Effects of atrazine on acetylcholinesterase activity in midges (Chironomustentans) exposed to organophosphorus insecticides

Acetylcholinesterase activity was determined for midge larvae (Chironomus t entans) exposed to either organophosphorus insecticides (OPs) alone or OP i nsecticides in binary combination with atrazine (200 mug/l). Although atraz ine by itself did not reduce the level of acetylcholinesterase activity, at razine in combination with chlorpyrifos significantly decreased acetylcholi nesterase activity as compared to chlorpyrifos only treatments. Although si milar trends existed for malathion and methyl parathion, differences were n ot statistically significant. These results match previously published toxi city data where atrazine, although not acutely toxic even at much higher le vels, decreased EC50 values for chlorpyrifos by a magnitude of 4, decreased methyl parathion values by a magnitude of 2, and did not decrease values f or malathion. (C) 2001 Elsevier Science Ltd. All rights reserved.