Swiss College of Agriculture, Zollikofen

Organic pollutants in compost and digestate of Switzerland

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F), dioxin-like PCBs, polybrominated flame retardants, perfluorinated alkyl substances, chlorinated paraffins and phthalates were found in compost, digestate and presswater originating from 39 composting and digestion plants. The concentrations were mostly in the range of μg/kg dry weight (dw) but above background contents of soils. PAHs exhibited the highest concentrations ranging between 600 and 12470 μg/kg dw. About 25 % of the samples were above the guide value of ChemRRV (4000 µg/kg dw). Digestate showed higher concentrations compared to compost for most compounds. Incineration was likely to be the main source of PAHs. The loads of PAHs to soil due to the application of compost and digestate were significantly higher compared to manure and sewage sludge constituting 18 % of the total load. The other compounds were of lower importance. The results of the ecotoxicological studies indicated that the distribution of organic pollutants due to the application of compost and digestate does not pose a direct risk for the soil. For compounds such as PAHs, measures to reduce the contamination are recommended with respect to the precautionary principle and the quality of these recycling fertilizers.

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