Hydrolysis of permethrin,a pyrethroid insecticide,by rainbow trout and mouse tissues in vitro: A comparative study

Permethrin, a pyrethroid insecticide, is highly toxic to fish relative to its toxicity to mammals and the role of permethrin metabolism in this differential toxicity has not been investigated. A previous study, however, has shown that little hydrolysis of permethrin occurs in vivo in rainbow trout in contrast to mammals where ester hydrolysis is a major detoxification reaction. In the present study, the rates of permethrin hydrolysis in rainbow trout and mouse tissues in vitro were estimated. Mouse liver, kidney, and plasma incubated at 37°C, hydrolyzed trans-[¹⁴C]permethrin approximately 166, 38, and 59 times faster, respectively, than the same rainbow trout tissues incubated at 12°C. At an incubation temperature of 37°C trout liver microsomes hydrolyzed trans-permethrin approximately 45 times slower than mouse liver microsomes. When the total capacity of trout and mouse tissues to hydrolyze trans-permethrin was compared on a whole body basis mice hydrolyzed trans-permethrin 184 times faster than rainbow trout. The results suggest that rainbow trout tissues have a much lower capacity than mouse tissues to hydrolyze permethrin, and this may explain the relative absence of permethrin hydrolysis products in permethrin-exposed raibow trout. It is impossible that the high toxicity of permethrin to rainbow trout is in part related to a low capacity to hydrolyze permethrin.