###### Abstract  
Although toxicogenic moulds have been identified in municipal waste and composting facilities, only a few reports exist on the occurrence of mycotoxins in compost. Those reports mostly concern sewage sludge as a substrate, tested only a limited range of mycotoxins, and did not monitor the production of mycotoxins during the composting process. Therefore, this study aimed to investigate whether mycotoxins are produced during composting of selectively collected kitchen and garden waste. The study was carried out at pilot scale (550 L reactor with passive aeration). Kitchen waste (59.0% \(w/w\)), garden leaves (28.2%), and wood chips (12.8%) were used as a substrate, which was sampled every five days to determine its basic physicochemical characteristics (temperature, moisture, size-fraction content, loss on ignition) and resiprometric activity (AT4). The substrate and leachate samples were also tested for the content of eight mycotoxins by HPLC-MS/MS. To screen the local compost market, commercial organic-composed samples were analysed for mycotoxin contamination. The substrate was successfully stabilized after 45 days (thermophilic peak of 62.6 \({}^{\circ}\)C, 40.4% mass reduction, 26.9% loss of organic matter, increase in the share of particles in the smallest size fraction, AT4 of 9.82 g O\({}_{2}\)/kg). Although the substrate was colonised by moulds at an early stage, only trace amounts of mycotoxins were detected in a few samples. Similarly, little or no mycotoxins were found in the commercial compost. Our results suggest a low risk of mycotoxin contamination in biowaste compost produced under appropriate technological conditions. Future research should focus on screening compost produced at smaller scales (e.g., in agricultural/residential compost piles) and on identifying factors associated with the risk of mycotoxin contamination in compost. composting; circular economy; organic recycling; risk assessment +
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Mycotoxins belong to a large and diverse group of secondary metabolites produced by fungi, including many mould species that frequently infect plant material and lead to contamination of crops and cereals worldwide [6; 7; 8]. Although hundreds of mycotoxins have been identified to date, only a few fungal metabolites have been the subject of toxicological research and public concern. Among these natural contaminants of food and feed, aflat produced by the common moulds _Aspergillus flavus_ or _A. parasiticus_ are considered the most harmful, due to their hepatotoxic and carcinogenic properties. These mycotoxins are among the most abundant worldwide, along with fumonisins, trichotecenes (e.g., deoxynivalenol, T-2 toxin), zearalenone, which can be produced by various _Fusarium_ strains, and ochratoxins, produced by _Peniculum_, [9]. Although many toxicogenic genera of these moulds have been identified in composting substrates and composting facilities [10; 11], few studies have provided information on the presence of mycotoxins in compost [12; 13; 14]. Moreover, these publications mostly concern sewage sludge as a substrate, tested a limited range of mycotoxins, and none of them monitored the formation of mycotoxins during the entire composting process. The limited number and scope of such studies might be due to the assumption that mycotoxins are naturally degraded to less harmful products. However, most studies on mycotoxin degradation only tested the ability of isolated strains of bacteria or fungi under in vitro conditions, not in realistic scenarios [15]. To the best of our knowledge, the ability of the composting process to degrade mycotoxins has only been tested for aflatoxin B1 [16; 17]. Moreover, there are other mycotoxins that are considered chemically stable and heat resistant [18; 19]. When mycotoxins are actually produced during composting, they can pose a health risk to not only wildlife or domestic animals [13] but also farmers and workers in composting facilities [10; 20; 21].