Palynology
Contributed by Vaughn M. Bryant
Palynology (the study of pollen and spores) has historically been underutilized as trace evidence in forensic science. The focus of “forensic palynology” is on evidence obtained from the study of pollen and spores that is associated with a crime scene or is considered evidence related to situations involving the law. As a discipline, the first recorded use was a little more than one-half century ago, but even today the use of this technique is relatively unknown or under-utilized in many regions of the world.
The analysis of pollen and spores (collectively called palynology) is recognized as an effective forensic tool for a number of reasons. First, many types of pollen producing plants (angiosperms and gymnosperms) and spore-producing cryptograms (algae, fungi, ferns, mosses, liverworts, etc.) disperse vast quantities of pollen or spores as part of their reproductive process and rely mostly upon wind currents to carry these single-celled pollen or spores from the dispersal source to another location where they can carry out part of the reproductive cycle. The inefficiency of this process results in the majority of these dispersed cells falling to the ground and forming a record of the vegetation in the immediate area. Even though there is not a one-to-one correlation between the percentages of each pollen or spore type with the actual percentages of plants in the local vegetation, the record for each location becomes an effective way to identify various regions in the world. A second important aspect as to why pollen and spores are effective forensic clues relates to their microscopic size that enables them to become trapped or deposited on almost any type of surface. That aspect enables them to become effective clues that can often link a suspect, or some object, with a precise geographical region or a specific crime scene. A third factor that makes forensic palynology useful is that each plant species produces a unique type of pollen or spore, which can often be identified to the genus or species level using various types of microscopy including: light microscopy (LM), scanning electron microscope (SEM) and/or the resolution precision of transmission electron microscopy (TEM). Because crime scenes and other geographical locations often contain a unique blend of plants, the pollen and spore evidence from suspects or items can often link them with precise locations. The fourth reason that palynology becomes a useful type of forensic evidence is that the majority of pollen and spores are highly resistant to destruction or decay. That ability enables critical evidence, if collected and stored properly, to be examined and validated for years, decades, or even longer after a crime or event has occurred.
There are two different fields of forensic palynology, based upon the types of information or investigations that each pursues. Although some forensic palynologists work in both areas, each group tends to specialize and focus mostly on one type of investigation. The primary type of forensic palynologist works directly with the investigation of crimes as they pertain to situations involving victims, suspects, actual crime scenes, or associated items. They usually work directly with local, state, or national law enforcement agents as part of those agencies or as personnel in forensic agencies. The second type of forensic palynologist works mostly with questions related to finding the original locations of objects. That type of individual often examines items of unknown origin and is asked to use the pollen and spore evidence associated with the item to determine the item’s geographical origin.
During the past decade the world has become a more dangerous place to live. The availability of rapid travel and instant communication across continents, coupled with the worldwide rise in terrorism and local/regional conflicts have created many unsafe regions. Although there is no simple solution to all of these problems, the wider use of forensic palynology as trace evidence might help identify and prevent the wider spread of criminal activity and international terrorism.
Additional References:
1. Milne, L.A., Bryant, V.M., and Mildenhall, D.C., Forensic palynology. In: Forensic botany: principles and applications to criminal casework (ed. H. Coyle), CRC Press LLC, Boca Raton, FL, pp. 217–252. (2005).
2. Bryant, V.M., and Jones, G.D. 2006. Forensic palynology: current status of a rarely used technique in the United States of America. Forensic Science International 163: 183–197.