John Wiley & Sons, Ltd.

Analysis and dissipation of the antiparasitic agent ivermectin in cattle dung under different field conditions

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Cattle treated with the veterinary parasiticide ivermectin (IVM) fecally excrete residues. Here we report the exposition and dissipation characteristics of these residues in dung of IVM‐treated cattle, and in soil beneath this dung, on pastures including Canada, France, Switzerland, and The Netherlands. Residues were quantified for dung collected from cattle after 3, 7, 14, and 28 d post‐ treatment, and subsequently exposed in the field for up to 13 months. We first optimized a high performance liquid chromatography ‐ fluorescence detection method to detect IVM residues in dung and soil matrices. We showed that a solid phase extraction and purification step generally can be eliminated to reduce the time and cost of these analyses. We also found that the addition of water to relatively dry samples improves the extraction efficiency of residues. We then analyzed the field samples to document differences in IVM dissipation in cattle dung among sites, with DT50 values of up to 32 d and DT90 values >396 d (DT50/DT90: dissipation time of 50%/90%). We further showed that the dissipation characteristics of residues are comparable between dung of IVM‐treated cattle and in dung to which IVM has been added directly. Lastly, we report the first use of a desorption electrospray ionization ‐ high resolution ‐ mass spectrometry method to detect residues of metabolites in a dung matrix. This article is protected by copyright. All rights reserved

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