Very large amounts of tetracycline antibiotics are used annually in agriculture to treat diseases in animals and to promote animal growth. However, most antibiotics are excreted by animals, either unaltered or as metabolites, and this makes them potentially hazardous to the environment. The most common pathway for antibiotic release in the terrestrial environment is via the application of animal manure and biosolids containing excreted antibiotics to agricultural land as fertilizers. Anaerobic digestion is one of the most common methods used to reduce the concentrations of antibiotics in the manure before it is applied on agricultural fields. Here, tetracycline antibiotics (tetracycline, oxytetracycline, and chlortetracycline) were spiked on swine, cattle, and poultry manure that was diluted with distilled water. The diluted manure was digested inside air-tight PVC batch reactors for 64 days in the laboratory at room temperature. Samples of the digested manure were taken every 8 days and the tetracyclines extracted using a mixture of methanol and the McIlvaine buffer solution. The sample extracts were cleaned using weak cationic exchange cartridges, after which the tetracyclines were released from the cartridges using 0.1M citric acid in 95% methanol. The tetracycline concentrations and those of their main metabolites (4-epi-tetracycline, 4-epi-oxytetracycline, and isochlortetracycline) in the digested manure were determined using liquid chromatography-mass spectrometry (LC-MS). The rates of degradation and the half-lives of the tetracyclines in the 3 different types of manure used in this study will be presented.

Degradation kinetics of tetracycline antibiotics in agricultural manure during anaerobic digestion

255th National Meeting (2018)

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