A Radioimmunoassay Method to Screen for Antibiotics in Liquid Waste at Confined Livestock Operations, with Confirmation by Liquid Chromatography/Mass Spectrometry

Approximately one-half of the 50 million pounds of antibiotics produced in the United States are used in agriculture. Because of the intensive use of antibiotics in the management of confined livestock operations, the potential exists for the transport of these compounds and their metabolites into the Nations’s water resources. A commercially available radioimmunoassay method, developed as a screen for tetracycline antibiotics in serum, urine, milk, and tissue, was adapted to analyze water samples at a detection level of approximately 1.0 part per billion. This method has a semiquantitative analytical range of 1 to 20 parts per billion. Six liquid waste samples from hog lagoons, 14 surface water samples, and 3 ground-water samples were used to test the radioimmunoassay method as a screen for tetracycline antibiotics. The radioimmunoassay tests yielded positive results for tetracycline antibiotics in samples from all six hog lagoon samples and one surface-water sample. Dilutions of 10 to 100 fold of the hog lagoon samples indicated that tetracycline antibiotic concentrations ranged from approximately 1 to several hundred parts per billion in liquid hog waste. A new liquid chromatography/mass spectrometry method was used to confirm the radioimmunoassay and also to identify the tetracycline antibiotics to which the radioimmunoassay test was responding. The new liquid chromatography/mass spectrometry method with online solid-phase extraction and a detection level of 0.5 microgram per liter confirmed the presence of chlortetracycline in one hog lagoon sample and in one surface-water sample.