Introduction: Plastic and biodegradable films are important mulching materials in modern agriculture. Mulches protect crops from adverse weather conditions, reduce weed growth, retain soil moisture and reduce nutrient leaching. Despite their numerous advantages, their use contributes to microplastic pollution in agricultural environments. The degradation of biodegradable and fossil polymer (PE) mulch films, which are often loaded with pesticides, is associated with the release of adsorbed, potentially harmful substances into the environment. This can cause negative effects on the soil microbiome and the wider ecosystem. Their degradation is largely caused by exposure to UV light and aqueous hydrolysis. Purpose: The research focuses on the effect of the adsorbed fungicide azoxystrobin (AZO) on conventional and biodegradable films on the growth of the mould Penicillium expansum, which is a model microorganism present in the soil ecosystem. The fungus produces the toxin patulin (PAT), which in our study serves as a chemical measure of mould activity on films in the presence of AZO). Methods: We studied the effect of the adsorbed fungicide AZO on the growth of P. expansum mould on new and aged conventional and biodegradable mulch films (PBAT/PLA, TPS, PE). AZO was applied to sterilised pieces of film measuring 3 × 3 cm, obtained from a field in Jablje, in three concentrations (0.56 mg m-2; 1.11 mg m-²; 1.67 mg m-²). The films were placed on the surface of a non-nutritive solid medium with inorganic salts and without a carbon source, and sterile filter paper discs were placed on them, onto which a suspension of P. expansum mould conidia was inoculated. After 21 days of incubation at 25 ℃, the diameter of the colonies was measured and the concentration of the mycotoxin PAT was determined chemically by high-performance liquid chromatography with a diode array detector (HPLC-DAD), as were all other solutions containing AZO. The results obtained were processed statistically and the influence of different types of mulch films and concentrations of adsorbed fungicide on mould growth and PAT formation was compared. Results: The mould P. expansum grew successfully on all biodegradable mulch films used, TPS and PBAT/PLA, while growth on PE films was very poor. There were no statistically significant differences in colony diameter between aged and new films. The presence of adsorbed fungicide AZO affected mould growth, but this depended on the type of film and the concentration of the fungicide. PAT determination showed changes in mould activity that did not necessarily coincide with colony growth, which emphasises the importance of monitoring both parameters. We found that the type of mulch film can significantly affect the development of the mould and its metabolic activity in agricultural soils. Discussion and conclusion: AZO proved to be an effective fungicide in inhibiting the growth of the mould P. expansum and can be a good model compound for studying the vectorial impact of adsorbed pesticides on MPs. The greatest effect was observed on PE mulch film, where growth was completely inhibited. On biodegradable mulch film, inhibition was lower, suggesting that the polymer affects the binding affinity of AZO and the mould response. PAT formation was not directly related to colony diameter, as lower concentrations of AZO promoted its synthesis, while higher concentrations inhibited synthesis. In particular, biodegradable films reduced PAT formation even in the absence of AZO, which is probably related to changes in the surface properties of the materials during exposure to environmental factors. The combination of fungicides and mulch film properties significantly affects the growth of this mould and its metabolic activity in agricultural soils.
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