Occupational determinants of chlorpyrifos adducts to plasma cholinesterase in chlorpyrifos exposed agricultural workers in Washington State

Chlorpyrifos is a broad-spectrum chlorinated organophosphorus (OP) insecticide, acaricide, and miticide utilized around the world to control a variety of pests. It is primarily a non-systemic contact poison that interferes with the activity of acetylcholinesterase (AChE), an enzyme essential for nervous system function for humans and insects alike. Chlorpyrifos is the common name for 0,0-diethyl-0-(3,5,6-trichloro-2-pyridinyl)-phosphorothioate. This chemical is a colorless to white crystalline solid that possesses a mild mercaptan-like (thiol) odor. With a low solubility of 1.12 mg/L of water at 240C (Racke, 1993) and being hydrophobic, chlorpyrifos is generally mixed with oily liquids instead of water before application (ATSDR, 1997)