Effect of piperonyl butoxide on disposition of di-2-ethylhexyl phthalate by rainbow trout.

1. Piperonyl butoxide in vitro inhibits the oxidation and hydrolysis of di-2-ethylhexyl phthalate, and the hydrolysis of the butyl ester of 2,4-dichloro-phenoxyacetic acid by liver homogenate fractions and serum from rainbow trout. 2. The rates of oxidation and hydrolysis of di-2-ethylhexyl phthalate by liver homogenates from rainbow trout pre-exposed to piperonyl butoxide (1 mg/l) were considerably lower than those by liver homogenates from control trout. 3. Disposition of di-2-ethylhexyl [14C]phthalate in rainbow trout in vivo was modified by pre-exposure to piperonyl butoxide. The piperonyl butoxide-treated trout had lower levels of 14C in bile and higher levels of 14C in blood and muscle than control trout. 4. Muscle of control and piperonyl butoxide-exposed trout showed similar concentrations of mono-2-ethylhexyl phthalate but the concentration of di-2-ethylhexyl phthalate in muscle from piperonyl butoxide-exposed trout was three times the control value.