Biodegradability of metronidazole, olaquindox, and tylosin and formation of tylosin degradation products in aerobic soil-manure slurries

The use of veterinary drags (primarily antibiotics) in animal husbandry har bors the risk that these compounds end up in the farmland when manure is us ed as fertilizer, The biodegradability of three compounds, olaquindox (OLA) , metronidazole (MET), and tylosin (TYL), was simulated in soil-manure slur ries with 50 g of soil per liter, Supplemental batch sorption tests reveale d that insignificant amounts of OLA and MET were located in the soil phase, whereas only 0.1 to 10% of the added amounts of TYL remained in the liquid phase. This may reduce the bioavailability and thus biodegradation rates o f TYL, Unidentified metabolites of OLA and TYL and four known TYL metabolit es were detected using HPLC, However, none of these substances were seen to persist in the biodegradation experiments, indicating that OLA and TYL mos t likely were mineralized in the experiments. Neither the use of sandy or c layey soil nor the use of 0, 1, or 10% (V/V) of manure added to these soils had a significant effect on the degradation rates. Degradation half-lives for the primary degradation were 3.3-8.1 days for TYL, 5.8-8.8 days for OLA , and 13.1-26.9 days for MET, Based on comparisons of results obtained with the benchmark chemical aniline and degradation half-lives of this compound in nature, it was assessed that results obtained with the current test met hod slightly overestimate real-world biodegradation rates, (C) 2001 Academi c Press.