Long-Term Sorption and Sequestration Dynamics of the Antibiotic Sulfadiazine: A Batch Study
- Stephan Sittig *,
- Roy Kasteel,
- Joost Groeneweg and
- Harry Vereecken
Understanding the long-term sequestration of veterinary antibiotics into soil fractions with different bioavailability is important in terms of assessing their eco-toxicological impact. We performed 60-d batch sorption experiments with radiolabeled sulfadiazine (SDZ) using samples from two agricultural soils. Sequential extraction with CaCl2/MeOH (easily accessible fraction), microwave (residual fraction, RES), and combustion (nonextractable residues, NER) was used to quantify the sequestration dynamics of the 14C-derived SDZ-equivalent concentration. Multiple harsh extractions allowed us to mathematically extrapolate to the amount of SDZ equivalents that can be potentially extracted, resulting in halving the NER fraction after 60 d. A modified two-stage model with irreversible sorption combined with global parameter optimization was able to display the sequestration dynamics. We demonstrated this with sterilized samples in which no transformation of the parent compound was observed. This also showed that transformation was primarily biologically driven. These modeling results verified the procedure, which was then applied to nontreated samples from both soils to estimate effective parameter values for SDZ-derived equivalents. Observed initial sorption, to which up to 20% of the kinetic sorption sites attributed, was included in the model. Both the RES and NER fractions reached a sorption plateau, with NER occupying about 30% of the kinetic fraction (RES+NER) for all soils. The sorption and sequestration of SDZ were soil-specific and dominated by kinetics. Sequestration in the RES fraction was much slower (characteristic time: 60 d) than the redistribution in the NER fraction (characteristic time: <6 d). The work presented here contributes to the prediction of the dynamics of (bio-)availability.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
Copyright © 2012. . Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.