During the period of September 4 through 16, 2011 Dr Daniela Šojic, asist. prof. and Vesna Despotovic, associate researcher stayed at the Institute of Material Sciences and Engineering, University of Szeged in order to continue the joint research in the frame of the IPA project. Bearing in mind that the degradation of metoprolol and thiamethoxam in the presence of O3 appeared to be faster in Danube and thermal waters than in the deionized water, it was continued with the investigations of the effect of other ions, such as sulphates (100, 10, 0.1 and 0.01 mmol/dm3) and humic acids (40, 20 and 10 mg/dm3) on the rate of degradation of the target compounds. Also, toward simulation of natural composition of Danube and thermal waters, in thiamethoxam and metoprolol solutions was added the appropriate content so far investigated anions and humic acids. The substrate degradation was followed by LC-DAD method. In addition, samples were taken for investigations of toxicity and mutagenicity in the case of both compounds using UV, O3 and UV/O3 reactors.