Chlortetracycline and related tetracyclines: detection in wheat and rye grain

BACKGROUND: Antibiotic drugs are excreted to a large proportion by livestock. Thus, antibiotics are distributed on fields with slurry and can be taken up by plants. In the present study, hydroponic experiments were performed to reveal whether the widely administered chlortetracycline is taken up into wheat grain in a concentration-dependent manner. A further goal was to determine (chlor)tetracyclines in wheat and rye grain from agricultural practice. RESULTS: Increasing chlortetracycline deposition in wheat grain was observed with a rising chlortetracycline spiking level in the hydroponic solution. In 371 selected wheat and rye samples from three growing years of agricultural practice, the overall detection frequency was 21% for tetracyclines. In the most highly contaminated sample, tetracyclines occurred at 18.2 mu g kg(-1). Tetracycline residues were also found in rye grain. Conversion and degradation products of (chlor)tetracycline such as tetracycline, doxycycline and demeclocycline were detected in grains from hydroponic experiments and from agricultural practice. CONCLUSION: Concentrations of tetracyclines found in wheat and rye grains were of no concern with respect to toxicity regarding human consumption. However, antibiotic concentrations below the minimum inhibitory concentration can select for antibiotic resistance in bacteria. Thus, low levels of different tetracycline residues contained in food should be taken into account regarding risk assessment. (C) 2018 Society of Chemical Industry