Residues of veterinary antibiotics in solid natural and organic fertilizers—method development and sample analysis

Abstract

Livestock excrement is used around the world as natural fertilizers or, after processing, as organic fertilizers for crops andgrasslands. But due to the presence of veterinary antibiotics in them, they may pose a threat not only to the natural environ-ment, mainly to soil microorganisms, but also to human and animal health. This article describes a method for detecting 21antibacterial substances in solid natural and organic fertilizers. Antibiotics from fertilizers were extracted with a mixture ofacetonitrile and McIlvain-Na 2EDTA buffer, twice. The extracts were purified by solid phase extraction technique on Strata-Xcartridges and analyzed with the use UHPLC-MS/MS technique. The method was validated in accordance with EU Com-mission Implementing Regulation 2021/808; the obtained recovery ranged from 93.6 to 116.6% (depending on the analytes),and the linearity ranged from 50 to 1000 μg/kg. The developed method was used to analyze 73 samples of solid natural andorganic fertilizers. Our research has shown that over 38% of natural fertilizers were contaminated with antibiotics, mainlydoxycycline in concentrations reaching several dozen milligrams per kilogram of fertilizers. In the case of processed organicfertilizers, the presence of antibiotics was found in over 37% of the analyzed samples. The research results showed that thedeveloped and validated analytical method may be useful for assessing the presence and content of antibacterial substancesin solid natural and organic fertilizers.