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Adefoliant is anyherbicidal chemical sprayed or dusted on plants to cause theirleaves to fall off. Defoliants are widely used for the selective removal of weeds in managing croplands and lawns. Worldwide use of defoliants, along with the development of other herbicides andpesticides, allowed for theGreen Revolution, an increase in agricultural production in mid-20th century.[1] Defoliants have also been used in warfare as a means to deprive an enemy of food crops and/or hiding cover, most notably by theUnited Kingdom during theMalayan Emergency and theUnited States in theVietnam War. Defoliants were also used by Indonesian forces in various internal security operations.[2]
A primary application of defoliants is the selective killing of plants. Two of the oldest chemicalherbicides used as defoliants are2,4-Dichlorophenoxyacetic acid (2,4-D) and2,4,5-Trichlorophenoxyacetic acid (2,4,5-T). 2,4-D and 2,4,5-T are absorbed by broad-leafed plants, killing them by causing excessive hormonal growth.[1] Thesephenoxy herbicides were designed to selectively kill weeds and unwanted plants in croplands. They were first introduced at the beginning ofWorld War II and became widespread in use in agriculture following the end of the War.
Defoliants have a practical use in the harvesting of certain crops, particularlycotton, in theUnited States as well as a number of other cotton-producing countries. The use of defoliants aids in the effective harvesting of cotton and finer lint quality.[3] The effectiveness of defoliant use in cotton harvesting depends on the type of defoliant(s) used, the number of applications, the amount applied, and environmental variables. Common harvest-aiding chemical defoliants include tribufos, dimethipin, andthidiazuron. According to a 1998 report by theU.S. Department of AgricultureNational Agricultural Statistics Service (NASS), tribufos and thidiazuron accounted for 60% of crop area that was treated by defoliants during that crop year.[4][5]
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In Southeast Asia during the Vietnam War, theRainbow Herbicides were a group of tactical-use chemicals used by theUnited States military. The environmental destruction caused by this defoliation has been described by Swedish Prime MinisterOlof Palme, lawyers, historians and other academics as anecocide.[6][7][8][9][10]
In 1998, theU.S. Environmental Protection Agency (U.S. EPA) concluded that the use of agricultural defoliants led to increased risks of water contamination and dangers to freshwater andmarine life.[4] High doses of tribufos were labeled as a possiblecarcinogen and a toxin to freshwater and marineinvertebrates. Dimethipin has also been labeled as a possible human carcinogen.
A published study in theJournal of Agricultural and Food Chemistry reported that through successivesurface runoff events in defoliated cotton fields, defoliant concentrations decreased exponentially within the test area and could negatively affect marine life in the runoff zones.[4]
Agent Orange, a defoliant used by theUnited Kingdom during theMalayan Emergency in the 1950s and theUnited States during theVietnam War to defoliate regions of Vietnam from 1961 to 1971,[11][12] has been linked to several long-term health issues. Agent Orange contains a mixture of 2,4-D and 2,4,5-T as well asdioxin contaminants. Members of the Air Force Ranch Hand and theArmy Chemical Corps who served in theVietnam War were occupationally exposed toAgent Orange have a higher incidence of diabetes, heart disease, hypertension, and chronic respiratory diseases.[13]
Among other occupations, farmers are at a significantly higher risk of developingAlzheimer's disease due to a greater chance of defoliant exposure.[14]
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