DEPARTMENT OF BIOCHEMISTRY AND MOLECULAR BIOLOGY
HARVARD UNIVERSITY

MEMORANDUM
TO: PILE NW
RE: INCIDENT AT BAN SA TONG

DATE: 25 APRIL 1986

A) The event. On Friday 19 February 1982, residents of the
village of Ban Sa Tong in Thailand, about 10 kilometers from the
Cambodian border, reported an unusual event. A village health
officer, according to an interview with a UN investigating team,
saw a plane circling Ban Sa Tong at 9:00-9:30 in the morning and
at about 10:00 was told by villagers that deposits of a yellow
material had been noted. He collected samples of it and radioed a
report to the authorities. The Thai Border Patrol Police arrived
to investigate. They too collected samples and ordered the
villagers not to drink the water. Later in the day, Provincial
health authorities came to investigate. The District Officer of
Pong Nam Ron district, in which Ban Sa Tong is located, said that
the plane was white and single-engined and that the two adjacent
villages of Ban Sa Tong and Ban Sub Tha Mau both had deposits of
the yellow material, with the greater amount at Ban Sa Tong. By
coincidence, a television crew from Bangkok channel seven came
through both villages on Feb 19 and filmed the deposits. These
appear in the film as yellow spots, in agreement with
descriptions by local residents (UN General Assembly Document
A/37/259, 1 Dec 1982).

According to the Bangkok Post of 21 Feb 82, the yellow deposits
resembled "small drops of candle wax". The article also stated
that samples were collected by Border Patrol Police and by Thai
Marine units, both of whom warned villagers not to drink the
water until tests were done, and by U.S. Embassy officials.
According to the Bangkok "Nation Review" of 21 Feb, the
Provincial Governor came to inspect the area on the 20th and
announced that preliminary tests showed the substance to contain
"bio-toxin". But the Bangkok Post of 24 Feb reported that on the
previous day the Minister of Health said that mice injected with
the yellow material showed no symptoms.

On 5 March, two weeks after the incident, a medical team from
Canadian National Defense Headquarters in Ottawa, sent to
investigate allegations of chemical warfare in Southeast Asia,
arrived in Ban Sa Tong ( "An Epidemiological Investigation of
Alleged CW/BW incidents in SE Asia", Surgeon General Branch,
National Defense Headquarters, Ottawa, 11 August 1982).

According to the Canadian report, "On 19 Feb 82, at 0930 hrs, a
single-engine unmarked plane circled the Thai village of Ban Sa
Tong located 20 kms north of Pong Nam Ron and 10 kms west of the
Cambodian border. After five or six circuits it dropped a yellow
2.

substance from a height of about 5,000 feet. Six houses in the
south-east sector of the village were liberally covered with a
yellow powder which stuck to roofs, walls, foliage and ground."

The Canadian team also reports the village of Ban Sub Tha Mau to
have experienced depositions of yellow spots on numerous
occasions in February and March, with fresh deposits occurring
even during the time the team was investigating. The Canadian
report concludes that "The yellow substance is being blown over
the border from Cambodia where it is being used in and around
Pailin by Vietnamese forces." The distance to Pailin is given as
13 kilometers.

B) Medical investigation. The Canadian team noted that there was
no significant increase in visits to the village clinic following
the incident of 19 Feb. Daily clinic visits averaged about twenty
per day before and after the incident and also during the same
period in 1981. The team noted that "The only significant symptom
in patients examined at the clinic for the period 19 Feb-28 Feb
inclusive when compared with the same period in 1981 was upper
respiratory infection/common cold."

On March 5,6,12 and 14 the Canadian team interviewed a total of
33 residents of Ban Sa Tong. The interview form they employed
asks respondents where they were and what they were doing “at
the time of the attack". The interview form then asks questions
regarding symptoms experienced “upon exposure".

The symptoms most often reported in the Canadian interviews at
Ban Sa Tong are, in order of decreasing frequency, cough (17
persons), headache, dizziness, dry throat, loss of appetite,
fatigue, weakness, and itching (10 persons). The only residual
effects actually seen by the Canadian team ascribed to the yellow
material were coughing and fear. According to their report,
",..grandmothers were extremely apprehensive".

On 14 March, the Canadians interviewed 57 residents of Ban Mai,
chosen as a control village because it reported no yellow rain
incidents. Ban Mai is 8-9 kilometers west of Ban Sa Tong. Since
there was no presumption of chemical attack in Ban Mai,
interviews there could not have asked about the effects of
exposure to presumed toxic materials. The Canadian report does
not specify how this problem was dealt with in the control
interviews. Except for headache (22 persons), none of the
symptoms cited by villagers in Ban Sa Tong were cited by more
than a few of the persons in the control group.
3.

The conclusion of the Canadian report regarding the incident at
Ban Sa Tong is that " The team could not identify any possible
causal mechanisms common to all those affected except the yellow
substance dropped on the village at 0930 hours, 19 Feb 82". They
also concluded the yellow substance was responsible for health
effects cited by villagers in Ban Sub Tha Mau, 3 kilometers east
of Ban Sa Tong, where they conducted 23 interviews, with results
generally similar to those in Ban Sa Tong.

A completely different explanation of the health effects reported
by villagers was given by a Ban Sa Tong health officer appearing
on a BBC "Horizon" television documentary (# H 71202). According
to the BBC translation, he stated that a few days after the
incident, villagers reported "A few slight headaches and fevers,
common complaints". The village health officer considered the
affair a "mild hysteria" and said that "It was probably some kind
of neurosis...because they were already afraid."

The Canadian team do not discuss the liklihood that affirmative
responses to interview questions about illness following
appearance of the yellow substance resulted not from any toxicity
but rather from common maladies and from psychological and
psychosomatic effects of the highly unusual attention and
apprehension provoked by the suspicion of chemical warfare
attack. This would certainly focus the attention of those being
interviewed on common symptoms which they might otherwise
dismiss.

CONCLUSION, There were no significant clinical manifestations.
The recollection of mild effects by villagers in interviews is
unremarkable, considering the likely effects of psychological and
psychosomatic factors in a population apprehensive that it may
have been exposed to chemical attack. There is no significant
evidence for any exposure to toxic substances.

The yellow material, All available photographs and samples of
the yellow deposits from Ban Sa Tong and Ban Sub Tha Mao show
them to be indistinguishable in size, color and general
appearance from the feces of wild honeybees from the same region.
Microscopic examination of the material by Thai, Canadian, US and
French laboratories has without exception shown it to be mainly
pollen.

Photomicrographs of the pollen are published in a 1982 Thai
scientific report ("Examination of the Yellow Spot Samples
Collected from Thailand Border Close to Cambodia", Sukroongreung,
et al., Siriraj Hospital Gazette 34, 643-647) and in a recent
Canadian report (Final Summary Report on the Investigation of
"Yellow Rain Samples from Southeast Asia", Defense Research
4.

Establishment Ottawa, February, 1986). The pollen is diverse,
with several different morphotypes particularly abundant. These
appear to be the same types found in samples of known honeybee
feces from Thailand.

Showers of feces from wild honeybees flying too high to be seen
or heard are now known to occur in the region. They may last
several minutes, covering areas up to an acre or more with
hundreds of thousands of yellow fecal spots. The distribution of
spots on leaves collected at Ban Sa Tong suggests that there were
10-100 spots per meter on exposed surfaces in the affected area.
This is well within the range observed for honeybee fecal showers
in China and Thailand (Zhong Zhangying et al. (1977), Keksue
Tongbao 22, 409-412; Seeley et al. (1985) Scientific American
Sept., 128-137. Questioning of numerous Thai villagers has shown
that they are generally unable to identify spots of bee feces
shown to them on vegetation.

The limited area of deposition of yellow spots in Ban Sa Tong
(six adjacent houses) is quite consistent with a shower of bee
feces. However, being ignorant of the defecation behavior of
Southeast Asian honeybees, the Canadian team hypothesized that

" ..a container had been used that would drop to a relatively low
height where it would explode, releasing the substance." The
Canadian team was correct to believe that a spray released from
high altitude cannot be targeted on a limited area. But they
failed to address the inconsistency of their scenario of low-
altitude release for targeting effectiveness with their
conclusion that yellow spots were carried several kilometers from
Cambodia to Thailand by the wind. Low altitude release is
irreconcilable with any significant degree of long distance wind
dispersal. In fact, even if released from 5,000 feet, drops the
size of those observed could not travel the requisite distance
without there being wind speeds of hundreds of kilometers per
hour.

According to the 1986 Canadian report, some samples of the yellow
spots cut out from leaves contained minute amounts of
trichothecene mycotoxins near the limit of reliable detection

but these were judged "...comparable to the levels reported
worldwide for natural occurrences of trichothecenes on stored
cereal..."

CONCLUSION.There is no basis for concluding that the yellow
material deposited on Ban Sa Tong and Ban Sub Tha Mau was
anything other than honeybee feces.

In its 1982 report, the Canadian team noted
that “During a subsequent visit to Ban Sa Tong, one of the
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villagers produced a plastic bag which he claimed had fallen from
the plane at the same time as the yellow rain. This bag was
forwarded to Canada although the team was skeptical that it was
the real container.”

The February 1986 report of the Canadian Defense Research
Establishment Ottawa cited above shows photographs of the bag in
question. In the photographs it appears partly crumpled up and
torn but otherwise largely intact. It resembles the thin
polyethylene bags sold for kitchen use and might be 6 to 12
inches on a side if flattened out. Some brown material and a few
small yellowish spots are visible. The 1986 Canadian report
states that "The bag was burst and had yellow spots on the
outside surface."

Sections of the bag were cut out and extracted with solvents.
After centrifugation to remove debris, the solvent was
evaporated, giving a solid residue. The residue from one section
of the bag is reported by one laboratory to have a concentration
of trichothecenes T-2 and HT-2 of 85-230 and 52-117 parts per
million, respectively. Residue from another section of the bag,
analysed by a different laboratory, using a more discriminating
analytical technique, is reported to have a concentration of 6.3
and 6.0 parts per million of these mycotoxins. The residue
weights on which these concentrations are based are not reported,
making it impossible to estimate the amount of trichothecenes
that may have been associated with the bag. Pollen grains are
not evident in scanning electron micrographs of a yellow spot.
The samples were evidently not subjected to acetolysis before
microscopy, as is sometimes necessary to reveal pollen grains.

It has been speculated that the bag may have been a weapon for
explosively disseminating toxins. Among the difficulties
confronting this speculation are the following:

1) Only one villager claimed that a bag was dropped by the
plane.

2) No one, not even the provider of the plastic bag, reported
hearing any explosion.

3) The provider of the plastic bag apparently did not see fit
to come forward for more than two weeks after the incident,
during which time he could have informed the resident village
officials, the numerous Thai District, Provincial and National
investigators, the TV film crew or the Canadian team during their
first visit, starting March 5.

4) There is no significant medical evidence that villagers
were exposed to any toxic material.

5) The bag resembles those commonly used in the kitchen and
for other ordinary purposes.

6) The bag is largely intact and no evidence is presented for
powder burns.
6.

7) There is no evidence for the presence of an altimeter, a
timer or any release mechanism.

8) Samples of the substance that the villagers said fell from
the sky on the morning of 19 February all contained copious
amounts of pollen and are clearly honeybee feces. If anything
else was deposited, it apparently was not noticed and not
sampled.

9) A coincidence in place and time of a shower of honeybee
feces with a chemical attack is exceedingly unlikely, indicating
that only the former actually occurred.

10) The parts-per-million values given in the Canadian report
refer only to laboratory residues and not to the actual amount of
toxin that was in or on the bag. It is therefor not evident that
the amounts associated with the bag were sufficient to be of any
toxicological significance.

11) Fusarium semitectum was isolated from both of two pollen-
containing yellow spots received from the Pong Nam Ron area by
Sukroongreung et al. on 22 Feb, 1982, as reported in their
publication cited above. One isolate was tested in mice and found
to be toxic. Workers at Agriculture Canada isolated Fusarium
semitectum and Fusarium equiseti from a leaf collected at Ban Sa
Tong after the 19 Feb 82 incident. An isolate of the latter
produced approximately 1,000 parts per million (dry weight basis)
of the trichothecene deoxynivalenol in laboratory culture
(Greenhalgh, et al. "Toxigenic Potential of Some Fusarium
Isolates From Southeast Asia", Applied and Environmental
Microbiology, 50 550-552, 1985). These and other recent studies
of trichthecene mycotoxins in the natural environment of the
Asian tropics indicate the need for caution in assigning any
particular significance to the findings of trace amounts of
trichothecenes in the unknown materials associated with the
plastic bag.

CONCLUSION. The plastic bag is not a device for releasing
chemical warfare agents. ,

QVERALL CONCLUSION, The incidents at Ban Sa Tong and Ban Sub Tha
Mau resulted from harmless showers of honeybee feces, mis-
interpreted by some as a chemical warfare attack.