Diatoms are specifically microalgae found in water bodies, moist areas, and even on soils. They are mostly photosynthetic, unicellular, and evolved several million years ago. Diatoms contain a variety of taxon around 100,000 species. They can be seen in both marine and freshwater mediums. It is the type of organism which carries importance during their lifetime and even after death.
There are various species of diatoms on earth. This causes quite confusion when one comes to the identification of species. The issue can be solved by the designs of frustules. The diatoms cell wall is composed of silica which made from silicic acid and is coated with organic layers, pectins, cellulose, and many polysaccharides The silica contained cell wall of diatoms forms like pillbox cover consist of overlapping halves; which are:
Gridle is the region where both theca fits together. Diatoms are divided into 2 symmetries; Centrals [radially symmetrical] and pennales [bilaterally symmetrical] in pennales there is the presence of slits called raphe. There are species that lack raphe called pseudoraphethis raphe is interrupted at its middle point by a thick wall known as central nodules. The polar nodules are also characterized by the thickening.
Each theca consist of 2 parts:
- Valve; the upper flattened top
- Cingulum; connecting band
Domain = Eukaryota
Kingdom = Chromalveolata
Phylum = Heterokontophyta
Class = Bacillariophyceae
Order = Centrales , Pennales
- Diatoms play a valuable role in oceans by producing 45 % of the total primary production of ocean bodies. It also offer enormous oxygen to the atmosphere and they are the source of food to various organisms in the environment.
- Diatoms use the energy of the sun and convert it into chemical energy.
- Diatoms have a fossil record, some rocks are formed by the fossils of diatoms known as diatomite / diatomaceous earth. The silica sedimentary rocks are used in the production of toothpaste, insecticides, and various paints. The transformed silica from the cell wall of diatoms is transformed into stones that are identical to gemstone opal.
- Diatoms are widely known as’’ Quality checker of aquatic bodies’’.
Diatoms play an important role in the conclusion of drowning cases. The diatoms can act as trace evidence and help to link the suspect and crime scene. By performing the diatom test, one can estimate the postmortem interval or time since death. Different species of diatoms can be seen in different areas depending on the environment, seasons.
The person in the water medium contains diatoms, which can move to alveolar spaces and blood circulation by inhalation during drowning. The diatoms can be transferred into various organs of the body. These diatoms can be observed after the diatom test and used as corroborative evidence of the drowning cases and can find the drowning is antemortem or postmortem. The collection of diatoms from bone marrow [which is usually taken from the femur] can be used for confirmation of drowning.
- Nitric acid method [mostly used method]
- Sulphuric acid method
A 26 -year old female body has found near the bank of wular lake [sited in bandipora district in Jammu & kashmir]. The autopsy report traced the injury on the head and neck. the lake water contains 2 diatom species (nitzschia subtitles and navicula radiosa ) the bone marrow has tested by nitric acid test from sternum and clavicle extract. There was no presence of diatoms that were negative. This led to the conclusion that the death was not due to drowning. Later by questioning the relatives investigation officers found it was murder by her husband because of extramarital affairs.
The diatoms are significant in investigations related to drowning. Since morphologically variant species are present in different areas this also helps to determine the location and site of drowning or primary crime scenes.
Sources & References
1. Role of diatoms in the forensic diagnosis of drowning cases from Jammu & Kashmir, India(2014) http://bbrc.in/bbrc/papers/pdf%20files/Volume%207%20-%20No%201%20-%20Jun%202014/BBRC_014.pdf
2. Study of diatoms Biodiversity study of Ganga river and residential pond water https://www.slideshare.net/cammyr1/study-of-diatoms
3. Diatoms UCL https://www.ucl.ac.uk
AMRUTHA P DHASARAD
B.Sc. (FORENSIC SCIENCE)
JAIN ( Deemed -to-be-university)