Disposition and toxicokinetics of diquat in channel catfish

Abstract

The disposition of the aquatic herbicide diquat was studied in channel catfish ( Ictalurus punctatus) after water exposure to 14C-diquat dibromide concentrations of 5 and 20 μg/ml for up to 6 days. An apparent steady-state plasma concentration of 0.6% of the exposure water concentration was achieved after 24 h, and steady-state tissue levels were reached by 72 h. The highest steady-state concentration of diquat occurred in the trunk kidney, which was about 100 times that observed in plasma. Diquat concentrations in white muscle were low and similar to plasma levels of diquat. Autoradiographs of sagittal sections of a catfish exposed to 14C-diquat dibromide also indicated that the highest concentration of residue present in the animal was located in the trunk kidney and that lower concentrations were associated with the liver and gills. The majority of liver residue, and especially that in the bile, was unidentified metabolites. After intravascular administration of 1 mg/kg, toxicokinetic analysis of the plasma concentration-time profile of diquat using a two-compartment model provided the following values: steady-state volume of distribution (V ss) = 2920 ± 740 ml kg −1; total body clearance (Cl b) = 87.8 ± 27 ml h −1 kg −1 and elimination halflife (t 1 2 ,β ) = 35.8 ± 8.9 h .