Primary biodegradation of veterinary antibiotics in aerobic and anaerobic surface water simulation systems

The primary aerobic and anaerobic biodegradability at intermediate concentr ations (50-5000 mug/l) of the antibiotics olaquindox (OLA), metronidazole ( MET), tylosin (TYL) and oxytetracycline (OTC) was studied in a simple shake flask system simulating the conditions in surface waters. The purpose of t he study was to provide rate data for primary biodegradation in the scenari o where antibiotics pollute surface waters as a result of run-off from arab le land. The source of antibiotics may be application of manure as fertiliz er or excreta of grazing animals. Assuming first-order degradation kinetics , ranges of half-lifes for aerobic degradation of the four antibiotics stud ied were 4-8 days (OLA), 9.5-40 days (TYL), 14-104 days (MET) and 42-46 day s (OTC). OLA and OTC were degraded with no initial lag phase whereas lag ph ases from 2 to 34 days (MET) and 31 to 40 days (TYL) were observed for othe r substances. The biodegradation behaviour was influenced by neither the co ncentrations of antibiotics nor the time of the year and location for sampl ing of surface water. Addition of 1 g/l of sediment or 3 mg/l of activated sludge from wastewater treatment increased the biodegradation potential whi ch is believed to be the result of increased bacterial concentration in the test solution. Biodegradation was significantly slower in tests conducted in absence of oxygen. Assessments of the toxic properties of antibiotics by studying the influence on the biodegradation rates of C-14-aniline at diff erent concentrations of antibiotics showed that no tests were conducted at toxic concentrations. (C) 2001 Elsevier Science Ltd. All rights reserved.