Something From “Nothing”-Eight Weak Estrogenic Chemicals Combined at Concentrations Below NOECs Produce Significant Mixture Effects

Centre for Toxicology, Department of Pharmacology, The School of Pharmacy, University of London.
Environmental Science and Technology (Impact Factor: 5.33). 05/2002; 36(8):1751-6. DOI: 10.1021/es0101227
Source: PubMed

ABSTRACT 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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Available from: Elisabete Silva, Sep 27, 2015
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    • "Importantly, the toxicity of single chemicals can be modified when present in a mixture through toxicokinetic interactions with cosolutes , solubility addition (Smith et al., 2013b) or a joint action at the target site, which can enhance or inhibit the effect of endogenous hormones (Carpenter et al., 2002; Silva et al., 2002). It has also been shown that minor changes in mixture composition can cause larger shifts of endocrine responses (Kortenkamp, 2007). "
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    ABSTRACT: Persistent organic pollutants (POPs) accumulated in human tissues may pose a risk for human health by interfering with the endocrine system. This study establishes a new link between actual human internal POP levels and the endocrine active dose in vitro, applying partitioning-controlled dosing from silicone to the H295R steroidogenesis assay: (1) Measured concentrations of POPs in silicone breast implants were taken from a recent study and silicone disks were loaded according to these measurements. (2) Silicone disks were transferred into H295R cell culture plates in order to control exposure of the adrenal cells by equilibrium partitioning. (3) Hormone production of the adrenal cells was measured as toxicity endpoint. 4-Nonylphenol was used for method development, and the new dosing method was compared to conventional solvent-dosing. The two dosing modes yielded similar dose-dependent hormonal responses of H295R cells. However, with the partitioning-controlled freely dissolved concentrations (Cfree) as dose metrics, dose-response curves were left-shifted by two orders of magnitude relative to spiked concentrations. Partitioning-controlled dosing of POPs resulted in up to 2-fold increases in progestagen and corticosteroid levels at Cfree of individual POPs in or below the femtomolar range. Silicone acted not only as source of the POPs but also as a sorption sink for lipophilic hormones, stimulating the cellular hormone production. Methodologically, the study showed that silicone can be used as reference partitioning phase to transfer in vivo exposure in humans (silicone implants) to in vitro assays (partition-controlled dosing). The main finding was that POPs at the levels at which they are found in humans can interfere with steroidogenesis in a human adrenocortical cell line. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Environment International 08/2015; 84:107-114. DOI:10.1016/j.envint.2015.07.008 · 5.56 Impact Factor
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    • "Most gymnasts are female (N 70%), 80% are under the age of 18 years old (USA Gymnastics, 2014), which may place them at a greater risk of adverse health consequences to PBDE exposure. Also, consideration of the full complement of xenobiotics one is exposed to is important as these may interact toxicologically (Silva et al., 2002). Besides PBDEs, PBDE replacement-FRs have also been detected in dust from gymnastic studios including: 2-ethylhexyl 2,3,4, 5-tetrabromobenzoate (TBB), 2- ethylhexyl 2,3,4, 5-tetrabromophalate (TBPH), tris(1-chloro-2-propyl) phosphate (TCPP) and tris(1, 3-dichloro-2-propyl) phosphate (TDCPP) (Carignan et al., 2013). "
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    Environment international 06/2015; 79. DOI:10.1016/j.envint.2015.02.014 · 5.56 Impact Factor
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    • "Unfortunately EE2 is not only one pharmaceutical found in environment. There are several studies, which shows effect of pollutant mixtures on different water organisms (Silva & Kortenkamp, 2002). Different pharmaceuticals are found in environment in low "
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