Determination of persistent tetracycline residues in soil fertilized with liquid manure by high-performance liquid chromatography with electrospray ionization tandem mass spectrometry.

Little is known about the occurrence and the fate of veterinary drugs in the environment. Therefore, a liquid chromatography/tandem mass spectrometry method was developed and employed to investigate in detail the distribution and persistence of the frequently used tetracyclines and tylosin in a field fertilized with liquid manure on April 2000 and April 2001; soil sampling was performed in May 2000, November 2000, and May 2001. We detected 4.0 mg/kg tetracycline and 0.1 mg/kg chlortetracycline in the liquid manure of April 2000, as well as comparable amounts in the liquid manure of April 2001. In the soil samples of May 2001, the highest average concentrations of 86.2 (0-10 cm), 198.7 (10-20 cm), and 171.7 microg/kg (20-30 cm) tetracycline and 4.6-7.3 micro/kg chlortetracycline (all three sublayers) were found. At soil depths between 30 and 90 cm, as well as in soil or groundwater, tetracyclines could not be detected. In addition, oxytetracycline and tylosin could not be detected in any sample investigated. We conclude that tetracyclines enter the environment in significant concentrations via repeated fertilizations with liquid manure, build up persistent residues, and accumulate in soil. Therefore, tetracyclines may have a potential risk and investigations on the environmental effects of these antibiotics are necessary.