Limnology is the study of inland waters as an interacting ecosystem and the relationships between the organisms living in them and their relationship with their medium. Therefore, forensic limnology can be considered the application of Limnology in a legal scenario.
However, Forensic limnology focuses primarily on the presence of microscopic algal organisms known as diatoms in crime scene samples and victims. These organisms are found mainly in freshwater environments, and their abundance and uniqueness of diatoms allow for their study to be of great use in certain legal investigations.
Forensic limnology is a sub-field of forensic botany that examines the presence of diatoms in crime scene samples and victims. Currently, the primary application of the study of diatoms in forensic investigations is in diagnosing drowning as the cause of death.
What are Diatoms and its Significance
With more than 8000 known species, various colors, sizes (typically less than 200um), and shapes, these diverse asexually reproducing, mostly unicellular microorganisms (some form simple colonies) are defined by their unique cell walls. Most diatoms are non-motile and are found in suspension in aquatic environments and soils, and a range of other moist environments.
Diatoms are classified as algae because they use photosynthesis to generate energy. They use chlorophylls a and c and accessory pigments fucoxanthin and beta-carotene for photosynthesis. These accessory pigments give diatoms their distinct golden color.
The unique silica-based cell wall (known as frustules) causes significant variations in different morphological features of different diatom species. It is made up of two distinct halves or valves in all sorts of odd shapes and sizes. In addition, their shells contain distinct patterns and perforations, allowing substances to pass in and out of the cell. This feature allows for diatoms to be easily identified and distinguished from one another. In addition, these frustules being particularly resistant to decay, enable scientists to detect diatoms in heavily decomposed bodies of drowning victims.
Diatoms can also verify the time of year when samples were taken. They can also identify the species of organisms living in a given region. The species and numbers of diatoms present in a body of water can vary depending on the environment and even the time of year, with diatom populations increasing or decreasing seasonally. For example, in early spring and autumn, the ratio of living diatoms to dead diatoms is high. However, in summer and winter, the amount of dead diatoms out populates the living.
They can also determine the characteristics of the ecosystem.
For example, a higher ratio of periphytic diatoms (i.e., those attached to a substrate), the higher the vegetation concentration, and the shallower the water.
Various features of diatoms make these organisms an excellent candidate for analysis in forensic investigations. Their trace size allows them to transfer readily from the crime scene to the victim and suspect. Their peculiar morphology facilitates easier species identification, plus their predictable and constant variable populations produce unique assemblages of diatoms to identify different water ecosystems.
Analysis of Diatoms:
When they die, the frustules become part of the water sediment. Therefore, The frustules of dead organisms can be compared with those of the living diatoms to measure the environment’s characteristics.
Identification of species commonly can be identified using the light microscope. In addition, scanning electron microscopy (SEM) typically used when viewing the organism as a whole, and Transmission electron microscopy (TEM) is utilized to produce images with greater magnification and resolution when focussing on specific features of the diatom’s morphology. Different methods are employed for its analysis, yet all these techniques aim to identify various diatomic colonies’ ratios present in the samples collected from the victim or suspect to compare with those collected from crime scenes, human bodies, or water bodies.
The extraction of diatoms from human remains is often achieved through acid extraction of the tissue sample or bone marrow, such as nitric or sulphuric acid.
