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Diquat Dibromide - Herbicide Profile 3/85

                                       diquat
      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
                          Fernhurst, Haslemere,
                          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).
      APPLICATION METHOD(S):
           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
             areas.
             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).
                                  I.  EFFICACY
      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)
                          (58).
      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).
      TOXICOLOGY
           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
                          damaged (58).
                        Diquat is absorbed through human skin only after
                          prolonged exposure; shorter exposure can cause
                          irritation and a delay in the healing of cuts and
                          wounds (62).
               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)
                          (62).
               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
      ion/kg (rabbit).
           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
             conditions.
      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
      Control Center.
      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
                function.
           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
                     supervenes.
      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
           (25).
                        VI.  FIRE AND EXPLOSION INFORMATION
           Commercial formulation is an aqueous salt solution, nonflammable
      (58).
                                VII.  COMPATIBILITY
           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
      (17i).
      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
      clothing (17i).
                       IX.  PROCEDURES FOR SPILLS AND LEAKS
                     IN CASE OF EMERGENCY, CALL, DAY OR NIGHT
                                  (800) 424-9300
                      PESTICIDE TEAM SAFETY NETWORK/CHEMTREC
                               X.  LITERATURE CITED
       8b. Thomson, W.T.  1981.  Agricultural chemicals - book 2:
               herbicides.  Revised ed.  Thomson Publications, Fresno, CA.
               274 pp.
      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.
               116 pp.
      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.
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