Cholinesterase (ChE) response and related mortality among birds fed ChE inhibitors.

Patterns of mortality and inhibition of brain and plasma ChE in birds treated with ChE inhibitors were studied in an attempt to determine the validity of using ChE activity as a monitoring and diagnostic technique. Analysis of brain ChE activity proved to be reliable for diagnosing and monitoring effects of selected ChE inhibitors in birds. Brain ChE inhibition exceeding 20 percent indicated exposure, and inhibition greater than 50 percent was sufficient for diagnosing cause of death. Individuals that died from dietary exposure to parathion-1 or carbofuran had brain ChE activities below 55 percent of normal; although individuals could survive with brain ChE activity lower than 50 percent. Problems associated with collection, storage, and analysis of tissues for ChE activity are discussed.