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