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Mixtures of Estrogenic Chemicals Enhance Vitellogenic Response in Sea Bass

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      Abstract

      Background

      The potential impact of natural and synthetic estrogens on aquatic ecosystems has attracted considerable attention because it is currently accepted that their joint effects are more severe when they are present in mixtures. Although it is well-known that they occur as mixtures in the marine environment, there is little information about the combined effects of estrogenic chemicals on marine biota.

      Objective

      In 14-day tests with juvenile sea bass, we analyzed singly and in combination the estrogenic activity of estradiol (E 2), ethynylestradiol (EE 2), and bisphenol A (BPA) using vitellogenin induction as an end point.

      Methods

      Fish were exposed to each compound, and on the basis of these concentration–response data, we predicted mixture effects by applying the model of concentration addition. The mixtures were tested using a fixed-ratio design, and the resulting mixture effects were compared to the predictions.

      Results

      EE 2 was the most potent steroid, with an EC 50 (median effective concentration) of 0.029 μg/L, 3.6 times more potent than E 2 (EC 50 = 0.104 μg/L); BPA was the least potent chemical, with an EC 50 of 77.94 μg/L. The comparative assessment yielded a good agreement between observed and predicted mixture effects.

      Conclusions

      This study demonstrates the potential hazard of these compounds to seawater life by their ability to act together in an additive manner. It provides evidence that concentration addition can be used as a predictive tool for assessing the combined effects of estrogenic chemicals in marine ecosystems.

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      Most cited references 41

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      Vitellogenesis as a biomarker for estrogenic contamination of the aquatic environment.

      A rapidly increasing number of chemicals, or their degradation products, are being recognized as possessing estrogenic activity, albeit usually weak. We have found that effluent from sewage treatment works contains a chemical, or mixture of chemicals, that induces vitellogenin synthesis in male fish maintained in the effluent, thus indicating that the effluent is estrogenic. The effect was extremely pronounced and occurred at all sewage treatment works tested. The nature of the chemical or chemicals causing the effect is presently not known. However, we have tested a number of chemicals known to be estrogenic to mammals and have shown that they are also estrogenic to fish; that is, no species specificity was apparent. Many of these weakly estrogenic chemicals are known to be present in effluents. Further, a mixture of different estrogenic chemicals was considerably more potent than each of the chemicals when tested individually, suggesting that enhanced effects could occur when fish are exposed simultaneously to various estrogenic chemicals (as is likely to occur in rivers receiving effluent). Subsequent work should determine whether exposure to these chemicals at the concentrations present in the environment leads to any deleterious physiological effects.
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        Something from "nothing"--eight weak estrogenic chemicals combined at concentrations below NOECs produce significant mixture effects.

        We tested whether multicomponent mixtures of xenoestrogens would produce significant effects when each component was combined at concentrations below its individual NOEC or EC01 level. The estrogenic effects of eight chemicals of environmental relevance, including hydroxylated PCBs, benzophenones, parabenes, bisphenol A, and genistein, were recorded using a recombinant yeast estrogen screen (YES). To ensure that no chemical contributed disproportionately to the overall combination effect, a mixture was prepared at a mixture ratio proportional to the potency of each individual component. The performance of four approaches for the calculation of additive combination effects (concentration addition, toxicity equivalency factors, effect summation, and independent action) was compared. Experimental testing of the predictions revealed that concentration addition and its application, the toxicity equivalency factor approach, were valid methods for the calculation of additive mixture effects. There was excellent agreement between prediction and observation. In contrast, independent action and effect summation led to clear underestimations of the experimentally observed responses. Crucially, there were substantial mixture effects even though each chemical was present at levels well below its NOEC and EC01. We conclude that estrogenic agents are able to act together to produce significant effects when combined at concentrations below their NOECs. Our results highlight the limitations of the traditional focus on the effects of single agents. Hazard assessments that ignore the possibility of joint action of estrogenic chemicals will almost certainly lead to significant underestimations of risk.
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          Guide for the care and use of laboratory animals

           SW Barthold,  K Bayne,  M Davis (2011)
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            Author and article information

            Affiliations
            [1 ] CIIMAR-Centre of Marine and Environmental Research, Environmental Toxicology Laboratory, Porto, Portugal
            [2 ] Instituto de Bioquímica, Facuidade de Medicina de Lisboa, Unidade de Biopatologia Vascular, Institute de Medicina Molecular, Lisboa, Portugal
            [3 ] Centre for Toxicology, The School of Pharmacy, University of London, London, United Kingdom
            [4 ] ICBAS-Instituto de Ciências Biomédicas de Abel Salazar, Porto, Portugal
            [5 ] Institute for Environmental Studies, Vrije Universiteit, Faculty of Earth and Life Sciences, Amsterdam, the Netherlands
            [6 ] Instituto de Acuicultura de Torre la Sal (CSIC), Torre la Sal, España
            Author notes
            Address correspondence to A.D. Correia, CIIMAR-Centre of Marine and Environmental Research, Environmental Toxicology Laboratory, Rua dos Bragas, 289, 4050–123 Porto, Portugal. Telephone: (351) 223401833. Fax: (351) 223390608. E-mail: anacorreia@ 123456ciimar.up.pt

            The authors declare they have no competing financial interests.

            Journal
            Environ Health Perspect
            Environmental Health Perspectives
            National Institute of Environmental Health Sciences
            0091-6765
            December 2007
            8 June 2007
            : 115
            : S-1
            : 115-121
            2174414
            18174959
            10.1289/ehp.9359
            ehp0115s1-000115
            This is an Open Access article: verbatim copying and redistribution of this article are permitted in all media for any purpose, provided this notice is preserved along with the article's original DOI.
            Categories
            Monograph

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