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Dynamics of degradation and residues of veterinary medicines in manure amended soil.

Prof. Dr. A. Schäffer, Dr. B. Schmidt, RWTH Aachen

Summary

Goal of the subproject was the evaluation of the fate of two veterinary pharmaceuticals (sulfadiazine, SDZ, and difloxacine, DIF) in soil using different chemical and analytical methods such as radio-thin layer chromatography (radio-TLC), radio-high performance liquid chromatography (radio-HPLC), gas chromatography mass spectrometry (GC-MS), gas chromatography coupled to a flame ionization detector (GC-FID), and liquid chromatography tandem mass spectrometry (LC-MS/MS). A special focus was to study the influence of maize plants and a potential rhizosphere effect on the fate of the two pharmaceuticals. Only very small quantities of the two pharmaceuticals were taken up by maize plants from the investigated soil. This indicates a poor availability of both antibiotics for uptake by maize. Also the fraction of both 14C- labeled pharmaceuticals that was mineralized to 14CO2 was very small. For both antibiotics the formation of non-extractable residues (NER) dominated their fate in soil. Neither for SDZ nor for DIF significant differences between the extractability from root-free soil and root-near soil were found. Also manure had no effect on the extractability of DIF.

The only metabolite of SDZ was 4-OH-SDZ, which was formed in soil so that its concentrations increased during the course of incubation experiments with soil. No metabolites of DIF were detected in incubations studies, only the parent compound was found in the extracts.

For an in-depth analysis of non-extractable residues, humic substances of the investigated soil were fractionated into fulvic acids, humic acids, and humin. Furthermore, soil that had been extracted using accelerated solvent extraction (ASE) were separated into their sand, silt, and clay particle size fractions in order to assess the distribution of NER in these fractions.

Because large quantities of applied radioactivity were recovered in the fulvic acids, this fraction was investigated in more detail using size exclusion chromatography. The chromatograms showed two radioactivity peaks, a broad one with high molecular weight eluting early and second sharp one eluting later. Based on peak shape and experiments with pure fulvic acids and the two antibiotics we hypothesized that the second low-molecular weight peak represented free molecules of the parent drugs and its metabolites that were not bound to the fulvic acids. A further analysis of the two molecular weight fractions using LC-MS/MS confirmed the existence of the parent compound SDZ in the fulvic acid fraction of NER. During the first days of the incubation experiment, non-extractable SDZ and 4-OH-SDZ occurred almost exclusively in free form in the later-eluting fraction. With increasing incubation time the fraction of free SDZ and 4-OH-SDZ decreased indicating a progressively stronger binding or entrapment of the two compounds into the fulvic acids. An in-depth characterization of DIF-containing fulvic acids with LC-MS/MS was not feasible because only very small amounts of radioactivity could be extracted from soil.

 

begutachtete Publikationen:

  1. Junge, T., Meyer, K.C., Cielinski, K., Adams, A., Schäffer A., Schmidt, B., 2011. Characterization of non-extractable C-14- and C-13-sulfadiazine residues in soil including simultaneous amendment of pig manure. Journal of Environmental Science and Health B 46, 137-149.
  2. Junge, T., Classen, N., Schäffer, A., Schmidt, B., (2012): Fate of the veterinary antibiotic C-14-difloxacin in soil including simultaneous amendment of pig manure with the focus on non-extractable residues. Journal of Environmental Science and Health B 47, 858-868.

 

Weitere Publikationen:

  1. Junge, T. (2012): Abbau und Rückstandsdynamik von Tierarzneimitteln in Boden-Pflanzen-Systemen. Dissertation, RWTH Aachen, 148 pp.
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