Rainbow Herbicides: Defoliants Used in the Vietnam War

Today it is widely known that during the Vietnam War the U.S. Military used chemical defoliants to clear vegetation. This was part of the herbicidal warfare used by the military during Operation Ranch Hand, which was meant to destroy crops and deny the enemy combatants the cover of foliage. To that end, it accomplished its mission. However, it also accomplished one of the largest toxic exposures our military has ever seen.

The term “Rainbow Herbicides” refers to the variety of chemical mixtures used in Vietnam, named for the color-coded bands on their 55-gallon storage drums: Agent Orange, Agent Orange II, Agent Purple, Agent Pink, Agent Green, Agent White, and Agent Blue. Each targeted specific types of vegetation and contained different combinations of active chemicals.

What Are the Differences Among Rainbow Herbicides?

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), an extremely toxic dioxin contaminant, formed during the manufacture of 2,4,5-T, so the amount of TCDD varied among formulations, manufacturers, and batches. Agent Orange, Agent Orange II, Agent Purple, Agent Pink, and Agent Green all contained 2,4,5-T. Decades of research have shown that exposure to TCDD has immune, endocrine, reproductive and developmental effects, with TCDD also classified as carcinogenic. The Institute of Medicine (now National Academies of Sciences, Engineering, and Medicine) regularly reviewed new findings, including in NASEM Update 11, 2018.

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How Were Rainbow Herbicides Used?

Defoliants are chemical agents designed to destroy vegetation, and while they were first developed for agricultural use, they later became tools of modern warfare. The U.S. and its allies began studying defoliants as early as World War II to limit enemy food production and visibility. British and U.S. military scientists continued these experiments after the war, creating the chemical foundations of what would later become Agent Orange, the most infamous defoliant of the Vietnam War.

During the Vietnam war, chemical defoliants were field tested in South Vietnam as Project AGILE. The success of this program led to the formal herbicide program Trail Dust from 1961-1971, which included Operation Ranch Hand, where defoliants were sprayed from aircraft over large portions of forests.

From 1961 to 1971, U.S. aircraft sprayed these herbicides to:

• Strip forest cover used for concealment by North Vietnamese forces
• Clear dense vegetation to prevent ambushes
• Destroy crops that supported enemy forces

Agent Orange accounted for nearly 60% of all herbicides sprayed during the war, totaling about 43 million liters (11.4 million gallons). Agent Orange II kept the same basic 50:50 division between 2,4-D and 2,4,5-T, but the n-butyl ester of 2,4,5-T used in standard Agent Orange was replaced by an isooctyl ester. Its herbicidal effects were similar to those of Agent Orange.

Agent Orange and Agent White were used mainly against broadleaf plants, woody vegetation, and forests. Agent Purple also targeted broadleaf plants, while Agent Pink and Agent Green were early 2,4,5-T formulations used in smaller quantities for defoliation.

The cacodylic acid in Agent Blue acted as a desiccant and was especially effective against grasses and grains. About half of the Agent Blue used in the U.S. military herbicide program went to crop-destruction missions, and it was the agent of choice for destroying rice crops.

When Did the Spraying Stop?

The Department of Defense suspended the military use of 2,4,5-T in April 1970. The phaseout of the whole herbicide program followed quickly. In February 1971, U.S. military command in Vietnam ended herbicide use for crop destruction, and the last Ranch Hand C-123 flew its final mission. After that, spraying was limited to areas around U.S. fire bases, done by helicopter or by ground troops. The last helicopter herbicide operation flew on October 31, 1971.

Tactical vs. Commercial Herbicides

The U.S. military made the distinction of tactical herbicides, defoliants used for combat operations and commercial herbicides, defoliants used for foliage control on bases to reduce the risks of wildlife, insects, and infections. Unfortunately, similar active ingredients were used for both tactical and commercial herbicides, so they had the same increased risk of adverse health effects in humans.

The Board of Veterans’ Appeals systematically denied claims based on exposure to a commercial herbicide, but this has changed in recent years. Hill & Ponton is now often able to get VA to concede exposure when the facts are on the veteran’s side.

Agent Purple, Agent Pink, and Agent Green

Agents Purple, Pink, and Green were used in the first half of the 1960s, before Agent Orange became the standard. Chemically, they were nearly identical to Agent Orange, and had even higher concentrations of TCDD.

Agent Purple

Agent Purple was a mixture of 2,4-D and 2,4,5-T similar to Orange, but the formula was not identical. It used a 50:30:20 mixture of the n-butyl ester of 2,4-D, the n-butyl ester of 2,4,5-T, and the isobutyl ester of 2,4,5-T. Agent Purple was used from 1962 through 1965 and was effective on broadleaf plants. Because it was more volatile, it was replaced by Agent Orange in 1965. Early production also resulted in heavier TCDD contamination than was typical of the later 2,4,5-T formulations.

Agent Pink

Agent Pink consisted entirely of 2,4,5-T, in a 60:40 mixture of the n-butyl and isobutyl esters. Unlike Agent Orange and Agent Purple, it contained no 2,4-D. It was used in small quantities during the early herbicide program. NASEM records use in 1961 and 1965, but official spray records from the early years are incomplete. Because Agent Pink contained 2,4,5-T, it was also contaminated with TCDD.

Agent Green

Agent Green was the simplest of the early color-coded formulations. It consisted of the n-butyl ester of 2,4,5-T and contained no 2,4-D. It was used only in small quantities, primarily in defoliation missions. NASEM records its use in 1961 and 1965. Like Pink and Purple, Agent Green contained 2,4,5-T and therefore carried TCDD contamination.

Agent White

Agent White was a 4:1 mixture of 2,4-D and picloram. The U.S. military used over 20 million liters of this chemical, making it the second most common herbicide in the war. It was often deployed in areas where Agent Orange had failed to completely clear the vegetation.

Unlike the components of Agent Orange, which degrade relatively quickly in the environment, picloram is significantly more stable. It can persist in the soil for years, meaning it posed a long-term threat to both the environment and those living near or working in sprayed areas. Scientific studies on picloram have indicated potential neurotoxic effects on brain cells, showing that it can trigger oxidative stress and damage neuronal branching.

Agent Blue, the Arsenic-Based Toxin

While most rainbow herbicides contained 2,4,5-T, Agent Blue relied on a completely different toxic mechanism: arsenic. Its active ingredient was cacodylic acid, an organic arsenic compound specifically chosen to destroy rice crops and starve enemy forces. Between 1962 and 1971, the military distributed over 7.8 million liters of Agent Blue. About half was used for crop destruction, while the rest was used for defoliation or vegetation control around base perimeters.

Does VA Offer Compensation for All the Rainbow Herbicides?

Although VA regulations and compensation programs most often use the name “Agent Orange,” the legal definition of a herbicide agent is based on the chemicals involved. VA regulations cover 2,4-D; 2,4,5-T and its contaminant TCDD; cacodylic acid; and picloram. Each of the Rainbow Herbicides contained one or more of those chemicals.

For VA purposes, exposure to Agent White, Agent Blue, Agent Purple, Agent Pink, or Agent Green is therefore not excluded simply because the veteran was exposed to a lesser-known color-coded agent rather than Agent Orange.

The Department of Veterans Affairs treats all the “tactical herbicides” used during the Vietnam War equally when determining service connection. That means veterans exposed to any of these defoliants are potentially eligible for the same benefits as those exposed to Agent Orange.

Even if a condition related to herbicide exposure is not presumptive, it can be claimed by providing information that links it to the exposure. Surviving family may qualify for VA benefits based on the veteran’s herbicide exposure, as may children of Vietnam veterans born with certain birth defects.

How Does VA Know Where Herbicides Were Sprayed?

VA relies on Department of War records to establish where tactical herbicides were used. For Vietnam, those are records of spray missions. For other places, VA publishes the Department of War’s list of locations where tactical herbicides were tested, used, or stored, divided into locations in the U.S. and locations outside the U.S. Each listing gives the dates, the herbicide, and who applied it.

If a base is on the list and a veteran served there during the dates shown, VA has a record that supports herbicide exposure. If the base is not on the list, it’s still possible to prove herbicide exposure with unit records, personnel records, and statements from fellow service members.