Residue study of mebendazole and its metabolites hydroxy-mebendazole and amino-mebendazole in eel (Anguilla anguilla) after bath treatment.

Mebendazole (MBZ) is extensively used in eel culture for treatment of Pseudodactylogyrus spp. infections. This use may lead to residues of MBZ in eel tissues. Consequently, the residue profile of MBZ in eel after treatment with the drug is of special concern. Therefore, a residue study was performed in European eels (Anguilla anguilla), bath-treated with MBZ at a dose of 1 mg/liter for 24 hr and kept at a water temperature of 25 degrees C. Liver, kidney, fat, skin, and muscle tissues samples were collected at intervals during and after treatment and analyzed for MBZ and its metabolites, hydroxy-MBZ (MBZ-OH) and amino-MBZ (MBZ-NH2), by HPLC. Results showed that MBZ is extensively metabolized to MBZ-OH and MBZ-NH2. Liver and kidney were found to contain the highest levels of MBZ metabolites, and fat contained the highest levels of the parent compound. Skin contained higher residue levels for all three compounds, compared with muscle tissue. MBZ and its hydroxy metabolite were eliminated within 5 days from the edible parts (muscle and skin) of the eels, whereas MBZ-NH2 could be detected by the 14th day after the end of the treatment period. Consequently, although MBZ and MBZ-OH constitute the residues of toxicological concern, MBZ-NH2 should be taken as the compound of interest for estimating the withdrawal time for consumption of eel treated with MBZ.