Determination of the persistence of tetracycline antibiotics and their degradates in manure-amended soil using enzyme-linked immunosorbent assay and liquid chromatography-mass spectrometry

The persistence of manure-borne oxytetracycline in soil was investigated under field conditions. Soil cores were collected approximately once a month for over a period of two years and subsampled at depth increments of 0-5, 5-10, 10-15, 15-36, and 36-71 cm. Soil samples were analyzed by enzyme-linked immunosorbent assay (ELISA) and/or by liquid chromatography-mass spectrometry (LC-MS). Whereas LC-MS showed that oxytetracycline declined to <50% of its initial soil concentration after 3 weeks, ELISA showed that the total tetracyclines did not decline significantly 5 months after manure application. The differences between ELISA and LC-MS results are attributed to the broad cross-reactivity of the antibodies employed, which detect many structurally related tetracyclines, including their isomers and degradation products. Only trace amounts (≤ 1.0 μg/kg) of oxytetracycline were observed in the subsurface soil, and none was detected in water samples from field lysimeters, suggesting that oxytetracycline has low mobility in soil.