Bipyridyl contact herbicides and pre-harvest crop desiccants, effective against mono-cotyledons and grasses. Used for weed control in vineyards, lucerne crops, rubber plantations, etc. Approved for aquatic weed control in the UK. Available commercially in the form of liquid concentrates and granules. Highly toxic compounds.


[affected.gif] Animals most affected
Cattle, dogs, hares, (sheep, pigs, most animals).


[etiology.gif] Etiology

Accidental poisoning


Deliberate poisoning
Dogs are the principal targets. (This is very common in Martinique where paraquat is used in banana plantations for weed control.) Note: the inclusion of a stenching agent and an emetic in every formulation has been relatively effective in deterring ingestion by animals.

Compounds in this category
Diquat, paraquat.


[toxic.gif] Toxicity
Caustic and irritant compounds, causing ulceration and necrosis of the skin and mucous membranes; in certain species (dogs, pigs, man) causes progressive, irreversible pulmonary fibrosis.
Toxic doses: see individual compounds.


[clinical.gif]
Clinical features

Deep caustic burns, pharyngitis, tracheitis and stomatitis;
Intense irritation and corrosion of the gastrointestinal tract with vomiting, profuse diarrhoea, melaena, severe and painful abdominal cramps;
CNS effects include apathy, lassitude or hyperexcitability with muscular contractions.

If the animal survives, the following may develop within 2-10 days post-exposure:

In dogs and pigs (not cattle) an irreversible progressive pulmonary fibrosis develops, leading to death due to cyanosis and asphyxiation (as occurs in man).
Chronic poisoning has been reported to cause cataracts in hares, though the relationship between cause and effect is disputed. Embryonic and teratogenic effects have been reported in poultry.


[lesions.gif] Lesions


[treatm~1.gif] Treatment
No antidote. Symptomatic care only:



[labinv~1.gif] Laboratory investigations

The compounds degrade very rapidly; samples need to be very fresh and frozen immediately. Plastic containers must be used.