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any one of several chemical compounds that, when applied to plants, can alter their metabolism, causing the leaves to drop off. In agriculture defoliants are used to eliminate the leaves of a crop plant so they will not interfere with the harvesting machinery. Their main military objective is to deprive the enemy of cover. In addition they have been used on food crops that have been considered potential sustenance for the enemy. Unfortunately, defoliants are not discriminating chemical weapons. Normally applied from the air, they are difficult to confine to a desired area and may thus contaminate watercourses, with disastrous effects on fish and other aquatic life. Human beings are also known to suffer toxic effects from them. Further, indigenous populations have suffered severe malnutrition when their food crops have been defoliated to prevent their use by the enemy. Possibly the severest and most long-lasting side effect of military defoliation is the disruption of the fragile jungle ecosystem. Contrary to appearances, the soils that underlie rain forests are not abundant in plant nutrients. Therefore, the ecosystem generally conserves and recycles the nutrients that do exist. Any massive disruption, such as killing or interfering with the metabolism of large numbers of plants, inevitably causes large amounts of nutrients to be washed away by rainfall. Also, when sunlight, which would normally be blocked by the leaves, falls on the claylike soil of the jungle, the soil bakes and becomes very hard. These conditions operate against reestablishment of normal vegetation. During the Vietnam War, U.S. forces used the defoliant Agent OrangeAgent Orange,
herbicide used by U.S. forces during the Vietnam War to expose enemy guerrilla forces in forested areas. Agent Orange contains varying amounts of dioxin. Exposure to the defoliant has been linked with chemical acne, non-Hodgkin's lymphoma, Hodgkin's disease,
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, which is widely thought to have led to cancer and other side effects among military personnel and civilians.
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A chemical sprayed on plants that causes leaves to fall off prematurely.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Also to be considered is the dioxin produced during bleaching, the chemical defoliants used to remove leaves prior to harvest of the cotton bolls, and other chemicals used in processing.
The soldiers who fought in America's least popular war and who returned home to face joblessness, post-traumatic stress, alienation and diseases caused by chemical defoliants, today say they feel compelled to tell young people about their experiences.
humanitarian assistance to help the country deal with on the consequences of the Vietnam War, including the lingering effects of the toxic, chemical defoliants used by U.S.
Vietnam is urging the U.S., with which it reestablished diplomatic ties in 1995, to help address the lingering consequences of war, including unexploded ordnance and exposure to chemical defoliants.
South Korea's prime minister at the time, Chung Il Kwon, also gave approval for the use of chemical defoliants in the DMZ, Yonhap said.

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