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The microscopic world of diatoms: How they reveal the truth in forensic investigations

Forensic science is a fascinating field that combines the latest scientific techniques with criminal investigation. From analysing DNA to examining fingerprints and other physical evidence forensic scientists use a variety of tools and techniques to uncover the truth behind even the most complex cases. One area of forensics which that has gained significant attention is the use of natural materials such as diatoms in criminal investigations which is particularly studied in the field of forensic limnology which is the branch of forensics that involves the study of freshwater ecosystems (such as lakes, rivers, and streams) to assist in the investigation of crimes.

Diatoms- What are they?

Diatoms are a type of single-celled algae belonging to kingdom Protista that play a crucial role in the world’s ecosystems. These microscopic organisms are found in almost every aquatic environment, from oceans to freshwater streams and even in soil. They are known for their intricate and beautiful silica-based shells, which make them an important tool for forensic scientists in determining the origin of a sample.
By analysing diatoms from the water samples, the lungs of ante-mortem and post-mortem drowning victims and other sources forensic investigators can determine the location where the sample was taken and potentially link it to a crime scene.

History of diatoms in forensic investigations

Diatoms have long been used in forensic investigations. It was first introduced in the 19th century by Austrian scientist Franz von Hochstetter, who used diatoms to determine the source of a soil sample. Since then, diatoms have been used in a wide range of forensic investigations, including homicide cases, drowning investigations, and even the investigation of oil spills.

Basic principle behind using diatoms in forensics

The basic principle behind using diatoms in forensic science is that diatoms are ingested by a person during drowning and can be found in various organs and tissues such as lungs, liver, and bone marrow. By analysing the diatom content of these organs and tissues, forensic investigators can determine whether a person was alive or dead when they entered the water.

Process of diatom examination

Diatoms need to be cleaned before being inspected. Removal of cell components, pigments, sand, sludge, and other materials that could obstruct microscope inspection is required. Femoral or sternal bone marrow are convenient places to get a sample for diatom analysis. It is important to use dry, clean tools to prevent contamination from foreign objects. A little window is cut into the sternum after the sternum has been removed, exposing the marrow. The marrow is scraped out in minute pieces and placed in a test tube. The marrow is then subjected to acid digestion by being combined with strong nitric acid and heated until a clear fluid is produced. This is cooled, followed by centrifuging, then microscopically examining the sediment.

Scanning electron microscope and Diatom analysis

SEM is particularly useful in forensic investigations as it can help identify diatom species that may be difficult to differentiate based on their physical characteristics alone. SEM can provide information on the shape, size, and ornamentation of diatoms that can aid in species identification.
Hence, SEM is a powerful tool in diatom analysis in forensic investigations. It allows for more detailed and accurate species identification, as well as providing additional information about the diatom samples that can be used in criminal investigations.

Advantages

One of the most significant advantages of using diatoms in forensics is their ability to withstand environmental changes. Unlike other types of evidence that can degrade over time or be contaminated by outside sources, diatoms are relatively stable and can survive in a sample for years. This makes them an ideal tool for cold cases or investigations where the evidence has been stored for an extended period.

Limitations

While diatoms are a valuable tool for forensic investigations, there are some limitations to their use. For example, diatoms can be difficult to identify accurately, and the process of analysing them can be time-consuming. Additionally, diatoms may not be present in all water samples, which can limit their usefulness in certain investigations.

Future advancements in diatom analysis

Advancements in diatom analysis are likely to focus on improving the accuracy and sensitivity of the technique, as well as making it more efficient and cost-effective. Some potential future advancements in diatom analysis may include, High-throughput sequencing, molecular biomarkers, automated analysis, nano-scale analysis and much more.
In conclusion, diatoms are an essential tool in forensic investigations, providing valuable insights into the location and timing of a crime. With continued research and development, diatoms may become even more useful in forensic investigations, leading to more accurate and reliable results.