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.
Animals most affected
Cattle, dogs, hares, (sheep, pigs, most animals).
ingestion of the actual product, or consumption of freshly treated vegetation
(mainly cattle are involved);
by transference into crops (e.g. lucerne) which have been recently treated with
the compound (hares are particularly vulnerable).
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
Caustic and irritant compounds, causing ulceration and necrosis of the skin and mucous
membranes; in certain species (dogs, pigs, man) causes progressive, irreversible
Toxic doses: see individual compounds.
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:
respiratory distress with dyspnoea and hyperpnoea, increasing congestion of the
lungs and pulmonary oedema.
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.
pulmonary oedema with progressive intra-alveolar fibrosis;
erosions and ulceration of buccal and pharyngeal tissue (although the oesophagus
appears not to become involved);
renal degeneration, renal tubular necrosis, anuria.
No antidote. Symptomatic care only:
oral adsorbents (activated vegetable charcoal, bentonite), soothing demulcents,
iv fluids, diuretics;
corticosteroids, pain killers.
The compounds degrade very rapidly; samples need to be very fresh and frozen immediately.
Plastic containers must be used.