The Rainbow Herbicides are a group of tactical-use chemicals used by the United States military in Southeast Asia during the Vietnam War. Success with Project AGILE field tests in 1961 with herbicides in South Vietnam was inspired by the British use of herbicides and defoliants during the Malayan Emergency in the 1950s, which led to the formal herbicidal program Trail Dust (see Operation Ranch Hand). Herbicidal warfare is the use of substances primarily designed to destroy the plant-based ecosystem of an agricultural food production area and/or to destroy dense foliage which provides the enemy with natural tactical cover.
The United States discovered 2,4-dichlorophenoxyacetic acid (2,4-D) during World War II. It was recognized as toxic and was combined with large amounts of water or oil to function as a weed-killer. Army experiments with the chemical eventually led to the discovery that 2,4-D combined with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) yielded a more potent herbicide.[1] Some batches of 2,4,5-T manufactured for Rainbow Herbicide use were later found to have been contaminated with synthesis-byproduct dioxins including 2,3,7,8-tetrachlorodibenzodioxin (TCDD). Work by researcher Alvin Lee Young identifies examples of Agent Pink and Agent Green containing as much as double the TCDD concentrations observed in Agent Purple or Agent Orange.[2]
This is a list of the different types of agents used, their active ingredients, and the years they were being used during the Vietnam War as follows:[3]
| Name | Content | used | |
|---|---|---|---|
| 100% n-butyl ester 2,4,5-T | prior to 1963 | ||
| 100% 2,4,5-T (60% n-butyl ester 2,4,5-T, and 40% iso-butyl ester of 2,4,5-T) | prior to 1964 | ||
| 1961–1965 | |||
| Agent Blue (Phytar 560G) | 65.6% organic arsenicical (cacodylic acid (Ansar 138) and its sodium salt sodium cacodylate) | 1962–1971 | |
| Agent White (Tordon 101) | 1966–1971[4] | ||
| Agent Orange Herbicide Orange (HO) | 50% n-butyl ester 2,4-D and 50% n-butyl ester 2,4,5-T | 1965–1970 | |
| Agent Orange II | 50% n-butyl ester 2,4-D and 50% isooctyl ester 2,4,5-T | after 1968[5] [6] | |
| Agent Orange III | 66.6% n-butyl 2,4-D and 33.3% n-butyl ester 2,4,5-T.[7] | ||
| Enhanced Agent Orange, Orange Plus, Super Orange (SO), or Dow Herbicide M-3393 | Standardized Agent Orange mixture of 2,4-D and 2,4,5-T combined with an oil-based mixture of picloram, a proprietary Dow Chemical Company product called Tordon 101, an ingredient of Agent White.[8] |
In Vietnam, the early large-scale defoliation missions (1962–1964) used 8208U.S.gal of Agent Green, 122792U.S.gal of Agent Pink, and 14500U.S.gal of Agent Purple. These were dwarfed by the 11712860U.S.gal of Agent Orange (both versions) used from 1965 to 1970. Agent White started to replace Orange in 1966; 145239853U.S.gal of White were used. The only agent used on a large scale in an anti-crop role was Agent Blue, with 142166656U.S.gal used.[9] The bombardment occurred most heavily in the area of the Ho Chi Minh Trail.
The rainbow herbicides damaged the ecosystems and cultivated lands of Vietnam, and led to buildup of dioxins in the regional food chain. About 4.8 million people were affected. The environmental destruction caused by this defoliation has been described by Swedish Prime Minister Olof Palme, lawyers, historians and other academics as an ecocide.[10] [11] [12] [13] [14]
In addition to testing and using the herbicides in Vietnam, Laos, and Cambodia, the US military also tested the "Rainbow Herbicides" and many other chemical defoliants and herbicides in the United States,[15] Canada, Puerto Rico, Korea, India, and Thailand[16] from the mid-1940s to the late 1960s. Herbicide persistence studies of Agent Orange and Agent White were conducted in the Philippines.[17] The Philippine herbicide test program was conducted in cooperation with the University of the Philippines College of Forestry, and was also described in a 1969 issue of The Philippine Collegian, the college's newspaper. Super or enhanced Agent Orange was tested by representatives from Fort Detrick and Dow Chemical in Texas, Puerto Rico, Hawaii, and later in Malaysia, in a cooperative project with the International Rubber Research Institute.[18] Picloram in Agent White and Super-Orange was contaminated by hexachlorobenzene (HCB) a dioxin-like carcinogen. The Canadian government also tested these herbicides and used them to clear vegetation for artillery training.[19]
A 2003 study in Nature found that the military underreported its use of rainbow herbicides by 2493792U.S.gal.[20]
Vietnam remains heavily contaminated by dioxin-like compounds, which are classified as persistent organic pollutants. These compounds remain in the water table and have built up in the tissues of local fauna. However, the contamination has begun to deteriorate, and the forest canopy has regrown somewhat since the Vietnam War.
Dioxins are endocrine disruptors and may have effects on the children of people who were exposed. Rainbow herbicides and other dioxin-like compounds are endocrine disruptors, and evidence suggests that they continue to have long-term health consequences many years after exposure. Because they mimic, or interfere with, hormonal function, adverse effects can include problems with reproduction, growth and development, immune function, and metabolic function. As an example, dioxins and dioxin-like compounds influence the hormone dehydoepiandosterone (DHEA), which has a role in the determination of male or female sex characteristics. There have been thousands of documented instances of health problems and birth defects associated with rainbow herbicide exposure in Vietnam, where tested levels remain high in the soil, water, and atmosphere, decades after initial exposure.
Soldiers exposed to Rainbow Herbicides in Southeast Asia reported long-term health effects, which led to several lawsuits against the U.S. government and the manufacturers of the chemical.