Transport of veterinary medicines from soils to groundwater under variable soil moisture and temperature conditions

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During the 1st and 2nd phase of this Research Unit we developed a model for sulfadiazine (SDZ) sorption in soil and evaluated SDZ transport in soil column and lysimeter experiments. These investigations showed that leaching of SDZ and its metabolites is strongly influenced by instantaneous sorption reactions and long-term degradation under variable atmospheric boundary conditions in lysimeters. There are strong indications that instantaneous sorption and degradation of SDZ are both affected by soil moisture. The goal of the proposed 3rd phase of our subproject is therefore to quantify soil moisture effects on the fast sorption of SDZ, its degradation, and transport in a Central Field Experiment and accompanying laboratory experiments after finalizing ongoing experiments addressing the transport and fate of difloxacin in lysimeters. The Central Field Experiment, which will be established and conducted by our subproject in collaboration with subproject A3 at the Merzenhausen test site, will encompass i) ambient soil moisture and temperature conditions, ii) constant soil moisture conditions close to 40% of the water holding capacity, and iii) extreme variations of soil moisture. Constant soil moisture and extreme variations of soil moisture will be achieved using transparent roofs and irrigation. Individual laboratory experiments will investigate the rapid sorption of SDZ in forms of different binding strength as well as its degradation at soil water contents of 0% (air-dried), 20%, 50%, and 100% of the maximum water holding capacity and in soil slurries (soil to solution ratio, w:v, 1:5). These experiments will contribute to testing the central hypothesis that drying and re-wetting cycles increase transformation reactions, sequestration, and NER formation of SDZ, and reduce its effects compared to static moisture conditions, and the extended hypothesis that under water saturated conditions, there is a pronounced mineralization of SDZ residues on time scales of months (90 days) at given temperature.