What is Diatom Analysis? A Forensic Test for Drowning

Diatom Analysis is a forensic technique that involves the isolation, identification, and comparison of microscopic algae called diatoms to support a diagnosis of drowning. Because diatoms have unique, durable shells and their species composition varies by location, this analysis can help determine not only if a person drowned but also where they may have drowned.

What Are Diatoms?

Diatoms are single-celled algae found in almost every aquatic environment on Earth, from oceans to rivers, lakes, and even damp soil. Their most important feature is a unique, ornate cell wall made of silica called a frustule. These silica shells are extremely durable and have species-specific shapes, allowing them to be identified long after the organism has died.

The Diatom Test for Drowning

The primary forensic application of diatom analysis is to help confirm drowning as the cause of death. The principle is as follows:

• If a person is alive when they enter the water, their involuntary breathing actions will cause them to inhale water deep into their lungs. The microscopic diatoms in that water can then pass through the alveolar walls into the bloodstream.
• The heart circulates this diatom-rich blood throughout the body, depositing the silica shells in distant organs, most importantly the bone marrow, liver, and kidneys.
• Conversely, if a person is already dead when placed in the water, there is no circulation. Water and diatoms may enter the lungs, but they will not be transported to the bone marrow or other internal organs.

Therefore, finding a significant number of diatoms within the sealed environment of the bone marrow is strong evidence that the person was alive and actively breathing when they were submerged in water.

Linking a Victim to a Location

Different bodies of water—a specific pond, a river, or a stretch of coastline—have their own unique ecological signature, including a distinct population of diatom species. By taking water samples from where a body was recovered, a forensic scientist can:

1. Create a profile of the diatom species present in the water.
2. Compare this profile to the species extracted from the victim’s body.

A strong match confirms the location of drowning. A mismatch suggests the person drowned in a different body of water and was subsequently moved.