WASHINGTON - The United States sprayed more than 19 million gallons of defoliant over the jungles of Vietnam, a tactic designed to kill the forests and deny cover to the enemy.
The chemical worked. Miles of vegetation withered and died.
It also exposed an estimated 3 million U.S. troops and millions more Vietnamese to dioxin, the same toxic chemical reportedly used to poison Viktor Yushchenko, a candidate in the disputed presidential election in the Ukraine.
Experts say it is unlikely that many, if any, Americans absorbed the dose Yushchenko ingested. Tests confirmed by three labs in the Netherlands and Germany showed that Yushchenko had 100,000 units of the poison per gram of blood fat.
Mark A. Brown, a toxicologist who heads the environmental agents service of the Veterans Affairs Department, said it is uncertain just how much dioxin that U.S. troops absorbed from their exposure to dioxin-contaminated Agent Orange in Vietnam.
A study years after the war ended suggested that U.S. ground forces probably had blood levels of dioxin in the range of five parts to 10 parts per trillion.
Troops handling the herbicide - named Agent Orange for the color of a stripe on 55-gallon shipping drums - may have developed blood levels of about 20 parts per trillion.
While a small dose in comparison to that given Yushchenko, it was enough, according to some studies, to cause cancer, diabetes, nerve damage and other diseases in susceptible individuals. Studies also linked the toxin to a birth defect, spina bifida, in children of Vietnam veterans.
Based on these studies, Congress instructed the department to assume that any of a long list of diseases developed by Vietnam veterans could be considered as caused by Agent Orange.
In effect, the government decided that the diseases were at least as likely to have been caused by dioxin in Agent Orange as they were to have been caused by anything else. Therefore, veterans were entitled to compensation and medical care without having to prove their disorder was caused by the herbicide.
At first, the diseases were relatively rare cancers, Brown said. Over time, new disorders were added. Today, the list includes 23 types of soft tissue cancer, four respiratory cancers, multiple myeloma, Hodgkin's disease, prostate cancer and a nerve disorder.