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Risk factors of liquid manure

04.12.2006
Antibiotics in animal excrements contaminate the soil

High amounts of antibiotics still are sad reality in large-scale livestock farming. According to the Bundesverband für Tiergesundheit e.V. (Federal Association for Animal Health), in Germany alone about 784 tons were used in 2005. What is supposed to protect pig, cow and chicken against infections, can also become dangerous to man. Structurally nearly unchanged antibiotics excreted from the animals are spread via liquid manure to agricultural soils and can re-enter the food chain via a plant uptake as recent studies prove.

To be able to confront this danger, the research group “Veterinary Medicines in Soil” sponsored by the German Research Foundation (DFG) examines the basic mechanisms and consequences of the use of antibiotics in livestock farming. With the goal to improve the risk assessment, scientists from Berlin, Aachen, Jülich, Braunschweig, Osnabrück, Dortmund, Trier and Bonn want to find out how and to what extend the drugs get in the environment and to what changes and chemical reactions they are subjected to.

The first step for the team of scientists around Prof. Dr. Michael Spiteller, head of the Institute of Environmental Research at Universität Dortmund, is to track the way of the drugs from the animal via liquid manure fertilization into the soil and to get exact data concerning type and amount of the active substances in the different phases for the first time.

In a first test series an antibiotic from the group of sulfonamides which are commonly used in large-scale livestock farming was orally administered to pigs. The radioactively labeled substance put the scientists in the position to establish exactly how much of the antibiotic stays in the animal and how much is excreted, by examining the excrements. The results give cause for concern: only 10 percent of the active substance stays in the animal, the rest is released into the environment via the excrements of the pigs. A maximum of 50 percent of the administered substance remains unchanged, and still exhibits full antibiotic activity, and about 50 percent accrue as metabolites – some of which are still biological active.

In the second part of the research project the scientists concentrate on the question, what happens with the active substances when they get into the soil via fertilization. Spiteller and his coworkers Dr. Sebastian Zühlke and Dr. Marc Lamshöft pursue two approaches to get data as precise as possible about the processes on and beneath the ground.

In the university’s own testing area liquid manure is applied under realistic agricultural conditions, and processes are examined. As the identification of active substances in the complex soil mix is rather complicated, the scientists complete the outdoor test with test series in the laboratory. Here they can also use radioactively labeled antibiotic substances and exactly identify metabolites developing in the soil with the highest accuracy. Latest instrumental analysis like high resolution mass spectrometry is used to verify the substances even in the smallest quantities. As the Dortmund environmental researchers describe it, “like looking for a needle in a haystack”.

The Dortmund scientist team found out that after 30 days the major part of the substances was composed or solidly bounded. But: two up to five percent remain in the soil – unbound – and therefore potentially able to get into the groundwater or food via plants. The scientists suspect that this pool of substances bound in the soil is virtually continuously regenerating. In case of these “free” substances there is the additional danger that they chemically – and hence also their effects – change, due to various processes going on in the soil.

Right now the scientists can give no serious statements about the exact risks the substances in the soil might represent. But even smallest quantities of antibiotic substances can cause bacteria to develop resistances which can restrict the use of human antibiotics against pathogenic germs. “And the effects on the microorganisms in the soil which on their part influence the soil fertility or the nitrogen supply, for example, have still not been completely explored”, Michael Spiteller states. Still a lot of work for the research group, which is trying to establish a scientific basis for a comprehensive risk analysis of antibacterial veterinary drugs in the soil, in project groups throughout Germany.

Ole Luennemann | alfa
Further information:
http://www.uni-dortmund.de

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