The toxic legacy of Agent Blue

Agent Orange’s use during the Vietnam War is well known. But the use of another herbicide during the war, known as Agent Blue, has remained largely unexplored. But one US researcher, who is a Vietnam Era veteran, is on a mission to raise awareness of this other so-called ‘rainbow’ arsenic-based herbicide that was used by the US military and its allies during the Vietnam War and the Second Indochina War.

Recently published research by Ken Olson, a soil scientist at the University of Illinois Urbana–Champaign, reports that arsenic’s present-day persistence in the Vietnam Mekong Delta groundwater is in part due to the spraying of Agent Blue more than five decades ago.

Agent Blue was a mixture of the organoarsenic compounds cacodylic acid (pictured) and sodium cacodylate. When it biodegrades arsenic is released. In contrast, Agent Orange was made up of equal amounts of two common agricultural herbicides – 2,4-dichlorophenoxyacetic acid (2,4-D), which is still used today, and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), which contained the contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD).

The US government stopped manufacturing 2,4,5-T in 1985 after it was found to cause cancer in animals. Dioxins are highly toxic and can cause reproductive and developmental problems, damage the immune system, disrupt the endocrine system and cause cancer, according to the World Health Organization (WHO). The US Department of Veterans Affairs (VA) has released a long list of diseases associated with Agent Orange exposure, mostly related to TCDD.

As of January 2022, the US government had spent $400 million (£314 million) to address the environmental and health effects of Agent Orange, including $112 million on environmental remediation at Danang airport, alongside Vietnam’s Ministry of Defense, and $183 million for a cleanup project begun in 2020 at Bien Hoa, which is the largest remaining Agent Orange hot spot in Vietnam, according to the US Institute of Peace.

Crop destruction

Olson, who served in the US Army from 1969 to 1973, first learned about Agent Blue during a 2016 trip to Ho Chi Minh City and the Củ Chi tunnels, used by the Viet Cong during the war. ‘When I was researching why the soil tunnels were so resilient, I noticed that the trees were really slender, young and not doing well,’ he recalls. ‘It was supposed to be the garden spot of Vietnam, so I started to find out why – the reason the vegetation was so young, slender and not doing well was because … the area had been sprayed with Agent Orange and Agent Blue during the Vietnam War to kill both the broad and narrow leaf vegetation and expose the openings to the soil tunnels.’ It took decades for the natural vegetation to re-establish itself, Olson says.

The US Air Force did most of the Agent Orange spraying with the goal of defoliating the jungle canopy to improve visibility. South Vietnam’s military – which was an ally of the US – focused on spraying Agent Blue for food denial as part of a ‘hamlet strategy’. Hamlets were villages that the South Vietnamese encouraged rural residents to move to so that the population could be controlled, protected and kept away from their rice fields so they wouldn’t be able to grow rice for the enemy or themselves, according to Olson.

A significant amount of Agent Blue was sprayed during the three or four years before the official start of the American Vietnam War in 1965. The US Air Force kept records on the spraying of Agent Orange in South Vietnam, but there is very little documentation about Agent Blue being sprayed in the Mekong Delta.

What records that exist indicate that 42% of the herbicide used in southern Vietnam before 1965 was Agent Blue, according to Olson. He says Ansul Chemical manufactured almost all the Agent Blue while Dow Chemical and Monsanto made most of the Agent Orange used during the Vietnam War and the Second Indochina War before it. These were two of several ‘rainbow’ herbicides used during the Vietnam War, named after the colour of the stripes on the barrels used to transport them.

‘If the US didn’t manufacture and transport these herbicides there would have been no herbicide use in South Vietnam – we then trained the Republic of Vietnam Army on how to use their helicopters, their spray packs, and many other types of sprayers to apply Agent Blue to the food crops and mangrove forests,’ Olson states. ‘The United States and the Republic of Vietnam were supposed to let international bodies know every time weapons, including chemical weapons, were brought into South Vietnam during the Vietnam War.’

Because the Geneva Conventions prohibit starving a civilian population during war, if the US military or government were involved in such operations that would have been ‘a big political issue with the United Nations and the World Court’, explains Bryan Higgins, an emeritus geography professor at the State University of New York, who is also a Vietnam veteran and is familiar with Olson’s research on Agent Orange and Blue.

Higgins served in the Army during the Vietnam War and in the US Army Chemical Corps, but the first time that he heard about Agent Blue was a few years ago when he read Olson’s previous research. Olson says he has published eight papers on Agent Blue since 2020.

Agent Blue was applied to kill narrow-leaf plants, including grasses, rice plants and bamboo, while Agent Orange was used to kill broad-leaf jungle plants. ‘Arsenic can attach to the organic matter, or the clay particles, and then they can be substituted by other cations and released into soil water solution. Since arsenic is water soluble it can leach from the root zone and into the groundwater,’ Olson explains.

Higgins cites independent research that estimates between approximately 30 and 50% of the drinking water in the Mekong Delta has arsenic above the WHO’s recommended limit of 10ppm. Tests in the Mekong Delta have shown that levels of arsenic can exceed the previous 50ppm standard for drinking water, according to Olson.

Diagnosing health problems caused by arsenic in drinking water is challenging because symptoms can be non-specific, vary between individuals and often take years to manifest, Higgins says. In addition, he says problems caused by arsenic can also be easily confused with other health conditions and the specific form of arsenic present in water can influence its toxicity.

The various stages of chronic arsenic poisoning are characterised by skin pigmentation, keratosis, skin cancer, effects on the cardiovascular and nervous system, as well as increased risk of lung, kidney and bladder cancer.

Arsenic recirculating

Exactly how much of the arsenic in the water in the Mekong Delta is natural or from Agent Blue is difficult to quantify. The Red River Valley near Hanoi, however, was never sprayed with Agent Blue, but it still has high arsenic levels resulting from natural and other anthropic sources. But the application of Agent Blue containing 1000 tonnes of arsenic to the South Vietnam rice paddies, soils and groundwater that was already arsenic-rich would have increased levels further.

One thing that concerns Olson is the 700,000 tube-wells that were installed in the Mekong Delta, in Cambodia and Vietnam, between 1975 and the present day. These bring up groundwater that is rich in arsenic – both natural and anthropic. They were installed to provide fresh water for shrimp ponds, rice paddies and drinking water for 20 million Vietnamese.

He concludes that most of the anthropic arsenic remains in south Vietnam’s environment to this day. ‘Surface runoff waters, with water-soluble cacodylic acid and arsenic components … flowed into the South China Sea or the Gulf of Thailand,’ Olson’s paper explains. ‘However, most of the Agent Blue was utilised to destroy rice crops and arsenic … [and] has remained in the rice paddy root zone soils and/or leached into the groundwater only to be returned to the soil surface by tube wells, for urban and agricultural use.’0

He is also worried about the bioaccumulation of arsenic from the many millions of people who have died and were buried in the Mekong Delta since the war ended in 1975. ‘If their bodies were high in arsenic and you bury them, what do you think is going to happen to the arsenic in their bodies?’ Olson asks. ‘When the bodies decompose the water-soluble arsenic goes back into the soil … and leaches back into the groundwater.’