Operation Ranch Hand - Defoliants

Defoliants

The herbicides used were sprayed at up to 50 times the concentration than for normal agricultural use. The most common herbicide used was Herbicide Orange, more commonly referred to as Agent Orange: a fifty-fifty mixture of two herbicides 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid). The other most common color coded Ranch Hand herbicides were Agent Blue (cacodylic acid) that was primarily used against food crops, and Agent White (picloram) which was often used when Agent Orange was not available.

The Agents used—known as the Rainbow Herbicides—their active ingredients, and years used were as follows:

• Agent Pink (60% – 40% n-butyl:isobutyl esters of 2,4,5-T) used in 1961, 1965
• Agent Green (n-butyl ester of 2,4,5-T) unclear when used, but believed to be at the same time as Pink
• Agent Purple (50% n-butyl ester of 2,4-D, 30% n-butyl ester 2,4,5-T, 20% isobutyl ester of 2,4,5-T) used from 1962–1965
• Agent Blue (cacodylic acid and sodium cacodylate) used from 1962–1971 (in powder and water solution)
• Agent White (acid weight basis: 21.2% tri-isopropanolamine salts of 2,4-D and 5.7% picloram) used from 1966–1971
• Agent Orange (50% n-butyl ester of 2,4-D and 50% n-butyl ester of 2,4,5-T) used from 1965–1970

The herbicides were procured by the U.S. military from Dow Chemical Company (all but Blue), Monsanto (Orange, Purple and Pink), Hercules Inc. (Orange and Purple), Thompson-Hayward Chemical Company (Orange and Pink), Diamond Alkali/Shamrock Company (Orange, Blue, Purple and Pink), United States Rubber Company (Orange), Thompson Chemicals Corporation (Orange and Pink), Agrisect Company (Orange and Purple), Hoffman-Taft Inc. (Orange), and the Ansul Chemical Company (Blue).

65% of the herbicides used contained 2,4,5-Trichlorophenoxyacetic acid that was found to have been contaminated with 2,3,7,8-Tetrachlorodibenzodioxin, a human carcinogen by all routes of exposure. About 12 million U.S. gallons (45,000 m3) of dioxin-contaminated herbicides were sprayed over Southeast Asia during American combat operations.

In 2005, a New Zealand government minister was quoted and widely reported as saying that Agent Orange chemicals had been supplied from New Zealand to the United States military during the conflict. Shortly after, the same minister claimed to have been mis-quoted, although this point was less widely reported. From 1962 to 1987, 2,4,5T herbicide had been manufactured at an Ivon Watkins-Dow plant in New Plymouth.