Interactions of 15N-Sulfadiazine and Soil Components As Evidenced by 15N-CPMAS NMR

The extensive use of sulfonamides (SNs) in animal husbandry has led to an unintentional widespread occurrence in several environmental compartments. The implementation of regulations and management recommendations to reduce the potential risk of development of antibiotic resistances necessitates detailed knowledge on their fate in soil. We present results from two independent incubation studies of N-15-labeled sulfadiazines (SDZ) which focused on identifying binding types in bound residues. In the first study N-15-amino labeled SDZ was incubated with two previously isolated humic acids in the presence and absence of Trametes versicolor laccase, while in the second study N-15-double-labeled SDZ was incubated with a typical agricultural Luvisol and the humic acid fraction isolated after sequential extraction of the soil. The freeze-dried humic acid fractions of both studies were then analyzed by N-15-CPMAS NMR and compared with the N-15-spectra of synthesized model compounds. In both studies amide bonds and Michael adducts were identified, while formation of imine bonds could be excluded. In the humic acid study, where less harsh extraction methods were applied, possible formation of H-bridging and sequestration were additionally detected.