PARENT SESSION

(03-06) Sorption of sulfonamide antibiotic pharmaceuticals in soil particle size fractions.

Thiele, Sören^*,1, Seibicke, Thilo¹, Leinweber, Peter¹, ¹ Institut für Bodenkunde und Pflanzenernährung, Universität Rostock, Rostock, Germany

ABSTRACT- Residues of potentially harmful antibiotic pharmaceuticals are found in soils but their behaviour is scarcely known. The mobility of xenobiotics in soil is usually characterised with sorption coefficients. Sorption is mainly determined by soil organic matter (SOM), hence, coefficients are normalised to the organic carbon content (K_OC). However, the K_OC-concept has limited validity since the molecular composition and properties of SOM vary between and within soils, depending on the size and structure of minerals. Thus, organo-mineral particle size fractions were used to determine the sorption of selected sulfonamide antibiotics. Batch trials were conducted with whole soil and fractions from a loess Chernozem using 0.01 M CaCl₂ as equilibrium solution for adsorption and methanol extraction to determine total desorption. Sulfonamides were analysed using HPLC-UV. Data were fitted with the linearised Freundlich isotherm. In general, K_F-values of adsorption decreased in the order of fine silt > clay > medium silt > sand > whole soil > coarse silt. K_F-values of desorption varied between antibiotics and soil fractions. K_OC-values of ad- and desorption were higher for medium silt, coarse silt, and sand than for fine silt and clay, while hysteresis between ad- and desorption was lowest for the latter fractions. SOM quantity and quality governed the extent and strength of adsorption in medium silt, coarse silt, and sand. However, both SOM and soil minerals adsorbed sulfonamides in fine silt and clay, resulting in a higher quantity of adsorption. In contrast, desorption from these fractions was much higher indicating a substantially lower strength of adsorption to soil minerals. Molecular-chemical properties of SOM were investigated with analytical pyrolysis and correlated with K_OC-values of sulfonamide sorption, enabling for molecular modelling of sulfonamide-soil interactions.

Key words: antibiotic pharmaceuticals, particle size fractions, sorption, soil organic matter