Passive sampling combined with ecotoxicological and chemical analysis of pharmaceuticals and biocides - evaluation of three ChemcatcherTM configurations

Passive sampling is a tool to monitor the presence and concentrations of micropollutants in the aquatic environment. We investigated the duration of integrative sampling and the effects of flow rate on the performance of three configurations of the Chemcatcher - a sampler for polar organic compounds. Chemcatchers were fitted with EmporeTM styrenedivinylbenzene (SDB) XC disks (XC), SDB-RPS disks (RPS) or SDB-RPS disks covered with a polyethersulfone membrane (RPS-PES). Samplers were either exposed to treated sewage effluent for 5 days at various flow rates, or at a single flow rate with overlapping exposures of 3 to 24 days. Chemical analysis focused on a set of pharmaceuticals and biocides and ecotoxicological analysis measured inhibition of photosystem II in algae. For compounds with logKow > 2, both XC and RPS disks respond dynamically to higher flow rates; uptake increased up to five-fold when flow increased from 0.03 to 0.37 m s-1. At a flow rate of 0.13 m s-1 the integrative window of SDB disks approached 6 days for more hydrophobic compounds (logKOW > 3.5). The RPS-PES configuration was less affected by flow and also showed an extended integrative window (up to 24 days). The membrane causes a lag phase of up to 2.3 days which thwarts a sound interpretation of data from sampling periods of less than 10 days

Mixture toxicity of the antiviral drug Tamiflu® (Oseltamivir Ethylester) and its active metabolite oseltamivir acid

Tamiflu® (oseltamivir ethylester) is an antiviral agent for the treatment of influenza A and B. The prodrug Tamiflu® is converted in the human body to the pharmacologically active metabolite, oseltamivir acid, with a yield of 75%. Oseltamivir acid is indirectly photodegradable and slowly biodegradable in sewage works and sediment/water systems. A previous environmental risk assessment has concluded that there is no bioaccumulation potential of either of the compounds. However, little was known about the ecotoxicity of the metabolite. Ester hydrolysis typically reduces the hydrophobicity and thus the toxicity of a compound. In this case, a zwitterionic, but overall neutral species is formed from the charged parent compound. If the speciation and predicted partitioning into biological membranes is considered, the metabolite may have a relevant contribution to the overall toxicity. These theoretical considerations triggered a study to investigate the toxicity of oseltamivir acid (OA), alone and in binary mixtures with its parent compound oseltamivir ethylester (OE). OE and OA were found to be baseline toxicants in the bioluminescence inhibition test with Vibrio fischeri. Their mixture effect lay between predictions for concentration addition and independent action for the mixture ratio excreted in urine and nine additional mixture ratios of OE and OA. In contrast, OE was an order of magnitude more toxic than OA towards algae, with a more pronounced effect when the direct inhibition of photosystem II was used as toxicity endpoint opposed to the 24 h growth rate endpoint. The binary mixtures in this assay yielded experimental mixture effects that agreed with predictions for independent action. This is consistent with the finding that OE exhibits slightly enhanced toxicity, while OA acts as baseline toxicant. Therefore, with respect to mixture classification, the two compounds can be considered as acting according to different modes of toxic action, although there are indications that the difference is a toxicokinetic effect, not a true difference of mechanism of toxicity. The general mixture results illustrate the need to consider the role of metabolites in the risk assessment of pharmaceuticals. However, in the concentration ratio of parent to metabolite excreted by humans, the experimental results confirm that the active metabolite does not significantly contribute to the risk quotient of the mixture. Copyright © 2009 Elsevier B.V. All rights reserved

Toxic equivalent concentrations (TEQs) for baseline toxicity and specific modes of action as a tool to improve interpretation of ecotoxicity testing of environmental samples

The toxic equivalency concept is a widely applied method to express the toxicity of complex mixtures of compounds that act via receptor-mediated mechanisms such as induction of the arylhydrocarbon or estrogen receptors. Here we propose to extend this concept to baseline toxicity, using the bioluminescence inhibition test with Vibrio fischeri, and an integrative ecotoxicity endpoint, algal growth rate inhibition. Both bioassays were validated by comparison with literature data and quantitative structure-activity relationships (QSARs) for baseline toxicity were developed for all endpoints. The novel combined algae test, with Pseudokirchneriella subcapitata, allows for the simultaneous evaluation of specific inhibition of photosynthesis and growth rate. The contributions of specific inhibition of photosynthesis and non-specific toxicity could be differentiated by comparing the time and endpoint pattern. Photosynthesis efficiency, measured with the saturation pulse method after 2 h of incubation, served as indicator of specific inhibition of photosynthesis by photosystem II inhibitors. Diuron equivalents were defined as toxicity equivalents for this effect. The endpoint of growth rate over 24 h served to derive baseline toxicity equivalent concentrations (baseline-TEQ). By performing binary mixture experiments with reference compounds and complex environmental samples from a sewage treatment plant and a river, the TEQ concept was validated. The proposed method allows for easier interpretation and communication of effect-based water quality monitoring data and provides a basis for comparative analysis with chemical analytical monitoring

Elimination of organic micropollutants in a municipal nutrient removal plant upgraded with a full-scale post-ozonation followed by sand filtration

The aim of the project MicroPoll (www.umwelt-schweiz.ch/micropoll) is to compile decision-support information and to develop a strategy for reducing the release of micropollutants from wastewater treatment plants (WWTPs) in Switzerland. Within the project the WWTP of Regensdorf near Zurich (current load 15,000 inhabitants plus 10,000 population equivalents) was upgraded with a full-scale ozonation step after secondary treatment and prior to sand filtration. The method developed for the screening of micropollutants is comprehensive and can also be applied for other enhanced or advanced water treatment processes. The full-scale reactor proves ozonation to be an efficient technique for the elimination of micropollutants from secondary effluent as well as for disinfection at reasonable additional energy consumption. The specific and non-specific toxicity is significantly reduced by ozonation indicating that no further toxic compounds are produced. Additional sand filtration is useful for elimination of N-nitrosodimethylamine and biodegradable compounds formed during ozonation