Allegations
The charges stemmed from events in Laos and Vietnam beginning in 1975, when the two governments, which were allied with and supported by the Soviet Union, retaliated against Hmong tribes, peoples who had sided with the United States during the Vietnam War. Refugees described events that they believed to be chemical warfare attacks by low-flying aircraft or helicopters; several of the reports were of a yellow, oily liquid that was dubbed "yellow rain". Those exposed claimed neurological and physical symptoms including seizures, blindness, and bleeding. Similar reports came from the Vietnamese invasion of Cambodia in 1978.
A 1997 textbook produced by the U.S. Army Medical Department asserted that over ten thousand people were killed in attacks using chemical weapons in Laos, Cambodia and Afghanistan. The descriptions of the attacks were diverse and included air-dropped canisters and sprays, booby traps, artillery shells, rockets and grenades that produced droplets of liquid, dust, powders, smoke or "insect-like" materials of a yellow, red, green, white or brown color.
Secretary of State Alexander Haig announced in September 1981 that:
- For some time now, the international community has been alarmed by continuing reports that the Soviet Union and its allies have been using lethal chemical weapons in Laos, Kampuchea, and Afghanistan. ... We have now found physical evidence from Southeast Asia which has been analyzed and found to contain abnormally high levels of three potent mycotoxins--poisonous substances not indigenous to the region and which are highly toxic to man and animals.
The Soviet Union described these accusations as a "big lie" and in turn accused the US government of using chemical weapons during the Vietnam war. The American accusations prompted a United Nations investigation in Pakistan and Thailand. This involved five doctors and scientists who interviewed alleged witnesses and collected samples that were purported to come from Afghanistan and Cambodia. However, the interviews produced conflicting testimony and the analyses of the samples were inconclusive. The UN experts also examined two refugees who claimed to be suffering from the after-effects of a chemical attack, but the refugees were instead diagnosed as having fungal skin infections. The team reported that they were unable to verify that chemical weapons had been used but noted that circumstantial evidence "suggestive of the possible use of some sort of toxic chemical substance in some instances."
The US mycotoxin analyses were reported in the scientific literature in 1983 and 1984 and reported small amounts of mycotoxins called trichothecenes, ranging from the parts per million to traces in the parts per billion range. The lowest possible limit of detection in these mycotoxin analyses is in the parts per billion range. However, several inconsistencies in these reports caused a "prolonged, and at times acrimonious, debate on the validity of the analyses". A 2003 medical review notes that this debate may have been exacerbated since "Although analytical methods were in their infancy during the controversy, they were still sensitive enough to pick up low levels of environmental trichothecene contamination.".
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