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the US asserted that control samples were negative. It is thus not clear
whether testing in the Minnesota laboratory included suitable blanks
(samples known not to contain trichothecenes, to control for false-posi-
tive results) or matched control samples (environmental and biomedical
samples taken from locations and people not exposed to alleged attacks,
but otherwise similar or identical). Without this information, it is not pos-
sible to evaluate the reported positive results.
Even more embarrassing, samples of yellow rain—dried yellow spots
2-6 millimeters in diameter on samples of vegetation or rocks—were
shown to be honeybee feces, consisting largely of digested pollen residue.
Many honeybees, including ones common in Southeast Asia, conduct
“purging flights” in which they periodically leave the hive en masse and
defecate collectively. The purging flights are conducted up to several hun-
dred feet, where the swarm is usually invisible and inaudible, and the re-
sult is a shower of sticky yellow or brownish droplets that can cover an
area of thousands of square meters. with yellow spots reaching densities
of several hundred per square meter. 109
Biomedical samples reported by the Minnesota laboratory as contain-
ing trichothecenes (29 out of 80 samples from alleged victims) may also
have been false positives. It is impossible to know, in the absence of com-
plete information about controls. However, even if the biomedical results
were credible, their significance would be unclear. Most positive samples
had been taken many weeks or even months after the alleged attack. An-
imal studies show that trichothecenes are cleared from the body rapidly,
and there is no reason to believe humans to be significantly different.
That toxins were claimed after such an interval should have suggested re-
cent dietary exposure as a more likely explanation. In the most thor-
oughly studied case, tissue samples from an autopsy of a Democratic
Kampuchea soldier, who died a month after an alleged attack, were re-
ported positive for trichothecenes, and this finding was offered as evi-
dence of weapons use. However, very high concentrations of another
group of mycotoxins—aflatoxins—were also reported, indicative of di-
etary mycotoxin sources. Of the five tissues analyzed, the greatest tri-
chothecene concentration was reported in stomach tissue, again suggest-
ing a dietary source. No effort was made to test the victim's food or
messmates. 110
A later serological study by a Canadian team took 270 biomedical sam-
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