2. Gulf War Syndrome

3. Chemical weapons in history

4. The nerve of this gas

5. Agent Orange revisited

6. Dioxin on trial

7. Most poisonous substance?

Update: Gulf War Syndrome

This mangrove jungle was totally destroyed by defoliants. (Cape Camau, 1976)
© Goro Nakamura courtesy of Tokyo Kaleidoscope.

A helicopter sprays agent orange (or "defoliation agent" in government-speak) on a dense jungle area in the Mekong delta.
Courtesy NARA

An unwanted agent
Long before gulf war syndrome, there was dioxin, a poison that contaminated more than 12 million gallons of the herbicide agent orange used by the United States in Vietnam. Between 1962 and 1970, the U.S. military sprayed agent orange on about 10 percent of the area of southern Vietnam.

The goal of history's largest defoliation campaign was to deny the enemy food or cover in Vietnam's dense forests.

Agent orange was a 50/50 blend of two herbicides: 2,4-D and 2,4,5-T. The latter contained traces of the most toxic form of dioxin (defined).

The agent orange sprayed over Vietnam contained 170 kilograms of 2,3,7,8-tetrachlorodibenzo-p-dioxin -- thankfully abbreviated TCDD. It was the largest dioxin release in history.

The ecological effects of the spraying were sudden and severe: one dose killed the enormous mangrove forests that protected the coastline and provided breeding and nursery quarters for large numbers of river and ocean fish. Vast inland forests were replaced by grassland, where frequent fires continue to kill seedling trees (more on fire and tropical forests.)

The human health effects of dioxins, which are considered among the most toxic chemicals known, got much more attention, especially regarding the 3 million U.S. soldiers who served in Vietnam. According to the Committee to Review the Health Effects in Vietnam Veterans of Exposure to Herbicides of the U.S. Institute of Medicine, there is strong evidence that dioxin causes the skin disease chloracne (defined), and three cancers: soft-tissue sarcoma, non-Hodgkin's lymphoma, and Hodgkin's disease.

The committee also found suggestive links with respiratory cancer, prostate cancer, and multiple myeloma, plus an elevated risk of spina bifida (defined) among veterans' kids.

But how did dioxin affect the millions of Vietnamese living in the 10 percent of South Vietnam that was defoliated by agent orange? Their exposures were longer and more intense, judging from tissue samples reported in "Chlorinated Dioxins..." (see bibliography). Although a lack of good scientific instruments has hampered a perfect understanding of those effects, many Vietnamese doctors believe dioxin caused widespread birth defects and cancer. Before we continue, why is dioxin research confusing?

Dioxin comes in 75 flavors, each with a unique chemical structure and toxicity. Scientists sum up exposure to the many forms with an imperfect but necessary simplification called the Dioxin Toxic Equivalent (TEQ).

Several large groups of related compounds, including the 209 PCBs and the 135 dibenzofurans, have similar effects.

These "persistent organic pollutants" can have effects in a few parts per trillion, forcing the use of delicate, expensive, and error-prone measurements.

Exposure to dioxin depended on the number of defoliations, dietary and other habits, and the rates of movement and decay of the toxins in the ecosystem and body.

Cancer is just one of many possible health effects. Other problems attributed to dioxin include immune disorders, lowered sperm counts, diabetes, reproductive and developmental damage, and endocrine disruption.

The damage may affect several generations: researchers have found cancer, spina bifida and immune problems, in offspring of people exposed to dioxin.

Can you please answer my simple questions about dioxin?