PARAQUAT

4.2 Terrestrial toxicity
Paraquat is moderately toxic to mammals and
birds (US EPA 2009).
The European Commission‘s Scientifi c
Committee on Plants expressed concern in 2002
about the effects of paraquat on wildlife welfare,
especially on hares and birds. They concluded
that it “can be expected to cause lethal and
sublethal effects and this is confi rmed by fi eld
reports” (EC 2002).
Mammals
Acute toxicity – LD 50 (US EPA 1997):
• male rat = 334 mg/kg bw
• female rat = 283 mg/kg bw
• rabbit = 110 mg/kg bw
• Belgian hare = 35 mg/kg bw
Based on toxicity to rodents, US EPA (1997)
concluded that paraquat is moderately acutely
toxic to small mammals, and lethal below
25 ppm after 12 weeks exposure. Freshly
sprayed foliage can induce death in rabbits, and
especially the hare.
Birds
Paraquat is generally less toxic to birds than it is
to mammals. Nevertheless exposure, especially
chronic exposure, remains a risk and especially
to reproduction. Eisler (1990) reported that some
birds are very much more sensitive than others,
with adverse effects at 10 mg/kg bw in nestlings of
the American kestrel (Falco sparverius) causing
reduced growth; 20 mg/kg in the diet of northern
bobwhite (Colinus virginanus) causing reduced
egg deposition; and 40 mg/L in the drinking water
of domestic chickens (Gallus sp.) increasing the
number of abnormal eggs produced. The lowest
doses of paraquat causing measurable adverse
effects in sensitive species of birds were 0.2
mg/kg bw administered by single intravenous
injection to Japanese quail, causing anemia; and
0.25 mg/kg applied in oil solution to the surface
of mallard eggs, producing reduced survival,
reduced growth, and increased frequency of
developmental abnormalities (Eisler 1990).
These are considerably lower values than LD 50 s
reported by FAO.
Acute toxicity – LD 50 (96 hr):
• unspecified = 35 mg/kg (EC 2003)
• Bobwhite quail = 127 mg/kg bw (FAO 2008)
• Mallard duck = 144 mg/kg bw (FAO 2008)
Acute toxicity – NOEL:
• Bobwhite quail = 72 mg/kg bw (FAO 2008)
Dietary toxicity – LC 50 (FAO 2008):
• Bobwhite quail = 711 mg/kg diet
• Mallard duck = 2,932 mg/kg diet
• Japanese quail = 703 mg/kg diet
Reproductive toxicity – NOEC
• Unspecifi ed = 30 mg/kg diet (EC 2003)
• Bobwhite quail = 100 mg/kg (FAO 2008)
• Mallard duck = 30 mg/kg (FAO 2008)
Signs of oral paraquat intoxication in birds
include excessive drinking and regurgitation,
usually within 10 min of exposure. Other signs
appearing after 3 hours include diarrhoea,
ruffled feathers, lack of coordination, imbalance,
wing drop, slowness, weakness, running and
falling, constriction of pupils, and terminal
convulsions. Additional signs reported after
dermal exposure include blistering and cracking
of skin, lacrimation, wingspread, and wing
shivers. Death usually occurred between 3 and
20 hours (Eisler 1990).
The US EPA (1997) concluded that paraquat is
moderately toxic to birds on both an acute and
sub-acute dietary basis; and that it can affect
reproduction or hatchability of eggs when adult
birds are exposed.
The European Commission‘s Scientifi c
Committee on Plants stated that “the possible
effects on the reproduction from spray solutions
reaching eggs in nests and resulting in reduced
hatching and abnormalities could be of serious
concern” (EC 2002).
At concentrations less than the recommended
application rate, paraquat is embryotoxic to
developing eggs of migratory waterfowl (0.056
kg/ha) (Eisler 1990).
Paraquat has caused pseudofeminization of
male chicken and quail embryos; testes showed
intersexual phenomena and Mullerian duct
abnormalities; both sexes had a reduction in the
number of gonocytes (germ cells responsible
for spermatogenesis in males, and oogenesis in
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