Organophosphorus insecticide exposure in hawks inhabiting orchards during winter dormant-spraying

Exposure to organophosphorus pesticides (OPs) was evaluated in hawks caught near 40,000 acres of almond orchards in Butte County, CA. Blood and excreta samples were analyzed for the presence of OP-inhibited cholinesterases (ChEs) and OP excretory metabolites. The results of these experiments demonstrate both depression and reactability of blood ChEs and the presence of excretory and feather OP residues indicating significant pesticide exposure. Low levels of excretory alkyl phosphates indicate that the exposure probably occured at sub-lethal doses leading to cummulative toxicity.