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(46-11) Fate and behaviour of the antibacterial agent triclosan in surface waters. Tixier, Céline*,1, Singer, Heinz1, Canonica, Silvio1, Müller, Stephan1, 1 Swiss Federal Institute for Environmental Science and Technology (EAWAG), Dübendorf, Switzerland ABSTRACT- Triclosan, 5-chloro-2-(2,4-dichlorophenoxy)phenol, is a broad-spectrum antibacterial agent widely used in personal care products (e.g. toothpaste, deodorant, cosmetics) or incorporated in polymers and fibers to give these materials antibacterial properties. So it is used in mattress pads, shoes and sportswear. Due to these applications, triclosan reaches sewage treatment plants where it is eliminated with an efficiency of 85-95%. However the triclosan residual amount in these wastewaters reaches surface waters. Recent findings indicate a possible bacterial resistance to this compound but further research is currently being undertaken to evaluate these findings. Since triclosan presents a high toxicity to certain algae, an improved risk assessment of triclosan to the aquatic environment is needed, which requires a detailed knowledge of its aquatic concentrations and transformation processes. A combined approach of laboratory experiments, field studies and modelling was then used to determine and quantify the main transport and transformation processes of triclosan in surface waters. The overall objective was to develop a model describing the fate of triclosan in natural waters. The chosen field system is a small lake (Greifensee) in the Swiss midlands. Rough theoretical calculations revealed three main processes responsible for triclosan elimination from this lake: photodegradation, sorption to particles followed by sedimentation and elimination by the outflow. A detailed photochemical study was then performed to define the parameters characterising this elimination process. These experimental data were combined (using the computer programs GCsolar and Aquasim) with actual meteorological data and field measurements (triclosan input into the lake and vertical concentration profiles) to model triclosan vertical concentration profiles in Greifensee. For the period studied (August-October 1999), direct phototransformation accounted for about 80% of the observed triclosan elimination from the lake, the remaining mainly corresponding to outflow. We will discuss how these results can be used to assess triclosan fate in other surface waters. Key words: triclosan, surface water, photodegradation, fate |
