Residues of Nitrofuran and Corresponding Metabolites in Tilapia

Nitrofurans were the most common antimicrobial agents, widely-used as broad-spectrum synthetic antibacterial agents, as well as food preservatives and food additives. In this paper, we demonstrated for the first time the distribution and residence time of nitrofurans including furazolidone, furaltadone, nitrofurazone, and nitrofurantoin, and corresponding metabolites AOZ, AMOZ, SC, and AH in tilapia. Fish were bathed in 5 mg/l aqueous solutions of each nitrofuran for 1 h, and muscle, liver, gill, and skin samples were collected in triplicate during the experiments on days 1, 2, 4, 8, 16, 24, and 30 after treatment, whereupon residual nitrofurans and metabolites were extracted from the homogenized tissues. Extracted metabolites were further treated with 2-nitrobenzaldhyde to the form of 2-nitrophenyl derivative. Both the residual nitrofurans and the residual derivatives of metabolites were analyzed by LC-ESI-MS/MS, and the results showed that residual nitrofurans had disappeared from muscle and skin tissue within a period of 24 h after treatment. The peak concentrations of metabolites were observed immediately after bathing; the concentration then dropped to lower than 5 μg/kg on the 4^(th) day post-treatment in skin and the 8^(th) day in muscle. Comparisons between the concentrations of non-bonded metabolites, which were consistent at around 1-2 μg/kg in both muscle and skin for 1 month after the end of medication, and those of bonded metabolites, which had dropped to less than 5 μg/kg after 4 days, were also made.