Dissipation and sequestration of veterinary medicines in soil under dynamic moisture conditions

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In the 1st phase of this Research Unit, we found that sulfadiazine (SDZ) and its 4-OH-metabolite are sequestered in soil in significant amounts when applied with animal manure under controlled laboratory conditions. N-Ac-SDZ decayed rapidly to the parent compound. The results of the 2nd phase suggested that the sequestration processes are driven by entropy, i.e., diffusion into small voids. Dissipation of SDZ and its metabolites under field conditions could be predicted reasonably well by temperature-adjustment of dissipation rates derived from the laboratory incubation of the 1st phase (10°C) and a mesocosm experiment of the 2nd phase (21°C). Nevertheless, the results of the field trial indicate a deviation from predicted dissipation at extremely dry and very wet conditions, suggesting a pronounced influence of soil moisture on dissipation and sequestration of SDZ in soil. It is therefore the major goal of our project to elucidate the relevance of changing soil moisture on the field sequestration of SDZ. In particular we aim at (i) quantifying to which extent drying-wetting cycles accelerate sequestration (ii) testing the use of the stable-isotope signature of SDZ to characterize the “age” of SDZ contaminations, and (iii) finalizing running experiments on the dissipation and sequestration of difloxacin under field conditions. We will establish and coordinate a central field experiment II at the Merzenhausen test site with manipulated soil moisture together with project A4. Our project will be responsible for the quantification of SDZ concentrations in soil over time in the central field experiment and the accompanying central laboratory experiment.