Agent Orange is one of several herbicidal (plant-killing) preparations that was used by the U.S. military to destroy forests and enemy crops in Vietnam in the 1960s. Agent Orange was created by mixing equal quantities of two agricultural herbicides commonly used to kill weeds: 2,4-D and 2,4,5-T. Present in the 2,4,5-T as an impurity was 2,3,7,8-tetrachlorodibenzo-p-dioxin (usually abbreviated to TCDD), a dioxin contaminant that is highly toxic to some animals. (Dioxin is a term used collectively for a group of chemical by-products of papermaking and other manufacturing processes.)
During the Vietnam War (1961–75; a civil war between the communist North and the democracy-seeking South), North Vietnamese guerrillas found cover in the lush jungles of South Vietnam. To deprive their opponents of hiding places and food crops, the U.S. military instituted a program called Operation Ranch Hand, which involved the aerial spraying of herbicides. Ground spraying from boats, trucks, and backpacks occurred as well. In all, U.S. troops sprayed approximately 19 million gallons (72 million liters) of Agent Orange and other herbicides over 4 million acres (1.6 million hectares). This military strategy is thought to have saved the lives of many U.S. combat soldiers who had been sent to fight on behalf of the South Vietnamese.
Chloracne: A rash of skin lesions on the face, neck, and back caused by exposure to TCDD.
Herbicide: A chemical substance used to destroy or inhibit plant growth.
Hodgkin's disease: A type of cancer characterized by enlargement of the lymph nodes, spleen, and liver and with accompanied weight loss, heavy sweating, and itching of the skin.
Mangrove: Tropical coastal trees or shrubs that produce many supporting roots and that provide dense vegetation.
Non-Hodgkin's lymphoma: Tumors that develop from cells in lymph nodes, bone marrow, spleen, liver, or other sites in the body.
Soft-tissue sarcoma: A rare but varied group of tumors that arise in the muscles, connective tissue, inner layer of skin, bone, and other tissues.
Toxicity: The degree to which a chemical, in sufficient quantities, can poison humans and other organisms.
Concerns about the health effects of exposure to Agent Orange were initially voiced in 1970, following a study that reported the incidence of birth defects in laboratory mice given high doses of the herbicide 2,4,5-T. TCDD, a dioxin contaminant of 2,4,5-T, was isolated as the actual cause of the birth defects. A commission established in 1970 to study the effects of herbicides on the ecology and population of South Vietnam reported that herbicides had not only destroyed vegetation and food, but 2,4,5-T and its associated dioxin contaminant might possibly have caused birth defects among South Vietnamese people who were exposed to it.
On April 15, 1970, all use of 2,4,5-T in the United States was suspended, except for the killing of weeds and brush on non-crop land. On May 9, 1970, Operation Ranch Hand flew its last mission in Vietnam, and U.S. forces stopped ground spraying in 1971. The herbicide was banned completely in 1985 by the Environmental Protection Agency.
Toxicity of TCDD. TCDD is a by-product of the manufacture of trichlorophenol, a chemical used to produce 2,4,5-T. Workers involved in accidents or spills at factories where the herbicide 2,4,5-T is manufactured have developed a condition called chloracne, a rash of skin lesions on the face, neck, and back. After researchers developed a method to produce trichlorophenol with a reduced level of TCDD as a by-product, the number of chloracne cases among factory workers in the herbicide industry decreased substantially.
The toxicity of the dioxin contaminant TCDD is the subject of continuing controversy and study. While some animals are very sensitive to TCDD, others are more tolerant to it. A very small amount can kill 50 percent of guinea pigs exposed to it, but a dose thousands of times larger is needed to cause the same number of deaths in hamsters.
Serious health symptoms reported in 1977 by veterans of the Vietnam War spurred both the White House and the Veterans Administration (VA) to institute studies to evaluate the possible long-term health effects of herbicides and contaminants.
Exposure to TCDD in humans is measured by the amount of the contaminant found in blood and fatty tissue, where it tends to accumulate. Studies determined that levels of TCDD in the blood of chemical plant workers were strongly related to length of time of exposure.
Inadequate records of herbicide spraying and troop movements have made it difficult to determine to what degree individuals were exposed to herbicides and TCDD in Vietnam. Ranch Hand personnel who were heavily exposed to Agent Orange had significantly higher TCDD levels than other veterans. The average TCDD concentrations of Vietnam veterans who might have been exposed to Agent Orange on the ground did not differ significantly from that of other veterans and civilians.
The Agent Orange Act of 1991, passed by the U.S. Congress, ordered the National Academy of Sciences (NAS) to review and evaluate information regarding the health effects of exposure to Agent Orange and its components. Lacking enough information about the levels of herbicide exposure among Vietnam veterans to make any conclusions
regarding health effects, the NAS instead reviewed existing studies of people known to have been exposed to herbicides. In 1993, the 16-member panel of experts classified possible health effects in four categories, depending on the degree to which they could be associated with TCDD exposure.
In a 1996 update, the Institute of Medicine (IOM) reported new evidence upholding the 1993 finding of sufficient evidence of an association between TCDD exposure and various disorders with symptoms including tumors and skin lesions, including soft-tissue sarcoma, non-Hodgkin's lymphoma, Hodgkin's disease, and chloracne. Porphyria cutanea tarda (a rare skin disease) was downgraded from sufficient to "limited/suggestive evidence of an association," a category that also includes prostate cancer, multiple myeloma (cancer of bone marrow cells), and respiratory cancers (cancers of the lung, larynx, or trachea).
The IOM also reported there was new "limited/suggestive evidence" to show an association between TCDD exposure and the congenital birth defect spina bifida (incomplete closure of the spinal column at birth) in Vietnam veterans' children. A neurological disorder suffered by veterans was also placed in this category. The remaining two categories include cancers or disorders that have insufficient or no evidence of an association with TCDD exposure.
The damage to the plant life of South Vietnam caused by the spraying of Agent Orange is still visible today. The most severe damage occurred in the mangrove forests (tropical trees and shrubs) of coastal areas where spraying left barren, badly eroded coastlines. The number of coastal birds declined dramatically, and with the disappearance of the web of water channels beneath the mangrove trees, fish were deprived of important breeding grounds. It is estimated that full recovery of the man-grove forests to their former state will take at least 100 years.
The loss of commercially useful timber due to aerial spraying of Agent Orange over dense inland forests was significant. About 10 percent of the tall trees making up the forest canopy were killed. Smaller shrubs now comprise the majority of vegetation in affected areas. Tussock grasses and bamboo replaced woody plants destroyed by the spraying. The beginnings of natural recovery can be seen, but it will be many years before the forests will approach their former productivity.
As the rich, diverse tropical forests disappeared, so did animal habitats. As a result, the number of bird and mammal species living in the areas that were sprayed declined dramatically. Wild boar, wild goat, water buffalo, tiger, and various species of deer became less common once the cover and food resources of the forest were removed. Domestic animals such as water buffalo, zebus (an Asian ox), pigs, chickens, and ducks were also reported to become ill after the spraying of Agent Orange.
The contaminant TCDD is not easily or quickly broken down in soil, and there is concern that herbicide residues might inhibit the growth of crops and other plants. These by-products, which can be toxic, could then be passed to humans through the food chain.
[ See also Agrochemical ]