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What is Dioxin?

Often when Agent Orange is invoked, it refers to Dioxin, specifically the toxic contaminant 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) found in the phenoxy chemical 2,4,5-T, one of two components of Agent Orange.

Viktor Yushchenko, Ukrainian presidential candidate, poisoned by Dioxin, photographed in 2004.
Viktor Yushchenko, Ukrainian presidential candidate, poisoned by Dioxin, photographed in 2004.

Dioxin originated as an unintended byproduct in the deliberately accelerated manufacture of 2,4,5-T for use in the U.S. war efforts in Vietnam, Laos, and Cambodia. According to research by Jeanne Stellman, it is possible that between 221 and 366 kilograms of Dioxin was in the herbicides used during the war. Dioxin is normally measured in parts per trillion, which, to put into perspective, is a few drops of water in an Olympic-size swimming pool.

TCDD is the most toxic of all the Dioxins and Dioxin-like compounds. The Dioxin-contaminated 2,4,5-T component, found not only in Agent Orange but also in Agents Pink, Purple and Green, was later discovered to alter the expression of specific genes in humans.

Key Dioxin Facts

  • Dioxin is a member of the class of persistent organic pollutants that is produced through combustion, in the bleaching of paper and pulp or in the chemical manufacturing process.

  • 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD), in particular, was a byproduct of the deliberately accelerated production of the phenoxy herbicide 2,4,5-T. Agent Orange was an equal mixture of 2,4,5-T and the other phenoxy herbicide 2,4-D.

  • The U.S. National Toxicology Program (NTP) and the International Agency for the Research on Cancer list TCDD as a “known human carcinogen.”

  • Dioxin has been found to be an endocrine disruptor that can cause chloracne, certain cancers, and reproductive and developmental effects (at least in animals).

  • ​Dioxin is not absorbed by most plants nor is it water soluble. Only zucchini species and water locusts, so far, have been found to absorb Dioxin.

  • Dioxin can attach to fine soil particles or sediment, which are then carried by water downstream and settle in the bottoms of ponds and lakes where it can accumulate in the food chain.

  • The half-life of Dioxin varies depending on where it is found. In humans the half-life is between 7 and 11 years; in surface soil that has been fully exposed to sunlight, it’s between 1 and 3 years; and in subsurface soils and sediment it can be more than 100 years.

Nations around the world have signed onto the Stockholm Convention on Persistent Organic Pollutants (POPs) and committed to reducing their inventory of Dioxins in their countries and eliminating their production.


Agent Orange and Dixion

Agent Orange, also known as Herbicide Orange, was the most widely used of the many color-coded herbicides of the tactical “Rainbow Herbicides” that U.S. forces sprayed over Vietnam, Laos, and Cambodia during the war. The tactical herbicides were deployed by the U.S. Air Force as part of the defoliation program, code-named Operation Ranch Hand, to denude the tropical landscape and destroy croplands over large areas that provided cover and subsistence for counterinsurgency forces.


Production of Agent Orange and its military use ended in 1970, and existing stocks were subsequently destroyed after Operation Pacer Ivy in 1971. Production of 2,4,5-T for domestic use continued until it was halted in the 1980s. In most countries, 2,4-D is still produced by Dow Agroscience and is a common component of over 70 products, including Scott’s Weed and Feed, Miracle-Gro Shake ‘n Feed, and Weed B Gone, among many others.


Agent Orange damaged large swaths of land in Vietnam, Laos, and Cambodia. Pre-war Vietnamese forests had an ecologically balanced mixture of large numbers of species of flora and fauna and will take centuries of natural regeneration to fully heal and recover from mass erosion, among other geomorphic processes, that occurred as a result of systematic defoliation. The wartime uses of herbicides not only lowered soil nutrient levels but also introduced invasive plant species, profoundly altering the land.


The level of TCDD in human blood in industrialized nations has been decreasing since the 1970s. Studies have found that by the late 1990s TCDD levels in the blood of those tested had dropped from a high of nearly 20 parts per trillion to between 2 and 5 ppt. But populations directly exposed to TCDD have been found to have higher levels in their blood. This includes veterans who directly handled the contaminated chemicals during Operation Ranch Hand, whose body burden of Dioxins when tested in 1999 (more than 20 years after they served in Vietnam) ranged from less than 6 ppt to over 130 ppt. Studies conducted in Vietnam in the last decade found high levels of dioxin in the blood of those who ate fish or duck from the ponds at the Bien Hoa or Da Nang air bases where Ranch Hand was based during the war.

Scientists are still trying to understand how Dioxin causes reproductive and developmental abnormalities in humans and impacts the expression of human genes. As an endocrine disrupting chemical, Dioxin has the ability to impact almost all the systems in the body; it is also believed to cause birth defects through epigenetic changes during development, i.e., it changes how genes are read and expressed. Advances in epigenetic research will hopefully bring greater understanding.

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