| Summary: | The laboratory studies on the fate of doxycycline during storage of liquid pig manures
and digestates was investigated. The storage tests were conducted to investigate the
behavior of doxycycline during storage in manure as well as digestate. The incubation
period was 170 days for manure and 120 days for digestate samples with the
termination interval of 0, 7, 35, 84, 120 and 170 days. Residue analysis method was
carried out to treat the samples prior to analysis. The identification and quantification of
the target compounds were performed using liquid chromatography tandem mass
spectrometry with electrospray ionization in positive mode (LC-(ESI+)-MS/MS).
Moreover, the epimerization and matrix effects were studied additionally.
The results show that doxycycline remained about 39% or 9.5 mg/kg within 170 days
storage in liquid pig manures. As for digestate samples, the concentration of doxycycline
dropped to 32% or 6.4 mg/kg after 120 days. Matrix effects were observed in both
manure and digestate samples for doxycycline, demeclocycline and tetracycline.
Moreover, the results of epimerization studies indicated that the storage temperature,
exposure of light and addition of acid could accelerate the degree of epimerization.
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