Body size and the toxicokinetics of trifluralin in rainbow trout

Rainbow trout (Oncorhynchus mykiss) ranging from 0.2 to 3395 g were exposed to trifluralin (TF) in water at concentrations of 0.6-2.0 micrograms/liter. Trout of all body sizes rapidly accumulated TF from the water. The uptake clearance (P, ml hr-1g-1) of TF from the water decreased as body weight (BW, g) increased. This decrease followed the allometric equation P (ml/hr) = 182.BW0.66. Other kinetic parameters affected by body size were the steady-state volume of distribution which had a BW exponent value of 1.07 and the biological half-life which increased in larger fish. The relatively larger volume of distribution in larger fish reflected an increased capacity for TF in peripheral compartment-associated tissues. Metabolic elimination and the bioconcentration factor of TF did not change systematically with changes in body size. Variation in total body lipid content could not adequately explain the increase in peripheral storage capacity for TF; the decreased plasma protein binding that was observed in larger trout may also have been involved.