for DBP, were found to be estrogenic to both fish species. The results demonstrated a difference in species sensitivity for NP with the zebrafish being about 5 times less sensitive. For the other compounds tested, no indications for a difference in species sensitivity was found. The results from this study demonstrated that both fish species can be used for the detection of VTG as biomarker for estrogenicity, taken into the potential interspecies differences in sensitivity which might be important for the evaluation of fish population effects.