Pollution of the aquatic ecosystem with xenobiotics, microplastics (MP) and pharmaceuticals is increasing due to anthropogenic influences, such as the excessive use of plastic packaging, industrial development and the consumption of medicines, which consequently leads to their release into the environment. MP is considered a pollutant because it has become a global threat due to its ubiquity, bioinertness, hazard to aquatic organisms, and impact on human health. Pharmaceuticals such as antibiotics and antivirals form a group of pollutants that can seriously threaten the health of non-target organisms. Pollution of the aquatic ecosystem has become a worldwide problem, and scientists, in cooperation with legislative bodies, are looking for solutions to prevent further pollution of the environment. In order to assess the toxicity of MP, antibiotics and antivirals and their mixtures in water, in this work laboratory toxicity tests were conducted with the water flea Daphnia magna, a common freshwater zooplankton crustacean. Daphnia magna was exposed to four types of MP, polystyrene (PS), poly(ethylene-terephthalate) (PET), poly(vinyl-chloride) (PVC) and polyethylene (PE) with particle sizes of 100 – 300, 300 – 500 and 500 – 700 μm, and toxicity testing confirmed that these particle sizes are too large to be taken into the body and cause toxic effect. For this reason, the tocix effect of smaller PS particles of 0,5 and 2 μm, which were applied in concentrations of 0,1; 0,5; 1; 2 and 10 mg/L were estimated. Given that it corresponds to the size of the water flea's food, the toxic effect of particles with a size of 2 μm has been confirmed, which increases with increasing concentration, and the effect on 50 % of water fleas calculated as an EC50 value is 0,02 mg/L. The antivirals used in the experiment are atazanavir (ATA) at a concentration of 0,003 mmol/L and emtricitabine (EMT), nirmatrelvir (NIR), oselfamivir (OSE), ribavirin (RIB) and sofosbuvir (SOF) at a concentration of 0,1 mmol/L, which at these environmental concentrations did not have a toxic effect. The antibiotic azithromycin (AZ) used was tested in five concentrations of 0,001; 0,01; 0,1; 0,25 and 0,5 mmol/L, and according to the obtained results, toxicity increased with increasing concentration and the effect on 50 % of water fleas calculated as EC50 value is 0,6 mmol/L. In binary and ternary combinations, the most significant toxic effect was observed at a concentration of 0,5 mmol/L AZ with PE, or PET, which resulted in only 20 % of motile water fleas. The obtained experimental results were processed using statistical analysis of variance (ANOVA), which also confirmed that toxicity of xenobiotics to Daphnia magna depends on the concentration and particle size.