Rapid screening for benzimidazole residues in bovine liver

Rapid enzyme immunoassays for benzimidazole anthelmintic and/or fungicide residues were developed using monoclonal antibodies that specifically bind methyl benzimidazolecarbamates (MBCs, including albendazole, fenbendazole, and oxfendazole) and thiazole-containing compounds (thiabendazole, its Ei-hydroxy metabolite, and cambendazole). Bovine liver samples were extracted by homogenization in water. Extracts were clarified by centrifugation, and dilutions of the supernatants were analyzed using both a commercialized immunoassay (EnviroGard thiabendazole kit, Strategic Diagnostics, Inc., Newark, DE) and an MBC-specific assay described previously. Two sets of 40 blank, fortified, or incurred samples were analyzed for the thiazole benzimidazoles, and an additional set of 31 samples was analyzed for methyl benzimidazolecarbamates only. Using the thiabendazole kit, all samples were analyzed correctly by ELISA, including all 34 samples containing fortified or incurred residues (60-120 ppb) of thiabendazole or related compounds. Using the method for MBCs, all unknowns were correctly scored. The simple water extraction and rapid ELISAs appear to function well for regulatory screening of bovine liver for residues of fenbendazole, oxfendazole, and thiazole-containing benzimidazoles. Although the marker residue for albendazole is not detected by these procedures, residues can be estimated from the analysis of albendazole sulfoxide and sulfone.