Abstract
The fate of 14C-labeled sulfadiazine (14C-SDZ) residues was studied in time-course experiments for 218 days of incubation using two soils (Ap horizon of loamy sand, orthic luvisol; Ap horizon of silt loam, cambisol) amended with fresh and aged (6 months) 14C-manure [40 g kg−1 of soil; 6.36 mg of sulfadiazine (SDZ) equivalents per kg of soil], which was derived from two shoats treated with 14C-SDZ. Mineralization of 14C-SDZ residues was below 2% after 218 days depending little on soil type. Portions of extractable 14C (ethanol-water, 9:1, v/v) decreased with time to 4–13% after 218 days of incubation with fresh and aged 14C-manure and both soils. Non-extractable residues were the main route of the fate of the 14C-SDZ residues (above 90% of total recovered 14C after 218 days). These residues were high immediately after amendment depending on soil type and aging of the 14C-manure, and were stable and not remobilized throughout 218 days of incubation. Bioavailable portions (extraction using CaCl2 solution) also decreased with increasing incubation period (5–7% after 218 days). Due to thin-layer chromatography (TLC), 500 μg of 14C-SDZ per kg soil were found in the ethanol-water extracts immediately after amendment with fresh 14C-manure, and about 50 μg kg−1 after 218 days. Bioavailable 14C-SDZ portions present in the CaCl2 extracts were about 350 μg kg−1 with amendment. Higher concentrations were initially detected with aged 14C-manure (ethanol-water extracts: 1,920 μg kg−1; CaCl2 extracts: 1,020 μg kg−1), probably due to release of 14C-SDZ from bound forms during storage. Consistent results were obtained by extraction of the 14C-manure-soil samples with ethyl acetate; portions of N-acetylated SDZ were additionally determined. All soluble 14C-SDZ residues contained in 14C-manure contributed to the formation of non-extractable residues; a tendency for persistence or accumulation was not observed. SDZ's non-extractable soil residues were associated with the soluble HCl, fulvic acids and humic acids fractions, and the insoluble humin fraction. The majority of the non-extractable residues appeared to be due to stable covalent binding to soil organic matter.
Acknowledgments
We wish to thank the German Research Foundation (DFG) for financial support of the research unit (DFG For 566), BAYER HealthCare and BAYER CropScience for providing the authentic SDZ reference compound and 14C-manure of the SDZ treated shoats, and Dr. J. Groeneweg and Dr. Putz (Institute of Chemistry and Dynamics of the Geosphere, Research Center Jülich) for organization, preparation and transportation of the 14C-manure amended soils.
Notes
a Maximum water holding capacity.
a Based on moist soil.
b Based on air-dried, Soxhlet-extracted soil.
c Not determined.
a Based on moist soil.
b Based on air-dried, Soxhlet-extracted soil.
c Not determined.
a Based on moist soil.
b Based on air-dried, Soxhlet-extracted soil.
c Not determined.