Organic pollutants in Swiss compost and digestate

Composting (aerobic treatment of organic wastes) and digestion (anaerobic treatment of organic wastes combined with biogas production) are important waste management strategies with increasing significance in the European Union and Switzerland. Most of the compost produced is applied to agricultural soils, which hereby recycles nutrients and influences soil properties beneficially. However, compost can contain pollutants that may be hazardous for the soil ecosystem. The problem related to heavy metals had been recognised and measures for reduction were taken. Regarding organic pollutants, the current knowledge is insufficient for quality control and risk assessment. This thesis provides a comprehensive overview on organic contaminates in compost, digestate, and presswater and describes factors that may influence them. In the beginning an extensive literature review was carried out to summarize the current data. Compound classes to be analysed in Swiss composts and digestates were prioritized and analytical methods established. Polychlorinated biphenyl concentrations (∑ of PCB 28, 52, 101, 118, 138, 153, 180) were significantly higher in urban (median: 30 μg/kgdry weight (dw), n=52) than in rural samples (median: 14 μg/kgdw, n=16), which points – together with low concentrations in general – to aerial deposition on feedstock material as major input pathway to compost. Median polycyclic aromatic hydrocarbon (PAH) concentration was 3010 μg/kgdw (∑ of 16 PAH defined by the US EPA except dibenzo[a,h]anthracene, n=69). PAH levels were influenced by the organic matter degradation process (higher levels in digestate than in compost), the season of input material collection (spring/summer>winter>autumn), the particle size (higher concentrations in unsieved or sieved >20mm than in sieved to ≤ 20mm products), and maturity (lower concentrations in more mature composts). One fourth of the samples exhibited PAH concentrations above the Swiss guide value for compost (Ordinance on the Reductions of Risks linked to Chemical Products). These elevated concentrations can lead to considerable input of PAH to soil by compost application. To assess the major contributors of PAH in compost, characteristic PAH ratios and some molecular markers were considered, which pointed mainly to combustion origin of these contaminants. Multifactor statistical analysis indicated traffic emission, straw combustion and some asphalt abrasion as potential additional sources. Concentrations of other organic pollutants determined (dibenzo-p-dioxins and -furans, dioxin-like PCB, brominated flame retardants (BFR), perfluorinated alkyl substances (PFAS), di(2-ethylhexyl)phthalate, nonylphenol and chlorinated paraffins) were mostly above levels found in background soil, except for nonylphenol, which was not detected. Out of 269 pesticides analysed, 30 fungicides, 14 herbicides, eight insecticides and one acaricide were detected. For the first time, the fate of organic pollutants during full-sc