Emily C. Lennert
pollen, trace, indoor, ornamental, plant, botany, palynology
- Nguyen, P.; Weber, M. Forensic value of pollen from ornamental indoor plants. Grana. 2015, 54, 236-246.
The opinions expressed in this review are an interpretation of the research presented in the article. These opinions are those of the summation author and do not necessarily represent the position of the University of Central Florida or of the authors of the original article.
The analysis of pollen for forensic purposes, i.e. forensic palynology, is a discipline that examines pollen as a potential form of trace evidence. To understand pollen as a form of trace evidence, one must investigate the source of the pollen and understand how pollen “behaves” in an environment, e.g. how persistent is the pollen, how abundant, etc. In this study, several ornamental indoor plants were examined within an apartment and the pollen deposition in each plant containing room was studied. By studying pollen profile of each room, the authors were able to determine which plants produced more dominant pollen, i.e. more likely to be seen in trace evidence, as well as distinguish between common and rare pollen types.
An apartment with no pets and two occupants was selected for the experiment. Two rooms, the kitchen and living room, were sampled over an approximately 11 month period, October to September. Flowering plants and cut flowers were placed in the apartment. A total of 6 plants were placed in the kitchen: Alstroemeria sp., Callistemon sp., Caryophyllaceae, Clivia miniata, Fuchsia sp., and Lilium sp. 6 plants were placed in the living room: Caryophyllaceae, Euphoria leuconeura, Fuchsia sp., Hibiscus sp., Lavandula stoechas, and Spathiphyllum sp. Ilex sp. was placed in the entrance hall. A figure depicting the location of the plants can be seen within the study, Figure 1. Samples were collected using Swiffer® Dusters™ by dusting the entire floor of the selected room with a single, new duster. Pollen samples were also taken directly from each plant as reference samples.
A total of 66 samples, 33 per room, were collected. The intervals at which samples were taken were inconsistent, but generally 3 samples were collected per month with the exception of February (4 samples per room) and June (1 sample per room). Samples were processed as follows: after collection, the duster was washed with distilled water. The sample was then centrifuged to separate the liquid and solid phases, i.e. water and pollen. The solid remains were then processed. First, the solid was rinsed with 100% acetic acid, which was then decanted and followed by an acetolysis solution: acetic anhydride and sulphuric acid in a ratio of 9:1. The sample was then heated in a water bath set to 100 ˚C for 8 minutes, then rinsed with acetic acid, followed by several rinses with distilled water. After rinsing with distilled water, the sample was dried by an ethanol rinse and the remaining solid, i.e. pollen, was placed in glycerine.
A small amount, 20 μL, of the pollen/glycerine mixture was then placed on a microscope slide for visual analysis. Pollen grains were counted: 300 pollen grains were counted per sample and the number of each pollen type was recorded to determine the percent of pollen from each plant within the sample. Microscopic images of several pollen types were taken and can be seen in Figure 2 a-j within the study.
Prior to the introduction of plants into the apartment, wind-pollinated, i.e. outdoor, species dominated the pollen profile of the rooms, as indicated by the authors’ previous work. Within 1 month of the introduction of the plants in the apartment, the pollen profile shifted and was dominated by indoor plants. Spathiphyllum dominated the living room profile from November through April. During this time, Alstroemeria and Clivia were also abundant in the living room profile. Then, in May, the pollen profile in the living room shifted and was dominated by wind-pollinated species once again.
In the kitchen, from November through April, Alstroemeria, Clivia, and Spathiphyllum were most abundant, although wind-pollinated species also accounted for a large portion of the pollen profile. From May through the end of the study, Callistemon dominated the kitchen pollen profile, with Lilium and wind-pollinated species in high abundance as well.
Dominant pollen types were determined to be Spathiphyllum, Alstroemeria, Clivia, Callistemon, and Lilium. During the sampling time, these pollen types were observed in high abundances in the kitchen and/or living room. The authors note that the addition of these ornamental indoor plants to a room may shift the pollen profile of the area, increasing the abundance of the selected pollen in the profile.
Rare pollen types, i.e. those observed in 5% or less abundance, were also recorded. Caryophyllaceae, Lavandula, Ilex, Euphorbia, and Fuchsia were all considered rare pollen types. Hibiscus was not observed in any of the samples.
- Spathiphyllum, Alstroemeria, Clivia, Callistemon, and Lilium were dominant pollen types, meaning the pollen produced by these plants dominated the pollen profile for a period of time.
- Caryophyllaceae, Lavandula, Ilex, Euphorbia, and Fuchsia were rare pollen types, and may not be seen frequently in pollen trace evidence.
- Hibiscus did not shed enough pollen to be observed in any samples.
Pollen is a form of trace evidence. To understand the value of pollen as evidence, and the likely evidence that would be gathered, one must understand the pollen deposition behavior of common plants.
Of the plants studied, Spathiphyllum, Alstroemeria, Clivia, Callistemon, and Lilium may be more likely to be seen in pollen trace evidence, due to their dominance, i.e. abundance, in the pollen profiles.