The BBC's Robin Denselow reports on the chemical legacy of the Vietnam war

The Vietnam war has been over for 23 years, and the nation is now at peace. Areas once famous for brutal high-tech battles are today a tourist destination.

However, one weapon that was used by the Americans is still lethal. New research shows it is still creating environmental chaos, poisoning the food chain and causing serious concern over its effects on human health.

11m gallons of Agent Orange were poured over South Vietnam

Dioxin was found in Agent Orange, one of the herbicides sprayed from giant C 123 cargo planes to destroy the forests and fields that gave cover to the VietCong fighters.

In total, 11m gallons were poured over South Vietnam between 1961 and 71, over 10% of the country - 14% of the area targeted was farmland.

Agent Orange was a cocktail of chemicals that were stored in drums marked with an orange band. It was contaminated with TCDD, the most poisonous dioxin, known to cause cancer and other diseases.

Remains of old trees stand on bare hillsides

The Vietnamese have long claimed that Agent Orange - and the dioxin it contained - has seriously damaged the health of those living in the areas where it was used.

The US says there is no proof and that all this is just propaganda. And yet, in the States, Vietnam veterans who handled Agent Orange can claim compensation for a whole range of other diseases recognised as being associated with dioxin.

They range from skin diseases such as Chloracne, through to conditions that affect the nerves and lymphatic glands as well as a range of cancers - of the lung, larynx and prostate.

Vietnamese scientists studying dioxin levels have been hampered by lack of resources.

Proof of contamination

But an independent Canadian team, Hatfield Consultants, have studied the levels of dioxin that still exist in one area that was heavily sprayed and found disturbing results.

Dioxins have found their way into the food chain

Team member David Levi said: "We should not think of this as a historical problem. This is a present-day contamination issue.

"The dioxins that are present are entering the food chain today, and also being taken up by the people living in the area today."

The lasting legacy of the Agent Orange drop has even staggered some war veterans.

Chuck Starey, of the Vietnam Veterans of America Foundation, said: "Any sprays, poisons that are sprayed from the airplanes and helicopters you have to have some concerns about, but I never imagined it would be as devastating as apparently it has been over the years."

Vietnamese scientists have been shocked by the Canadian team's findings. There is talk of evacuating contaminated areas - a quarter of a century after the spraying stopped.

High dioxin levels were found in the blood of local children

Dr Nguyen Viet Nhan, who has studied child health in areas where Agent Orange was used, is aware that dioxin is known to cause cancer and brain damage in children, but argues that it is also causing the large amount of deformities found in the sprayed areas.

Dr Nguyen's pilot study compared the health of children in one area that had been sprayed with those in another that had not.

Children in areas that had been sprayed were:

• More than three times as likely to have cleft palates
• More than three times as likely to be mentally retarded
• More than three times as likely to have extra fingers or toes
• Nearly eight times as likely to suffer hernias

The Vietnamese government claims there are so many children born with problems caused by dioxin that they have had to set up a network of 11 special schools - so called 'peace villages' - across the country.

Unexploded bombs

Agent Orange is not the only still-remaining lethal legacy of the American war. Areas such as Quang Tri Province, north of the Aloui valley, are still littered with unexpoded bombs. In total, it is estimated that six million are still scattered across Vietnam.

Detonating unexploded bombs in areas where dioxin is in the soil is likely to re-activate the chemical. This means demining must be followed by decontamination if land is to be made fully safe.

In addition to the Aluoi Valley it is thought there could be at least nine other heavily contaminated 'hot spots'. The cost of a clear-up operation could be enormous.