The discovery of plastics has greatly simplified people’s lives; but its continued use and improper disposal have led to an accumulation of plastic waste in the environment. Due to environmental processes, plastic breaks down into smaller particles known as secondary microplastics (MPs). By definition, these are particles with a size of 1 μm to 1 mm. In addition, primary MPs, which are intentionally produced in small sizes, are also released into the environment. In recent years, biodegradable plastics have been increasingly used to solve environmental problems. It is assumed that they mineralize in the environment and break down into inorganic products such as carbon dioxide and water. However, it has been shown that the degradation of many biodegradable polymers is very slow or incomplete under natural environmental conditions. Furthermore, the rate of degradation of the same polymer varies depending on the environment in which the degradation takes place. The use of biodegradable plastics is gaining importance in agriculture, where conventional mulching films made of low density polyethylene (LDPE) are being replaced by biodegradable films made of polybutylene adipate terephthalate (PBAT). Consequently, biodegradable MPs are present in agricultural soils and may also enter the aquatic environment, where their biodegradation and behavior are not yet well understood. In this master thesis, we compared the properties of conventional LDPE MPs and biodegradable PBAT MPs used as mulching films in agriculture. We also exposed these plastics to UV radiation to simulate natural outdoor conditions. The biodegradability of the MPs was tested using a respirometric method based on the measurement of oxygen consumption during biodegradation. After the test, we analysed the ionic composition of the test medium, evaluated the changes in the physico-chemical properties of the MPs, and assessed the effects of MPs before and after biodegradation on the free-floating plant Lemna minor. The results showed that neither conventional LDPE MPs nor biodegradable PBAT MPs are readily biodegradable in water under natural environmental conditions. The highest biodegradation rate was achieved with UV irradiated PBAT MPs, which was 56,7 % within 28 days. Ion analysis indicated the occurrence of nitrification processes during biodegradation. After biodegradation, the MP samples had a smoother surface. Using Fourier transform infrared spectroscopy (FT-IR), we detected signs of photo-oxidation in the PBAT samples that had been previously exposed to UV radiation, whereas no such signs were observed in the LDPE samples. In toxicity tests, MPs affected root growth of Lemna minor, with less impact observed in post-biodegradation samples, while no effects on specific growth rate or chlorophyll a content were determined.
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