Existing environmental risk assessment procedures are limited in their ability to evaluate the combined effects of chemical mixtures. We investigated the implications of this by analyzing the combined effects of a multicomponent mixture of five estrogenic chemicals using vitellogenin induction in male fathead minnows as an end point. The mixture consisted of estradiol, ethynylestradiol, nonylphenol, octylphenol, and bisphenol A. We determined concentration–response curves for each of the chemicals individually. The chemicals were then combined at equipotent concentrations and the mixture tested using fixed-ratio design. The effects of the mixture were compared with those predicted by the model of concentration addition using biomathematical methods, which revealed that there was no deviation between the observed and predicted effects of the mixture. These findings demonstrate that estrogenic chemicals have the capacity to act together in an additive manner and that their combined effects can be accurately predicted by concentration addition. We also explored the potential for mixture effects at low concentrations by exposing the fish to each chemical at one-fifth of its median effective concentration (EC50). Individually, the chemicals did not induce a significant response, although their combined effects were consistent with the predictions of concentration addition. This demonstrates the potential for estrogenic chemicals to act additively at environmentally relevant concentrations. These findings highlight the potential for existing environmental risk assessment procedures to underestimate the hazard posed by mixtures of chemicals that act via a similar mode of action, thereby leading to erroneous conclusions of absence of risk.
The aerobic biodegradation of nonylphenol ethoxylates (A9PEO) was kinetically investigated in a laboratory-scale bioreactor filled with riverwater, spiked at a concentration of 10 mg L(-1) nonionic surfactants. Analyses of the samples applying liquid chromatography-electrospray mass spectrometry (LC-ES-MS) after solid-phase enrichment revealed a relatively fast primary degradation of A9PEO with >99% degradation observed after 4 days. Contrary to the generally proposed degradation pathway of EO chain shortening, it could be shown that the initiating step of the degradation is omega-carboxylation of the individual ethoxylate chains: metabolites with long carboxylated EO chains are identified (A9PEC). Further degradation proceeds gradually into short-chain carboxylated EO with the most abundant species being AgPE2C. The oxidation of the nonyl chain proceeds concomitantly with this degradation, leading to metabolites having both a carboxylated ethoxylate and an alkyl chain of varying lengths (CAPEC). The identity of the CAPEC metabolites was confirmed by the fragmentation pattern obtained with LC-ES-MS/MS. Both A9PEC and CAPEC metabolites are still present in the bioreactor after 31 days. In the aerobic degradation pathway, A9PEO2 is formed only to a minor extent and is even further degraded in several days. The endocrine disruptor nonylphenol was not found as a metabolite in this study.
Fluorochemicals are persistent contaminants that are globally distributed in air, water, sediments, and biota. Wastewater treatment plants (WWTPs) play an important role in mitigating pollutant releases from municipalities to aquatic and terrestrial environments. However, because WWTPs are point sources of fluorochemicals, it is important to understand their contribution to fluorochemical burdens in the greater context of watersheds. To this end, over a 1 week period, the mass flows of 11 fluorochemicals from seven WWTPs that discharge effluent into the Glatt River in Switzerland were measured and compared to the measured mass flows within the Glatt River. Overall, the fluorochemicals were not removed efficiently during wastewater treatment. Effluents from WWTPs and Glatt River water were dominated by perfluorooctane sulfonate, which was detected in all samples, followed by perfluorohexane sulfonate and perfluorooctanoate. The mass flows of fluorochemicals emanating from WWTPs were found to be conserved within the 35 km Glatt River, which indicates that input from the WWTPs is additive and that removal within the Glatt River is not significant. Per capita discharges of fluorochemicals were calculated from the populations served by the WWTPs studied; the values determined also account for the fluorochemical content of Lake Greifen (Greifensee), which is a lake at the headwaters of the Glatt River that also receives treated wastewater.
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