DFG Research Unit 'Veterinary Medicines in Soil – Basic Research for Risk Analysis'
Recently, ecologically active concentrations of antibiotics in soil were detected. A major emission path of veterinary medicines is via manure, which is applied as fertilizer in large amounts onto agricultural soils. Manure often contains residues of antibiotics as well as microorganisms carrying antibiotic resistance genes. However, in order to make a comprehensive risk analysis, basic modelling approaches are missing.
In February 2005, the DFG (German Research Foundation) Research Unit “Veterinary Medicines in Soils: Basic Research for Risk Analysis” was established to investigate the fate of veterinary antibiotics in soil and their effects and risks on the environment.
The activities of the Research Unit are characterized by an intensive cooperation between the single subprojects, which are assigned to soil science, environmental chemistry, microbiology and modelling. Experimental investigations are carried out within the context of a central experiment, i.e. they are based on samples of a central experimental setup analyzed by all subprojects. The single investigations can be assigned either to ‘exposure and dynamics’ (fate) or ‘effects’. Sulfadiazine (SDZ) and difloxacin (DIF) are the model compounds studied primarily by the Research Unit.
Our subproject C ‘Integrated modelling’ deals with the mathematical modelling of the investigated processes and with the integration of the results of the single subprojects into a consistent modelling framework for risk assessment. The single investigations of the subprojects (Fig. 1) are supposed to elucidate significant processes, which determine fate and effects of veterinary antibiotics in manured soils.
Figure 1: Overview of the Research Unit 'Veterinary Medicines in Soils – Basic Research for Risk Analysis'
After successful evaluations each in 2008 and 2011, the Research Unit was prolonged for further three and two years, respectively. In the first three years, the most important processes determining the concentration dynamics, the effects on soil microorganisms and on the resistance gene abundances in soil could be identified. The easily available concentrations of SDZ in soil decreased very fast after manure application but persisted on a long-term low concentration level. SDZ and its metabolites were mineralized only little in soil. Therfore, dissipation of SDZ was primarily determined by formation of non-extractable residues (NER), which were confirmed by using radioactive compounds.
Effects on the structure of the bacterial community in soil, on microbial nitrogen transformations and on resistance gene abundances were confirmed, but the effects showed a time-delay with regard to the occurrence of the maximum SDZ concentrations in soil. In contrast to SDZ, DIF sorbed very fast and strongly to soil resulting in very low bioavailability.
In the second project phase, investigations were extended to soil/plant systems and to repeated applications of manure, which were realized in mesocosm experiments under controlled conditions as well as in field experiments. The increased microbial activity in the rhizosphere and caused by application of manure accelerated dissipation of SDZ in soil and enhanced its effects. Besides, varying temperature and moisture conditions in the field experiments showed considerable influence on the concentration dynamics and effects. Therefore, in the current third phase of the Research Unit, the effect of varying soil moisture conditions on the processes should be specified.
Scientific employees in Osnabrück:
Prof. Dr. Michael Matthies (since 2005)
Dr. Jörg Klasmeier (since 2005)
Dipl. Geoökol. Tanja Müller (since 2008)
2005-2011: Dr. Andreas Focks
2005-2008: Dr. Christiane Zarfl