The Tales Pollen Tells

In 1988 Marion True, at that time the J. Paul Getty Museum's antiquities director, paid a record $18 million for a 5th century BC Greek statue that she said would become "the single greatest piece of classical art in our collection." It is still one of its most prized artifacts. Almost 20 years later, True is on trial in Rome for trafficking in looted art, and her conviction or release may hinge on an analysis of the pollen found in the folds of the excavated statue's robes. If the pollen is of Sicilian origin, it may have been looted from a site there after Italy's 1939 prohibition on exporting antiquities without a permit. But if it is of North African origin, where similar statues have been found, there is no problem. Viewed under the microscope, pollen grains have an endlessly diverse variety of forms. The shell of pollen grains is highly resistant to degradation, so pollen grains can fossilize, and are used to track and date geological strata. They can also be used in tracking and solving crimes and other puzzles. During the massacre of Bosnians in and around Srebrenica in the summer of 1995, one execution and burial site was in a field of wheat. Later, the bodies were dug up and reburied in smaller numbers elsewhere, to diminish the evidence for a massacre. Their origin was traced to the wheat field through the presence of distinctive pollen in soil recovered from them. This finding was important court evidence against those involved in the Srebrenica atrocities. Between 1975 and 1978, after the end of the Vietnam War, a story emerged from the Hmong tribesmen who live in the hills bordering Laos and Cambodia, of a so-called yellow rain alleged to have fallen from the sky, often after planes had passed over. The "rain" caused heavy bleeding from the nose and gums, blindness, tremors, seizures, other neurologic symptoms, and death. It led to serious allegations of chemical warfare by the United States against the Soviet Union, which was supposed to have supplied chemical weapons to the Vietnam government. Samples of yellow spots on leaves were submitted for chemical analysis and initially gave positive results for mycotoxins, fungal poisons that can cause a variety of symptoms and, in the long run, liver cancer. But this result was unreproducible. Eventually, microscopic analysis showed that the yellow spots were bee feces containing tree pollen. A swarm of bees had erupted from a tree-top hive, like a bucket brigade carrying out the slops, dumping them all over the neighborhood. This new finding for apiology [study of bees] was confirmed by actual observation in the hill forest by entomologists, who were caught in a yellow fecal shower during a field trip to the location of an alleged attack. It strains credulity that Russian chemical warfare agents went around harvesting tree pollen in large quantities to disguise a mycotoxin weapon. In 1999, at a conference of the Missouri Botanical Society, a pollen specialist with the Israel Antiquities Authority reported that pollen spores found on the Shroud of Turin were typical of those of plants growing around Jerusalem. A Swiss police criminologist, who had earlier been in trouble for faking evidence, had given the samples of the shroud to him, thus leaving the finding in doubt. The late Andy Spielman of Harvard University, a highly respected medical entomologist, had a bee in his bonnet about pollen and malaria. He claimed that the recent large increase in malaria transmission in parts of sub-Saharan Africa was linked to the increase in the cultivation of maize in those areas. Huge quantities of pollen produced by the crop settle on the mud puddles, which are the preferred breeding sites for the Anopheles arabiensis mosquito, providing a rich food supply for the larvae and producing bumper crops of the malaria vector. Many of his associates and students thought he was a bit unhinged about the subject, but he has been vindicated by the finding that the large increase in malignant tertian malaria in parts of Ethiopia is in fact correlated with the intensification of maize cultivation. Thus the lowly pollen grain has shown its utility in the fields of archaeology, criminology, biowarfare investigation, and epidemiology, far beyond its primary purpose of acting as simply the transmitter of DNA from one plant generation to the next. Remember that, the next time you curse pollen for your spring allergy or for messing up the shine on your automobile. Woodall is former director of the Nucleus for the Investigation of Emerging Infectious Diseases in the Institute of Medical Biochemistry at Brazil's Federal University of Rio de Janeiro. jwoodall@the-scientist.com

The Tales Pollen Tells

The rise of forensic palynology, a once obscure science.

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