Chronic neurological effects of organophosphate pesticides

Subclinical damage does occur, but longer follow up studies are needed

Organophosphate pesticides have replaced organochlorines in the past 20 years and are widely used in both agricultural and structural applications. People working with these compounds receive the highest exposures, but the public can be exposed during structural applications or by drift from aerial spraying. The immediate toxic effects of organophosphates are well described; what remain controversial are the longer term effects.

Organophosphates inhibit the neurotransmitter acetyl cholinesterase, leading to symptoms related to the autonomous nervous system (abdominal cramps, nausea, diarrhoea, salivation, miosis) and the central nervous system (dizziness, tremor, anxiety, confusion). Symptoms usually occur within hours of exposure and typically disappear within days or weeks as new cholinesterase is synthesised. The degree (or rate) of inhibition required to produce symptoms is controversial.

On the basis primarily of animal data and human case reports we know that some organophosphates (such as methamidophos, leptophos, fenthion, merphos) inhibit a second enzyme, neuropathy target esterase. Severe inhibition of this enzyme (animal data suggest inhibition by 70% or more) may be accompanied by a peripheral neuropathy 10-14 days after exposure. This delayed neuropathy typically affects the motor and sensory nerves of the legs and is caused …