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Study on degradation processes of bioplastics
Fojt, Jakub ; Koutný, Marek (referee) ; Gregor, Tomáš (referee) ; Kučerík, Jiří (advisor)
Biodegradable bioplastics are currently developed as a more environmentally friendly replacement for conventional plastics to be used in agriculture or packaging materials. As the production of these products increases, so will the likelihood of introducing them in the environment. Biodegradable materials are expected to biodegrade rapidly, thereby they should reduce the number of microplastics in the environment. Biodegradability is currently determined by biodegradation tests, the parameters of which are defined in very general terms and often do not reflect the actual conditions under which the bioplastic will degrade in the environment. There is a lack of knowledge about the fate and impact of these particles in different ecosystems (especially in soil, where contamination is expected to be highest). Therefore, in this dissertation, we critically evaluate the ISO soil biodegradation test and extend it with a subsequent determination of bioplastic residues in soil. For this reason, an analytical method for the determination of polyhydroxybutyrate and polylactic acid microplastics based on methods used for the determination of conventional microplastics. The effect of microbioplastics on soil is also discussed, focusing on the effects that may pose problems in agriculture. The influence of microbioplastics on abiotic (soil water properties, soil structure) and biotic (soil diversity, nutrient cycling) soil properties immediately after their entry into the soil are described. The effect of biodegradation and long-term presence of microbioplastics in soil on soil organic matter, nutrient content, and soil microbial diversity (described by determining the activity of 5 key enzymes involved in carbon, nitrogen, and phosphorus cycling) are also studied. The last chapter demonstrates the potential problems that can be encountered when bioplastic products are applied in agriculture, where the growth of fungi and molds naturally occurring in the soil can be accelerated. As a result of this dissertation, a comprehensive view of bioplastics in the environment is presented, which can serve to assess the suitability of the application of current generation bioplastic products in agriculture and the possible management of bioplastic waste.
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