It’s time to shine a spotlight on one of forensic science’s emerging disciplines: diatom analysis. Contrary to what you might think, diatom testing is not a new area of forensic analysis. Some of the earliest research into diatoms as a method for investigating drowning cases started emerging in the late sixties – early seventies.
However, like all methods of forensic analysis, it is not without its limitations. The conclusions drawn by diatom analysis can be very indefinitive, and because of this it goes through peaks and troughs of usage in a forensic setting. Academic papers in the seventies and eighties established diatom analysis as a proof of concept, with it subsequently picking up as a discipline in the nineties. It then fell off the radar for a while, and we’ve now started using it again because we believe that it’s an element of forensic ecology research that can be very useful within an investigation.
To break it down, diatoms are a form of algae that are specifically known as microalgae. They are found primarily within oceans, waterways (rivers, lakes, canals) and soils all over the world. Different types (species) of diatoms can be found in different water/soil types and can be used as an ecological indicator. A marine diatom, for example, will indicate a marine environment.
Now, we’re sure you’re wondering, how can diatoms be used in forensic investigation?
Diatom analysis of water and soils can be used to establish their presence in the environment – known as a control sample. Soils seized from exhibits (such as clothing, shoes, upholstery from vehicles etc…) can be examined for diatoms as can organ tissue from a victim submerged in water. The control samples can then be compared with exhibits for a geographical match, or in the case of organ analysis, determine key questions in investigations such as potential drowning.
As a form of evidence, diatom analysis does stand up well in court. The issue currently is that the research into thresholds for understanding what makes an assemblage in an organ in a definitive case for drowning, for example, is quite complex. Academic researchers are currently looking into this area of diatom analysis, so while it is an emerging discipline, it is still being continually examined for its useability.
As such, in the context of drowning cases, diatom analysis tends to be used in collaboration with post-mortem reports and the wider context of an investigation. This can include looking into other factors, such as as:
- Where the person was found
- Is it likely that the person was in water at the time?
- Is it usual for that person to be in water?
Despite the focus thus far on drowning cases, there are other uses for diatom analysis. Diatoms also live in wet soils, and so they can be included in forensic ecology surveys.
For example, in a recent case, an urban vehicle was linked to a suspect for the movement of a body into a woodland area. We studied the wooden soils from the crime scene and noticed that they were packed full with specific wet soil diatoms. We then used CSI tapings that the CSI team had taken of the vehicle to demonstrate that the soils found in the car – such as in the footwell – had diatoms present that were associated with soils in the wooded area. This linked the suspect to the location of where the body was discovered.
For the team at Alecto Forensics, diatom analysis is still a new element of forensic ecology. We are taking it step-by-step and there are some areas of research related to diatom analysis that we still want to cover,but there is a whole host of potential and possibility to be seen for this type of evidence.
In relation to other methods of testing, diatom analysis is about pattern matching, so it is comparable to DNA analysis in the sense that it involves looking at one pattern of diatoms from an environment and matching them to a pattern of diatoms within human tissue or soils from a suspect’s vehicle, for example. It’s the same level of the “does this match with what we’ve got” approach that comes with DNA testing, involving visual pattern matching as opposed to molecular pattern matching.
At the moment, diatom analysis is quite an undervalued tool and we have spent the past two years attempting to get it back off the ground. It’s fair to say that diatom specialists were quite nervous to utilise it in the forensic context, but we have been able to demonstrate, through a number of successful cases, that it is in fact a valuable tool in forensic investigations.
Furthermore, police forces can be nervous about using diatom analysis because it involves human tissue, and that in itself can be quite complicated. Time and time again we have been asked whether we are covered by the Human Tissue Act 2004, which was established to regulate the removal, storage and use of human tissue, bodies and organs for scheduled purposes. The answer is no we are not, because we are allowed to undertake forensic diatom analysis without Human Tissue Act compliance due to it being part of an ongoing investigation. In this sense, it is a useful additional tool to the already existing lines of inquiry, and because of this it can be built into an investigation incredibly effectively without being a separate, costly tool.
It is also important to note that diatom analysis is not limited to live cases. We have demonstrated diatom analysis’ potential for use in a cold case investigation only recently, whereby we studied items of clothing from a woman who disappeared thirty years ago. The standout feature of diatoms is that they are very hardy critters, so they survive in the environment and can survive on clothing, and potentially tissue, over quite a long period of time. In this sense they are incredibly durable, and so they are gold dust to a cold case investigation. If we’re looking at an environment for example, even if it’s a thirty year cold case, the environment may well have changed during that time. However, what we can do is try to establish what the diatom pattern is within that environment, and see if we can reflect back to the environment at the time a person went missing. Because of this, diatom analysis can be a very useful tool for cold case review.
Alecto Forensics is a UK leading forensic ecology service provider, delivering specialist forensic services and expertise to police forces across the UK.
We have over twenty years of forensic ecology experience within major crime investigation and pride ourselves on being an independent, quality-driven forensic service provider. We have a host of accredited experts and our expertise is available 24 hours 7 days per week.
We offer a full provision of service, from initial advice and support to scene deployment, laboratory analysis and final reporting.