Review and Analysis: Agent Blue, the Arsenic Based Herbicide, Used during the Second Indochina and Vietnam Wars to Destroy the Rice Crop

The Republic of Vietnam and the United States (US) militaries began destroying food crops (rice) in November of 1962, primarily via aerial applications in the Mekong Delta and Central Highlands of South Vietnam. Spraying of Agent Blue on mangrove forests and rice paddies just before rice harvest time resulted in the destruction of the standing crop and rendered the land contaminated with arsenic (As). Agent Blue (cacodylic acid, C2H7AsO2) was the most effective of all the Rainbow herbicides in killing rice and grasses. Manufacturing of cacodylic acid began in the late 1950s in the US at the Ansul Company chemical plant in Marinette, Wisconsin and Menominee, Michigan. During the Vietnam War, ocean-going ships were loaded with 208-liter Agent Blue barrels and shipped via the St. Lawrence Seaway to the coast of South Vietnam. Arsenic (As) is a naturally occurring element that is found throughout SE Asia deltas, including the Mekong Delta. Arsenic-contaminated rice and groundwater are growing concerns as neither naturally occurring arsenic nor anthropic arsenic has a half-life and cannot be destroyed. Water-soluble arsenic primarily leaches into the soil root zone and the groundwater. The As in the contaminated rice paddy soil, sediment and water are taken up by fish, shrimp or crop vegetation and trace amounts can end up in the food supply (rice grain) or be bioaccumulated by the fish, shrimp and birds, which, when eaten, are bioaccumulated in the Vietnamese people. This research reinforces the urgent need for mitigation of arsenic exposure from drinking water and food grown in flooded rice production systems. The uptake of trace amounts of As in rice is indeed a critical food security and human health issue and requires mitigation.