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(40-20) Sulfonamides in soils: An example of weak, pH-dependent sorption. Cavallo, Romina1, Gebbink, Wouter1, Tolls, Johannes*,1, 1 IRAS Environmental Toxicology & Chemistry, Utrecht, Netherlands ABSTRACT- Sulfonamides are an important group of antibiotics. While they constitute a minor share of the antibiotics in human medicine they account for about third of the amount of antibiotics used to treat farm animals. Since the excreta of the treated animals are applied as fertilizer, sulfonamides reach the soil environment. In order to assess their mobility in the soil, we determined soil sorption coefficients following established protocols. Seven sulfonamides differing in acidity from pKa 4.5 to about 7.5 were included in our study. For sulfochloropyridazine, the lead compound in our study, we found that sorption can generally be described by linear isotherms. Saturation of the soil solids was not observed at concentrations as high as 40 mg/L. In different soils, KD-values for sulfochloropyridazine varied from 0.5 to 7 L/kg. Amendment of the soil with pig manure resulted in a decrease of the observed KD-values. This can be explained by the decease of KD with increasing pH corresponding to stronger sorption of the neutral than the anionic species. This is a feature common to all sulfonamides, which at neutral pH ranged in KD from 0.4 to 6 L/kg at pH 6.5 Hence, sulfonamide antibiotics sorb weakly to soils and might be easily transported with by soil water. Key words: pharmaceutical, soil, sorption, distribution |
