Since several decades by now, microplastics has been detected in the environment which it reaches either by wastewater or is being created within from degradation of plastic waste by influence of physical or chemical environmental forces. During the plastics production many various additives and catalysts are being used which may leak into the environment during the plastics' degradation and as such they present possible polluting effect. Due to significant amounts of plastics produced in the world, it is necessary to research the behaviour of the release of such chemicals into the aquatic environment and their possible impact on living organisms. The aim of this work is to use analytical and bioanalytical methods to determine the rate of release and concentration of the additive bisphenol A and antimony catalyst from UV-aged and non-aged PET plastic samples in an aqueous medium. Likewise, the influence of the toxicity of the released substances on the bioluminescent bacteria Vibrio fischeri was monitored by measuring the values of EC50, EC20 and EC10. The conducted tests showed the release of bisphenol A and antimony into the aqueous medium from both UV-aged and unaged PET samples. The release of antimony was also observed, albeit its amount was much lower from the UV-aged sample. Leached samples with Antimony and bisphenol A also showed an inhibitory effect on Vibrio fischeri bacteria. The concentrations of bisphenol A and antimony were monitored by high performance liquid chromatography and inductively coupled plasma with a mass spectrometer respectively. The standard method ISO 11348-2:2007 was used to measure ecotoxicity.