INFLUENCE OF PIPERONYL BUTOXIDE ON THE TOXICITY OF ORGANOPHOSPHATE INSECTICIDES TO 3 SPECIES OF FRESH-WATER BENTHIC INVERTEBRATES

Toxicity tests were conducted with amphipods (Hyalella azteca), chironomids (Chironomus tentans) and oligochaetes (Lumbriculus variegatus) exposed to a series of organophosphate insecticides in the absence or presence of piperonyl butoxide (PBO), an inhibitor Of cytochrome(s) P450, Piperonyl butoxide effectively reduced the toxicity to H, azteca and C. tentans of three organophosphates (diazinon, chlorpyrifos, azinphos-methyl) which undergo metabolic activation by cytochrome(s) P450, Coadministration of PB with another organophosphate (dichlorvos) which is not activated by cytochrome(s) P450, did not reduce the toxicity to the two species, Lumbriculus variegatus was relatively insensitive to the organophosphates, and PBO did hot reduce their toxicity to the oligochaete. These data indicate that both H, azteca and C. tentans possess cytochrome P450-mediated MOs capable of metabolizing organic xenobiotics. However, the degree to which L, variegatus might be capable of the oxidative metabolism of organic xenobiotics is uncertain.