Forensic Palynology: Pollen Transfer to Shoes

Every seed plant produces pollen, some of them in big quantities. Through wind, animals or water pollen is transferred from the anther to the stigma to enable fertilization and sexual reproduction. Not all pollen grains reach the female reproduction organ and therefore pollen can be found virtually anywhere, even at indoor locations (pollen rain). Pollen accumulations are extremely heterogeneous. Forensic palynology takes advantage of this "omnipresence" and heterogeneity and uses pollen and spores (mosses, ferns; fungi) in legal cases. Samples taken from suspects are compared with samples from crime scenes, items or victims in order to relate them to each other. However, little is known about indoor pollen and its use in forensic investigations. In this project a room will be examined for its pollen content and its variation over the year. The transfer of pollen from the room to shoes will be monitored, too. Additionally it will be examined if the pollen content can be significantly changed by deliberately putting (flowering) indoor plants in a room. The investigated room and shoes will be compared regarding their pollen content to answer following questions: Can someone deliberately create a unique pollen composition at an indooor location? Can this composition serve as a marker to prove without a doubt that a certain pair of shoes (person) has been to this specific site?

Pollen is everywhere and every location has its specific pollen spectrum. These two facts make pollen grains an excellent tool in the investigation of criminal cases. Previously little attention was paid on indoor pollen from a forensic point of view. The results of the project clearly show that dust samples taken from different apartments at the same time have different pollen assemblages. On the one hand, the pollen spectra reflect the surrounding vegetation, on the other hand the annual flowering seasons of the plants. Pollen from wind-pollinated plants is dominant. By the end of the year respectively flowering season all pollen types can be found in similar percentages in the apartment. That shows that regular cleaning activities in the apartment cannot eliminate pollen. This result also means that indoor pollen may affect people suffering from pollen allergy long after the flowering season of allergenic plants. By introducing animal-pollinated ornamental plants into the apartment, the existing pollen spectrum is remarkably modified and thus specific pollen markers are added to the existing pollen assemblage. How much of these pollen grains are ending up in the dust is depending on the plant species. Pollen from animal-pollinated plants have a high forensic potential, as their spread radius is very limited in contrast to wind-pollinated plants. Finally, the transfer of indoor pollen, including the marker pollen grains, to shoe soles could be confirmed. The pollen trace from the apartment on the soles got blurred, depending on the weather and length of the escape route, but in most cases pollen from the apartment were still delectable at the end of a 1.8 km escape route. That means that it can be possible to link a burglar to an indoor crime scene and can answer legal questions.