The use of diatoms in forensic:

Diatoms are aquatic unicellular plants with around 100'000 species. Usually used to determine the quality of water.

If a person drowns water will flow into the lung. During the respiration, diatoms are able to slip through the lung into the blood. As soon the diatoms are in the blood stream, they travel through the system. From the lungs into the heart, to the liver, kidney, bone marrow, brain and so on.

This process only can happen if the person still is alive at the time of being in the water. The drowning process can take several minutes, especially if the person is conscious.

There comes the significance of the diatoms. Diatoms should only be found in bodies which where alive of the time of being in water.

This sounds very easy, but it isn't.

There are many factors that make the value of this method doubtful and difficult.

Are there a lot diatoms in the water?
If the person was unconscious was there enough time for the diatoms to flow into the system?
If it was a heart attack, was the heart still beating to transport the diatoms into the system?

Diatoms are not only found in water but as well in air and earth. Diatoms are of course as well on the skin and clothing of a recovered body from the water. This makes the possibility of contamination very high.

To extract the diatoms from a body, organs and fluids can be taken as samples such as liver, kidney, bone marrow, brain, blood, and lung and so on. What samples are taken depends on the policy of the morgue.

The most important thing during taking those samples is cleanliness to avoid contamination.

To determine contamination the diatoms found in the samples have to be compared with the diatoms found in the water at the possible drowning location. This can be at the same place where the body was found (lake) or maybe at the place where the body is believed to be drowned (in case of a river the body most probably was transported down the river a while after drowning).

The fact that there are so many different species allows the diatomist to compare the diatoms from the water samples and from the samples from the body.
If the diatoms are not the same, a contamination is possible.

To isolate / extract the diatoms different methods are known. We used chemical digestion method (cooking the organs with acid) others are using enzymatic digestion method or the ashing method.

Diatoms in forensic is a field with a lot pro's and cons. Papers are written about it for almost 100 years.

Conclusion:
I was part of a research team for over 4 years and we had several successes, but also many difficulties. In my opinion the science of the diatoms is worth it, but only in special cases. This because it is very time consuming and expensive.

Important points:

Contamination free taking of samples
Taking a water sample of the drowning location
Involving of a experienced diatomist