Bioconcentration and Metabolism of Thiabendazole [2-(4-Thiazolyl)-1H-benzimidazole] in Bluegill Sunfish, Lepomis macrochirus

Abstract

The steady-state bioconcentration of thiabendazole (TBZ) in the bluegill sunfish was determined in a dynamic (flow-through) bioconcentration test. Fish were exposed to 2.24 ppb of 14 C-labeled TBZ. The TBZ concentration was monitored in both the fish and water during a 28-day uptake period and the subsequent 14-day depuration period. Uptake rate constants (k 1 ), depuration rate constants (k 2 ), and steady-state bioconcentration factors (BCF, k 1 /k 2 ) were calculated for whole fish, viscera, and edible tissues. The resulting BCF values were 96.5 (whole fish), 637.6 (viscera), and 23.0 (edible portion). Clearances of TBZ residue of >95% for the whole fish and >98% for the viscera occurred by the end of the depuration period. Homogenates of edible and visceral tissues were incubated with Glusulase; the ethyl acetate extracts of the incubates were purified and analyzed by HPLC for TBZ and 5-hydroxy-TBZ (5-HO-TBZ), the major mammalian metabolite of TBZ. Of the radioactivity isolated from the edible tissues, 59% was associated, on the basis of its HPLC behavior, with TBZ; smaller portions (32 and 7%, respectively) were associated with 5-HO-TBZ and an unidentified TBZ-related compound. With respect to the radioactivity isolated from the visceral tissues following sequential use of Glusulase and acid hydrolysis, approximately half was associated with 5-HO-TBZ and ∼8% with TBZ. Low-level peaks of radioactivity were observed at five other retention times; these unidentified species accounted for about 28% of the radioactivity isolated from the visceral tissues, with none accounting for more than 10% of the isolated radioactivity.