Agriculture Reference
In-Depth Information
Toxicity and Mode of Action
These are contact herbicides which, in high concentrations, causes foliar
desiccation and collapse. Their mode of action appears to be their ability to
uncouple oxidative phosphorylation and hence inhibit ATP synthesis. Since
this process is common in plants and mammals, it is not surprising that dini-
trophenols have high mammalian toxicities.
Nitroaromatic compounds are highly toxic to humans and animals. Most
nitrophenols and nitrocresols are absorbed efficiently from the gastrointestinal
tract, across the skin, and by the lung when fine droplets are inhaled. Fatal
poisonings have occurred as a result of dermal contamination. Except in a few
sensitive individuals, the comopunds are only moderately irritating to the skin
and mucous membranes.
h.
Bipyridyliums or Dipyridyls
Mode of Action and Toxicology
These compounds act as contact herbicides, rapidly killing all green plant
growth on which they fall. They are rapidly translocated from foliage, but not
from the plant roots, because they are deactivated on contact with soil.
In solution, bipyridiums almost completely dissociate into ions, and in
chloroplasts, during photosynthesis, the positive ion is reduced to a stable free
radical. In the presence of oxygen, the free radicals are reorganized to the
original ion and hydrogen peroxide, which destroys the plant tissue.
Particularly in concentrated form, paraquat causes injury to tissues with
which it comes into contact. It leaves the skin of the hands dry and fissured,
sometimes resulting in loss of fingernails. Prolonged contact with skin may
cause blistering and ulceration, with subsequent absorption of paraquat in suf-
ficient dosage to cause systemic poisoning. Prolonged inhalation of spray
droplets may cause nosebleed. Eye contamination results in severe conjuncti-
vitis and sometimes protracted and even permanent corneal opacification.
When ingested in adequate dosage, paraquat has life-threatening effects on the
gastrointestinal tract, kidney, liver, heart, and other organs.
Diquat is somewhat less damaging to skin than paraquat, but irritation ef-
fects may appear following dermal contamination. Diquat has severe toxic
effects on the central nervous system that are not typical of paraquat.
Paraquat
is a synthetic nonselective contact herbicide, usually marketed as
the dichloride salt. Dimethyl sulfate salts are also produced. Liquid technical
products range from 20% to 50% concentration. Trade names of liquid con-
centrates are Ortho Paraquat CL, Ortho Paraquat Plus, Cekuquat, Crisquat,
Herbaxon, Herboxone, Dextrone, Esgram, Gramocil, Gramoxone, Goldquat
