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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Diquat dibromide

Trade and Other Names: Trade names include Aquacide, Aquakill, Dextrone, Diquat, Reglone, Reglox, Reward, Tag, Torpedo, Vegetrole, and Weedtrine-D.

Regulatory Status: Diquat dibromide is a moderately toxic compound in EPA toxicity class II [1,2]. It is a General Use Pesticide (GUP). Labels for products containing diquat dibromide must bear the Signal Word WARNING.

Chemical Class: dessicant

Introduction: Diquat dibromide is a nonselective, quick-acting herbicide and plant growth regulator, causing injury only to the parts of the plant to which it is applied. Diquat dibromide is referred to as a desiccant because it causes a leaf or an entire plant to dry out quickly. It is used to desiccate potato vines and seed crops, to control flowering of sugarcane, and for industrial and aquatic weed control. It is not residual; that is, it does not leave any trace of herbicide on or in plants, soil, or water.

Formulation: Not Available

Toxicological Effects:

• Acute toxicity: Diquat dibromide is moderately toxic via ingestion, with reported oral LD50 values of 120 mg/kg in rats, 233 mg/kg in mice, 188 mg/kg in rabbits, and 187 mg/kg in guinea pigs and dogs [1,87]. Cows appear to be particularly sensitive to this herbicide, with an oral LD50 of 30 to 56 mg/kg [17]. The acute dermal LD50 for diquat dibromide is approximately 400 to 500 mg/kg in rabbits, indicating moderate toxicity by this route as well [58,87]. A single dose of diquat dibromide was not irritating to the skin of rabbits, but repeated dermal dosing did cause mild redness, thickening, and scabbing [58]. Moderate to severe eye membrane irritation occurred when diquat dibromide was administered to rabbits [88]. Ingestion of sufficient doses may cause severe irritation of the mouth, throat, esophagus, and stomach, followed by nausea, vomiting, diarrhea, severe dehydration, and alterations in body fluid balances, gastrointestinal discomfort, chest pain, diarrhea, kidney failure, and toxic liver damage [87]. Skin absorption of high doses may cause symptoms similar to those that occur following ingestion [89]. Very large doses of the herbicide can result in convulsions and tremors [88]. Test animals (rats, mice, guinea pigs, rabbits, dogs, cows, and hens) given lethal doses of diquat dibromide showed a delayed pattern of illness, with onset approximately 24 hours following dosing, subsequent lethargy, pupil dilation, respiratory distress, weight loss, weakness and finally death over the course of 2 to 14 days after dosing [58,87,89]. There have been reports of workers who have had softening and color changes in one or more fingernails after contact with concentrated diquat dibromide solutions [87]. In some instances, the nail was shed, and did not grow in again [87]. Several cases of severe eye injury in humans have occurred after accidental splashings [87]. In each case, initial irritation was mild, but after several days, serious burns and sometimes scarring of the cornea developed. Direct or excessive inhalation of diquat dibromide spray mist or dust may result in oral or nasal irritation, nosebleeds, headache, sore throat, coughing, and symptoms similar to those from ingestion of diquat [87].
• Chronic toxicity: Chronic effects of diquat dibromide are similar to those of paraquat [87]. Cataracts, a clouding of the eyes which interferes with light entering the eye, occurred in rats and dogs given 2.5 mg/kg/day and 5 mg/kg/day of diquat dibromide, respectively [87]. Cataracts increased in proportion to the dose given in test animals (cats and dogs) [17,88]. Chronic exposure is necessary to produce these effects [87]. Other effects on the eye (hemorrhage, retinal detachment) may occur at higher dosages [87]. Rats fed dietary doses of 2.5 mg/kg/day over 2 years did not exhibit signs of toxicity other than reduced food intake and decreased growth [17]. In another study using rats, oral doses of 4 mg/kg/day over 2 years produced no behavioral or other changes in general condition [87]. At this dose level no evidence of change in the kidneys, liver, or mycocardium (heart muscle) were seen. This dosage (but not 2 mg/kg/day) caused changes in lung tissues [87]. Repeated or prolonged dermal contact may cause inflammation of the skin, and, at high doses, systemic effects in other parts of the body. These may include damage to the the kidneys [58]. Chronic exposure may damage skin, which may increase the permability of the skin to foreign compounds [88].
• Reproductive effects: Diquat dibromide generally did not reduce fertility when tested in experimental animals [89]. Rats receiving 1.25 mg/kg/day decreased their food intake and showed slowed growth, but had unchanged reproduction [89]. Fertility was reduced in male mice given diquat dibromide during different stages of sperm formation [87]. Neither fertility nor reproduction was affected in a three-generation study in rats given dietary doses of 12.5 or 25 mg/kg/day of diquat dibromide, although some growth retardation was seen at the 25 mg/kg/day dose [87]. Based on this evidence it is unlikely that diquat dibromide will cause reproductive effects in humans under normal circumstances.
• Teratogenic effects: Offspring of pregnant rats given a fatal injected dose of 14 mg/kg of diquat dibromide showed evidence of skeletal defects of the collar bone, as well as little or no ear bone formation upon examination [58,87]. No deformities were found in the unborn offspring of pregnant rats that were injected intraperitoneally with 0.5 mg/kg/day of diquat daily during organogenesis, the stage of fetal development in which organs are formed [26]. Growth retardation was seen in test animals given extremely high doses of diquat. While no actual teratogenesis occurred in rats given single abdominal injections during days 7 to 14 of pregnancy, many rats did not have normal weight gain and bone formation in the unborn was decreased [23]. It is unlikely that diquat dibromide will cause teratogenic effects in humans under normal circumstances.
• Mutagenic effects: There is no evidence that diquat dibromide causes permanent changes in genetic material [87]. For example, no mutagenic effects were seen in mice given oral doses of 10 mg/kg/day for 5 days [23].
• Carcinogenic effects: An 80-week feeding study showed that dietary doses of 15 mg/kg/day of diquat did not cause tumors in rats [90]. Likewise, dietary levels of 36 mg/kg/day for 2 years did not induce tumors in rats [87]. Based on the evidence, it appears that diquat dibromide is not carcinogenic.
• Organ toxicity: In animals, diquat dibromide may affect the gastrointestinal tract, eyes, kidneys or liver, and the lungs.

• Fate in humans and animals: Absorption of diquat dibromide from the gut into the bloodstream is low [87]. Oral doses are mainly metabolized within the intestines, with metabolites being excreted in the feces [87,30]. Rat studies showed only a small percentage of the applied oral dose (6%) was absorbed into the bloodstream and then excreted in the urine [87]. Dermal, inhalation, or intravenous exposure results in little processing and rapid elimination in the urine [87]. Following subcutaneous injection in rats, excretion of about 90% of the dose occurred in the urine on the first day and almost all of the remainder on the next day [87]. Complete elimination of the herbicide was seen in urine and feces of rats within 4 days of administration of single oral doses of 5 to 10 mg/kg of diquat dibromide [87].

Ecological Effects:

• Effects on birds: Diquat dibromide ranges from slightly to moderately toxic to birds [91]. The reported acute oral LD50 in young male mallards is 564 mg/kg [8]. The oral LD50 for diquat dibromide is 200 to 400 mg/kg in hens [8]. The 5-day dietary LC50 is about 1300 ppm in Japanese quail [36].
• Effects on aquatic organisms: Diquat dibromide is moderately to practically nontoxic to fish and aquatic invertebrates. The 8-hour LC50 for diquat dibromide is 12.3 mg/L in rainbow trout and 28.5 mg/L in Chinook salmon [28]. The 96-hour LC50 is 16 mg/L in northern pike, 20.4 mg/L in fingerling trout, 245 mg/L in bluegill, 60 mg/L in yellow perch, and 170 mg/L in black bullhead [37,92]. Research indicates that yellow perch suffer significant respiratory stress when herbicide concentrations in the water are similar to those normally present during aquatic vegetation control programs [93]. There is little or no bioconcentration of diquat dibromide in fish [8].
• Effects on other organisms: Diquat dibromide is not toxic to honey bees [1]. Since diquat dibromide is a nonselective herbicide, it may present a danger to non-target plant species [91]. Cows are particularly sensitive to the toxic effects of this material [17].

Environmental Fate:

• Breakdown in soil and groundwater: Diquat dibromide is highly persistent, with reported field half-lives of greater than 1000 days [11]. It is very well sorbed by soil organic matter and clay [11]. Although it is water soluble [11], its capacity for strong adsorption to soil particles suggest that it will not easily leach through the soil, be taken up by plants or soil microbes, or broken down by sunlight (photochemical degradation). Field and laboratory tests show that diquat usually remains in the top inch of soil for long periods of time after it is applied [94].
• Breakdown in water: Studies on the erosion of diquat-treated soils near bodies of water indicate that diquat dibromide stays bound to soil particles, remaining biologically inactive in surface waters, such as lakes, rivers, and ponds [95]. When diquat dibromide is applied to open water, it disappears rapidly because it binds to suspended particles in the water [95]. Diquat dibromide's half-life is less than 48 hours in the water column, and may be on the order of 160 days in sediments due to its low bioavailability [94,95]. Microbial degradation and sunlight play roles in the breakdown of the compound [95]. At 22 days after a weed infested artificial lake was treated, only 1% of the applied diquat dibromide remained in the water and 19% was adsorbed to sediments [9].
• Breakdown in vegetation: Diquat dibromide is rapidly absorbed into the leaves of plants, but usually kills the plant tissues necessary for translocation too quickly to allow movement to other parts of the plant. The herbicide interferes with cell respiration, the process by which plants produce energy. Diquat dibromide is broken down on the plant surface by photochemical degradation [58]. It is rapidly absorbed by aquatic weeds from the surrounding water and concentrated in the plant tissue [8]. Thus, even low concentrations of the herbicide can control aquatic weeds [8].

Physical Properties:

• Appearance: Technical diquat dibromide, which is greater than 95% pure, forms white to yellow crystals [1].
• Chemical Name: 1,1'-ethylene-2,2'-bipyridyldiylium dibromide salt [1]
• CAS Number: 85-00-7
• Molecular Weight: 344.06
• Water Solubility: 700,000 mg/L @ 20 C; v.s. [1]
• Solubility in Other Solvents: i.s. in nonpolar solvents such as chloroform, diethyl ether, and petroleum ether [1]; s.s in alcohol and hydroxylic solvents [1]
• Melting Point: Decomposes above 300 C [1]
• Vapor Pressure: Negligible @ 20 C [1]
• Partition Coefficient: -4.6021 [1]
• Adsorption Coefficient: 1,000,000 (estimated) [11]

Exposure Guidelines:

• ADI: 0.002 mg/kg/day [12]
• MCL: 0.02 mg/L [65]
• RfD: 0.0022 mg/kg/day [13]
• PEL: Not Available
• HA: Not Available
• TLV: 0.1 mg/m3 (8-hour) (respirable fraction) [17]

Basic Manufacturer:

Zeneca Ag Products
1800 Concord Pike
Wilmington, DE 19897

• Phone: 800-759-4500
• Emergency: 800-759-2500
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.