Estrogen Mimics Research Articles

The effect of environment on breast cancer risk.

Environmental factors are believed to explain a large proportion of breast cancer incidence. Known risk factors for breast cancer, which are related to the reproductive life of women, and other factors, such as inheritance and socioeconomic status, explain only about half of the breast cancer cases in the US. Ionizing radiation is a well established environmental risk factor for breast cancer. Chemicals that induce mammary cancer in rodents have served as leads for studies in humans, but occupational and environmental exposure to these chemicals have for the most part lacked association with breast cancer risk. However, there is recent evidence in rats that cadmium at very low doses acts as an estrogen mimic, indicating a need to investigate the effects of metals on breast cancer risk. Studies suggest that circadian rhythm disruption is linked with breast cancer, but too few studies have been done to be conclusive. Over the years, cigarette smoking as a risk factor for breast cancer has remained controversial. However, recent research has found passive smoke exposure to be associated with increased breast cancer risk, which is hypothesized to be accounted for on the basis of an antiestrogenic effect of smoking. Solar radiation has been noted to be associated with reduced breast cancer, supporting the hypothesis that vitamin D plays a protective role in reducing this risk. Although, most of the environmental factors discussed in this review have not been convincingly found to influence breast cancer risk, research suggests that environmental exposure in combination with genetic pre-disposition, age at exposure, and hormonal milieu have a cumulative effect on breast cancer risk.

Proteomics in zebrafish exposed to endocrine disrupting chemicals.

Embryonic zebrafish were examined for changes in protein expression following exposure to sublethal concentrations of 17beta-estradiol (E2) and the estrogen mimic 4-nonylphenol (4-NP). Protein Expression Signatures were derived from embryo homogenates by two-dimensional electrophoresis and digital imaging. In both experiments approximately 30% of the proteins sampled were specific to either E2 or 4-NP and about 33% were common to the control, 4-NP and E2. However, of the proteins induced by either E2 or 4-NP, 28% were common to both chemicals at 1 ppm but only 7% were common to both at 0.1 ppm. While there are many proteins that respond specifically to each chemical, relatively few are common to the two chemicals suggesting that the response pathways of the two chemicals are distinct.

Induction of vitellogenin synthesis in an Atlantic salmon (Salmo salar) hepatocyte culture: a sensitive in vitro bioassay for the oestrogenic and anti-oestrogenic activity of chemicals

A variety of organic compounds have been documented to bind to the oestrogen receptor and induce oestrogenic effects in different vertebrates. The presence of these environmental oestrogens or oestrogen mimics in the aquatic environment has been suspected of disrupting the normal endocrinology of wild populations of fish. In this study, induction of vitellogenin synthesis in primary hepatocytes from Atlantic salmon (Salmo salar) was optimized and validated as an oestrogenic in vitro bioassay using a sensitive capture vitellogenin enzyme-linked immunosorbent assay. After proper optimization (cell media supplements, cell density, temperature and exposure time), this assay gave a sensitive and reproducible response to both endogenous steroids (relative potency: 17β-oestradiol≫oestriol>oestrone>17α-oestradiol) and a range of common oestrogen mimics (relative potency: ethynyloestradiol and diethylstilboestrol≫genistein and zearalenone≫bisphenol A and 4-t-octylphenol>4-n-nonylphenol and 2′-chloro,4-chloro-diphenyltrichloroethane (o,p′-DDT). However, the androgen testosterone and the putative oestrogen mimics dieldrin and toxaphene were not shown to be oestrogenic using this hepatocyte bioassay. Oestrogen-induced vitellogenin synthesis was efficiently inhibited by the anti-oestrogen ZM 189.154, suggesting that this bioassay may be used for testing both the oestrogenic and the anti-oestrogenic properties of chemicals.

Estrogens and phytoestrogens: brain plasticity of sexually dimorphic brain volumes

Sexually dimorphic brain volumes (sexually dimorphic nucleus of the preoptic area (SDN-POA) and anteroventral periventricular (AVPV) nucleus) are influenced by estrogens. Phytoestrogens, derived from plants (especially soy products), are molecules structurally and functionally similar to estradiol. The purpose of this study was to examine: the consumption of phytoestrogen (using a phytoestrogen-rich (Phyto-600) versus a phytoestrogen-free (Phyto-free)) diets from conception to adulthood (or changing the diets during adulthood) and characterizing (a) circulating plasma phytoestrogen levels, (b) testosterone levels in males, (c) sexually dimorphic brain volumes (i.e. the SDN-POA and AVPV) and (d) the presence of apoptotic cells in these brain structures in Long-Evans rats. Phyto-600 fed animals displayed total serum phytoestrogens levels 37-fold higher compared to Phyto-free values. Circulating testosterone levels were not significantly altered by the diets. Female SDN-POA volumes were not altered by the diets. Whereas, males fed a Phyto-free diet displayed decreased SDN-POA volumes compared to male Phyto-600 values. Females fed the Phyto-600 diet displayed larger AVPV volumes compared to males on the same diet or females on the Phyto-free diet. Males fed the Phyto-free diet had the largest AVPV values compared to Phyto-600 fed males. When the SDN-POA region was examined in lifelong Phyto-free fed males, apoptotic cells were present versus males fed the Phyto-600 diet and in the AVPV region the opposite results were obtained. In summary, consumption of dietary phytoestrogens (estrogen mimics) can alter hormone-sensitive hypothalamic brain volumes in rodents during adulthood.

Dietary exposure to xenoestrogens in New Zealand.

Continuing evidence of the feminising effects of xenoestrogens on a range of wildlife species increases the need to assess the human health risk of these estrogen mimics. We have estimated the exposure of New Zealand males, females and young men to a range of naturally occurring and synthetic xenoestrogens found in food. Only estrogenic compounds that act by interaction with the estrogen receptor have been included. Theoretical plasma estrogen activity levels were derived from estrogen exposure estimates and estrogenic potency data. Theoretical plasma levels were compared with published data for specific xenoestrogens. There was surprisingly close agreement. Xenoestrogenicity from dietary intake was almost equally attributed to naturally occurring and synthetic xenoestrogens. Relative contributions for a male, for example were isoflavones (genistein and daidzein) (36%) and bisphenol A (34%) with smaller contributions from alkyl phenols (18%) and the flavonoids (phloretin and kaempferol) (12%). It is suggested that dietary xenoestrogens might have a pharmacological effect on New Zealand males and postmenopausal women, but are unlikely to be significant for pre-menopausal women.

The effects of anti-androgenic and estrogenic disrupting contaminants on breeding gland (nuptial pad) morphology, plasma testosterone levels, and plasma vitellogenin levels in male Xenopus laevis (African clawed frog).

Nuptial pads are areas, digits, and forearm characterized by epidermal keratin hooks and dermal breeding glands opening on the epidermis surface in male frogs. The presence of the epidermal hooks and secretory activity of the breeding glands are androgen-dependent and considered functioning during mating. Chemical pollutants released into the aquatic environment by humans are suspected of disrupting the normal hormonal pathways and functioning. Among the best known of these endocrine-disrupting contaminants (EDCs) are compounds that mimic the steroid 17beta-estradiol. However, recently specific anti-androgenic activity by certain EDCs, including DDE and several fungicides, have been shown in mammalian studies. The African clawed frog, Xenopus laevis, has been proposed as an ideal species to be used as a model system for screening of endocrine disruptors. In this study we employed a newly developed ELISA for the measurement of plasma vitellogenin (VTG), normally produced in the liver of females under the influence of estrogens but also in males when exposed to exogenous estrogens. Furthermore, we investigated the potential of breeding (nuptial) gland activity to be employed as a biomarker system for screening for anti-androgenic activity by certain EDCs. Our results indicate that the pharmaceutic anti-androgen flutamide did significantly (p < 0.05) effect the androgen-dependent breeding (nuptial) glands and plasma testosterone concentrations in male X. laevis. Our results further confirm that the dicarboximide fungicide vinclozolin mimics the anti-androgenic action of flutamide. Vinclozolin, however, did not significantly effect the plasma testosterone concentration. Results also confirm the ability of 17beta-estradiol to stimulate production and release of VTG in the liver of male X. laevis, although we could not confirm the in vivo induction of VTG by estrogenic mimics octylphenol and nonylphenol. Although more dose-response research is needed, this preliminary study confirms the potential of VTG production and breeding gland activity as biomarkers to screen chemicals and environmental samples for estrogenic and anti-androgenic activity using X. laevis males.

Endocrine active industrial chemicals: Release and occurrence in the environment

Of the xenobiotic endocrine active substances (EASs), tributyltin (TBT) has had the clearest link to an impact on aquatic ecology. Its release from marine antifouling paints had a drastic impact on dogwhelk populations in polluted harbors due to a masculization effect. 4-tert-nonylphenol is seen as the most significant of the industrial xenobiotic estrogen mimics, being implicated as the dominant endocrine disruptor in certain industrialized river reaches. Apart from hot spots associated with particular industries, the estrogenic alkylphenols, phthalates, and bisphenol A are present in effluent and receiving water at concentrations below that which would give cause for concern. Other more bioaccumulative compounds such as polybrominated flame retardants, dioxins, furans may possess some endocrine active properties. The possibility of additivity effects may yet mean that low concentrations of xenobiotic EASs will need careful consideration. It is noted that considerable quantities of many of these compounds are often found in sewage sludge and sediments.

Endocrine disruptors: from Wingspread to environmental developmental biology

The production and release of synthetic chemicals into the environment has been a hallmark of the “Second Industrial Revolution” and the “Green Revolution.” Soon after the inception of these chemicals, anecdotal evidence began to emerge linking environmental contamination of rivers and lakes with a variety of developmental and reproductive abnormalities in wildlife species. The accumulation of evidence suggesting that these synthetic chemicals were detrimental to wildlife, and potentially humans, as a result of their hormonal activity, led to the proposal of the endocrine disruptor hypothesis at the 1991 Wingspread Conference. Since that time, experimental and epidemiological data have shown that exposure of the developing fetus or neonate to environmentally-relevant concentrations of certain synthetic chemicals causes morphological, biochemical, physiological and behavioral anomalies in both vertebrate and invertebrate species. The ubiquitous use, and subsequent human exposure, of one particular chemical, the estrogen mimic bisphenol A (BPA), is the subject of this present review. We have highlighted this chemical since it provides an arresting model of how chemical exposure impacts developmental processes involved in the morphogenesis of tissues and organs, including those of the male and female reproductive systems, the mammary glands and the brain.

Increases in mouse uterine heat shock protein levels are a sensitive and specific response to uterotrophic agents.

There is increasing consensus that the uterotrophic estrogenicity assay should be coupled with other morphometric or molecular end points that might enhance its sensitivity. We have previously shown that bisphenol A (BPA), similarly to 17ss-estradiol (E2), increases levels of uterine heat shock proteins (hsps), mainly hsp90alpha and glucose-regulated protein (grp) 94. In this study we investigated whether increases in uterine hsp levels are a specific response of estrogens or estrogen mimics. We therefore examined the ability of a) E2, diethylstilbestrol (DES), and tamoxifen (TAM); b) the xenoestrogens coumestrol (CM), methoxychlor (MXC), BPA, and dibutyl phthalate (DBP); c) the progestin medroxyprogesterone (MED); d) the glucocorticoid dexamethasone (DEX); and e) phytol (PHY), a precursor to a retinoid X and peroxisome proliferator-activating receptor agonist, to increase uterine weights and alter uterine morphology and hsp levels. We showed that DES, TAM, CM, MXC, and BPA significantly increased uterine weights and uterine hsp90alpha and grp94 levels. Even though the doses of CM, MXC, and BPA used were much higher than the E2 dose, those treatments resulted in lower increases in uterine weight. On the other hand, increases in grp94 levels were equal to those induced by E2 treatment. Treatments with MED, DEX, DBP, or PHY did not significantly alter uterine weight or morphology and had no significant effects on uterine hsp levels. The results of this study suggest that only the estrogens increase uterine hsp90alpha and grp94 levels, and that this hsp effect is a more sensitive uterotrophic response than uterine weight increase.

Validation of an ex Vivo Xenopus Liver Slice Bioassay for Environmental Estrogens and Estrogen Mimics

A sensitive ex vivo bioassay for detecting environmental estrogens and estrogen mimics was developed using Xenopus liver slice culture. Vitellogenin synthesis by these cultures was used as biomarker for estrogenic activity of environmental water samples. Sensitization of the assay for estrogens and mimics was accomplished by employing tissue from animals after in vivo preexposure to estrogen. Effects of various tissue culture factors were investigated in order to obtain optimum conditions for the bioassay. It was found that endogenous vitellogenin and/or estrogen could be “washed out” of cultures and that not only uncontaminated males but also estrogen-pretreated males and females can successfully be used as bioindicators. Estrogenicity was detected, using the ex vivo Xenopus liver slice culture assay, in sewage effluent, lake water, and dam water. This article presents an optimized protocol for effective estrogen detection in environmental water samples.

Environmental estrogens interact with and modulate the properties of plasma sex steroid-binding proteins in juvenile Atlantic salmon (Salmo salar)

Environmental chemicals may modulate the endocrine system through interaction with plasma sex steroid-binding proteins (SBP) and SBP-regulated processes. Some of these chemicals, which are known to interact with the estrogen receptor (ER), were found to bind competitively to the Atlantic salmon (Salmo salar) SBP and potentially disrupt the endocrine function of these proteins. Furthermore, both weakly acting (di-n-butyl phthalate) and potent estrogen mimics (ethynylestradiol), were able to induce a substantial up-regulation of circulating levels of SBP in vivo. Interestingly, modulation of SBP-levels was found to be a more sensitive endpoint than chemically induced interference with classical ER-mediated mechanisms for weakly acting estrogen mimics like di-(n-butyl) phthalate. Interference with the endocrine function of SBPs may thus introduce a novel mechanism for endocrine disruption, and give additional answers to the question why some weakly acting xenoestrogens are causing “estrogen-like” reproductive disturbances in developing males.

The impact of oestrogenic and androgenic contamination on marine organisms in the United Kingdom—summary of the EDMAR programme

This paper summarises results of the EDMAR programme which is investigating oestrogenic and androgenic endocrine disruption in UK coastal waters. Most of the data concern fish. Four species (flounder, viviparous blenny and two sand gobies) are experiencing feminisation in industrialised estuaries. In males this includes vitellogenin (VTG) synthesis, ovotestis induction and/or feminised sexual characteristics. Although reproductive success may be impaired in some cases, implications for fish populations are still unclear. Suspected causative contaminants include natural oestrogenic substances and synthetic oestrogen mimics. The majority of the oestrogenic activity is adsorbed to sediments, and routes of exposure may include benthic food chain transfer. Some natural androgenic substances are also being discharged to estuaries, but their activity appears low.

Estrogen Mimics Bind with Similar Affinity and Specificity to the Hepatic Estrogen Receptor in Atlantic Salmon (Salmo salar) and Rainbow Trout (Oncorhynchus mykiss)

A variety of organic chemicals have been documented to bind to and activate the estrogen receptor (ER) and consequently induce estrogenic effects in different animals. Although the function of the ER seems phylogenetically conserved in vertebrates, a considerable interspecies variation in the structure of the ER has been demonstrated. In this study, the hepatic ER from Atlantic salmon (Salmo salar) and rainbow trout (Oncorhunchus mykiss) were partly characterized, and the ligand-binding preference for a range of endogenous steroids and environmental estrogens (estrogen mimics) was determined by receptor-radio ligand studies. The results show that both Atlantic salmon and rainbow trout livers contain ERs that bind 1,2,4,6,7-[3H]estradiol ([3H]-E2) with high affinity and low capacity (Kd = 2.5–4.4 nM and Bmax = 27–97 fmol/mg protein). The Atlantic salmon ER (asER) and rainbow trout ER (rtER) exhibit similar [3H]-E2 binding characteristics, although livers from female fish contained a two to three times higher amounts of ER than the males in the two species. In competition studies with [3H]-E2, the asER and rtER were found to bind both native steroids (E2 > estrone > 17β-estradiol 17-glucuronide ⪢ testosterone and 11-ketotestosterone) and putative estrogen mimics (diethylstilbestrol, 4-hydroxytamoxifen, ethynylestradiol > genistein, zearalenone > 4-t-octylphenol, 4-n-nonylphenol, and o,p′-DDT). The pesticides toxaphen and dieldrin, which are proposed to bind to and activate the human ER, did not display significant binding affinity for the fish ER, however. In general, the asER and rtER were found to bind both native steroids and estrogen mimics with similar affinity and specificity. The present results suggest that closely related species such as Atlantic salmon and rainbow trout display similar ER ligand-binding requirements, although interspecies differences in ER affinity and specificity between divergent species such as fish and humans may exist.

Multigenerational Exposure to Dietary Nonylphenol has No Severe Effects on Spatial Learning in Female Rats

Nonylphenol is a common intermediate in the production of many consumer compounds and reportedly acts as an estrogen mimic. Because estrogen affects the spatial learning and memory in rats, the effects of nonylphenol exposure on the performance of female rats in the Morris water maze were investigated. Here, Sprague–Dawley rats (F 0) consumed soy-free diets containing 0, 25, 200 or 750 ppm nonylphenol (≈0, 2, 16 or 60 mg/kg per day) beginning on postnatal day (PND) 42 and continuing for two generations (F 1 and F 2) with breeding occurring within treatments. Females to be behaviorally tested ( n=7–8 per treatment per generation) were ovariectomized at adulthood and assessed for spatial learning and memory between PND 125–150 (young adult age). Each rat was tested for four consecutive days (three trials per day) in the Morris water maze with the platform in a fixed location. One week later, each subject was primed with estrogen and progesterone and assessed on a single day (three trials). The F 1 rats continued on the same diets until PND 380–395 (middle aged) when they were re-tested as above (four consecutive days followed 1 week later with hormonal priming and a single test day). Latency to find the platform, path length and swim speed were averaged over the three trials per day and analyzed using repeated measures analyses of variance. There were no consistent effects of dietary nonylphenol exposure and no interactions of nonylphenol exposure on any measure of performance in either generation at the young age nor at the middle age in the F 1 generation. When tested at the young adult age, however, hormone priming resulted in latencies and path lengths that were significantly shorter than in those exhibited during the unprimed test days, and there was no such effect when tested at middle age. Middle aged rats exhibited better performance than the same animals tested at a young age, likely as a result of familiarity and practice with the test paradigm. These data suggest that multigenerational dietary nonylphenol exposure does not cause gross alterations in Morris water maze performance in young adult or middle aged ovariectomized female rats.

Interaction of estrogen mimics, singly and in combination, with plasma sex steroid-binding proteins in rainbow trout ( Oncorhynchus mykiss)

The plasma sex steroid-binding protein (SBP) is believed to be involved in regulating circulating endogenous sex steroids as well as cellular signal transduction to nuclear steroid receptors in sex steroid-sensitive tissues. In this study, a variety of estrogen mimics (EMs), which may contribute to the endocrine disrupting effects observed in fish, were tested for the ability to interact with the rainbow trout plasma sex steroid-binding protein (rtSBP) either singly or in binary combinations. The EMs ethynylestradiol, diethylstilbestrol, 4-hydroxytamoxifen, genistein, zearalenone, 4- t-octylphenol, bisphenol A and o,p′-DDT were all able to displace 1,2,4,6,7-[ 3H]estradiol from the sex steroid-binding site at the rtSBP ( K d=2.1±0.5 nM, B max=2963±303 fmol estradiol/mg protein) in a dose-dependent and competitive manner. The plastizicer n-butyl benzyl phthalate only displayed weak binding affinity for the rtSBP, whereas the pesticide dieldrin was not able to compete for the high affinity estradiol-binding sites in plasma. None of the compounds tested was able to clearly promote the binding of the others when given in combination, indicating that synergy did not occur at the ligand-SBP binding level. The rtSBP binding affinity for EMs ranged over several orders of magnitude, but were consistently lower than those for the endogenous sex steroids (about 10 2–10 6 less potent). The results suggest that the presence of rtSBP may potentially modulate the bioavailability of EMs to estrogen receptors relative to each other and to the endogenous sex steroids themselves. Since the binding of the endogenous ligands is reversible, SBP-bound estrogens (or androgens) potentially may also become displaced by potent EMs.

The effects of endocrine disrupting chemicals on the ovary.

Endocrine disrupting chemicals (EDCs) are natural or synthetic chemicals that mimic, enhance, or inhibit endogenous hormones. In this article, we review possible targets of EDCs within the ovary and explore whether EDCs may be acting as estrogen mimics, interfering with apoptosis, altering cell signaling pathways, or affecting estrogen metabolism. Though the study of EDCs has remained controversial, it is important to study them because our society continues to release large amounts of industrial chemicals into our environment and uncovering the mechanisms of action may lead to treatments of any potential adverse effects. In addition, studying how EDCs affect the ovary may lead to serendipitous discoveries about ovarian function and dysfunction. Finally, understanding the science behind endocrine disruption may influence the political and regulatory handling of EDCs.

Enantiomer-specific activity of o, p′-DDT with the human estrogen receptor

There is a growing concern that environmental xenobiotics may be affecting human and wildlife health by disrupting normal endocrine function via interaction with steroid hormone receptors. Several of these persistent contaminants are chiral and may have enantiomer-specific biological properties. Previous experiments have demonstrated that (−)- o,p′-DDT enantiomer is a more active estrogen-mimic than the (+)-enantiomer in rats. However, these results have not been extrapolated to other biological systems. This study used a yeast-based assay to assess the enantiomer-specific transcriptional activity of DDT with the human estrogen receptor (hER). (+)-17β-estradiol, racemic DDT and individual DDT enantiomers were added to yeast cultures and hER activity was measured by quantification of β-galactosidase. The relative activity of o,p′ -DDT was weak compared to estradiol. For o,p′-DDT, the (−)-enantiomer was the active estrogen mimic whereas the hER activity of (+)- o,p′-DDT was negligible. The presence of the (+)-enantiomer at relatively greater concentration decreased the transcriptional activity of (−)- o,p′-DDT. This data demonstrates the need to consider stereochemistry of environmental contaminants and their potential influence on biological responses.

A rapid receptor–ligand assay determination of estrogens using surface plasmon resonance

A rapid and simple assay has been developed for the determination of estrogen and estrogen like compounds using surface plasmon resonance (SPR) that might be of use in epidemiological studies and potentially may aid the diagnosis of male infertility. The interaction between hER and an immobilised estradiol-BSA conjugate can be suppressed if the receptor is pre-incubated with estradiol or with the estrogen mimic, diethylstilbesterol (DES). The binding response of hER to immobilised estradiol-BSA was 184±40 ( n=3) resonance units (RU). When preincubated with either free estradiol or DES, the response was reduced to 93±8 and 103±19 RU, respectively ( P≤0.018). There was no significant difference in the extent to which the level of binding was reduced when these two compounds were compared ( P=0.47). When receptor was pre-incubated with estradiol to establish if binding of the receptor to a zearlenone-BSA (Z-BSA) conjugate also decreased, there was a substantial decrease in binding to Z-BSA, the difference in response being significant ( P=0.034). The increased speed with which data may be obtained using SPR compared with traditional biological assays permits greater sample throughput and provides a more quantitative approach to defining levels of estrogen and estrogen like compounds in body fluids.

Estrogen and estrogen mimics contamination in water and the role of sewage treatment

The yeast estrogen screen was applied to sewage treatment process waters to identify the presence of estrogenic activity and to investigate the fate and behavior of estrogenic substances through treatment. Hydrophobic fractions in the water phase were extracted and concentrated using C18 cartridges for the effective extraction of 17β-estradiol (E2) and other estrogen mimics. Clear dose-dependent elevation in the synthesis of β-galactosidase in the yeast screen was observed with all the samples tested, demonstrating that these samples were estrogenic. However, estrogenic activity tended to reduce during the treatment, especiallyiin the biological process. Quantification results of the yeast estrogen screen in terms of E2 equivalent were compared with actual E2 concentrations measured by an ELISA. E2 occupied 34% of the whole estrogenicity in the raw sewage, while almost 100% in the final effluent. The analyses of the sewage treatment process waters revealed that human estrogens are major causative substances in terms of estrogenic activity in sewage and its treated effluent. Although findings of possible correlation of environmental estrogens with the real impact on human health and the ecosystem are still the focus of scientific debate and investigation, proper management should be established in the sewage treatment process which receives various environmental contaminants.

Bioconcentration and distribution of 4- tert-octylphenol residues in tissues of the rainbow trout ( Oncorhynchus mykiss)

Branched chain alkylphenols are weak oestrogen mimics which are present in the aquatic environment and have been implicated in the feminisation of fish. This study reports the biotransformation, bioconcentration and tissue distribution of the xenoestrogen 4- tert-octylphenol ( t-OP) in juvenile rainbow trout. Fish were exposed for 10 days to a concentration of 4 μg/l of [ 14C] t-OP in a flow-through system and were sampled after 1, 4, 7 and 10 days of exposure. t-OP residues were extracted from all tissues and analysed by radio-high-performance liquid chromatography. After 1 day of exposure radioactive residues were detected in all tissues and reached steady state conditions in the whole fish after 4 days of exposure. The concentration of t-OP residues were highest in bile, followed by faeces, pyloric caeca, liver and intestine. In these tissues the majority of alkylphenol was in the form of two metabolites which were identified by gas chromatography–mass spectroscopy as the glucuronide conjugates of t-OP and t-octylcatechol. t-OP accumulated as the parent compound in fat with a bioconcentration factor (BCF) of 1190, and in brain, muscle, skin, bone, gills, and eye with BCFs of between 100 and 260. This study suggests that exposure to water-borne alkylphenols results in rapid conjugation and elimination of the chemical via the liver/bile route, but that high amounts of the parent xenoestrogen can accumulate in a variety of other fish tissues.