All over the world, large amounts of plastic waste are thrown into the environment every year. One of the problems is single-use plastic and underdeveloped waste management systems that have led to the accumulation of plastic. Once discarded, plastic can be present in the environment for many years. Under the influence of various weather and external conditions, it breaks down into smaller particles known as microplastics. In addition, microplastics are produced with the intention of being added to various cosmetic and personal care products. Polystyrene is one of the most commonly used types of plastic, and therefore often found in the environment. The influence of MP on the organism and human health has not yet been sufficiently investigated, but the fact that it is ubiquitous and found even in the most remote places on earth has caused great attention and concern. A large specific surface capable of binding various pollutants from the environment as well as various pathogens contributes to this. For this reason, various ecotoxicity tests are increasingly carried out on a wide number of organisms. In addition to becoming familiar with all the possible consequences of exposure to MP, it is important to develop effective ways of removing it from the environment. The work is challenging because due to its small size, MP successfully passes through various filtration systems. MP biodegradation processes are promising green methods that need to be developed and adapted to specific types of plastics and microbial communities. When testing MP, it is important to use appropriate characterization methods to obtain complete information. In this paper, the biodegradation of MP particles of PS by the bacterial culture Delftia acidovorans was examined according to the full factorial plan. The optimal conditions for the biodegradation process were tested; pH-value, the number of revolutions of the rotary shaker and the optical density of a bacterial cell. The experiment lasted 30 days, and during this period the values of total, organic and inorganic carbon, and the number of living bacterial cells were determined. Potentially released additives were analyzed by LC/MS method, and changes in structure by FTIR_ATR. The ecotoxicity of the filtrate was also tested using the marine bacterium Vibrio fischeri. The results showed that there was a certain biodegradation of MP. The obtained optimal conditions are pH-value (8), OG (0.5) and the number of revolutions of the rotary shaker of 172.12 rpm.