Delayed neurotoxicity caused by a single massive dose of dichlorvos to adult hens.

A moderate neuropathic response was obtained in hens 2 weeks after being given a single massive s.c. dose of dichlorvos (100 mg/kg of active ingredient in a commercial 50% formulation). 1 day after dosing inhibition of neurotoxic esterase in peripheral nerve was 79-90%, in spinal cord 70-81% and in brain 89-92%. It is unlikely that repeated exposure of man to dichlorvos could cause neuropathy except at doses causing severe cholinergic effects at every exposure.