DIQUAT (or Diquat dibromide) is a widely used herbicide. It has been used since the 1950s in the production of many common crops, including potatoes, cotton, and rapeseed. It is also used for industrial and aquatic weed control. In the proper quantities, it can be used not only to kill plants, but also as a dessicant, plant growth regulator, and to suppress the flowering of sugar cane. Diquat is typically found as an organic solid made up of colorless of brown crystals, and when mixed with water it becomes red-brown. It is sold under the trade names Aquacide, Aquakill, Aqua-Clear, Dextrone, Reglone, Reglox, Reward, Tag, Torpedo, Vegetrole, and Weedtrine-D, among others. Diquat tends to cost about US$90 to US$100 per gallon.
CHEMICAL PROPERTIES
Chemically, diquat is considered to be a dessicant. It is nonselective, meaning (in this case) that it dessicates anything it comes into contact with, but it is not known for spreading throughout the system of a plant. It causes affected areas to dry out very quickly. Once neutralized, it does not leave a residual trace.
TOXIC EFFECTS
Diquat is moderately toxic if ingested. Rats, mice, rabbits, guinea pigs and dogs all demonstratre an oral LD50 of around 200 mg/kg, but cows are highly sensitive, with a LD50 of no higher than 56 mg/kg, and possibly as low as 30. It causes irritation of any area it comes in contact with. Consumption results in irritation of the mouth, throat, esophagus, and stomach, followed by nausea, vomiting, diarrhea, severe dehydration, gastrointestinal discomfort, chest pain, kidney failure, and toxic liver damage. High enough dosages absorbed through the skin have similar effects to the results of ingestion. Very high doses can result in convulsions and/or tremors. It can cause fingernails to grow back incorrectly, or not at all. In general, it's not a very good thing to come in contact with.
As far as reproduction is concerned, while diquat is unlikely to harm your reproductive system, it may cause birth defects if you come into contact with unusually large quantities of it while pregnant. It is not thought that it will cause birth defects if one comes into contact with small quantities of it as may happen during use. The other major concern with many chemicals is any carcinogenic properties, but diquat does not appear to have any. Feeding rats 10 mg/kg of diquat per day orally for 80 weeks did not cause tumors.
Long-term exposure to diquat has been linked to the development of cataracts.
DIQUAT IN DRINKING WATER
The Safe Drinking Water Act of 1974 requires the EPA to determine the safe levels for potentially hazardous chemicals to appear in drinking water. A Maximum Contaminant Level Goal (or MCLG) is then set. The MCLG for diquat has been set at 20 parts per billion.
ENVIRONMENTAL EFFECTS
Diquat may have harmful effects on plants and animals in the area of treatment. This is especially significant because it is generally used for weed control in open bodies of water, which could lead it to be harmful to fish and waterfowl. The oral LD50 in young male mallards is 564 mg/kg. It is 200-400mg/kg in hens. However, it is effectively harmless to most fish, with an 8-hour LC50 of 12.3 mg/L for rainbow trout and 28.5 mg/L in Chinook salmon. Yellow perch, however, have a 96-hour LC50 of 60mg/L, which is sufficient to cause them harm during normal use for aquatic weed-clearing. There is little or no bioconcentration of diquat dibromide in fish.
Diquat dibromide is unfortunately very well absorbed by both soil and clay, and has a half-life in the field of over 1,000 days. Tests indicate that it usually remains in the topmost inch of soil for long periods of time after application. In water, it quickly binds to suspended particles (especially silt) in the water, so it cannot be used to clear weeds in muddy areas. It is also rapidly absorbed into plants, but generally kills the parts of the plant it is absorbed into too rapidly to be carried through the plant.
References:
Webpage: Extoxnet PIP, Diquat Dibromide (http://ace.orst.edu/info/extoxnet/pips/diquatdi.htm)
Subreferences: (references quoted in the above article)
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EPA Office of Water, Consumer Factsheet on: DIQUAT (http://www.epa.gov/safewater/dwh/c-soc/diquat.html)