An Assessment of the Model of Concentration Addition for Predicting the Estrogenic Activity of Chemical Mixtures in Wastewater Treatment Works Effluents

The effects of simple mixtures of chemicals, with similar mechanisms of action, can be predicted using the concentration addition model (CA). The ability of this model to predict the estrogenic effects of more complex mixtures such as effluent discharges, however, has yet to be established. Effluents from 43 U.K. wastewater treatment works were analyzed for the presence of the principal estrogenic chemical contaminants, estradiol, estrone, ethinylestradiol, and nonylphenol. The measured concentrations were used to predict the estrogenic activity of each effluent, employing the model of CA, based on the relative potencies of the individual chemicals in an in vitro recombinant yeast estrogen screen (rYES) and a short-term (14-day) in vivo rainbow trout vitellogenin induction assay. Based on the measured concentrations of the four chemicals in the effluents and their relative potencies in each assay, the calculated in vitro and in vivo responses compared well and ranged between 3.5 and 87 ng/L of estradiol equivalents (E2 EQ) for the different effluents. In the rYES, however, the measured E2 EQ concentrations in the effluents ranged between 0.65 and 43 ng E2 EQ/L, and they varied against those predicted by the CA model. Deviations in the estimation of the estrogenic potency of the effluents by the CA model, compared with the measured responses in the rYES, are likely to have resulted from inaccuracies associated with the measurement of the chemicals in the extracts derived from the complex effluents. Such deviations could also result as a consequence of interactions between chemicals present in the extracts that disrupted the activation of the estrogen response elements in the rYES. E2 EQ concentrations derived from the vitellogenic response in fathead minnows exposed to a series of effluent dilutions were highly comparable with the E2 EQ concentrations derived from assessments of the estrogenic potency of these dilutions in the rYES. Together these data support the use of bioassays for determining the estrogenic potency of WwTW effluents, and they highlight the associated problems for modeling approaches that are reliant on measured concentrations of estrogenic chemicals

Concentration–response curves for binary mixtures of E and EE (), E and E (), E and NP (), and E and NP () obtained in a recombinant yeast estrogen screen

<p><b>Copyright information:</b></p><p>Taken from "An Assessment of the Model of Concentration Addition for Predicting the Estrogenic Activity of Chemical Mixtures in Wastewater Treatment Works Effluents"</p><p></p><p>Environmental Health Perspectives 2005;114(S-1):90-97.</p><p>Published online 21 Oct 2005</p><p>PMCID:PMC1874186.</p><p>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</p> (○) Represents individual responses at each concentration. (—) Regression line showing the observed mixture response and is based on the results of five assays in which each chemical mixture was tested in duplicate. ( ) Regression line showing the predicted response for each mixture based on the concentration–response curves in for each individual chemical. All lines were calculated using a four-parameter logit regression model

Comparison of calculated and measured E EQs determined for final WwTW effluents sampled from 43 locations across England and Wales

<p><b>Copyright information:</b></p><p>Taken from "An Assessment of the Model of Concentration Addition for Predicting the Estrogenic Activity of Chemical Mixtures in Wastewater Treatment Works Effluents"</p><p></p><p>Environmental Health Perspectives 2005;114(S-1):90-97.</p><p>Published online 21 Oct 2005</p><p>PMCID:PMC1874186.</p><p>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</p> ( ) Represents the measured E EQs in the recombinant yeast screen. (○, ▵) Represent the predicted E EQs calculated based on the measured concentrations of the four target estrogenic chemicals in the individual effluents and their relative estrogenic potencies in the recombinant yeast screen (○) and for the induction of VTG in juvenile rainbow trout (▴). Both the measured and predicted responses are based on results from two sampling occasions for each effluent

Concentration–response curves for EE, E, E, and NP obtained in a () recombinant yeast estrogen screen, and () 14-day juvenile rainbow trout screening assay (VTG induction)

<p><b>Copyright information:</b></p><p>Taken from "An Assessment of the Model of Concentration Addition for Predicting the Estrogenic Activity of Chemical Mixtures in Wastewater Treatment Works Effluents"</p><p></p><p>Environmental Health Perspectives 2005;114(S-1):90-97.</p><p>Published online 21 Oct 2005</p><p>PMCID:PMC1874186.</p><p>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</p> The different colored symbols represent the individual responses at each concentration in a series of independent experiments for each chemical. Black regression lines for each chemical were calculated using a four-parameter logit regression model and are based on the results of five assays (each chemical tested in duplicate) and two, five, one, and three exposures conducted for EE, E, E, and NP, respectively