| There is growing concern that antibiotics used in livestock production are contaminating surface and ground waters and contributing to the development and spread of antibiotic resistance in the environment. It is estimated that between 9 and 13 million kg of antibiotics are used annually in the United States for veterinary purposes, with the majority being used subtherapeutically (i.e. growth promotion and prophylaxis). The research in this thesis deals with the potential fate and transport pathways of veterinary antibiotics in the environment. Specific objectives were to: (1) develop a method for detecting trace levels of monensin, in environmental samples, (2) quantify antibiotic losses from unprotected manure stockpiles, (3) quantify leaching and runoff losses of antibiotics from land application of manure, (4) determine the extent of antibiotic uptake by vegetable plants grown on manure-amended soil, and (5) evaluate the effectiveness of composting to reduce antibiotic concentrations in manure prior to land application. Antibiotics evaluated included chlortetracycline, monensin, tylosin, and sulfamethazine, commonly used livestock subtherapeutic antibiotics.; Antibiotic losses from unprotected manure stockpiling ranged from 0.2-1.9% of the total antibiotics in manure. Antibiotic losses in leaching and runoff from manure-applied land were generally less than 1% of the total amount applied with manure. Relative antibiotic losses from land application of manure and manure pile runoff were primarily a function of water losses. Our research also showed that antibiotics can be taken up by plants grown on manure-amended soil; however, relative uptake was less than 0.1% of the total amount of antibiotics in soil. Finally, the manure composting study showed that several antibiotics degraded by more than 50% of initial levels. The results from these studies suggest that small quantities of veterinary antibiotics may appear in aquatic environments or food supplies; however, manure management practices can be an effective option to reduce some of the environmental risks. |
