Modeling tetracycline antibiotic sorption to clays.
Sorption interactions of three high-use tetracycline antibiotics (oxytetracycline, chlortetracycline, tetracycline) with montmorillonite and kaolinite clays were investigated undervaried pH and ionic strength conditions. Sorption edges were best described with a model that included cation exchange plus surface complexation of zwitterion forms of these compounds. Zwitterion sorption was accompanied by proton uptake, was more favorable on acidic clay, and was relatively insensitive to ionic strength effects. Calcium salts promoted oxytetracycline sorption at alkaline pHs likely by a surface-bridging mechanism. Substituent effects among the compounds in the tetracycline class had only minor effects on sorption edges and isotherms under the same solution pH and ionic strength conditions. At low ionic strength, greater sorption to montmorillonite than kaolinite was observed at all pHs tested, even after normalizing for cation exchange capacity. These results indicate that soil and sediment sorption models for tetracyclines, and other pharmaceuticals with similar chemistry, must account for solution speciation and the presence of other competitor ions in soil or sediment pore waters.
Figueroa
Raquel A
RA
Environmental Engineering Program, University of Connecticut, 261 Glenbrook Road, U-2037, Storrs, Connecticut 06269-2037, USA.
Leonard
Allison
A
MacKay
Allison A
AA
D000327:Adsorption; D000538:Aluminum Silicates / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000737:chemistry*; D000077215:Clay; D019015:Geologic Sediments / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008962:Models, Theoretical; D016062:Porosity; D012989:Soil Pollutants / Q000032:analysis*; D013752:Tetracycline / Q000737:chemistry*; D014873:Water Pollutants / Q000032:analysis
D000538:Aluminum Silicates; D000900:Anti-Bacterial Agents; D012989:Soil Pollutants; D014873:Water Pollutants; D013752:Tetracycline; D000077215:Clay