Forensic Biology: Pollens and Diatoms in Forensic Investigation

Medium-band UGC-NET Forensic Science Paper II Unit VII drill covering forensic palynology, pollen morphology, and diatom-based drowning analysis. The set opens with pollen wall architecture: the bilaminar exine divided into the outer sexine (ektexine) and the inner nexine (endexine), the sculptured surface of the sexine that distinguishes taxa under SEM, and the role of sporopollenin in conferring near-indestructible preservation. Aperture classification follows: monocolpate, tricolpate, and triporate pollen types; colpate (elongated furrow), porate (circular pore), and colporate (combined furrow-pore) configurations that form the first axis of pollen identification in palynology. Forensic palynology applications are examined next: how an airborne or soil-deposited pollen assemblage links a suspect, vehicle, or footwear to a geographic origin or crime scene; landmark case studies from Mildenhall and colleagues; and the Indian research context of Bera and Anita Reddy on regional pollen flora that underpins casework by AIIMS Delhi forensic medicine and CFSL Kolkata. Pollen preservation in soil (acid-resistant sporopollenin survives pH extremes), on clothing fibres (mechanical retention), and in airway mucus (inhaled antemortem record) is covered with its evidentiary significance.

The diatom half of the set covers the siliceous frustule of class Bacillariophyceae, pennate versus centric symmetry, and the diagnostic genera Naviculaceae (family), Pinnularia, Cymbella, and Synedra used in Indian drowning casework. The diatom test for drowning is explained mechanically: when a living person inhales water containing diatoms, frustules enter the pulmonary circulation, cross into the systemic bloodstream, and are deposited in distal sites including the bone marrow of the femur. Post-mortem immersion does not drive this passive circulation. Acid digestion of femur marrow using concentrated nitric acid or sulfuric acid with hydrogen peroxide destroys organic matter and releases intact siliceous frustules for microscopic counting. The accepted quantitative threshold of more than five to ten frustules per 100 microlitre aliquot, the Ganges-Yamuna diatom flora as the reference assemblage for North Indian cases, and test limitations including false positives from environmental inhalation and false negatives from small-volume drowning complete the set.

Topics covered:

• Pollen wall layers: sexine (ektexine), nexine (endexine), sporopollenin chemistry
• Aperture types: colpate, porate, colporate, and their taxonomic significance
• Forensic palynology: linking pollen assemblages to geographic locations and crime scenes
• Pollen preservation in soil, clothing, and airway mucus
• Diatom frustule, Bacillariophyceae class, pennate versus centric symmetry
• Diatom drowning test: circulation principle and femur marrow deposition
• Acid digestion of marrow (HNO3 and H2SO4/H2O2) to recover frustules
• Diatom genera: Pinnularia, Cymbella, Synedra, Naviculaceae

Work through each question before checking the explanation, and revisit every wrong answer against the cited Saferstein, Knight and Saukko, Sharma B.R., and Mildenhall references. Allow 30 minutes.