Modelling of the Environmental Fate and Effects of Veterinary Medicines in Soil under Field Conditions
Final Report Abstract
The overall objective of subproject C was the development of an integrated fate and effect model for veterinary antibiotics (particularly sulfonamides) in soil as basis for sound and comprehensive risk assessment. Based on experimental results within the Research Unit for the model substance sulfadiazine (SDZ), relevant physical, chemical and biological processes that govern fate and effects of sulfonamide antibiotics in soil were identified and integrated into a consistent simulation model. The developed conceptual kinetic fate model well describes concentration dynamics of SDZ and its metabolites 4- hydroxy-SDZ (4-OH-SDZ) and N-acetyl-SDZ (N-Ac-SDZ) observed in laboratory batch and mesocosm experiments and it can also largely explain the dynamics observed in field experiments. The model considers (pseudo-)first-order transformation reactions within the easily extractable fraction (EAS) as well as reversible translocation from EAS into the residual fraction (RES) and irreversible dissipation into the fraction of non-extractable residues (NER). The phenomenon that extractability of SDZ is instantaneously reduced after its application to soil was confirmed in experiments. It was proven that a rapid dissipation process occurs along with the slow first-order kinetics considered in the model. On the field scale, the fate model could preliminary quite well describe EAS concentration dynamics when considering simple temperature and moisture correction functions as well as reasonable adaptions of rate constants for reversible sequestration. Results of targeted experiments with different isotope-labelled compounds on the quantitative effect of temperature on fate processes were not sufficient to deduce consistent correction factors. For de-acetylation and NER formation, temperature sensitivities expressed as Q10 values were much higher than average values known for pesticide degradation in soil, which is hypothesized to be due to overlying effects related to the amendment of the substance with manure. A major finding of the experiments was that a direct pathway from N-Ac-SDZ into NER must exist which had not been considered in the original fate model. For uptake and accumulation of sulfonamides in bacteria, a dynamic model considering intra- and extracellular pH values and the substance specific pKa value was established, which helps to explain the different activities of sulfonamides as inhibitor of bacterial growth. In-vitro microtiter plate tests with E.coli demonstrated that the two major metabolites 4-OH-SDZ and N-Ac-SDZ were not able to exhibit bacteriostatic effects. For N-Ac-SDZ, this is in accordance with the inactivation of the aniline moiety by substitution, while for 4-OH-SDZ it is most likely due to keto-enoltautomerism. Therefore, only the parent compound SDZ has to be considered in risk assessment. Models describing the effect of sulfonamides on bacteria considered growth inhibition of nitrifying bacteria (AOB) and resistance gene selection. It could be demonstrated that ammonia-oxidizing archaea (AOA) maintain the respective soil function in case of deficiency of AOB through the inhibitory effect of antibiotics (functional redundance). The chemical fate model was successfully coupled with the effect model for AOB and AOA. Sensitivity and uncertainty analysis of the integrated fate and effect model clearly showed that the general dynamics of important output variables is robust enough against uncertainties to allow for interpretable predictions of the effect of antibiotics on soil functions such as nitrification. Due to the extremely strong sorption of the second model compound difloxacin (DIF) to soil, long-term accumulation can be expected, but potential release and effects cannot yet be predicted.
Publications
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(2008): A mechanistical model for the uptake of sulfonamides by bacteria. Chemosphere 70, 753–760
Zarfl C, Matthies M, Klasmeier J
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(2008): Chemical Fate of Sulfadiazine in Soil: Mechanisms and Modelling Approaches. PhD Thesis. Shaker Verlag (Aachen). ISBN 978-3-8322-7491-7
Zarfl C
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(2008): Fate of sulfadiazine administered to pigs and its quantitative effect on the dynamics of bacterial resistance genes in manure and soil. Soil Biology and Biochemistry 40, 1892–1900
Heuer H, Focks A, Lamshöft M, Smalla K, Matthies M, Spiteller M
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(2008): Growth-inhibitory effects of sulfonamides at different pH: Dissimilar susceptibility patterns of a soil bacterium and a test bacterium used for antibiotic assays. Chemosphere 72, 836–843
Tappe W, Zarfl C, Kummer S, Burauel P, Vereecken H, Groeneweg J
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(2009): Analysis, fate and effects of the antibiotic sulfadiazine in soil ecosystems. Trends in Analytical Chemistry 28, 612–618
Schauss K, Focks A, Heuer H, Kotzerke A, Schmitt H, Thiele-Bruhn S, Smalla K, Wilke BM, Matthies M, Amelung W, Klasmeier J, Schloter M
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(2009): Dynamics and functional relevance of ammonia-oxidizing archaea in two agricultural soils. Environmental Microbiology 11, 446–456
Schauss K, Focks A, Leininger S, Kotzerke A, Heuer H, Thiele-Bruhn S, Sharma S, Wilke BM, Matthies M, Smalla K, Munch JC, Amelung W, Kaupenjohann M, Schloter M, Schleper C
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(2009): Effects of Sulfadiazine in Soil: Integrative Modelling Approaches as a Basis for Environmental Risk Assessment. PhD Thesis. Dr. Hut-Verlag (München), ISBN 978-3-86853-041-4
Focks A
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A conceptual model describing the fate of sulfadiazine and its metabolites observed in manure-amended soils. Chemosphere 77, 720-726
Zarfl C, Klasmeier J, Matthies M
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(2010): The mechanistic link between sulfonamide uptake and effect on the growth of bacteria: Model development and application to experimental data from two soil microorganisms. Environmental Toxicology and Chemistry 29, 1445–1452
Focks A, Klasmeier J, Matthies M
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(2011): Accumulation of sulfonamide resistance genes in arable soils due to repeated application of manure containing sulfadiazine. Applied and Environmental Microbiology 77, 2527–2530
Heuer H, Solehati Q, Zimmerling U, Kleineidam K, Schloter M, Müller T, Focks A, Thiele-Bruhn S, Smalla K
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(2013): Short-term extractability of sulfadiazine after application to soils. Environmental Pollution 172, 180–185
Müller T., Rosendahl I, Focks A, Siemens J, Klasmeier J, Matthies M
