The study and analysis of pollen, otherwise known as palynology, is becoming increasingly popular in the field of forensics. Forensic palynology is used to help match suspects to crimes or victims through the analysis of pollen evidence from geographical regions relevant to the crime scene. Because pollen is easily dispersed, it can be found almost anywhere, particularly in soil. Forensic palynologists must extract and analyse pollen spores from soil samples gathered as forensic evidence.
- Skill level:
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Things you need
- Soil sample evidence
- Light microscope
- Microscope slides
- Electron microscope (optional)
- Extraction protocol
- Various acids and alkali chemicals
- Sieve with specific micron pore size
- Staining chemical of choice
- Pollen samples from known geographic regions
Separate or extract the pollen grains from the soil sample using whatever protocol is standardised and approved at the institution for which you are analysing the pollen. One common method, published by Horrocks, 2004, involves using strong acids and alkalis to remove mineral and organic matter, filtering the sample through a porous membrane or sieve to isolate the particular size fraction of pollen, staining the pollen for better visualisation and mounting the pollen residue on microscope slides for analysis. Pollen is highly resilient and withstands the extraction process well.
Identify the pollen sample by microscopic visualisation to determine the variety or species of pollen. Use the highest magnification necessary, and if required, obtain the use of an electron microscope to enlarge the specimen further. There are a wide variety of sizes, shapes and surface characteristics of pollen that help with the identification process.
Analyse the pollen further by matching the identified pollen in a forensic sample to pollen in a known geographic location. It is also necessary to determine the pollen production and dispersal pattern to be able to create a "pollen fingerprint" for that region. That way, pollen can be used as forensic evidence to connect suspects to crime scenes with a high level of confidence.
Tips and warnings
- In order to obtain credible and accurate pollen analysis results, the soil samples from which pollen originated must be collected very carefully to avoid contamination, preferably by a palynologist. Care must be taken to avoid contamination throughout the extraction and analysis processes by using clean, disposable containers, equipment and supplies and avoiding cross contamination between different samples.
- Pollen may come from a wide variety of soil types. If possible, have alternate extraction methods available, and try more than one if necessary to acquire the cleanest and purest pollen sample for analysis.
- It is common for the soil sample containing the pollen to be in short supply. It may come from forensic evidence such as the bottom of a shoe or the tip of a shovel, for example. Care must be taken to avoid destruction of the entire forensic sample the first time. There may not be enough sample to try multiple extraction methods or to repeat analysis due to errors.
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