AVIAN PLASMA CARBOXYLESTERASE ACTIVITY AS A POTENTIAL BIOMARKER OF ORGANOPHOSPHATE PESTICIDE EXPOSURE

Plasma cholinesterase (ChE) and carboxylesterase (CaE) activities were measured in pigeons (Columba livia), captive and wild American kestre ls (Falco sparverius), red-tailed hawks (Buteo jamaicensis), Swainson' s hawks (Buteo swainsoni), Cooper's hawks (Accipiter cooperii), and re d-shouldered hawks (Buteo lineatus). The effect of organophosphate (OF ) insecticides on pigeon ChE and CaE activities was determined. Pigeon plasma CaE activity showed distinct groups averaging 12.4 and 138 nmo l/min/ml plasma. The CaE activity for raptors was less than 20 nmol/mi n/mI plasma. Both ChE and CaE activities were inhibited by 0.4 mg/kg e thyl parathion, but CaE activity was not inhibited by 10 mg/kg methida thion. There was no difference in the blood ChE activities of pigeons with low or high blood CaE after treatment with parathion. In general, CaE activity was less severely depressed and recovery was less predic table than was ChE activity.