WORLD HEALTH ORGANIZATION FOOD AND AGRICULTURE
ORGANIZATION
ORGANISATION MONDIALE DE LA SANTE ORGANISATION POUR L'ALIMENTATION
ET L'AGRICULTURE
VBC/DS/79.40
ORIGINAL: ENGLISH
DIQUAT
It must be noted that the issue of a Data Sheet for a
particular pesticide does not imply endorsement of the pesticide by
WHO or FAO for any particular use, or exclude its use for other
purposes not stated. While the information provided is believed to
be accurate according to data available at the time when the sheet
was compiled, neither WHO nor FAO are responsible for any errors or
omissions, or any consequences therefrom.
The issue of this document does Ce document ne constitue pas une
not constitute formal publication. Il ne doit faire
publication. It should not be l'objet d'aucun compte rendu ou
reviewed, abstracted or quoted résumé ni d'aucune citation sans
without the agreement of the l'autorisation de l'Organisation
Food and Agriculture des Nations Unies pour
Organization of the United l'Alimentation et l'Agriculture
Nations or of the World Health ou de l'Organisation Mondiale de
Organization. la Santé.
CLASSIFICATION:
Primary use: Desiccant
Secondary use: Herbicide
Chemical group: Bipyridylium compound
Date issued: April 1979
1. GENERAL INFORMATION
1.1 COMMON NAME: Diquat (ISO)
6,7-dihydrodipyrido[1,2-a:2',I'-1'-c]pyrazinediium
1.1.1 Identity: Available only as a salt, generally as the dibromide
1.1.2 Synonyms: Deiquat
Local synonyms:
1.2 SYNOPSIS - A non-residual desiccant and herbicide of moderate
toxicity that does not accumulate in body tissues, but has been
shown, in some experimental animals, to initiate cataract
formation on prolonged ingestion.
1.3 SELECTED PROPERTIES
1.3.1 Physical characteristics - The pure compound exists as the
monohydrate of white to yellow crystals which decompose above
300°C. The technical material containing not less than 250 g
diquat/l is a dark reddish-brown aqueous solution.
1.3.2 Solubility - In 700 g/l water at 20°C: diquat is slightly soluble
in alcohol and hydroxylic solvents, and practically insoluble in
non-polar organic solvents.
1.3.3 Stability - Stable in acid and neutral solution, but unstable
under alkaline conditions. It is inactivated by inert clays and
by anionic surfactants. The formulated compound contains
corrosion inhibitors.
1.3.4 Vapour pressure - Non-volatile and has no measurable vapour
pressure.
1.4 AGRICULTURE, HORTICULTURE AND FORESTRY
1.4.1 Common formulations - Liquids, aqueous concentrates containing
140-240 g/l. Water soluble mixtures with paraquat (Data Sheet No.
4).
1.4.2 Pests mainly controlled - Broad-leaved weeds in crops; submerged
and floating weeds in still water or slow streams; potato haulm
destruction; seed crop desiccation; pre-planting weed contol.
1.4.3 Use pattern - Potato haulm destruction 560-840 g/ha.
Seed crop desiccation 420-1960 g/ha.
Aquatic weed control 420-1120 g/ha.
Pre-plant weed control 280-840 g/ha.
1.4.4 Unintended effects - Concentrated solutions can cause irritation
to eyes and skin. The formulated product can be corrosive.
1.5 PUBLIC HEALTH PROGRAMMES - No public health use.
1.6 HOUSEHOLD USE - Can be used in a mixture with paraquat (q.v.)
as a garden herbicide.
2. TOXICOLOGY AND RISKS
2.1 TOXICOLOGY - MAMMALS
2.1.1 Absorption route - Gastrointestinal absorption occurs on
ingestion. Skin absorption through intact skin is low.
Inhalation of diquat can cause irritation of the nasopharynx but
no systemic effects.
2.1.2 Mode of action - The mode of action of diquat is not understood
Toxic effects in vivo include severe dehydration after oral
administration and tremors and convulsions after large parental
doses. In vitro the diquat molecule is capable of microsomal
reduction to a reactive free radicle but the relevance of this to
toxicity is not known. On prolonged feeding diquat is
cataractogenic to rats and dogs.
2.1.3 Excretion products - Following an oral dose of diquat 96-100% has
been recovered in 4 days. Levels in the urine were 4-6% and in
faeces 90-96%. However, after subcutaneous dosing 90-98% was
recovered, 88-98% in urine and 0-2% in faeces. It has been
suggested that it may be degraded by bacterial in the alimentary
tract.
2.1.4 Toxicity, single dose
Oral: LD50 rat (F): 231 mg/kg (cation)
Dermal: LD50 rabbit (M and F): 400 mg/kg (cation)
2.1.5 Toxicity, repeated doses
Oral: Administration of 10 mg/kg bw to a cow for five days
resulted in its death within 15 days. Post mortem findings
included kidney infarct and intestinal catarrh. Another cow
dosed at 5 mg/kg bw daily for 14 days showed inappetance after
two days, slight haemorrhage as indicated by blood in faeces and
temporary impairment of vision.
Inhalation: Groups of male and female mice and guinea-pigs,
two female rabbits and a male dog, exposed to 15 daily, six-hour,
treatments with diquat in aerosol form at 1.06 µg/l air showed no
adverse effects.
Cumulation of compound - Diquat is not cumulative in body
tissues.
Cumulation of effect - Lens opacities have occurred after
prolonged ingestion of diquat in some laboratory animals.
2.1.6 Dietary studies
Short-term: Five groups of two sheep, and three groups of
one calf each, were given diquat at dosages of 0, 1, 5, 10 and 2O
mg/l and 0, 5 and 20 mg/l respectively in drinking-water for one
month. These levels caused no toxicological effect over the
trial period as evidenced by growth, food consumption and
observation.
Long-term: Groups of 25 male, and 25 female rats were fed
diquat dichloride for two years at dosages of 0, 125, 150, 500 or
1000 mg/kg diet. After 56 days, the 100 mg/kg level was
discontinued because of lack of growth and mortality in both
males and females. At 125 mg/kg, a partial lens opacity was seen
at 207 days. All males and 19 out of 21 females were so affected
by 657 days. At 250 and 500 mg/kg lens opacities were produced
in all animals within 155 and 124 days respectively. At 500
mg/kg a reduction of female bodyweight was apparent after 20
weeks and in males after 5 weeks. In another study, rats were
fed for two years with diquat dibromide at rates equivalent to 0,
15, 25 and 75 mg/kg diquat cation. Dose-related cataracts
occurred only at the highest rate. The "no-effect" level is
considered to be 25 ppm diquat cation.
2.1.7 Supplementary studies of toxicity
Carcinogenicity: No increased incidence of tumours has been
observed in 2 two-year dietary feeding experiments in rats.
Teratogenicity: Diquat dibromide monohydrate was administered
orally to groups of pregnant rabbits at doses of 1.25 mg/kg, 2.5
mg/kg and 5 mg/kg cation. No adverse effects were seen in the
foetuses.
Groups of pregnant rats were maintained throughout gestation
on diets containing 0, 125 or 500 mg cation/kg diet. Foetuses
delivered from animals receiving 500 mg/g were of significantly
lower body weight than controls. This effect was associated with
reduced maternal body weight gain and food consumption. The
incidence of foetal abnormalities was within the normal range for
the rat apart from a slight increase in the incidence of
subcutaneous haemorrhages.
Mutagenicity: A dominant lethal test demonstrated on mice that no
mutagenic effects could be detected if the compound was
administered up to 10.0 mg/kg bw/day for the first five days of
pregnancy.
2.2 TOXICOLOGY - MAN
2.2.1 Absorption - Diquat is for practical purposes only hazardous when
absorbed from the gastrointestinal tract.
2.2.2 Dangerous doses
Single: Approximately 20 ml formulated product. This does not
apply to mixtures with paraquat where the latter is much more
hazardous.
Repeated: Not known.
2.2.3 Observations of occupationally exposed workers - Diquat has
caused nail damage, when concentrates have been handled without
gloves. There may be discolouration, with white bands across the
finger nails and sometimes complete loss of the nail. Bleeding
from the nose has been associated with inhalation of concentrated
mists. Isolated cases of cataract have been reported in
individuals occupationally exposed to diquat.
2.2.4 Observations on exposure of the general population - With correct
usage, the general population should not be exposed to diquat.
2.2.5 Observations of volunteers - No information available.
2.2.6 Reported mishaps - There have been few reported incidents with
diquat. Accidental ingestion in one case was followed by oral
ulceration and diarrhoea. The man recovered after forced
diuresis though traces of diquat could be found in his urine as
long as eleven days after ingestion. In a suicide case, symptoms
included ulceration of mucus membranes, renal failure, toxic
liver damage, cerebral damage caused by bleeding in the brain
stem and pulmonary complications, though with no evidence of
proliferation or fibroplastic change as seen in paraquat
poisoning.
2.3 TOXICITY TO NON-MAMMALIAN SPECIES
2.3.1 Fish - 96 hour TLm values for fish range from 2.1 µg/ml in
walleyes (Stizostedion vitreum vitreum) (4) to 36-70 µg/ml in
bluegill sunfish (Lepomis macrochirus) (5). Diquat is not
stored by fish.
2.3.2 Birds - Toxic (hens, LD50 200-400 mg/kg (cation)).
2.3.3 Other species - The technical product is toxic to livestock.
However, cattle have been fed diets containing up to 100 mg/kg
diquat as dibromide for one month without ill-effect and with no
significant residues in meat or milk. In longer-term studies,
cattle have been fed for 257 days with desiccated sunflower seed
containing diquat residues, again without effect.
3. FOR REGULATORY AUTHORITIES - RECOMMENDATIONS ON REGULATION OF
COMPOUND
3.1 RECOMMENDED RESTRICTIONS ON AVAILABILITY
(for definition of categories, see introduction)
Formulations over 5%, Category 4
Formulations of 5% or below, Category 5
3.2 TRANSPORTATION AND STORAGE
Formulations in Category 4 should be transported or stored in
clearly labelled rigid and leakproof containers. No food or
drink should be transported or stored in the same
compartment. Storage should be under lock and key, and
secure from access by unauthorized persons and children.
Formulations in Category 5 should be transported or stored in
clearly leakproof containers, out of reach of children, away
from food and drink.
3.3 HANDLING
Formulations in Category 4 - Protective clothing (see paragraph
4.1.3 in part 4) should be used by those handling concentrates.
Adequate washing facilities should be available close at hand.
Eating, drinking and smoking should be prohibited during handling
and before washing after handling.
Formulations in Category 5 - No facilities other than those
needed for the safe handling of any chemical need to be required.
3.4 DISPOSAL AND/OR DECONTAMINATION OF CONTAINER - Container must
either be burned or crushed and buried below topsoil. Care must
be taken to avoid contamination of water sources. Container may
be decontaminated (for method see paragraph 4.3 in part 4).
Decontaminated containers should not be used for food and drink.
3.5 SELECTION, TRAINING AND MEDICAL SUPERVISION OF WORKERS
Formulations in Category 4 - Training of workers in techniques
to avoid contact essential.
Formulations in Category 5 - Warning of workers to minimize
contact essential.
3.6 ADDITIONAL REGULATIONS RECOMMENDED IF DISTRIBUTED BY AIRCRAFT
All formulations - Pilots and loaders should receive special
training in application methods. Use of flagmen not recommended.
Flagmen, if used, should wear overalls and be located well away
from the dropping zone.
3.7 LABELLING
Formulations in Category 4 - Minimum cautionary statement -
Diquat is a toxic substance and is poisonous if swallowed; it may
be absorbed through the skin or inhaled in spray mists. Avoid
skin contact, wear protective gloves and clean protective
clothing while using the material. Wash thoroughly with soap and
water after using. Keep the material out of reach of children
and well away from foodstuffs, animal feed and their containers.
Formulations in Category 5 - Minimum cautionary statement - This
formulation contains diquat, a toxic substance. It is poisonous
if swallowed. Keep the material out of reach of children and
well away from foodstuffs, animal feed and their containers.
3.8 RESIDUES IN FOOD - Maximum residue limits for diquat have been
recommended by the Joint FAO/WHO Meeting on Pesticide Residues.
These are subject to change at annual reviews.
4. PREVENTION OF POISONING IN MEN AND EMERGEINCY AID
4.1 PRECAUTIONS IN USE
4.1.1 General - Diquat is a bipyridyl herbicide of moderate toxicity
which may be absorbed from the gastrointestinal tract by
inhalation of spray or mists, or through the intact skin.
Concentrated formulaticms should be handled by trained personnel
wearing protective clothing.
4.1.2 Manufacture and formulation
T.L.V.: 0.5 µg/m3 (ACGIH). Closed systems and forced ventilation
may be required to reduce as much as possible the exposure of
workers to the chemical.
4.1.3 Mixers and applicators - When opening the containers and when
mixing, protective impermeable boots, clean overalls, gloves and
a face shield should be worn. Mixing, if not mechanical, should
always be carried out with a paddle of appropriate length. When
sprayin- tall weeds or during aerial application a face shield
should be worn as well as an impermeable hat, clothing, boots and
gloves. The applicator should avoid working in spray mists and
contact with the mouth. Particular care is needed when equipment
is being washed after use. All protective clothing should be
washed immediately from the skin or eyes with large quantities of
water. Before eating, drinking or smoking, hands and other
exposed skin should be washed.
4.1.4 Other associated workers (including flagment in aerial
operations) - Persons exposed to diquat and associated with its
application should wear protective clothing and observe the
precautions described in 4.1.3 under "mixers and applicators".
4.1.5 Other populations to be affected - With good agricultural
practice, subject to 4.2 below, other populations should not be
exposed to hazardous amounts of diquat.
4.2 ENTRY OF PERSONS INTO TREATED AREAS - No restriction.
4.3 DECONTAMINATION OF SPILLAGE AND CONTAINERS - Residues in
containers should be emptied in a diluted form, into a deep pit
taking care to avoid contamination of ground waters. The empty
container may be decontaminated by rinsing two or three times
with water and scrubbing the sides. An additional rinse should
be carried out with 5% sodium hydroxide solution, which should
remain in the container overnight. Impermeable gauntlets and
face shield should be worn during this work and a soakage pit
should be provided for the rinsings. Decontaminated containers
should not be used for food and drink. Spillage of diquat and
its formulations should be contained and absorbed on to soil, and
the area rinsed with large quantities of water. Spillages must
not be washed into drains or watercourses.
4.4 EMERGENCY AID
4.4.1 Early symptoms of poisoning - Symptoms of poisoning may include
epigastric discomfort, vomiting and general malaise. There may
be irritation of mouth, pharynx and oesophagus with local
burning. Nose bleeding may occur if spray mists or aerosols are
inhaled. With massive doses there may be excitement and
convulsions.
4.4.2 Treatment before person is seen by a physician, if these symptoms
appear following exposure - The person should stop work
immediately, remove contaminated clothing, wash the affected skin
with soap and water, if available, and flush the area with large
quantities of water. If swallowed, vomiting should be induced.
A high fluid intake should be maintained and the patient taken
for medical attention. Particular note should be made if the
formulation was a mixture with paraquat, which is more hazardous.
5. FOR MEDICAL AND LABORATORY PERSONNEL
5.1 MEDICAL DIAGNOSIS AND TREATMENT IN CASES OF POISONING
5.1.1 General information - A bipyridyl herbicide of moderate toxicity
which may be absorbed from the gastrointestinal tract and weakly
through the intact skin and by inhalation. Isolated cases of
skin damage, and damage to finger nails have occurred with
diquat. Nose bleeding associated with inhalation of concentrated
mist has been reported. Repeated ingestion of high levels causes
cataracts in some laboratory animals. It is not persistent in
body tissues.
5.1.2 Symptoms and signs - Initial symptoms of poisoning may be
epigastric discomfort and vomiting along with general malaise,
and weakness. There may be irritation of the mouth, pharynx and
oesophagus with local burning. Later symptoms may include renal
failure, toxic liver damage, paralytic ileus and collapse. With
very large doses there may be excitement and convulsions.
5.1.3 Laboratory - The presence of diquat in the urine is indicative of
absorption of this compound. Urinary levels should be measured
at frequent intervals. Blood levels are very low and do not
provide a satisfactory method for determining the extent of
absorption.
5.1.4 Treatment - If the pesticide has been ingested a prompt effort
should be made to remove it as much as possible before absorption
takes place. Repeated vomiting should be induced. The stomach
should be washed out with care because of possible oesophageal
injury. A suspension of Fuller's earth 30% in water and a
cathartic should be introduced into the stomach to absorb
residual diquat. This may be repeated several times daily for
several days. Maintain a high fluid intake and possibly force
diuresis to aid excretion. Further treatment should be
symptomatic.
Haemodialysis or peritoneal dialysis may be indicated if there is
evidence of accompanying renal failure. Pulmonary complications
and cerebral damage caused by bleeding in the brain have been
reported in one case. The pulmonary symptoms were quite distinct
from those caused by paraquat, and there was no evidence of
proliferation or fibroplastic change.
5.1.5 Prognosis - There have been few reported cases of acute poisoning
with diquat, and the prognosis should be reasonably good.
5.1.6 References of previously reported cases - Okonek, S. & Hofmann,
A. (1975) Arch. Toxicol., 33, 251-257; Oreopoulus, D. & McEvoy,
J. (1969) Postgrad. Med. J., 45, 635-637; Schönborn, H. et al.
(1971) Arch. fur Toxikol, 27 (3/4), 204-216; Weirich, J. (1980)
Deutsche Gesunh., 24, 1956-1988.
5.2 SURVEILLANCE TESTS - Levels of diquat in the urine provide the
most readily available method for indicating absorption of
diquat. However, actual levels cannot be correlated with the
severity of intoxication because recovery is probably also
dependent on the amount of urine excreted and therefore the total
amount of diquat eliminated from the body.
5.3 LABORATORY METHODS
5.3.1 Detection and assay of compounds - References are given only.
Detection of diquat depends upon reduction to the free radical
with sodium dithionite. For examination of material derived from
cases of diquat poisoning admitted to hospital the following may
be helpful. Tompsett, S. L. (1970) Acta Pharmacol et Toxicol, 28,
346-358.
5.3.2 Other tests in cases of poisoning - None.