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         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.


    Primary use: Desiccant

    Secondary use: Herbicide

    Chemical group: Bipyridylium compound 

    Date issued: April 1979


    1.1   COMMON NAME: Diquat (ISO) 

    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. 


    1.3.1 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 


    1.4.1 Common formulations - Liquids, aqueous concentrates containing 
          140-240 g/l. Water soluble mixtures with paraquat (Data Sheet No. 

    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. 



    2.1.1 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 

    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

          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 

          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 

          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 

    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 

          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 


    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. 



          (for definition of categories, see introduction)

          Formulations over 5%, Category 4

          Formulations of 5% or below, Category 5


          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. 

          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. 


          Formulations in Category 4 - Training of workers in techniques 
          to avoid contact essential. 

          Formulations in Category 5 - Warning of workers to minimize 
          contact essential. 


          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. 



    4.1.1 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.

          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. 


    4.4.1 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 

    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. 



    5.1.1 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 

    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 

          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. 


    5.3.1 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, 

    5.3.2 Other tests in cases of poisoning - None.

See Also:
        Diquat (PIM 580F, French)
        Diquat dibromide (ICSC)
        Paraquat and diquat (EHC 39, 1984)