The use of numerous types of xenobiotics has undoubtedly contributed to the development and improvement of the quality of human life, but their negative impact on the entire ecosystem is becoming increasingly visible. After application, most xenobiotics end up in waste water, surface water and soil. Given that xenobiotics such as pesticides and pharmaceuticals cause certain pharmacological and physiological changes even in very small doses, it is important to monitor and assess their ecotoxicity. The main goal of this work is to determine the ecotoxicity of selected xenobiotics from the group of pesticides (acetamiprid, clothianidin, thiacloprid) and antiparasitics (albendazole, febantel, mebendazole) at pH-values 4, 7 and 10, then their binary and ternary mixtures and mixtures of all six selected xenobiotics. Rapid ecotoxicity tests with the bacterium Vibrio fischeri based on the standard method ISO 11348-3:2010 were used to determine the bioluminescence intensity of these test organisms. The pure active substance acetamiprid is the most ecotoxic in the acidic range, then in the neutral and, finally, in the alkaline range. Clothianidin showed minimal ecotoxicity in the acidic area, while other pure active substances were not toxic to Vibrio fischeri. The mixture of all selected xenobiotics is ecotoxic, mostly in alkaline, then acidic and, finally, neutral. There is a synergism between the components. The most harmful binary mixture is a mixture of albendazole and mebendazole, where a synergistic effect was observed, as in ternary mixtures of anthelmintics, while antagonism is more pronounced in ternary mixtures of neonicotinoids. The most ecotoxic ternary mixture is a mixture of albendazole, mebendazole and thiacloprid, which is not surprising considering that the most ecotoxic is a binary mixture of albendazole and mebendazole. Although mixtures of substances and less pure components are present in the environment, risk assessment is mainly focused on the analysis of the effect of pure substances. The problem with mixtures is the possibility of synergism, that is, an increase in ecotoxicity compared to the individual components, which is why it is extremely important to determine whether they have a harmful effect and to emphasize monitoring.