Thu. Jul 18th, 2019

Agent Orange continues to rot the soils of Vietnam 50 years later | Science

Agent Orange continues to rot the soils of Vietnam 50 years later | Science


In Vietnam, the US military maintained two wars: one against the Viet Cong and another against nature. In this, the US military used millions of liters of herbicides against the jungle where the Communists hid and the rice crops that fed them. The most used herbicide was the orange agent. A review of several studies shows that, 50 years after they stopped spraying, there are still highly toxic remains of this defoliant in soils and sediments from those entering the food chain.

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It was President Kennedy who, in the framework of a new strategy to prevent South Vietnam from collapsing under the pressure of the nationalists and communists of the North, opened the door to the greatest chemical war in history. The first herbicides reached Southeast Asia in January 1962 in an operation that would eventually be called Ranch Hand project. They used various chemical compounds, many of them developed during the world war to destroy the crops of Germans and Japanese.

Various reports from the US National Academies of Science (NAS) and government agencies such as USAID estimate that more than 80 billion liters of herbicides were used in the Vietnam War. The most used was the agent orange, a defoliant. The military did not break their heads very much when they named it: it went in barrels with a strip of that color to differentiate it from the white agent, the purple agent, the pink agent or the green agent (against broadleaf vegetation) and the blue agent (used against the rice fields).

20% of the country's forests and 10 million hectares of rice fields were sprayed at least once with doses 20 times greater than those recommended

The military logic was as follows: since the communists used the jungle as a weapon against them, it had to be neutralized. The work just published in a specialized magazine in soils shows that 20% of the jungles of Vietnam were fumigated at least once. But rice and other agricultural products were also objective. Up to 40% of the herbicides were used against crops. Although the military tried to differentiate between paddies of friends and enemies, some 10 million hectares were sprayed with blue agent, which ended with the harvest in hours. The third main use of the herbicides was to eliminate all the green around the US military bases, creating a security perimeter.

The effects of all herbicides were temporary and had to be re-sprayed every so often. For this they used from backpacks to the back to the boats to spray the banks. But it was a fleet of C-123 Provider aircraft and helicopters adapted to lift 3,800-liter tanks that led the Ranch Hand project with more than 19,000 departures between 1962 and 1971.

Agent Orange was actually a compound of equal parts of two herbicides, 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). They are hormonal regulators of growth and in a few days, weeks at most, they stop acting. But what was not known then was that Agent Orange contained a highly toxic dioxin, TCDD. To accelerate production, the temperature was raised by about 5 ° and the chlorine present in the compound at high temperatures generated between 6,000 and 10,000 parts per million (ppm) of TCDD more than under normal conditions. This carcinogenic substance is hydrophobic, so it does not dissolve in water. It is not absorbed either, but adsorbed. It stayed stuck like a limpet to the leaves that, when falling, took the dioxin to the ground and nature was in charge of propagating it.

The US Air Force carried out some 20,000 herbicide missions.
The US Air Force carried out some 20,000 herbicide missions.

"Polluting dioxin adheres to organic carbon and clay particles in soil in polluted areas and erosion processes move sediments contaminated by runoff to watercourses, rivers, ponds and lakes where anaerobic conditions protect dioxin from microbial degradation , understanding their half-life, "the soil expert and co-author of the study, the professor of the University of Illinois (USA), Ken Olson, comments in an e-mail.

Exposed to the action of the Sun, the TCDD degrades in less than three years. But, in soils protected by vegetation it takes to degrade up to 50 years and, if it is in fluvial or marine sediments, more than 100 years. "The fish and shrimp that feed on the bottom catch the contaminated sediments and dioxin builds up in their tissues, bigger fish eat these fish and the Vietnamese feed them," Olson recalls.

In one of the most recent reports reviewed by Olson and his colleague, the rural sociologist at Iowa State University, Lois Wright Morton, the official researchers analyzed the soils of the Bien Hoa air base and its surroundings. It was one of the main bases from which the herbicide missions departed and there were accumulated leftover drums when Ranch Hand was suspended. "They collected 1,300 soil samples from 76 different points of the base, nearby lands and lakes, some 550 samples had dioxin levels above the land use regulations of the Ministry of National Defense of Vietnam," says the American professor. .

Thirty years after being used in Vietnam, several aircraft still had dioxin stuck

The soils of other 16 US-base areas in both Vietnam and Thailand are contaminated and many of the Vietnamese and Americans exposed at the time developed diseases. But little is known about the impact of the agent orange that is beyond the bases. Next to Bien Hoa is the homonymous city where some 900,000 people live and fishing in rivers and lakes in the area is still prohibited.

The persistence of the TCDD is such that several of the planes that were used to spray the agent orange had to be removed from an auction and incinerated because, 30 years after returning from Vietnam, they still had the dioxin stuck. The last of the NAS reports on the effects of Agent Orange on war veterans, published last November, added new pathologies that appeared correlated with exposure to the herbicide. These reports are published every two years and they are a mandate of the US Congress.

Although it is estimated that there is still three million Vietnamese who suffer the effects of defoliants, there is no follow-up similar to that of American veterans. Of the few international studies on the persistence of TCDD in the environment, one that was published 10 years ago by Japanese and Vietnamese researchers stands out. In it, they compared the contamination levels of the soils of one of the villages sprinkled with Agent Orange with those of others that were spared. In the first, the presence of dioxin increased five times that of the second, although its concentration was lower than that observed in the Bien Hoa air base. The work also found higher levels of dioxin in breast milk, but it can not be ruled out that it is due to the most recent exposure to agricultural pesticides.

Olson believes that it would be an exaggeration and without a scientific basis to consider that all the soils sprayed 50 years ago are still contaminated today. In any case, only in Bien Hoa there are at least 414,000 cubic meters of soil that should be treated. For Olson, the definitive method to eliminate dioxin would be to incinerate them, to burn the earth.

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