THE INFLUENCE OF TEMPERATURE ON THE UPTAKE RATE CONSTANTS OF HYDROPHOBIC COMPOUNDS DETERMINED BY THE ISOLATED PERFUSED GILLS OF RAINBOW-TROUT (ONCORHYNCHUS-MYKISS)

Uptake rate constants of four hydrophobic and one less hydrophobic compound were determined using the isolated perfused gills of rainbow trout. Uptake rate constants thus obtained were in accordance with in vivo literature data. The four hydrophobic compounds (log K(d,oct) > 3) had similar uptake rate constants. The fifth, less hydrophobic compound, phenol in undissociated form (pH less-than-or-equal-to pK(a)) had a lower uptake rate constant. The uptake rate constants were reduced by lowering the temperature below the acclimation temperature of the fish. The temperature dependent decrease was most pronounced for hexabromobenzene, probably due to steric effects. The rate-limiting step in uptake seemed to be diffusion, either through the aqueous diffusion layer or through the lipid membrane, and not ventilation or blood flow-rate.