Fate in soil of ¹⁴C-sulfadiazine residues contained in the manure of young pigs treated with a veterinary antibiotic

Abstract

The fate of ¹⁴C-labeled sulfadiazine (¹⁴C-SDZ) residues was studied in time-course experiments for 218 days of incubation using two soils (A_p horizon of loamy sand, orthic luvisol; A_p 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.

Keywords:

• ¹⁴C-Labeled sulfadiazine
• metabolism
• ¹⁴C-labeled manure
• soil
• fate
• non-extractable residues
• mineralization
• bioavailability

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.