Introduction: Microplastics smaller than 5 mm pose a serious risk to terrestrial and aquatic ecosystems. The use of plastic films in agriculture contributes to microplastic pollution, which can adsorb hydrophobic organic pollutants. These pollutants have various, mostly negative, effects on soil structure, plants and groundwater, and consequently pose a threat to the environment and human health. Purpose: The aim of this MSc thesis is to investigate the adsorption capacity and desorption retention capacity of azoxystrobin on new and aged biodegradable films (poly(butylene adipate-co-terephthalate) / polylactic acid - PBAT/PLA and thermoplastic starch - TPS compositions) in comparison with conventional polyethylene (PE) films. Methods: In a laboratory experiment, the concentrations of adsorbed and desorbed fungicide on biodegradable (PBAT/PLA, TPS) and conventional (PE) microplastics were determined. The adsorption fraction was determined by mixing samples containing the selected microplastic and a solution containing the fungicide, while the desorbed fungicide fraction was determined by mixing samples containing the microplastic and a solution containing no fungicide. The concentrations of fungicide adsorbed to and desorbed from the microplastic particles were measured by liquid chromatography with an array of diode array detector (HPLC/DAD). For statistical treatment of the data, t-tests were used to test for statistically significant differences between the selected pairs of samples. Results: Statistical analysis of the results showed that biodegradable films exhibit high adsorption (> 85%) and desorption capacity, regardless of their age. In contrast, adsorption on conventional PE films is low, while desorption is comparable to biodegradable films and low in all cases. Ageing of PE films increases their adsorption (from 0% to > 22%) and desorption (from 0% to 10%) capacity, which is not the case for biodegradable films. For the latter, adsorption increases only marginally with age from 87% to 91%, while for desorption with age a decrease in the proportion of fungicide desorbed from 10% to 8% is observed. Discussion and conclusion: The study confirmed that fungicide adsorbs to and desorbs from microplastic particles. The adsorption is most influenced by the type of microplastic, while the influence of age is less pronounced. However, desorption is influenced by both the type and the age of the microplastic. This thesis has contributed to a better understanding of the influence of different types of microplastics on the adsorption and desorption of fungicide, with particular emphasis on the comparison between biodegradable and conventional films. The study provides a starting point for further studies on the effect of different fungicides on the adsorption of microplastics and suggests broadening the range of microplastic types investigated, including the study of the long-term effects of ageing of microplastics under realistic field conditions.
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