Increased estimates of Agent Orange levels sprayed in Vietnam 

A range of herbicides, including Agent Orange, were sprayed between 1961 and 1971 by United States forces during the Vietnam War at much heavier levels than previously thought, according to a recent report in the journal Nature.

C-123 spraying defoliant in Vietnam. Photo EW Pfeiffer

    Herbicide mixtures, nicknamed by the coloured identification band painted on their 208-litre storage barrels, were used by US forces to defoliate forests and mangroves, to clear perimeters of military installations and to destroy ‘unfriendly’ crops as a tactic for decreasing enemy food supplies. The best-known mixture was Agent Orange; others included Agent Pink, Green and Purple. About 65% of the herbicides contained the herbicide 2,4,5-T which was contaminated with varying degrees of TCDD dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin). From the beginning the military herbicide applications in Vietnam became a matter of controversy. By April 1970, 2,4,5-T was banned from most US domestic uses, on the basis of evidence of its teratogenicity (causing birth defects).
    In 1974, the US National Academy of Sciences published estimates of the extent and distribution of herbicides sprayed. Research using a more complete data set published in Nature has revised these earlier estimates. The spray inventory is expanded by more than seven million litres, in particular with heavily dioxin-contaminated herbicides. Estimates for the amount of dioxin sprayed are almost doubled. Census data analysed by the researchers reveal that millions of Vietnamese were likely to have been sprayed upon directly. Their identification of specific military herbicide targets has led to more coherent understanding of the spraying. Common errors in earlier interpretations of the spray data have also been unearthed.
    A report produced by the US Institute of Medicine states that the new work shows that it is feasible to perform large-scale epidemiological studies of the links between the herbicide spraying and the health of the Vietnamese population and US veteran soldiers. The Institute calls on the US government to fund such studies. (DB)

Jeanne Stellman, Steven Stellman, Richard Christian, Tracy Weber and Carrie Tomasallo, The extent and patterns of usage of Agent Orange and other herbicides in Vietnam, Nature, April 2003, 422, 17 681-687.

[This article first appeared in Pesticides News No. 60, June 2003, page 22]