Yellow rain was the subject of a 1981 political incident in which the United States Secretary of State Alexander Haig accused the Soviet Union of supplying T-2 mycotoxin to the Communist states in Vietnam and Laos for use in counterinsurgency warfare.
Refugees described many different forms of attacks, including a sticky yellow liquid falling from planes or helicopters, which was dubbed "yellow rain". The US government alleged that over ten thousand people had been killed in attacks using these chemical weapons. The Soviet Union denied these claims and an initial United Nations investigation was inconclusive.
Some samples of the supposed chemical agent that were supplied to a group of independent scientists turned out to be honeybee feces, suggesting that the "yellow rain" was due to mass defecation of digested pollen grains from large swarms of bees. Other scientists questioned the accuracy of the refugee accounts and the reliability of the chemical analyses presented by the US government. The majority of the scientific literature on this topic now regards the hypothesis that yellow rain was a Soviet chemical weapon as disproved. However, the issue remains disputed and the US government has not retracted these allegations, arguing that the issue has not been fully resolved.
Many of the US documents relating to this incident remain classified.
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.
- 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.".
C. J. Mirocha at the University of Minnesota conducted a biochemical investigation, looking for the presence of trichothecene mycotoxins, including T-2 toxin, diacetoxyscirpenol (DAS), and deoxynivalenol (DON) (10). This included chemical analyses of blood, urine, and tissue of alleged victims of chemical attacks in February 1982 in Laos and Kampuchea. "The finding of T-2, HT-2, and DAS toxins in blood, urine, and body tissues of alleged victims of chemical warfare in Southeast Asia provides compelling proof of the use of trichothecenes as nonconventional warfare agents....Additional significant findings lie in the trichothecenes found in the leaf samples (T-2, DON, nivalenol) and yellow powder (T-2, DAS)....The most compelling evidence is the presence of T-2 and DAS in the yellow powder. Both toxins are infrequently found in nature and rarely occur together. In our experience, copious producers of T-2 toxin (F. tricinctum) do not produce DAS, and conversely, good producers of DAS (F. roseum 'Gibbosum') do not produce T-2." (10)
In 1983, these charges were disputed by Harvard biologist and biological weapons opponent Matthew Meselson and his team, who traveled to Laos and conducted a separate investigation. Meselson's team noted that trichothecene mycotoxins occur naturally in the region and questioned the witness testimony. He suggested an alternate hypothesis that the yellow rain was the harmless fecal matter of honeybees. The Meselson team offered the following as evidence: separate "yellow rain drops" which occurred on the same leaf, and which were "accepted as authentic", consisted largely of pollen; each drop contained a different mix of pollen grains, as one would expect if they came from different bees, and the grains showed properties characteristic of pollen digested by bees (the protein inside the pollen grain was gone, while the outer indigestible shell remained). Further, the pollen mix came from plant species typical of the area where a drop was collected.
The US government responded to these findings by arguing that the pollen was added deliberately, in order to make a substance that could be easily inhaled and "ensure the retention of toxins in the human body". Meselson responded to this idea by stating that it was rather far-fetched to imagine that somebody would produce a chemical weapon by "gathering pollen predigested by honeybees." The fact that the pollen originated in Southeast Asia meant that the Soviet Union could not have manufactured the substance domestically, and would have had to import tons of pollen from Vietnam.:35 Meselson's work was described in an independent medical review as providing "compelling evidence that yellow rain might have a benign natural explanation".
After the honeybee hypothesis was made public, a literature search turned up an earlier Chinese paper on the phenomenon of yellow droppings in Jiangsu Province in September 1976. Strikingly, the Chinese villagers had also used the term "yellow rain" to describe this phenomenon. Many villagers believed that the yellow droppings were portents of imminent earthquake activity. Others believed that the droppings were chemical weapons sprayed by the Soviet Union or Taiwan. However, the Chinese scientists also concluded that the droppings came from bees.:46
Analyses of putative "yellow rain" samples by the British, French and Swedish governments confirmed the presence of pollen and failed to find any trace of mycotoxins. Toxicology studies questioned the reliability of reports stating that mycotoxins had been detected in alleged victims up to two months after exposure, since these compounds are unstable in the body and are cleared from the blood in just a few hours. An autopsy on a Khmer Rouge fighter named Chan Mann, a victim of a putative yellow rain attack in 1982, turned up traces of mycotoxins, but also aflatoxin, Blackwater Fever, and malaria.:33
Surveys also showed that both mycotoxin-producing fungi and mycotoxin contamination were common in Southeast Asia, casting doubt on the assertion that detecting these compounds was an unusual occurrence. For example, a Canadian military laboratory found mycotoxins in the blood of five people from the area who had never been exposed to yellow rain, out of 270 tested, but none in the blood of ten alleged victims, and a 1988 paper reported that illnesses from mycotoxin exposure may pose a serious threat to public health in Malaysia. It is now recognized that mycotoxin contamination of foods such as wheat and maize is a common problem, particularly in temperate regions of the world. As noted in a 2003 medical review, "The government research highlighted, if nothing else, that natural mycotoxicoses were an important health hazard in Southeast Asia."
Reliability of eyewitness accounts
In 1987 the New York Times reported that Freedom of Information requests showed that field investigations in 1983-85 by US government teams had produced no evidence to substantiate the initial allegations and instead cast doubt on the reliability of the initial reports, but these critical reports were not released to the public. A 1989 analysis of the initial reports gathered from Hmong refugees that was published in the Journal of the American Medical Association noted "marked inconsistencies that greatly compromised the validity of the testimony" and criticized the methods used in interviews by the US Army medical team that gathered this information. These issues included the US Army team only interviewing those people who claimed to have knowledge of attacks with chemical weapons and the investigators asking leading questions during interviews. The authors noted that individuals' stories changed over time, were inconsistent with other accounts, and that the people who claimed to have been eyewitnesses when first interviewed later stated that they had been relaying the accounts of others.
In 1982, Meselson had visited a Hmong refugee camp with samples of bee droppings that he had collected in Thailand. Most of the Hmong he interviewed claimed that these were samples of the chemical weapons that they had been attacked with. One man accurately identified them as insect droppings, but switched to the chemical weapons story after discussion with fellow Hmong.:46
Australian military scientist Rod Barton visited Thailand in 1984, and discovered that Thai villagers were blaming yellow rain for a variety of ailments, including scabies. An American doctor in Bangkok explained that the United States had been taking a special interest in yellow rain, and was providing medical care to alleged victims.:39–40
Possible US origin
A CIA report from the 1960s reported allegations by the Cambodian government that their forces had been attacked with chemical weapons, leaving behind a yellow powder. The Cambodians blamed the United States for these alleged chemical attacks. Some of the samples of "yellow rain" collected from Cambodia in 1983 tested positive for CS, which the United States had used during the Vietnam War. CS is a form of tear gas and is not toxic, but may account for some of the milder symptoms reported by the Hmong villagers.:39
Currently, two main viewpoints exist on the yellow rain controversy. One viewpoint sees these allegations as supported by insufficient evidence, or as having been completely refuted. For instance, a 1992 review published in Politics and the Life Sciences described the idea of yellow rain as a biological agent as conclusively disproved and called for an assessment by the US government of the mistakes made in this episode, stating that "the present approach of sweeping the matter under the rug and hoping people will forget about it could be counterproductive." Similarly, a 1997 review of the history of biological warfare published in the Journal of the American Medical Association stated that the yellow rain allegations are "widely regarded as erroneous", a 2001 review in the Annual Reviews in Microbiology described them as "unsubstantiated for many reasons", and a 2003 article in Annual review of phytopathology described them as "largely discredited". A 2003 review of the history of biological warfare described these allegations as one of many cases where states have produced propaganda containing false or unsubstantiated accusations of the use of biological weapons by their enemies.
In contrast, as of 1997 the US Army maintains that some experts believe that "trichothecenes were used as biological weapons in Southeast Asia and Afghanistan" although they write that "it has not been possible for the United States to prove unequivocally that trichothecene mycotoxins were used as biological weapons." They argued that presence of pollen in yellow rain samples is best explained by the idea that "during biological warfare attacks, dispersed trichothecenes landed in pollen-containing areas." (Essentially the same position is taken in a subsequent volume in the same series of US Army textbooks published in 2007.) Similarly, the US Defense Threat Reduction Agency argues that the controversy has not been resolved and state that a CIA report indicated the Soviet Union did possess weapons based on T-2 mycotoxin, although they state that "no trace of a trichothecene-containing weapon was ever found in the areas affected by yellow rain" and conclude that the use of such weapons "may never be unequivocally proved." A 2007 review published in Politics and the Life Sciences concluded that the balance of evidence strongly supported the hypothesis that some type of chemical or biological weapon was used in Southeast Asia in the late 1970s and early 1980s, but noted that they found no definitive proof of this hypothesis and that the evidence could not "identify the specific agents used, the intent, or the root source or sources of the attacks."
An episode of mass pollen release from bees in 2002 in Sangrampur, India, prompted unfounded fears of a chemical weapons attack, although this was in fact due to a mass migration of giant Asian honeybees. This event revived memories of what New Scientist described as "cold war paranoia", and the article noted that the Wall Street Journal had covered these 1980s yellow rain allegations in particular detail. Indeed, the Wall Street Journal continues to assert that the Soviet Union used yellow rain as a chemical weapon in the 1980s and in 2003 accused Matthew Meselson of "excusing away evidence of Soviet violations."
In the build-up to the 2003 invasion of Iraq the Wall Street Journal alleged that Saddam Hussein possessed a chemical weapon called "yellow rain". The Iraqis appear to have investigated trichothecene mycotoxins in 1990, but only purified a total of 20 ml of the agent from fungal cultures and did not manage to scale up the purification or produce any weapons containing these compounds. Although these toxins are not generally regarded as practical tactical weapons, the T-2 toxin might be a usable weapon since it can be absorbed through the skin, although it would be very difficult to manufacture it in any reasonable quantity.
Henry Wilde, a retired US Foreign Service Officer, has drawn parallels between the use of yellow rain allegations by the US government against the Soviet Union and the later exaggerated allegations on the topic of Iraq and weapons of mass destruction. Wilde considers it likely that states may again "use rumors and false or planted intelligence of such weapons use for propaganda purposes." and calls for the establishment of a more rigorous inspection process to deal with such claims. Similar concerns were expressed in a 2006 review published by the World Organisation for Animal Health, which compared the American yellow rain accusations to other cold-war accusations from the Soviet Union and Cuba, as well as to more recent mistaken intelligence on Iraqi weapons capabilities, concluding that such unjustified accusations have encouraged the development of biological weapons and increased the risk that they might be used, as they have discredited arms-control efforts.
In 2012 the science-themed show Radiolab aired an interview with Hmong refugee Eng Yang and his niece, author Kao Kalia Yang, to discuss Eng Yang's experience with yellow rain. The hosts took the position that yellow rain was unlikely to have been a chemical agent. The episode prompted a backlash among listeners, who criticized Robert Krulwich for insensitivity, racism, and their disregard for Yang's personal experience with the region in question. The negative response prompted host Robert Krulwich to issue an apology for his handling of the interview.
- Agent Orange
- Red rain in Kerala
- Sverdlovsk anthrax leak
- Aral smallpox incident
- Allegations of biological warfare in the Korean War
- Jonathan Tucker (Spring 2001). "The Yellow Rain Controversy: Lessons for Arms Control Compliance". The Nonproliferation Review.
- RW Wannemacher, SL Wiener (1997). "Trichothecene mycotoxins: in Medical Aspects of Chemical and Biological Warfare". U.S. Army Medical Department. Retrieved Feb 2010.
- "Yellow Rain Falls". New York Times. September 3, 1987. Retrieved 2009-01-02. "Yellow rain is the excrement of jungle bees. It's yellow from digested pollen grains, and it rains down from swarms of bees too high to be seen. His theory turns out to be exactly right. The Government's own studies, still unpublished, prove that the source is bees, not bombs."
- Madden LV, Wheelis M (2003). "The threat of plant pathogens as weapons against U.S. crops" ( PDF (235 KB)). Annu. Rev. Phytopathol 41: 155–76. doi:10.1146/annurev.phyto.41.121902.102839. PMID 12730385.
- Christopher GW, Cieslak TJ, Pavlin JA, Eitzen EM (August 1997). "Biological warfare. A historical perspective". JAMA 278 (5): 412–7. doi:10.1001/jama.278.5.412. PMID 9244333.
- Guillemin, Jeanne (2002-03). "The 1979 Anthrax Epidemic in the USSR: Applied Science and Political Controversy". Proceedings of the American Philosophical Society (American Philosophical Society) 146 (1): 18–36. ISSN 0003-049X. JSTOR 1558154. PMID 12068904.
- "Conflicting Evidence Revives "Yellow Rain" Controversy". James Martin Center for Nonproliferation Studies. Retrieved 2009-05-31. "Eyewitnesses claimed that Yellow Rain smelled like gunpowder and left a residue of sticky yellow spots on leaves, rocks, and rooftops. Exposure to high doses reportedly caused heavy bleeding from the nose and gums, blindness, tremors, seizures, other neurological symptoms, and death. Similar incidents were reported in Democratic Kampuchea (Cambodia) in 1978, after the Vietnamese Army invaded that country to topple the dictator Pol Pot and his murderous Khmer Rouge regime."
- Slavin, Barbara; Freudenheim, Milt (1981-09-20). "The World; Haig Implies Soviet Role in Poison Warfare". New York Times. Retrieved 12 February 2010.
- Report of the Secretary-General on Chemical and Bacteriological (Biological). Weapons, U.N. Doc. A/37/259, at 26-41 (Dec. 1, 1982)
- Mirocha, CJ; Pawlosky RA, Chatterjee K, Watson S, Hayes W (November 1983). "Analysis for Fusarium toxins in various samples implicated in biological warfare in Southeast Asia". J Assoc off Anal Chem 66 (6): 1485–99. PMID 6643363.
- Rosen, RT; Rosen, JD (October 1982). "Presence of four Fusarium mycotoxins and synthetic material in 'yellow rain'. Evidence for the use of chemical weapons in Laos". Biomed. Mass Spectrom. 9 (10): 443–50. doi:10.1002/bms.1200091007. PMID 6216925.
- Koch, P (October 2004). "State of the art of trichothecenes analysis". Toxicol. Lett. 153 (1): 109–112. doi:10.1016/j.toxlet.2004.04.027. PMID 15342087.
- Black, RM (December 2009). "History and perspectives of bioanalytical methods for chemical warfare agent detection". J Chromatogr B Analyt Technol Biomed Life Sci 878 (17–18): 1207–1215. doi:10.1016/j.jchromb.2009.11.025. PMID 20018570.
- Bennett, JW; Klich, M (July 2003). "Mycotoxins". Clin. Microbiol. Rev. 16 (3): 497–516. doi:10.1128/CMR.16.3.497-516.2003. PMC 164220. PMID 12857779.
- Nowicke, JW; Meselson, M (1984). "Yellow rain--a palynological analysis". Nature 309 (5965): 205–6. doi:10.1038/309205a0. PMID 6717598.
- Earl, C. (1984). "Yellow rain: Thai bees' faeces found". Nature 308 (5959): 485. doi:10.1038/308485b0. PMID 6709055.
- Marshall, E. (July 1986). "Yellow rain evidence slowly whittled away". Science 233 (4759): 18–9. doi:10.1126/science.3715471. PMID 3715471.
- Barton, Rod (2006). The Weapons Detective: The Inside Story of Australia's Top Weapons Inspector. Black Inc. ISBN 9780975076958.
- Zhang, Zhongying; Chen Yu-Ming, Chow Shu, and Li Min (1977). "A Study of the Origin and the Pollen Analysis of "Yellow Rain" in Northern Jiangsu". Kexue Tongbao (22): 409–412.
- Whiteside, Thomas (18 February 1911). "The Yellow Rain Complex (II)". The New Yorker: 44–68.
- "Yellow rain: British analyses find no toxin". Nature 321 (6069): 459. 1986. doi:10.1038/321459b0. PMID 3713819.
- Greenhalgh R, Miller JD, Neish GA, Schiefer HB (August 1985). "Toxigenic Potential of Some Fusarium Isolates from Southeast Asia". Appl. Environ. Microbiol. 50 (2): 550–552. PMC 238662. PMID 16346873.
- Desjardins, AE (June 2009). "From yellow rain to green wheat: 25 years of trichothecene biosynthesis research". J. Agric. Food Chem. 57 (11): 4478–84. doi:10.1021/jf9003847. PMID 19385595.
- Barss, Peter (February 1992). "Epidemic Field Investigation as Applied to Allegations of Chemical, Biological, or Toxin Warfare". Politics and the Life Sciences 11 (1): 5–22. ISSN 0730-9384. JSTOR 4235825.
- Salleh, B; Strange, RN (March 1988). "Toxigenicity of some fusaria associated with plant and human diseases in the Malaysian peninsula". J. Gen. Microbiol. 134 (3): 841–7. PMID 3183622.
- Desjardins, AE; Hohn, TM; McCormick, SP (September 1993). "Trichothecene biosynthesis in Fusarium species: chemistry, genetics, and significance". Microbiol. Rev. 57 (3): 595–604. PMC 372927. PMID 8246841.
- Boffey, Philip M. (1987-08-31). "Declassified Cables Add to Doubts About U.S. Disclosures on 'Yellow Rain'". New York Times. Retrieved Feb 2010.
- Hu H, Cook-Deegan R, Shukri A (August 1989). "The use of chemical weapons. Conducting an investigation using survey epidemiology". JAMA 262 (5): 640–3. doi:10.1001/jama.262.5.640. PMID 2746816.
- Hawley RJ, Eitzen EM (2001). "Biological weapons--a primer for microbiologists". Annu. Rev. Microbiol. 55: 235–53. doi:10.1146/annurev.micro.55.1.235. PMID 11544355.
- Frischknecht F (June 2003). "The history of biological warfare". EMBO Rep. 4 Spec No (Supp1): S47–52. doi:10.1038/sj.embor.embor849. PMC 1326439. PMID 12789407.
- A Note from History: Yellow Rain Defense Threat Reduction Agency
- Katz R, Singer B (March 2007). "Can an attribution assessment be made for Yellow Rain? Systematic reanalysis in a chemical-and-biological-weapons use investigation". Politics Life Sci 26 (1): 24–42. doi:10.2990/26_1_24. PMID 18208344.
- Pearce, Fred (2002). "Green rain over India evokes memories of cold war paranoia". New Scientist. Retrieved Feb 2010.
- Bartley, Robert (February 24, 2003). "Two Decades of Warnings, And Now Duct Tape: We've long known the dangers of bio warfare.". wsj.com. Retrieved 2010-02-12.
- Bryen, Stephen D. (2002-12-09). "Opinion: Ironic Chemistry: The U.N. Boosts Saddam's Threat". wsj.com. Retrieved 2010-02-12.
- Zilinskas, RA (August 1997). "Iraq's biological weapons. The past as future?". JAMA 278 (5): 418–24. doi:10.1001/jama.278.5.418. PMID 9244334.
- Stark AA (June 2005). "Threat assessment of mycotoxins as weapons: molecular mechanisms of acute toxicity". J. Food Prot. 68 (6): 1285–93. PMID 15954722.
- Paterson RR (September 2006). "Fungi and fungal toxins as weapons". Mycol. Res. 110 (Pt 9): 1003–10. doi:10.1016/j.mycres.2006.04.004. PMID 16908123.
- Wilde, Henry (2008). "The "Yellow Rain" controversy: are there lessons from the past?". Asian Biomedicine 2 (5): 421–429. Retrieved 2010-02-10.[dead link]
- Furmanski, M. (2006). "Misperceptions in preparing for biological attack: an historical survey". Scientific and Technical Review: World Organisation for Animal Health 25 (1): 53–70. Retrieved 2010-02-10.
- Evans, Grant (1983). The yellow rainmakers: are chemical weapons being used in Southeast Asia?. London: Verso. ISBN 0-86091-068-7.
- Martin, Susan Boyles; Anne Clunan; Lavoy, Peter R. (2008). Terrorism, war, or disease?: unraveling the use of biological weapons. Stanford, Calif: Stanford University Press. ISBN 0-8047-5977-4.