Estrogenicity and toxicity of environmentally relevant mixtures of endocrine active compounds

Abstract : The presence of endocrine active compounds (EACs) in wastewater, surface water, groundwater and even drinking water has become a major public concern worldwide. Exposure to a mixture of EACs has been predicted to result in additive or possibly synergistic effects, which is difficult to detect by chemical analysis. Bioanalysis, such as using in vitro or in vivo methods, has the advantage of measuring the mixture effects of EACs, but this has not been well studied using environmentally relevant mixtures of EACs. In a previous study, we evaluated the estrogenic effects of 11 EACs of high environmental concern using the in vitro yeast estrogen screen (YES) method. The full mixture of all these chemicals at an environmentally relevant ratio also showed weak anti-estrogenic activity. Further, EE2 did not have a prominent contribution to the estrogenic activity of the mixture. The objective of the current study was to evaluate the in vivo response to exposure to eleven endocrine active compounds (EACs) commonly found in surface water globally. We evaluated the mixture toxicity of three naturally occurring estrogens (17β-estradiol–E2, estrone–E1 and estriol–E3), one synthetic estrogen (17α-ethinyl estradiol–EE2), one phytoestrogen (genistein–GEN), three phenolic xenoestrogens (bisphenol A-BPA, nonyl phenol-NP, octyl phenol-OP) and three phthalates (dibutyl phthalate-DBP, butyl benzyl phthalate-BBP and bis(2-ethylhexyl) phthalate-DEHP) on the model aquatic organisms, zebrafish. This is the same set of EACs we used in the in vitro YES study. We followed the OECD 236 guideline and the U.S. Environmental Protection Agency (EPA) method EPA/600/4-91/002. The zebrafish embryos were exposed to 6 dilutions of the EAC mixture, varying from 0.1 to 100 times the environmental concentrations. A parallel set of experiments with the same chemicals will be conducted in the transgenic cyp19a1b-GFP zebrafish embryo assay (EASZY) to gain information on mixture effects in vivo. The transgenic zebrafish embryos will be exposed to 6 dilutions of the EAC mixture in the same range of concentrations. A comparison of the two methods will be presented at the meeting, after analysis is completed. For exposure experiments, EDCs mixtures at environmentally-relevant concentration level were used. Based on our preliminary analysis, we conclude that a holistic evaluation of the toxicity and estrogenic activity is necessary to evaluate the risk of exposure to a mixture of EACs in the environment.
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J. Caldwell, H. Yu, B. van Aken, François Brion, R. Suri. Estrogenicity and toxicity of environmentally relevant mixtures of endocrine active compounds. 1st International conference on risk assessment of pharmaceuticals in the environment (ICRAPHE), Sep 2016, Paris, France. ⟨ineris-01854272⟩

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