Characterization of non-extractable 14C- and 13C-sulfadiazine residues in soil including simultaneous amendment of pig manure

Abstract

Recently, we reported on soil fate of SDZ residues amended with pig manure treated with ¹⁴C-labeled sulfadiazine ¹⁴C-SDZ). The first objective of the present study was to determine whether this strategy can be substituted by application of ¹⁴C-SDZ to soil. The second objective was to characterize non-extractable SDZ residues by fractionation, size exclusion chromatography (SEC) and solid state ¹³C-NMR. The fate of ¹⁴C-SDZ was examined for 28 d, using two soils with and without amendment of pig manure. Mineralization of ¹⁴C-SDZ was low; extractable residues decreased to 7-30%. Compared to the previous study, results were similar. ¹⁴C-SDZ derived bound radioactivity was found in HCl-washings, fulvic, humic acids and humin. According to SEC, one bound ¹⁴C portion (70%) co-eluted with fulvic acids (above 910 g mol⁻¹); the other consisted of adsorbed/entrapped ¹⁴C-SDZ. The ¹³C-SDZ study was performed for 30 d; humic acids were examined by ¹³C-NMR. A signal (100-150 ppm) was referred to ¹³C-SDZ. SEC and ¹³C-NMR demonstrated rapid integration of SDZ into humics.