Use of radioimmunoassay as a screen for antibiotics in confined animal feeding operations and confirmation by liquid chromatography/mass spectrometry

Approximately one-half of the 50 000 000 lb of antibiotics produced in the USA 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 our nation's wa ter 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 ppb and a semiquantitative analytical range of 1-20 ppb. Liquid waste samples were obtained from 13 hog lagoons in three states and 52 surface- a nd ground-water samples were obtained primarily from areas associated with intensive swine and poultry production in seven states. These samples were screened for the tetracycline antibiotics by using the modified radioimmuno assay screening method. The radioimmunoassay tests yielded positive results for tetracycline antibiotics in samples from all 13 of the hog lagoons. Di lutions of 10-100-fold of the hog lagoon samples indicated that tetracyclin e antibiotic concentrations ranged from approximately 5 to several hundred parts per billion in liquid hog lagoon waste. Of the 52 surface- and ground -water samples collected all but two tested negative and these two samples contained tetracycline antibiotic concentrations less than 1 ppb. A new liq uid chromatography/mass spectrometry method was used to confirm the radioim munoassay results in 9 samples and also to identify the tetracycline antibi otics to which the radioimmunoassay test was responding. The new liquid chr omatography/mass spectrometry method with online solid-phase extraction and a detection level of 0.5 mu g/l confirmed the presence of chlorotetracycli ne in the hog lagoon samples and in one of the surface-water samples. The c oncentrations calculated from the radioimmunoassay were a factor of 1-5 tim es less than those calculated by the liquid chromatography/mass spectrometr y concentrations for chlorotetracycline. (C) 2000 Elsevier Science B.V. All rights reserved.