In September 1981, Secretary of State Alexander Haig accused "the Soviet Union and its allies in Vietnam, Laos, Kampuchea and Afghanistan" of employing a new breed of chemical warfare agent--mycotoxins, or "yellow rain." The charge was a serious one: the violation of two major treaties banning such warfare. Yet the evidence Haig and his successor, George Shultz, have offered to substantiate it does not stand up to close scrutiny. Not only is the evidence flawed and inconclusive; it also belies scientific fact, as well as military and political reality in Southeast Asia.
Reports of yellow-rain attacks first surfaced in 1977 after Hmong hill people who had fled from Laos into Thailand, some of whom were carrying on guerrilla actions, told journalists that Laotian Communists, the Pathet Lao, were using a toxic gas against them. The methods of delivery were variously characterized as rockets, aerial spray or bombs. The refugees said the substance emitted produced eye irritation, dizziness, bloody coughing, vomiting and diarrhea. Many deaths were reported. Descriptions of the substance differed. It was generally described as yellow, though some witnesses said it was red, blue, green or white. Some refugees recalled seeing a fine mist, others spoke of yellow raindrops, and still others said it took the form of particles about the size of a grain of rice and sounded like rain when it fell on their roofs.
The wide range of reported agents and symptoms baffled chemical warfare experts, since they did not correspond to any known chemical. The State Department, however, was not deterred by the inconclusiveness of the evidence.
In a speech in West Berlin, Secretary Haig claimed that the United States possessed "physical evidence from Southeast Asia" containing "abnormally high levels of three potent mycotoxins--poisonous substances not indigenous to the region." The physical evidence he mentioned consisted of two fragments of a single leaf weighing 0.4 grams. The mycotoxins were present in minuscule quanities.
Despite two State Department white papers and numerous statements by officials aimed at swaying public opinion in this country and abroad, the allegations regarding the use of yellow rain remain unproved. Indeed, after a sustained assault from scientists, journalists and other investigators, the evidence seems as fragile as Secretary Haig's leaf sample.
The U.S. government's evidence is of three kinds: scientific data procured in Southeast Asia, consisting of organic material allegedly contaminated by mycotoxins, as well as blood and tissue specimens from people allegedly exposed to them; refugee reports; and information from secret intelligence sources. Since much doubt has been cast on evidence in the first two categories, the State Department has come to rely increasingly on that in the third, which is not subject to public scrutiny. Scientific Evidence
Although the department claims that the United States obtained more than 350 samples from sites of alleged chemical attack, independent scientists have often been thwarted in their attempts to examine them. For months after the Haig speech, the department refused to divulge the source of the samples or the level of toxins found in them. The truth is that in only five of the government's environmental samples--comprising leaf fragements, scrapings from rocks and pond water--was the presence of toxins indicated by laboratory tests, and the accuracy of those tests has been questioned. Those five samples--the State Department's "smoking gun" of a massive Soviet chemical warfare campaign--have a combined weight of less than a large aspirin, 500 milligrams.
The tests were conducted by a single facility, a private laboraptory run by Chester Mirocha of the University of Minnesota. No one has been able to confirm them. The sample in which Mirocha reported finding the highest level of toxins was analyzed a year later by the Army's Chemical Research and Development Center at the Aberdeen Proving Grounds in Maryland, and no toxins were detected. …