Water pollution by pesticide residues is one of the major environmental challenges. Massive use of pesticides over the years has led to environmental pollution, water and food pollution. Because of their toxicity, which protects plants from pests, pesticides can harm other living things. Plastics that are used on a large scale every day and thus thrown away on a large scale also have an adverse effect on the environment. Nature gradually changes it, fragmenting large pieces of plastic into tiny microplastic particles. Sooner or later, both pesticides and microplastics end up in the aquatic environment on which all living beings, including humans, depend. The aim of this study was to determine the toxicity of pure pesticide solutions after photolysis, with and without the presence of microplastic particles. Solutions of acetamiprid, clothianidin and thiacloprid were prepared and tested. Chromatographic analysis of samples taken over a period of 24 hours of exposure of the solution to radiation such as sunlight was performed to detect possible degradation or transformation products of the tested pesticides. Toxicity tests were performed using bioluminescent bacteria Vibrio fischeri. Pure solutions of all three pesticides were found to be toxic at a concentration of 3 mg/L. Chromatographic analysis showed that clothianidin degrades after 5 hours of photolysis and does not produce degradation or transformation products, while acetamiprid and thiaclopride produce photolysis products that increase the toxicity of the solution. Also, microplastic particles under the influence of photolysis have been shown to form a new compound that significantly increases the toxicity of the solution in all three cases.