"Operation Ranch Hand" has an almost innocuous ring to it, but nothing could be further from the truth. From 1961 to 1971, under its umbrella, southern Vietnam became the dumping ground for almost 20 million gallons of herbicides and defoliants. Intended to kill enemy crops and decimate jungles in which the Viet Cong and North Vietnam Army (NVA) sought cover, the toxins were sprayed over some 16 percent of the country.

The most widely spread among them was the dioxin, Agent Orange. As Air Force pilots dropped it over swathes of foliage – at rates of up to 14 km in less than five minutes - they planted a problem with roots that have no immediately visible end: the health impact of exposure to their toxic cargo.

In the years following the spraying sorties, as both veterans and the Vietnamese population began to record increased rates of cancer, digestive, respiratory and skin disorders, as well as miscarriage and birth defects, questions about a correlation inevitably emerged.

Subsequent scrutiny of the specification of Agent Orange failed to produce evidence of anything that seemed a likely cause for the catalogue of symptoms. But further analysis of production samples showed contaminants to be a plausible source of the ill health. The dangerous compound was, in fact, a by-product.

More at work than Agent Orange?

As second, and now third generation children continue to be born with a high incidence of disability, including down's syndrome, cerebral palsy and extreme facial disfigurement, the questions regarding its potency and reach remain on the table. And are very hard to answer.

Jeanne Mager Stellman, Columbia University expert on the use of Agent Orange and other herbicides during the Vietnam War, has spent decades campaigning for the recognition of the health implications of dioxins - one of the most poisonous substances known - but says a lack of comprehensive research into the subject makes pinpointing their precise nature notoriously difficult.

"Despite all the certainty that everyone attaches to the diseases and the birth defects people are seeing, we really haven't sorted out exactly what the long-range impacts are," she told DW.

"Agent Orange raises a flag," Stellman continued, "but the other herbicides used were not benign." She cites Agent Blue as arsenical and an inhibitor to folic acid, which pregnant women are advised to take to ensure good fetal development.

Richard Guthrie, analyst on chemical and biological warfare, agrees it is important not to forget the possible effects of Agent Blue and Agent White, both of which were sprayed from 1966 onwards, but says he is "satisfied beyond reasonable doubt" that Agent Orange has had a lasting effect on the health of members of the Vietnamese population.

Equally, he describes as "very plausible" the suggestion that the dioxin is the direct cause of birth defects in children being born in the country today.

Divided opinions on the ground

But that is not the united view in Vietnam itself. Nick Keegan, Director of Business Development at the Kianh Foundation, which works with special needs children in the district of Dien Ban, told DW that even those whose children are born with disabilities attribute them to different causes.

"We have dealt with families who feel it is directly related to Agent Orange, but some, for cultural and spiritual reasons, think they have just been unlucky."

Of the 200,000 strong population in Dien Ban, more than 1,000 children are registered disabled. Keegan says there is no conclusive proof of a link between that figure and the dioxin, but admits that evidence of heavy bombing of the area during the war makes him stop and think.

"To have 1,000 children plus with disabilities is quite a high number, so you start to question the contributing factors," he said.

Inheritable changes to DNA?

The World Health Oganization (WHO) says once dioxins enter the body, "they last a long time because of their chemical stability and their ability to be absorbed by fat tissue." It gives them an estimated half life, which is the time needed to reduce concentration by half, of between 7 to 11 years.

Stellman, who says this gradual disappearence makes research all the more difficult, insists the real scientific question about dioxin is whether it exerts epigenetic effects -- changes in DNA and possibly RNA -- that are not mutations but other changes to the chemical structure, and whether these changes can be passed on for more than one generation.

"In the case of Vietnam, how much of this epigenetic change travels through the paternal line and is heritable?"

When trying to understand the pattern of birth defects, she also says it is essential to look at other factors - such as starvation, stress, parasitic disease, and the contemporary use of pesticides - where links have already been established.

No study in sight

The only way to better understand exactly what is going on in Vietnam and the extent to which Agent Orange is a factor in children's disabilities, is to conduct expansive research. That would not only require significant investment, but political engagement that Stellman regards as lacking.

"There is willful blocking by some elements of the US government," she said, adding there are also "potent forces" against a comprehensive investigation in Vietnam, which as an exporter of catfish and other food items doesn't want to give the world the idea that it is polluted with dioxin.

Against that backdrop, she questions whether such a study will ever happen. "The longer we wait, the more difficult it becomes," she said. "While everyone is arguing about the number of angels on the pinhead - no one is seriously addressing the underlying issue itself. It is all a large human tragedy."