Diquat Dibromide - Herbicide Profile 3/85
CHEMICAL NAME: 1,1'-ethylene-2,2'-bipyridylium ion (56)
TRADE NAME(S): Reglone, Reglox, Aquacide, Dextrone, Weedtrine-D (25)
FORMULATION(S): Only available as an aqueous solution of the
dibromide salt (58). Commercially available as the
dibromide 2 lb/gal (56).
TYPE: Dipyridyl herbicide
BASIC PRODUCER(S): ICI Plant Protection Division
Surrey GU27 3JE England
STATUS: General use
PRINCIPAL USES: Diquat is registered as a noncrop weed killer, a
general aquatic herbicide and as a preharvest top
killer or desiccant of seed crops. Desiccation of
seed crops of alfalfa, clover, castor beans, grain
sorghum, soybeans, and vetch is practiced. Soil
type or general climatic types do not directly
influence diquat usage (58).
Desiccation - apply from ground or air for complete coverage of
aerial portions of plant.
Aquatic weed control - submerged weeds: Water treatments may be
applied by injecting diquat below the water surface, or by pouring
it directly from the container into the water while moving slowly
over the water surface in a boat. Distribute evenly over infested
Floating weeds: Apply by thoroughly wetting foliage.
Non-crop weed control - apply for full coverage and thorough weed
contact to point of run-off. The younger the weeds, the better
will be the control obtained (58).
Important Weed Controlled: Practically all annual plants that it comes
in contact with as well as aquatic weeds. Annual grasses are less
susceptible than broadleaf plants (8b).
Aquatic weeds controlled by Ortho Diquat:
bladderwort Utricularia spp.
curlyleaf pondweed Potamogeton crispus
leafy pondweed Potamogeton foliosus
claspingleaf pondweed Potamogeton richardsonii
small pondweed Potamogeton pusillus
floatingleaf pondweed Potamogeton natans
sago pondweed Potamogeton pectinatus
common duckweed Lemna minor
common cattail Typha latifolia
American elodea Elodea canadensis
coontail Ceratophyllum demersum
salvinia Salvinia auriculata
southern naiad Najas quadalupensis
waterhyacinth Eichhornia crassipes
waterlettuce Pistia stratiotites
eurasian watermilfoil Myriophyllum spicatum
Conditional control by Ortho Diquat:
American pondweed Potamogeton nodosus
Not controlled by Ortho Diquat:
yellow waterlily Nuphar luteum
chara Chara spp. (17h).
II. PHYSICAL PROPERTIES
MOLECULAR FORMULA: C12 H12 N2 (62)
MOLECULAR WEIGHT: 184.2 (cation); 344.0 (dibromide salt) (58).
PHYSICAL STATE: Yellow solid (pure salt monohydrate); aqueous
solution is dark reddish-brown (58).
Normally, the solid dibromide is not isolated from
the technical product (>95% pure) (62)
MELTING POINT: See boiling point
BOILING POINT: Salts decompose at high tempertures, charring
rather than melting or boiling (pure compound)
DECOMPOSITION TEMPERATURE: Above 300 C (pure compound) (58).
VAPOR PRESSURE: Nonvolatile. Vapor pressure of salts is very low
and has not been measured (pure compound) (58).
SOLUBILITY: Soluble in water (pure compound) (58).
III. HEALTH HAZARD INFORMATION
OSHA STANDARD: NA
NIOSH RECOMMENDED LIMIT: NA
ACGIH RECOMMENDED LIMIT: TWA (Time Weighted Average) = 0.5 mg/m3; STEL
(Short Term Exposure Limit) - deleted (15c).
A. ACUTE TOXICITY
DERMAL: LD50 = >400 mg ion/kg (rabbit). The concentrate is
irritant to skin. Absorption through intact skin
is minimal, but may be facilitated if the skin is
Diquat is absorbed through human skin only after
prolonged exposure; shorter exposure can cause
irritation and a delay in the healing of cuts and
ORAL: LD50 = 230 mg diquat ion/kg (rat) (58).
LD50 = 231 mg/kg (rat), 125 mg/kg (mouse), 100-200
mg/kg (dog), 30 mg/kg (cow), 200-400 mg/kg (hen)
INHALATION: As diquat has no appreciate vapor pressure, there
is no hazard from inhalation. Prolonged, direct
contact with the spray mist may cause oral and
nasal irritation, and should be avoided (58).
It can cause temporary damage to nails and nose
bleeding if inhaled (62).
EYES: The concentrate is irritant to the eye (58).
B. SUBACUTE AND CHRONIC TOXICITY:
Subacute percutaneous LD50 (20 applications): 20 to 40 mg diquat
Prolonged feeding with diets containing diquat produced cataract in
rats and dogs. In the rats, the effect was seen after approximately
100 weeks at a dietary concentration of 36 ppm diquat ion, and in the
dog, after 15 months at 150 ppm diquat ion. The no-effect levels were
25 ppm and 50 ppm diquat ion respectively (58).
The only pathological symptom associated with long-term feeding
trials is the occurrence of bilateral cataracts. In 2-yr feeding trials
NEL in rats was 25 mg/kg diet; cataracts appeared after 124 days at 35
mg/kg diet. In 4-yr studies NEL in dogs was 50 mg/kg diet (62).
IV. ENVIRONMENTAL CONSIDERATIONS
Behavior In Or On Soils
1. Adsorption and leaching characteristics in basic soil types: An
important and unique property of diquat is its very rapid and
complete inactivation by soil. This results from reaction
between the double positively charged diquat cation and clay
minerals present in soils to form complexes with the negatively
charged sites on the clay minerals (and even insertion into the
layer planes of such minerals as montmorillonite).
Diquat cannot be removed from such sites by washing, even with
saturated solutions of salts, and can only be regenerated by
breaking down the clay mineral with 18 N sulfuric acid. Most
soils have sufficient capacity in the top inch of soil alone to
bind many hundred times the normal field rates of application of
diquat in this form. There are also other forms of binding of
diquat in soils - e.g., by reaction with humic acids and by
normal Langmuir type adsorption onto organic matter and soil
particles. In the case of this rather weaker binding there is a
true equilibrium between the quantity adsorbed and free diquat
in an aqueous phase in contact with the soil. However, even in
this case, fairly high concentrations in the soil are required
to give phytotoxic concentrations of diquat in the soil water.
2. Microbial breakdown: Experiments with microorganisms in culture
media have shown that certain of these are capable of
decomposing diquat in the absence of soil. However, they
degrade bound diquat with difficulty or not at all.
3. Loss from photodecomposition and/or volatilization: Loss of
diquat can occur by photochemical decomposition on sprayed leaf
surfaces and on dead and decaying vegetation. Photochemical
decomposition of diquat has also been shown in the laboratory by
irradiating thin layers of soil, but such decomposition on the
soil has not been unequivocally demonstrated under field
4. Resultant average persistence at recommended rates: When bound to
soil is very persistent but biologically unavailable (58).
Generally safe to wildlife and fish (58).
V. EMERGENCY AND FIRST AID PROCEDURES
The chemical information provided below has been condensed
from original source documents, primarily from "Recognition and
Management of Pesticide Poisonings", 3rd ed. by Donald P. Morgan,
which have been footnoted. This information has been provided in
this form for your convenience and general guidance only. In
specific cases, further consultation and reference may be required
and is recommended. This information is not intended as a sub-
stitute for a more exhaustive review of the literature nor for the
judgement of a physician or other trained professional.
If poisoning is suspected, do not wait for symptoms to develop.
Contact a physician, the nearest hospital, or the nearest Poison
SYMPTOMS: Vomiting, diarrhea, general malaise. Possibly kidney
and liver damage, dyspnea, and pulmonary oedema. With very large
doses, there may be tremors and convulsions (58).
DIQUAT INGESTION results in intense NAUSEA, VOMITING, and
DIARRHEA, with accompanying dehydration, and in melena and hematemesis
from gastrointestinal ulceration. INCREASED serum BUN and CREATININE,
and ANURIA result from acute tubular necrosis. Serum GOT, GPT, and
LDH and alkaline phosphatase elevations reflect liver injury. Early
COMA has sometimes occurred following suicidal ingestion of large
amounts and has also been noted in experimentally poisoned monkeys.
This could be a consequence of profound dehtdration, with electrolyte
disturbances, or of diffuse hemorrhages in the central nervous system,
as noted in one human poisoning (25).
SKIN CONTACT: Thoroughly wash contaminated skin, especially
following exposure to concentrate (58).
Contaminated SKIN must be FLUSHED with copious amounts of water.
Mild skin reactions usually respond to simple avoidance of further
contact, but the irritation may take several weeks to resolve. Severe
injuries, with cracking, secondary infection, or nail injury, should
be treated by a dermatologist (25).
INGESTION: Induce vomiting and send subject to hospital as
quickly as possible. Contact Chevron Environmental Health Center
(Phone # (415) 233-3737) for advice (58).
EYE CONTACT: After splashes in the eye, irrigate thoroughly for
a prolonged period and consult a physician (58).
Material splashed in the EYES must be removed by PROLONGED
IRRIGATION with clean water. Eye contamination should therefore be
treated by an ophthalmologist (25).
NOTES TO PHYSICIAN
1. After a DIPYRIDYL compound has been INGESTED, EVACUATE the
STOMACH, then LOAD the gastrointestinal tract with an effective
ADSORBENT, to minimize toxicant absorption. These measures must
be undertaken immediately, even though the patient is free of
signs of systemic toxicity, and even when, by all accounts, the
ingested dose was probably small and was taken as long as several
days prior to treatment.
INTUBATE the STOMACH, ASPIRATE content, then LAVAGE with at least
two liters of a slurry of ADSORBENT in normal saline. Then,
slowly instill several hundred additional ml of adsorbent slurry,
allowing the stomach and intestine to accommodate this volume
without overdistension and vomiting.
A. The ideal adsorbent is BENTONITE, administered as a 7 gm per
100 ml suspension. If not immediately available, use
ACTIVATED CHARCOAL, 30-50 gm in 300-400 ml of water, or any
concentration that will flow through the tube. As soon as
bentonite has been obtained, administer it as rapidly as the
patient will tolerate it. If patient cannot swallow
bentonite, administer it by stomach tube at the highest
concentration that will flow through the tube.
B. Initiate SALINE CATHARSIS. Give SODIUM SULFATE, 0.25 gm/kg,
and repeat in two hours if no bowel movement has occurred.
Magnesium salts are probably contraindicated, because of the
risk of magnesium retention in the presence of impaired renal
C. Continue administering bentonite suspension and sodium
sulfate until the gut has been thoroughly flushed. This may
require several days.
2. Secure samples of blood and urine for dipyridyl analysis.
3. Commence INTRAVENOUS INFUSIONS of glucose and electrolyte to
minimize toxicant concentrations in the tissues, and expedite
excretion of the dipyridyl. Attempt to establish a diuresis of
10-15 liters per day.
CAUTION: Monitor fluid balance and electrolytes continuously to
insure against fluid overload if acute tubular necrosis
4. The tubular necrosis produced by large doses of DIQUAT may require
protracted EXTRACORPOREAL HEMODIALYSIS.
5. The topical injuries to mucous membranes produced by ingested
dipyridyls are painful and may require topical local anesthetic
VI. FIRE AND EXPLOSION INFORMATION
Commercial formulation is an aqueous salt solution, nonflammable
Not compatible with some alkyl sulfonate or alkyl aryl sulfonate
wetting agents or alkali metal salts of hormone weed killers. Liable
to hydrolysis in the presence of alkaline materials including alkaline
waters. Diquat has been sucessfully mixed with 2,4-D, substituted
ureas, uracils, dalapon, and the s-triazines.
All materials used in construction of spray equipment have been found
satisfactory for using dilute diquat. Concentrated solutions corrode
aluminum rapidly. It is generally not advisable to store undiluted
diquat in contact with metals; the undiluted material is best kept in
the original container (58).
VIII. PROTECTIVE MEASURES
STORAGE AND HANDLING: Under normal storage conditions, in original
containers, shelf life is indefinitely long. The dry chemical is
somewhat sensitive to ultraviolet light. The product is stable to heat
beyond the range of ordinary ambient temperatures. The solution does
not crystallize at 0 C (58). Do not get material on skin, eyes or
clothing. Do not breathe spray mist in order to avoid nasal, throat
and respiratory tract irritation. Do not feed forage from treated
crops to livestock, keep livestock out of treated fields and crop areas
PROTECTIVE CLOTHING: Wear face shield, rubber gloves and rubber apron
when handling concentrate. When spraying or when contacting sprayed
vegetation wet with spray, dew or rain, wear waterproof footwear and
IX. PROCEDURES FOR SPILLS AND LEAKS
IN CASE OF EMERGENCY, CALL, DAY OR NIGHT
PESTICIDE TEAM SAFETY NETWORK/CHEMTREC
X. LITERATURE CITED
8b. Thomson, W.T. 1981. Agricultural chemicals - book 2:
herbicides. Revised ed. Thomson Publications, Fresno, CA.
15c. American Conference of Governmental Industrial Hygienists. 1984.
TLVs: threshold limit values for chemical substances and
physical agents in the work environment and biological exposure
indices with intended changes for 1984-85. Cincinnati, OH.
17h. Chevron Chemical Company, Ortho Division. 1971. Pamphlet:
Diquat. San Francisco, CA.
17i. Chevron Chemical Company, Ortho Division. 1984. Specimen label:
Diquat. San Francisco, CA.
25. Morgan, D.P. 1982. Recognition and management of pesticide
poisonings, 3rd ed. U.S. Environmental Protection Agency,
Washington, DC. 120 pp.
56. Farm Chemicals Handbook, 70th ed. 1984. R. T. Meister, G. L.
Berg, C. Sine, S. Meister, and J. Poplyk, eds. Meister
Publishing Co., Willoughby, OH.
58. Weed Science Society of America, Herbicide Handbook Committee.
1983. Herbicide handbook of the weed science society of
America, 5th ed. Weed Science Society of America, Champaign,
IL. 515 pp.
62. The Pesticide Manual: A World Compendium, 7th ed. 1983. C.R.
Worthing, ed. The British Crop Protection Council, Croydon,
England. 695 pp.