TA5 Ecotoxicity and Environmental Chemistry of Antibiotics
Room 17A/B, Level 4
8:00 AM - 12:00 PM, Tuesday, 11 November 2003
Chair: Aga, Diana ,
(208) Investigating the molecular interactions that affect the mobility of the oxytetracycline in the soil.
Kulshrestha, P1, Aga, D1, Giese, R1, 1 University at Buffalo, The State University of New York, Buffalo, NY, USA
ABSTRACT- The interactions of oxytetracycline with model clay adsorbents was investigated as a function of suspension pH. The clay adsorbents used were the natural montmorillonite clay (SWy-2), Na-montmorillonite clay (Na-SWy-2), and hexadecyl trimethyl ammonium bromide-montmorillonite clay (organo-clay). The adsorption of oxytetracycline in the model clay adsorbents was found to obey Freundlich type adsorption isotherms. The adsorption of oxytetracycline in the natural and sodium forms of montmorillonite clay decreases with increasing pH in the order pH 1.5 > pH 5.0 > pH 8.7 > pH 11.0, suggesting that cationic exchange interactions are dominant at lower pH values, when oxytetracycline has a net positive charge. On the other hand, the adsorption of oxytetracycline in organo-clay is highest at pH 5.0 due to strong hydrophobic interactions with organo-clay when oxytetracycline is zwitterionic. The adsorption of oxytetracycline on clay was also found to decrease with the addition of 10 mg/L humic acid in the suspension, suggesting that humic acids may increase the mobility of the molecule in the natural environment. Lastly, we will illustrate the utility of X-ray, FT-IR, and HyperChem calculations in elucidating the adsorption mechanisms of tetracycline antibiotics in clay.
Key words: oxytetracycline, antibiotics, ecotoxicity, montmorillonite clay adsorbents