21st International Symposium on Analytical and Environmental Problems 426 Identification of By-products Formed During the Oxidative Transformation of Phenylurea Pesticides Gergő Simon 1,2 *, Virág Farkas 1,2 , András Dombi 1 , Klára Hernádi 1 , Tünde Alapi 1,2 1 Research Group of Environmental Chemistry, University of Szeged, H-6720 Szeged, Rerrich Béla tér 1, Hungary 2 Department of Inorganic and Analytical Chemistry, University of Szeged, H-6720 Szeged, Dóm tér 7, Hungary e-mail: gsimon@chem.u-szeged.hu Abstract The goal of this study was to identify the by-products that form during the oxidative degradation of five phenylurea pesticides. Four advanced oxidation processes were used including photolysis, ozonation, heterogeneous photocatalysis, and the combination of photolysis with ozonation. After concentrating the by-products using solid phase extraction, our samples were analyzed by mass spectrometry. We have managed to identify the main products for each pesticide and process, from which we could determine that the main reactions during the application of AOPs were the dehalogenisation and hydroxylation of the aromatic ring, as well as the terminal demethylation and the oxidation of the methyl groups. Introduction Organic contaminants, such as pesticides, pharmaceuticals, etc. have become a major concern regarding the environment due to their persistence and low biodegradability that can lead to accumulation in soils and waters. [1] A large number of these contaminants have presumed or proven negative health effects (carcinogens, endocrine disruptors). Phenylurea herbicides are one such type of chemicals that are widely used for weed control, mostly in non-agricultural areas, and their high half-life in soils [2] causes them to wash into waters, even appearing in drinking water. Another problem is that regular water treatment methods often are ineffective in the removal of these contaminants. Therefore applicable methods are being developed based on advanced oxidation processes (AOPs) that are capable of the degradation of organic matter by forming highly reactive radicals. These methods include photolysis by ultraviolet light, ozonation, heterogeneous photocatalysis, Fenton-reaction, which can be effective themselves, but also can be further improved by their combination [3] , resulting in higher radical concentrations or different reaction pathways. This also means that the various processes will result in different by- products that can be identified using mass spectrometry. This information is essential for the development of analytical processes for these compounds and their metabolites. Materials and methods Four phenylurea pesticides were used for our experiments, as presented on Figure. 1.