Metabolization/ bound residues and mineralization of veterinary antibiotic residues in soil under dynamic soil moisture and temperature conditions

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The ultimate goal of the proposed project is to generate data on the mineralization, metabolization and bound residue formation of veterinary antibiotic residues under varying temperature and soil moisture conditions in a laboratory study in comparison to a field study to fully understand the fate and effects of the applied drug in soil. Manure containing 14C-labelled sulfadiazine (SDZ) and its bio transformed products will be mixed with Merzenhausen soil in an incubation experiment encompassing three treatments. The first treatment will be carried out under static temperature and constant moisture content of 40% of the water holding capacity. In the second treatment, we will use the same moisture conditions but the temperature will be varied within a range of ±10°C. The third treatment will be conducted under constant temperature with a simulation of drought and heavy rain. The radioactivity balance will be determined for all treatments and the soil will be extracted by repeated ASE (accelerated solvent extraction). In addition to LC-MS/MS analysis of the reversible sequestered residues, the non-extractable part will be dissolved under alkaline conditions and investigated by HPSEC (high performance size exclusion chromatography) and a radioactivity detector coupled online to a mass spectrometer to elucidate the chemical nature of the SDZ residues in soil. Additional incubation experiments with specifically 15N-labeled SDZ will be carried out to investigate the chemical nature of bound residues by liquid and solid state 15N-NMR. This analysis will shed light on the question how much of the applied drug is physically trapped or covalently bound to soil compounds under variable microclimatic conditions. Furthermore we will analyze the root surface (rhizoplane) by means of MALDI-MS imaging in order to localize the concentration of SDZ and its metabolites in highly active micro sites with a resolution of 50–100 μm. We will compare the results with highly active micro sites as determined by biological measurements.