It was the aim of the project to develop a method to determine the transformation of substances in liquid manure. In a first step, the heterogeneity of manure of different type and origin was tested. Furthermore, a procedure was tested which is capable to take samples homogeneously from a manure storage tank. Obviously, representative sampling is possible in case mixing devices which are routinely applied by the farmers are used prior to sampling. In order to get an overview on the variability of liquid manure of different type and origin (pig-/cattle manure; manure sampled in summer and winter, from different regions and livestock breeding) 30 manures were sampled and characterized. Furthermore, temperature (including a temperature profile) in manure tanks was reported in order to select a realistic test temperature. Six manures were selected to perform transformation studies of two veterinary medicinal products (Salicylic acid, Paracetamol) and a biocide. The experimental methodology which was developed in the project was used in a first inter-laboratory comparison (ring test) with 5 laboratories. Experiences of the participants were presented and discussed on a workshop and based on the results the developed test protocol was adapted.