Chlorpyrifos (Dursban)

Chlorpyrifos is an organophosphorus (OPO4) pesticide used widely in agriculture and in and about homes and businesses. Acute human poisoning from anticholinesterase activity, peripheral neuropathy from neurotropic esterase and chronic neurobehavioral impairment after being "overcome" have been described.

Exposure brought 16 patients for clinical examination, their numbers exceeded only by those exposed to indoor air. Sometimes sorting out Dursban, formaldehyde and indoor air used to indicate volatile organic chemical is impossible as overlap of these exposures is likely. The first family of three unknowingly occupied a log house sprayed before they occupied it. The second family had their home sprayed to eradicate termites and had long term effects. The third family moved into an apartment that had been sprayed (indoors) with Dursban to eradicate fleas. The tenth patient was exposed to residues and repeated, monthly application of Dursban in her office. Adults had headache, cough and sleep disturbance, muscle pain, tremors of the tongue and hands, and abnormal balance. Testing of the three women showed muscle pain evidence by muscle weakness and incoordination. In the 16 patients symptoms continued after leaving the exposure site and disability was permanent. A physician had abnormal blink reflex, abnormal POMS scores, and appeared within the normal ranges for recall, although his scores and problem solving/cognitive function were not commensurate with his doctorate and vocabulary test scores which revealed an outstandingly intelligence. Difficulty with recall and with concept formation interfered with his ability to write scientific papers and perform as a medical specialist.

 The sulfur content of chlorpyrifos confers its strong odor but the phosphorothalate anticholinesterases oxidize the phosphate sulfur bond to form phosphate oxygen bond. Although little has been published about the neurotoxicity of chlorpyrifos its effects in 16 patients ranged from these families moderate impairment to motor incoordination, difficulties with balance, trouble walking, seizures, diminished visual fields and total disability because of lack of memory, and inability to follow directions and impaired balance. As no patient has improved during observation this widely used insecticide-termiticide appears to irreversibly damage the human central nervous system.

Balance, simple and choice reaction time, blink reflex latency, visual fields, color discrimination, grip strength were compared to referents after adjustment for age, sex and height. Cognitive, recall, perceptual motor speed, embedded memory and moods were compared after similar adjustment adding educational attainment.

Exposed subjects had significantly impaired balance, visual fields, color discrimination, simple and choice reaction time, grip strength and hearing, cognitive, recall, remote memory and perceptual motor performance. No single or combination of confounding factors or other diagnoses explained these abnormalities.

Chlorpyrifos, a widely used OPO4 insecticide produced insidious chronic irreversible brain impairment after one day to 5 years of exposure to indoor residuals of spraying. It would be prudent to not use chlorpyrifos indoors.