Initial concerns about the effects of Agent Orange in Vietnam focused on the herbicide's effects on ecology. In the autumn of 1969, however, the emphasis shifted to health effects. Reports in the Saigon press at that time claimed that an unusually high incidence of birth defects might be related to the herbicide-spraying program. These reports were married with experimental evidence from animal studies showing that one component of Agent Orange (a one-to-one mixture of two herbicides: 2,4-D and 2,4,5-T) caused birth defects in two species of mice and one strain of rat. The animal studies were performed by the Bio netics Research Laboratory on behalf of the United States National Cancer Institute, and they implicated 2,4,5-T as a teratogen (cause of birth deformities). In the face of this evidence, it was no longer possible for the US Department of Defense to claim that there would be no “seriously adverse consequences” of the military use of herbicides in Vietnam; the study signaled the demise of the herbicide-spraying program.
Defoliants had been sprayed over areas that were supposedly sparsely populated in concentrations of 3 gallons per acre – ten times higher than the concentration recommended for users of 2,4,5-T in the US. In addition, occasional intense enemy groundfire would force aircrews to dump 1,000 gallons of herbicides in 30 seconds, rather than the usual 3 to 4 minutes, resulting in even higher concentrations.
Residual stocks of Agent Orange, stored on Johnson Island in the Pacific, were later analyzed for the presence of contaminants.