Agent Orange — so-called because of the colour of the stripes on the drums in which it was imported — is a defoliant which was extensively used during the Vietnam War to clear jungles.

It contained one of the most virulent poisons known to man, a strain of dioxin called TCCD.

It killed the rainforest before spreading to the food chain and, according to some, leading to a proliferation of birth deformities.

Vietnamese Red Cross records trace birth defects in 150,000 “Agent Orange babies” back to their parents’ exposure to the chemical during the war or the consumption of dioxin contaminated food since the war ended in 1975.

It has also been linked to a string of health problems among veterans, including chronic lymphocytic leukaemia, soft-tissue sarcoma, non-Hodgkin’s lymphoma, Hodgkin’s disease, Type Two diabetes, prostate cancer and chloracne.

Dr. Mark Brown, director of environmental agency services at the US Department of Veterans Affairs, has studied its effects.

He said former US Air Force serviceman Ronald Slater, who claims to have been involved in its disposal at Kindley Air Force Base during the 1960s, could have suffered health difficulties as a result.

Mr. Slater currently has Type Two diabetes, a large growth on his kidney and a small tumour on his arm.

“If a Vietnam veteran was diagnosed with Type Two diabetes they would have the benefit of the presumption that it was caused by exposure to Agent Orange,” said Dr. Brown.

“There’s no evidence today to tie any form of skin cancer to Agent Orange exposure, but new information can change that at any time.”

Dr. Brown said of toxic smoke sent over St. David’s when the substance was burned: “That could be dangerous. You sure couldn’t get away with that type of disposal today. Dioxins from incineration has been a big concern.”

However, he said it would be practically impossible to test the effects on residents’ health because the source of dioxins in the blood cannot be proved, especially if they have been there many years.

“There’s no real measurement now to verify what happened. When veterans ask about testing like that we discourage them. It can be very expensive and you can’t prove anything much from it.”

On the condition of land at the base 40 years later, he said: “Once there’s a question about any kind of site like that, you have to look at historical records, or do some soil sampling. If the site is derelict, that’s saying something.

“The larger concern would be the dioxin. Herbicide may have degenerated by now, but dioxins compared to other chemicals are very stable and do not degrade so easily. You could have soil contamination with dioxins.”