Agent Orange | Research & Encyclopedia Articles

Agent Orange

Agent Orange is one of several herbicide preparations used by the U.S. Defense Department to destroy forests and enemy crops in Vietnam in the 1960s. Agent Orange contains a 50:50 mixture of two herbicides: 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). A contaminant of 2,4,5-T is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), which is highly toxic to animals.

During the Vietnam conflict, North Vietnamese guerrillas found cover in the lush jungles of South Vietnam. To deprive their opponents of cover and food crops, the U.S. military sprayed Agent Orange and other herbicides on about 6,600 sq mi (1,709,000 ha), an area equivalent to one tenth of the land mass of South Vietnam. This military strategy is regarded as having saved the lives of many U.S. combat soldiers. The bulk of the herbicides were applied by "Operation Ranch Hand," a tactical program for spraying herbicides from airplanes by the Air Force.

Developed and tested during World War II, 2,4-D and 2,4,5-T were commonly used agricultural herbicides in the United States. In 1950, more than 10 million lbs (4.5 million kg) of these herbicides were applied annually for weed control in the United States. By 1960, their use had increased to 35 million lbs (16 million kg).

Between 1962 and 1971, over 10.5 million gal (40.5 million l) of Agent Orange were sprayed in Vietnam. Peak use occurred between 1967 and 1969. Agent Orange was sprayed in Vietnam at a rate that was approximately ten times that normally used in U.S. forestry. U.S. forces sprayed approximately 90% of Agent Orange on tropical forests in Vietnam; the remainder fell on crops and mangrove swamps. The herbicide was sprayed on the boundaries of military bases and river banks from sprayers on boats and trucks and backpack sprayers carried by men.

In 1969, a scientific study found that 2,4,5-T, one of the chemicals in Agent Orange, causes birth defects when given to mice in high doses. A later study revealed that 2,3,7,8 TCDD (tetrachlorodibenzo- p-dioxin), a contaminant of 2,4,5-T, actually caused the birth defects. In 1970, the American Association for the Advancement of Science (AAAS) established a commission to study the effects of herbicides on the ecology and population of South Vietnam. The commission 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 in South Vietnamese people.

A second study sponsored by the South Vietnamese Ministry of Health found no difference in the number of stillbirths and birth defects in the years during and after the herbicide spraying. The National Academy of Sciences also found no evidence for a higher rate of birth defects resulting from herbicide spraying in South Vietnam. However, a North Vietnamese study published in 1971 reported a high frequency of retarded and malformed children born to more than 900 South Vietnamese who had been exposed to herbicide spraying and later hospitalized in Hanoi.

On April 15, 1970, federal agencies responsible for regulating health and agriculture suspended all use of 2,4,5-T in the U.S, except for killing weeds and brush on non-crop land. On May 9, 1970, Operation Ranch Hand flew its last mission in Vietnam. U.S. forces ceased herbicide spraying in Vietnam in 1971.

Like aspirin and caffeine, 2,4-D and 2,4,5-T are moderately toxic: they can alter the body's normal chemical activities, but substantial quantities must be absorbed into the body to produce visible harmful effects. A substantial dose-0.0045 oz per lb of body weight (300 milligrams per kg body weight)-of these herbicides produces death in laboratory animals. An acute reaction occurs only at high doses because animals rapidly excrete these chemicals in the urine. Long-term exposure to 2,4-D and 2,4,5-T does not cause accumulated tissue damage.

The toxicity of TCDD, a contaminant of 2,4,5-T, is the subject of continuing controversy and study. The TCDD content of 2,4,5-T samples used in the 1969 animal studies was 30 parts per million, or 0.003%. In later studies, scientists found that when the level of the dioxin contaminant in 2,4,5-T samples was much lower, no birth defects occurred in test animals.

Since the early 1970s, TCDD has been known as the most toxic of all chlorodibenzodioxins. However, while some animals are very sensitive to TCDD, others are moderately tolerant to it. As little as 0.25 micrograms (a millionth of a gram) per lb body weight (0.6 microgram per kg) can kill 50% of the guinea pigs exposed to TCDD. But it takes a dose of TCDD that is 10,000 times larger to cause the same number of deaths in hamsters.

Workers involved in accidents or spills at factories where 2,4,5-T is manufactured have developed a condition called chloracne, a rash of skin lesions on the face, neck, and back. This condition is an easily observed toxic effect resulting from exposure to TCDD.

TCDD is formed during the synthesis of trichlorophenol, an ingredient needed to produce 2,4,5-T. After the TCDD contaminant was identified, researchers developed a method to produce trichlorophenol with a reduced level of TCDD in the final product. This change substantially decreased the number of chloracne cases among factory workers in the herbicide industry.

Since the liver is the body's specialized organ for handling poisons, it is not surprising that chemical plant workers exposed to TCDD in occupational accidents or activities suffered from enlarged livers and impaired liver functions. They also reported having neurological problems.

In 1977, veterans of the Vietnam war began to report serious health symptoms, which they believed to result from exposure to Agent Orange. In response to veterans' concerns, the White House established an Interagency Work Group to study possible long-term health effects of phenoxy herbicides and contaminants in 1979.

The Veterans Administration (VA) sponsored studies of Vietnam veterans and their families to evaluate any relationship between health problems and the spraying of Agent Orange. The agency also endorsed studies of exposure of workers in the herbicide industry to TCDD.

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. The blood and tissue levels of TCDD in Vietnam veterans suggest that, with the exception of Operation Ranch Hand personnel, troops in Vietnam received substantially lower exposures than did workers in chemical factories. Interpreting the measurements is difficult because TCDD comes from widespread sources in the United States: cigarette smoke, incinerator emissions, automobile emissions, charcoal grilled steaks, and paper products. The average level of TCDD in fatty tissue of Americans is four to seven parts per trillion (ppt).

Studies of workers at herbicide factories and Vietnam veterans have determined the following facts about exposure to TCDD: TCDD concentrations in the blood serum of chemical plant workers were strongly correlated with the length of time that the workers had been exposed to TCDD; median blood levels of TCDD in over 800 Ranch Hand veterans who were heavily exposed to Agent Orange were significantly higher (12.8 ppt) than in a comparable group of veterans (4.2 ppt); the average TCDD concentrations in fatty tissues and blood sera of Vietnam veterans who, based on records of herbicide spraying and troop positions, might have been exposed to Agent Orange on the ground, did not differ significantly from that of other veterans and civilians; the number of deaths or birth defects among people who suffered from chloracne after accidental exposure to TCDD at manufacturing plants did not differ significantly from those of other industrial workers.

As Vietnam veterans continued to express concern about the possible health effects of Agent Orange, the U.S. Congress passed Public Law 102-4, the "Agent Orange Act of 1991." This law ordered a comprehensive review and evaluation of information regarding the health effects of exposure to Agent Orange and its components by the National Academy of Sciences (NAS).

The NAS found that, except for individuals directly involved in the spraying of Agent Orange, information on the degree of herbicide exposure among Vietnam veterans was insufficient to make any conclusions about health effects. Therefore, the NAS evaluated studies of people who were actually exposed to herbicides-often at high levels and for long periods of time. After an extensive review of all available information, the NAS classified possible health effects in four categories, according to their likelihood of being caused by TCDD exposure:

I. Sufficient evidence of an association: Soft tissue sarcoma, Non-Hodgkin's lymphoma, Hodgkin's disease, chloracne, and porphyria cutanea tarda (a skin condition in genetically susceptible individuals). The CDC (Centers for Disease Control) found that service in Vietnam was associated with an increased risk of non-Hodgkin's lymphoma, but the evidence suggests that 2,4-D, rather than TCDD, is responsible.

II. Limited/suggestive evidence of an association: Respiratory cancers (lung, larynx, trachea), prostate cancer, multiple myeloma (cancer of bone marrow cells). Respiratory cancers were found to be related to TCDD only when workers were exposed to high levels of TCDD for prolonged periods of time. No conclusions could be made from studies of Vietnam veterans.

III. Insufficient evidence to determine whether an association exists: Liver, nasal, bone, female reproductive, kidney, testicular cancers, leukemia, spontaneous abortion, birth defects, stillbirths, low birthweight, childhood cancer in offspring, infertility, cognitive, neurological disorders, motor/coordination dysfunction, nervous system, metabolic and digestive, immune system, circulatory, and respiratory disorders.

IV. Limited/suggestive evidence of no association: Skin cancer, gastrointestinal tumors, bladder cancer, brain tumors.

Evidence gathered to date from animal studies and occupational exposures in the herbicide industry is still inadequate to resolve many of the veterans' concerns over possible health effects of Agent Orange. Consequently, the NAS recommends continuing the health study of Air Force Ranch Hand personnel and including in that study Army Chemical Corps veterans who also applied Agent Orange. In addition, the NAS concludes that if scientists can adequately estimate herbicide exposures by reconstructing the timing of Agent Orange applications and troop movements in Vietnam, they might be able to link the level of exposure to health effects-or lack of them-in veterans.

The damage to the flora of Indochina caused by the spraying of Agent Orange is still visible today. Although Agent Orange applications affected foliage over the diverse areas of Vietnam, the most severe damage occurred in the mangrove forests of coastal areas. About 306,280 acres (124,000 ha/1,240 sq km) of coastal mangrove, comprising about 40% of the mangrove swamps in South Vietnam, was sprayed at least once. The spraying killed extensive thickets of the dominant mangrove species, Rhizophora apiculata, which is very sensitive to Agent Orange herbicides, leaving barren, badly eroded coastlines. A 1970 National Academy of Sciences report described the harvesting of dead mangroves for fuel, an occupation that would sustain fewer people than it did before the war, as the supply of mangrove wood was not being renewed. The report warned of a future economic loss when the forest would be stripped, unless a vigorous replanting program was undertaken. The destruction of mature seed-bearing trees has made regeneration of mangroves slow and sporadic, and "weed" species have become dominant. The Academy of Sciences estimates that full recovery of the mangrove forest to its former state will take at least 100 years.

After the mangrove trees were destroyed, the number of coastal birds declined dramatically. The web of channels winding beneath the mangrove trees provide important breeding and nursery grounds for a rich variety of fish and crustaceans. The wartime spraying of mangrove swamps is thought to be the cause of a post-war decline in South Vietnam's offshore fishery.

Aerial spraying of Agent Orange over 14 million acres (5.8 million ha) of dense inland forests killed about 10% of the tall trees comprising the forest canopy. Defoliation of the trees was extensive, but some defoliated trees continued to live. Smaller shrubs, protected from the herbicides by the high canopy, or those which replaced dying trees-now comprise the majority of vegetation in affected areas. The total loss of commercially useful timber caused by the military application of herbicides in South Vietnam is estimated to be 26-61 million cu yards (20-47 million cu m). In areas that were sprayed repeatedly (approximately 34% of the sprayed land), all woody plants, except for a few resistant, commercially unimportant species ( Irvingia malayana and Parinari annamense ), were replaced by tussock grasses and bamboo. In the dry season, the stands of grass easily catch fire, and, if burned repeatedly, the lands are less likely to return to forests. The beginnings of natural recovery can be seen, but if the lands are left to natural processes, it will be many years before the forests will approach their former productivity.

As the rich, diverse tropical forests disappeared, so did animal habitat. A uniform grassland has poor habitat diversity compared to the complex, multilayered tropical forest. As a result, the number of bird and mammal species living in the areas that were sprayed declined dramatically. Most of the forest animals are adapted to living in one specific type of habitat and are unable to adjust to survival in the grassland. 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, pigs, chickens, and ducks were also reported to become ill after the spraying of Agent Orange.

Because Agent Orange herbicides might remain in the soil, there is concern that these residues might inhibit the growth of crops and other plants. Soil bacteria break down the herbicides into smaller molecules, but complete decomposition of 2,4,5-T requires that two types of bacteria be present in the soil. Studies performed 15 years after the spraying in South Viet Nam found degradation products of Agent Orange in the soil. These byproducts, which can be toxic, can be passed through the food web.

How much Agent Orange actually reached the soil is subject to question. A large proportion of the herbicides falling onto the forest are trapped by the canopy; few drops reach the soil directly. In open areas, however, virtually the entire application reached the soil.

The contaminant TCDD is quite persistent in soil, with a half-life of three to five years. (In that period of time, one half of the dioxin originally applied would still be present in the soil.) In studies conducted in the United States, samples from inland soils and sediments in mangrove areas treated with TCDD had substantial levels of the chemical after 10 years.

An indirect effect of the Agent Orange spraying is the poor fertility of soils in many areas, due to erosion following the destruction of soil-binding vegetation.

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