Pollen Grains
Source of Pollen Evidence
# Dirt, Mud or dust recovered from person/object # Hair & Fur # Woven cloth, bags, baskets & ropes # Imported/Exported goods - verify country of origin # Antique goods - validate age & authenticity (Coins)
Preservation
# Pollen evidence can remain at scene for many years after event # nature of fabric of items trapping pollen important factor # Loosely woven fabric - trap more pollen # Synthetic fabric - static electricity # Pollen Rain - pollens picked from C.S may not be only from current season but others deposited years ago
The significance of Pollen Evidence in a Forensic Context
# Pollens are MICROSCOPIC - widely dispersed by various ways in environment # EASILY RETAINED in Clothing - embedded in Carpets & in Soil # Highly resistant to DEGRADATION & can survive for many years # Pollen evidence collected from a burglary entrance & a suspect's shoes could provide a LINKAGE in a case # Pollen morphology can help identify the PLANT GENUS & GEOGRAPHICAL LOCATION
Various methods used to Extract Pollen Grains from Soil & Plant Material
ACETOLYSIS # Used to remove the cellulose # Glacial Acetic acid with Sulphuric acid (9:1) HYDROFLUORIC ACID # Dissolves silica & quartz present in soil KOH (potassium hydroxide) # Breaks down sediments & removes humic acid # Once extracted stain & mount for microsocopy
Abundance & Dispersal
AQUATIC TRANSPORT # Aquatic Angiosperms live submerged/release pollen underwater - water currents transport pollen from male anther to female stigma # Not preserved in sediments & oxides rapidly if removed from water # Litlle potential forensic value SELF-POLLENATION # little pollen needed - produce <100 pollen grains per anther # rarely dispersed in atmosphere - little forensic value ZOOGAMOUS TRANSPORT # Transported by insects/animals - readily preservable # Excellent forensic value - remain preserved in deposits for long period of time/ less susceptible to destruction - produced in low amounts thus not contaminate in pollen rain WIND POLLENATION # most inefficient method of dispersion - travel easily in air current # forensically useful as are aerodynamic - simple morphology with thin walls
Pollen background
PALYNOLOGY # the study of pollen # Pollen are male gametophytes of the angiosperms (flowering plants) & gymnosperms (have no flowers/fruit)
Methods used to collect pollen evidence & precautions taken
SAMPLE COLLECTION # Should be collected by EXPERIENCED PALYNOLOGIST (untrained staff may miss important areas) # Palynologist should visit scene ASAP before any CONTAMINATION takes place # Every C.S diff so palynologist should consult investigating team for appropriate SAMPLING STRATEGY # Comprehensive SITE SURVEY & PHOTOS taken Samples collected with CLEAN IMPLEMENT & placed in a STERILE CONTAINER # Sampling implement throughly clean after each sample taken - better to use NEW ONE each time PRECAUTIONS #If collected by hand - STERILE GLOVES worn # Avoid CONTAMINATION # Samples should be well LABELLED & SEALED in ZIP-LOCK BAG or SCREW TOP PLASTIC BOTTLES # Shouldnt be stored in paper bag ( may contain ambient pollen) # Sufficient CONTROL SAMPLES taken to understand variation of pollen rain over area
Pollen Morphology
SIZE # 20-60u # Easily picked up from a scene in Hair, Clothing, Fingernail - transported away from scene # Size can vary within a single anther SHAPE # Spherical, Oval, Triangular # Many grains occur singly, others as group PORES # Round pores SCULPTURE PATTERN on SURFACE # Outer layer (exine) - diff patterns within exine # Granules, Spines etc
