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At least two-thirds of the so-called “Rainbow herbicides” used during the war, a total of 20 million gallons, contained the Dioxin-contaminated phenoxy herbicide 2,4,5-T. It is estimated that the herbicides used, not just those contaminated with Dioxin, were up to 50 times the concentration recommended for killing plants.

By examining the spray data, Dr. Jeanne Stellman and her colleagues at Columbia University Mailman School of Public Health determined that up to 366 kilograms of Dioxin were sprayed on South Vietnam during the war. It was also discovered that, before they were destroyed, the surplus inventories of Agent Orange from Gulfport, MS, and Johnston Island, in the Pacific, contained between 6.2 to 14.3 ppt of Dioxin. Earlier testing found a barrel on Johnston as high as 47 ppt, that may have been Agent Purple used from 1962 to 1965 that was known to have higher concentrations of Dioxin than found in Agent Orange.

The Investigation

Since 1994, Hatfield Consultants, a Canadian environmental firm, has conducted extensive soil, animal and human testing to determine what level of Dioxin remains in the soil and sediment of Vietnam and the extent of the chemical’s accumulation in the food chain. Hatfield first began testing in the A Luoi Valley, just south of the demilitarized zone (DMZ), where the Ho Chi Minh Trail, established on the Laos side, entered Vietnam. The valley is extremely remote, with neither industry nor agricultural infrastructure.

About 224 spraying missions were flown over this area between 1965 and 1970. The U.S. military also had three special forces bases in the valley. One of those three bases was A So (A Shau) base, which was used for three years, and where barrels of herbicides were stored for use in the surrounding areas.

It was here, in the surrounding area of the former base, that Hatfield researchers found levels up to 897.85 ppt of Dioxin. Fish and ducks had high levels of Dioxin in their fatty tissues. The local population had elevated levels of Dioxin, found in blood and breast milk.

Just north of the base and other sprayed areas, however, Dioxin was not present in the soil. Only very low levels of Persistent Organic Pollutants (POPs) were detected. Where the herbicides were sprayed by aircraft, Dioxin, for the most part, has dissipated.

Thirty years after the spraying occurred, Dioxin levels ranged from zero to slightly elevated, with the latter pertaining to areas below the soil surface. The Dioxin that remained on the surface likely broke down from the hot tropical sun or washed away by years of heavy rain and soil erosion, and may have pooled in isolated spots.

Areas of the former Ta Bat and A Luoi special forces bases also had elevated levels of Dioxin, ranging from 4.3 ppt to 35 ppt.

The Bases

Hatfield theorized that there were other such Dioxin-laden areas, later designated “hotspots,” that were primarily former U.S. military-installed bases throughout south Vietnam. These bases were of particular concern, especially bases installed as Operation Ranch Hand hubs.

Since the mid-1990s, Hatfield has identified at least 28 of these bases where there are elevated levels of Dioxin contamination. Among these hotspots are the Da Nang, Phu Cat and Bien Hoa bases. Each of these bases had Dioxin contamination greater than 1,000 ppt TEQ (Toxic Equivalents) in the soil and 150 ppt in sediment, the standard for remediation in Vietnam. At the Da Nang air base, Hatfield found up to 361,000 ppt of Dioxin in areas where barrels of herbicides were loaded onto planes to be deployed. In this part of the base, many have observed a strong chlorine smell from the phenols, the solvents, in the weed-killing herbicides. The soil, in particular, is deeply blackened because of the oxidized chlorine molecules of the herbicides.

​Of greatest concern is the Dioxin that seeped into the sediment at the bottom of lakes at both Bien Hoa and Da Nang, where the local community fish. High levels of Dioxin were found in the fish and waterfowl in these lakes. The average was found to be about three times the accepted level of Dioxin contamination, yet some tilapia shockingly had 400 times the acceptable level. People who lived in adjacent areas and communities, as compared to the general population, had elevated levels of Dioxin and other Dioxin equivalents.

One 42-year-old man who used to fish in surrounding bodies of water, near the lake at Bien Hoa, had 1340 ppt of Dioxin in his blood, approximately 200 times the level found in the blood of those living in industrialized nations and more than 400 times the level found in the blood of those living in the north Vietnam. It is worth noting here that the average level of Dioxin in industrialized nations is less than 10 ppt and these levels have been decreasing over time.

The Vietnamese government identified Phu Cat, Da Nang and Bien Hoa bases as priorities for remediation. Of particular concern was the Da Nang base that after the war had become a vital domestic and international airport for the central coastal region of the country. The U.S. government committed to helping Vietnam address the Dioxin contamination at the Da Nang and Bien Hoa bases. The joint U.S.-Vietnam remediation project was completed in 2018 and in 2019, the U.S. and Vietnam began to work together to remediate the Bien Hoa base.

The remaining Dioxin hotspots throughout southern Vietnam were found to have much lower levels of contamination, most under the level of requiring remediation. Therefore, in these cases, mitigation efforts that reduce the movement of the contaminated soil or keep people and animals off the site are enough. Currently the A So Base in A Luoi, is undergoing remediation work by the Vietnamese Ministry of Defense.

Read on to learn more about how the term, "ecocidal warfare," came to be and the early testing period of tactical herbicides in military and manufacturing sites and the long-term impacts there.


Ecocidal Warfare

The destruction and devastation of the verdant, lush tropical-agricultural landscape was so great that the terms “ecological warfare” and “ecocide” were coined, and frequently invoked, to describe what took place in the war’s aftermath ...


Military Sites

As early as 1943, the U.S. military began studying various chemicals’ applications for vegetation control together with the University of Chicago. Then in early 1945, incipient mixtures of 2,4-D and 2,4,5-T were first tested by the U.S. military in Florida ...


Manufacturing Sites

Agent Orange-Dioxin contaminated not only areas of south Vietnam, but also where the chemical was manufactured, stored, tested or disposed of, in the U.S. and elsewhere in the world ...

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