The Toe Tag: Death and diatoms 

The unique ecosystem of each body of water can be used as a tool to identify crime scenes in and near them.

click to enlarge diatom2.png

Did you know that types of algae can be used to help link victims (and suspects) to death scenes in and near bodies of water because of their unique groupings?

Forensic limnology is the study of freshwater ecology, in a legal setting. More specifically, it is the study of diatoms. But what are diatoms and what do they have to do with death?

In brief, diatoms are photosynthetic, microscopic organisms that reside in lakes, oceans, swimming pools, ponds, rivers, reservoirs, and soil. They are best known for their silica frustules, or outer coatings. This unique glasshouse that surrounds the diatom allows them to be resistant to many things, and, even after the organism dies, the frustule can remain for centuries. The structure of their glasshouse is unique to their environment and species identification.

The pathologists at our office never talked about them, and during my tenure as a death investigator who worked many drownings, I had never encountered such a thing, but the science was originally developed in Europe in the 1960s. When a person dies, the forensic pathologist takes a sample of bone marrow, most commonly the femur, and dissolves it in acid. If present, the silica shell of what once was a living diatom will remain and be viewable under a microscope. Pathologists then compare the species of diatom to the suspected drowning media (whether that was a bathtub, lake, river, etc) and if the species matched the postmortem diatoms, they would use that as a basis for diagnosing drownings. Researchers think that for diatoms to enter the bone marrow, they must first be breathed into the lungs antemortem (before death) then perforate the alveolar-capillary barrier and migrate into cardiopulmonary circulation which disperses blood to the rest of the body, including bone marrow. The marrow is somewhat hollow and least susceptible to cross-contamination during autopsy. If the body was dumped postmortem, researchers think the diatoms won’t make it into the bone marrow due to lack of active breathing.

Diatoms are very resistant to many things, including most acids, and already exist in our human tissues for potentially lengthy periods. This is not likely from your average tap water, but maybe from summer lake trips, so the presence of diatoms in the marrow would make it difficult to diagnose drownings just by their presence. What diatoms can determine is whether a crime was committed in a specific water source based on the species. This method has also been used in cases of near-drownings. The sediment encrusted sneakers of the suspects were compared with that of the victim’s sneakers and a sample of water from a local pond where the incident occurred. Since all evidence items shared the exact same species of diatoms, this evidence was used in court to convict the suspects. The same method can be used by collecting samples from a drowning victim’s clothing or body, the suspect’s clothing, and the drowning medium itself, thus linking them to a common water source.

Although not a trusted source to diagnose death by drowning, diatoms prove to be a very underutilized and understudied tool in the forensic arena. Much more research needs to be done to increase their scientific rigor in court as they can be beneficial in cases of maritime crimes, assaults and homicides that occur in or near water. In many cases, These prehistoric organisms might be the link that brings justice to victims.

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