Microplastics (MP) is a pollutant of concern in the scientific community due to its ubiquity in the environment. The sources of MP are numerous and exposure to aquatic organisms is increasing, so a risk assessment is needed. To ensure that MP does not have adverse effects on aquatic organisms, it must be removed from the environment, and one of the most promising methods is bioremediation with bacteria, yeasts, molds, or a mixed consortium. In this dissertation, ecotoxicity tests were first conducted for five types of MP: polyethylene (PE), polypropylene (PP), polystyrene (PS), poly(vinyl-chloride) (PVC), and poly(ethylene-terephthalate) (PET) with microalgae of the genera Chlorella and Scenedesmus, the bacterium Pseudomonas putida, and the yeast Saccharomyces cerevisiae. PS and PVC MP showed the highest ecotoxic effects on the test organisms, and Saccharomyces cerevisiae was the most sensitive. Studies on bioremediation of MP contaminated water were also performed with the bacteria Bacillus cereus, Bacillus subtilis, Pseudomonas alcaligenes and Delftia acidovorans isolated from the MP enriched environment. The influence of seven parameters was pre-tested: concentration (50 – 1000 mg/L) and size (100 – 700 μm) of particles of MP, agitation speed of the rotary shaker (100 – 200 rpm), pH of the medium (6 – 8), temperature of the medium (15 – 25 °C), optical density (0.1 – 0.5) and addition of glucose (0 – 100 mg/L). The three most significant parameters were selected for each polymer by statistical analysis, and biodegradation optimization was performed based on these parameters. For the treatment with the bacterium Bacillus cereus, it was found that the three most statistically significant parameters for the biodegradation of PS MP were the size and concentration of MP and the agitation speed of the rotary shaker (optimum {413.29 μm; 66.20 mg/L; 100.45 rpm}). For the treatment of PVC MP, the size and concentration of MP and the optical density (optimum {400.00 μm; 658.40 mg/L; 0.40}) were found to be significant. Analysis of the degradation of MP by the bacterium Bacillus subtilis showed that the size of MP, the agitation speed of the rotary shaker, and the optical density were significant for the biodegradation of PS MP (optimal {440.65 μm; 162.12 rpm; 0.50}), while for PVC MP it was the pH of the medium, the number of agitation speed of the rotary shaker, and the optical density (optimal {8.00; 200 rpm; 0.50}). For biodegradation of PS MP by Pseudomonas alcaligenes, the nu agitation speed of the rotary shaker, the size of the MP particles, and the optical density (optimal {161.08 rpm; 334.73 μm; 0.35}) were significant, while for biodegradation of PVC, the pH of the medium, the MP concentration, and the optical density (optimal {8.00; 50.00 mg/L; 0.50}) were significant. Finally, in the biodegradation by the bacterium Delftia acidovorans, the same significant parameters were obtained for PS MP and PVC MP. These were the pH of the medium, the agitation speed of the rotary shaker and the optical density (optimal conditions {7.99; 104.93 rpm; 0.46} and {8.00; 200.00 rpm; 0.50}, respectively). Accordingly, the bacterial cultures, isolated from the environment, are capable of degrading MP.