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TECHNICAL REPORTS

Organic Compounds in the Environment

Effects of Ionic Strength, Temperature, and pH on Degradation of Selected Antibiotics

^a U.S. Geological Survey, Organic Geochemistry Research Lab., 4821 Quail Crest Place, Lawrence, KS 66049
^b Univ. of Missouri-Rolla, Dep. of Civil, Architectural, and Environmental Engineering, 1870 Miner Circle Dr., Rolla, MO 65401
^c U.S. Environmental Protection Agency-Region 7, P.O. Box 17-2141, Kansas City, KS 66117. Joint contribution of the U.S. Environmental Protection Agency (Project XP99795901-0), U.S. Geological Survey's Toxic Substances Hydrology Program, and infrastructural support from the Environmental Research Center at the Univ. of Missouri-Rolla

^* Corresponding author (kloftin{at}usgs.gov).

Received for publication May 7, 2007. Aqueous degradation rates, which include hydrolysis and epimerization, for chlortetracycline (CTC), oxytetracycline (OTC), tetracycline (TET), lincomycin (LNC), sulfachlorpyridazine (SCP), sulfadimethoxine (SDM), sulfathiazole (STZ), trimethoprim (TRM), and tylosin A (TYL) were studied as a function of ionic strength (0.0015, 0.050, or 0.084 mg/L as Na₂HPO₄), temperature (7, 22, and 35°C), and pH (2, 5, 7, 9, and 11). Multiple linear regression revealed that ionic strength did not significantly affect ( = 0.05) degradation rates for all compounds, but temperature and pH affected rates for CTC, OTC, and TET significantly ( = 0.05). Degradation also was observed for TYL at pH 2 and 11. No significant degradation was observed for LNC, SCP, SDM, STZ, TRM, and TYL (pH 5, 7, and 9) under study conditions. Pseudo first-order rate constants, half-lives, and Arrhenius coefficients were calculated where appropriate. In general, hydrolysis rates for CTC, OTC, and TET increased as pH and temperature increased following Arrhenius relationships. Known degradation products were used to confirm that degradation had occurred, but these products were not quantified. Half-lives ranged from less than 6 h up to 9.7 wk for the tetracyclines and for TYL (pH 2 and 11), but no degradation of LIN, the sulfonamides, or TRM was observed during the study period. These results indicate that tetracyclines and TYL at pH 2 and 11 are prone to pH-mediated transformation and hydrolysis in some cases, but not the sulfonamides, LIN nor TRM are inclined to degrade under study conditions. This indicates that with the exception of CTC, OTC, and TET, pH-mediated reactions such as hydrolysis and epimerization are not likely removal mechanisms in surface water, anaerobic swine lagoons, wastewater, and ground water.

Abbreviations: -apoOTC, -apooxytetracycline • β-apoOTC, β-apooxytetracycline • A, collision factor • ACTC, anhydrochlortetracycline • ATET, anhydrotetracycline • CAS, chemical abstract service • CTC, chlortetracycline • E_a, activation energy • isoCTC, isochlortetracycline • LC, liquid chromatography • LNC, lincomycin • MS, mass spectrometry • MW, molecular weight • OTC, oxytetracycline: pKa, acid dissociation constant • psig, pounds per square inch gauge • SCP, sulfachlorpyridazine • SDM, sulfadimethoxine • SIM, selected ion monitoring • STZ, sulfathiazole • TET, tetracycline • TRM, trimethoprim • TYL, tylosin A • 4-epi-ACTC, 4-epi-anhydrochlortetracycline • 4-epi-ATET, 4-epi-anhydrotetracycline • 4-epi-CTC, 4-epi-chlortetracycline • 4-epi-isoCTC, 4-epi-iso-chlortetracycline • 4-epi-OTC, 4-epi-oxytetracycline • 4-epi-TET, 4-epi-tetracycline