For the uninitiated: "Operation Ranch Hand" was a military program during the Vietnam War aimed at destroying the forests and crop fields of Vietnam to cripple the country and discourage the guerrilla warfare that was kicking the US Army's ass. There were six defoliants used as a part of the program: Agents Pink, White, Blue, Purple, Green, and the infamous Orange. Most people have heard of Agent Orange, but not the others. I'd like to know why that is. Was Agent Orange particularly destructive? The most widely used? Or is it just random chance that Agent Orange is the posterboy for deforestation during the Vietnam War?
There are two big reasons for this. The first is simply that it was the most widely used. Over 45.5 million litres of it were sprayed over Vietnam between 1965 and 1970. A further 3.5 million litres of Agent Orange II, a slight chemical variation, were shipped, although it is not known how much of this was sprayed. The other herbicides were not sprayed in comparable amounts. Agent White, the second most prolific of the agents, had only 20.5 million litres sprayed while Agent Blue had 4.7 million litres sprayed or scattered in powder form. Nearly 2 million litres of Agent Purple were sprayed, but Agents Pink and Green didn't even break the 100,000 litres barrier. Agent Orange was also more heavily sprayed in South Vietnam than other herbicides, which were aimed at crops and logistical routes. This prolific use meant that if US troops used herbicides, or observed herbicide use, it was likely Agent Orange.
The second reason is chemical contamination of Agent Orange. Pure Agent Orange is a mixture of two herbicidal chemicals, 2,4,5-T and 2,4-D (They have long and complicated systematic names I'll not copy here). However it is almost impossible to obtain pure Agent Orange. The chemical process that produces 2,4,5-T also produces a chemical called TCDD, which contaminated Agent Orange. TCDD is carcinogenic, and remains in the environment for a long time after being introduced to it. Both American troops and Vietnamese civilians exposed to Agent Orange have developed health problems as a result. In Vietnam, Agent Orange exposure is still a significant public health issue, as it affects foetal development, and can lead to birth defects and disabilities. The diplomatic issues between the US and Vietnam this has caused, as well as legal action by veterans against the companies that produced the herbicide, have ensured that Agent Orange has cemented its place in the public eye.
Source:
Stellman, J. et al, The extent and patterns of usage of Agent Orange and other herbicides in Vietnam, Nature, Vol 422, p681, available at http://stellman.com/jms/Stellman1537.pdf