A person, previously lying silently in the cold and murky depths of the lake-bed, is removed from their position and brought to shore. You watch closely as the unfortunate individual is pronounced dead at the scene, and as a forensic pathologist, you quickly realise that it isn’t as simple as it looks: a positive diagnosis of drowning as a cause of death can be difficult to come by. It’s even harder where physiological indications (indications on or inside the body, during a post-mortem) are completely absent.
So what hints or clues might be of immense help in determining whether someone drowned — or whether something more sinister is at work? Think about the glittering diamonds in the water’s depths: diatoms.
Diatoms are single-celled alga (you might think back to what you remember algae looking like — same subtance, vastly different appearance) with cell walls that are composed of silica. Silica is the same colourless material that is found in the mineral quartz, but imparts something unique to the appearance of these microorganisms who reveal their beautiful structures under the microscope.
There’s a library of information hidden within the secret chambers of these colourful little formations — it’s just up to you to figure out how to extract them. Luckily, we’re here to help you figure out how to reveal the startling clues hidden deep within their walls.
1. They’ll tell you precisely where a person drowned.
Diatoms only thrive in a freshwater ecosystems (limnology, by the way, is the study of freshwater ecology). If you find a person with diatoms in their lungs (or upper respiratory tract) that was located in saltwater body, chances are they floated in from some other location — or they were dumped there after a sequence of events of which you’re not aware. It’s time to stick your pencil behind your ear and do a bit of detective work.
Find them in the right kind of ecosystem — and you should analyse the number and diversity in the diatoms that are found within the body. The population should match the aquatic flora (or a sample) where the body was originally recovered. It’s been shown consistently that if you compare the flora (or the organisms) recovered from a victim’s tissues, it’s pretty well correlated to what you’ll find at a known drowning site.
2. They’ll tell you the time since a person died.
It’s pretty well-known that establishing the PMI (or post-mortem interval) is a seriously important task for any forensic pathologist — the critical bit is to figure out exactly what can give you an indication of how long it’s been since someone’s died. Fortunately for you, diatoms are great barometers: they are found in lots of different freshwater ecosystems, meaning that you’d be hardpressed not to find them; they persist throughout the year; and they can be identified to species with only a simple light microscope (no heavy-duty equipment for you).
As diatoms increase and decrease in population variably throughout a month, you can match a sample to a particular time period in the past thirty days in most situations. Of course, this isn’t terribly helpful if you’re looking to pinpoint PMI to a much smaller window — but in many cases, especially if a person has been missing for a length of time — it’s a handy tool and marker.
3. Their presence or absence can hint at whether a person even drowned at all.
If someone’s found in a freshwater ecosystem, most of us might well assume that there’s hardly any forensics to be done — the answer is simple and obvious. We’d be wrong, though, as people are often dumped in bodies of water, and it’s vital that a pathologist determines whether the ingestion of water lead to a person’s passing at all.
No diatoms found within a person’s respiratory system or bloodstream (if they ingested water and it was somehow metabolised within the body) would indicate that an individual died elsehwere and was later thrown in. Sometimes, it’s really the lack of evidence that helps us build the strongest conclusions.
Your Turn: Did you already know all the questions that algae could answer — and you think there’s something important to add? Fascinated by the wonderful structures they create under the microscope? Share your thoughts with us.