BIOCONCENTRATION AND DEPURATION OF AVERMECTIN B-1A IN THE BLUEGILL SUNFISH

A dynamic 42-d study was conducted to evaluate the bioconcentration of [H-3]avermectin B-1a in the bluegill sunfish (Lepomis macrochirus). A mean water concentration of 0.099 mu g/L was maintained for a 28-d ex posure period. Radioassay throughout the exposure period indicated a g radual uptake of radioactivity that reached steady state at about 10 t o 14 d; the day 28 tissue residue values were 6.8, 3.0, and 11 mu g/kg , in whole fish, fillet, and viscera, respectively. Following this 28- d uptake period, fish were placed in control water for 14 d to permit monitoring of elimination of radioactivity. Radioassay indicated 91 to 95% clearance, with the tissue residues dropping by day 14 of the dep uration period to 0.32, 0.27, and 0.53 mu g/kg, respectively. A one-co mpartment kinetic model was used for analysis of the uptake-depuration data and yielded for whole fish an uptake rate constant of 12 L kg(-1 ) d(-1), a depuration rate constant of 0.21 d(-1) (t(H) of 3.3 d), and a steady-state residue concentration of 5.5 mu g/ kg. The correspondi ng bioconcentration factor (BCF) for whole fish was 56 L/kg. Uptake an d depuration rate data for fillet and viscera were not significantly d ifferent (alpha = 0.05) than the values for whole fish. The BCF values for fillet and viscera were 28 and 84 L/kg, respectively. The data ar e consistent with rapid depletion of abamectin (and the structurally r elated anthelmintic ivermectin) from the tissues of other animals (rat s, sheep, cattle). Abamectin does not strongly bioconcentrate in aquat ic organisms and would not be expected to biomagnify.