On 30 June 2022, the OECD published test guideline No. 320: ‘Determining anaerobic transformation of chemicals in liquid manure’. This guideline describes a standardised method to investigate transformation of chemical substances in pig and cattle liquid manure under anaerobic conditions. The experiments are performed to determine the rate of transformation of the test substance, the identity, rates of formation and decline of transformation products, the amount of test substance that is mineralized to CO2 or CH4 or transformed to volatile transformation products, and the amount of non-extractable residues (NER). Such studies are relevant for substances, which are administered to livestock and subsequently excreted (e.g. veterinary medicinal products or feed additives), and for substances, which are applied in stables and may enter the manure (e.g. biocides).
Within the projects ‘Development of test guidance for transformation of veterinary pharmaceuticals and biocides in liquid manure’ and ‘Harmonisation of experimental exposure assessment for veterinary pharmaceuticals and biocides’, ECT contributed significantly to the development and standardisation of this method for evaluating transformation of chemicals in liquid manure. Development of the method is described in detail in Junker et al. (2020).