Lecture 19 - Advanced Evidence Types 2 Flashcards
what are 5 types of environmental trace evidence we looked at
diatoms
pollen
foraminifera
phytoliths
soil
what is a diatom
a type of phytoplankton which is a type of eukaryotic algae
a microorganism that exists in or near water - make up nearly half of the organic material in the ocean
why are diatoms good for the planet (2)
take in carbon and produce oxygen
part of the ocean food chain
how many species of diatom are there
approx 200,000
why is the use of diatoms in forensic investigation controversial
there have been many cases where a victim died due top something other than drowning but diatoms were found present
how big are diatoms and what are they made of
2-500 micrometre in diameter
composed mostly of a silica cell wall - a bacteria cell
how are diatoms typically related to being a type of trace evidence
to suggest the victim drowned
diatoms are said to enter the body upon drowning
what was introduced in the 90s relating to the use of diatoms as trace evidence
the diatom rule = a significant number of diatoms must be present while preforming diatom test before conclusions are made
give three other ways than drowning diatoms may enter the body
consumption of food - particularly seafood
inhaled in low-quality cigars
contamination of equipment used in evidence collection
what makes diatoms ‘unique’
they have a biochemistry that has not been seen elsewhere
they have a mechanism of transporting and transferring silica
give 5 reasons why diatoms are a good form of trace evidence
- they are a diverse group of species that are small so likely to enter or reside on the body - can also help suggest location changes before or after death
- hard silica cell wall so resistant to chemical changes
- trace so may still be available when other evidence is not
- their growth corresponds to specific parameters of the environment - can suggest cause and site of death
- easy to identify suggesting in research
what is the silica cell wall of a diatom also known as
a frustule - made up of two valves
what is included in the analytical workflow of diatoms (4)
count them under a microscope
chemical processing to identify the diatom specie
hydrogen peroxide fixing or acid/alkali treatment = to remove them from the organic sample
SEM imaging to give details
what is an environmental conditions that needs to be taken into account when analysing diatoms
seasonal variation
what is meant by acid/alkali treatment of diatoms
use of an acid to dissolve the organic material surrounding them
alkali treatment to remove any remaining impurities
helps obtain pure diatoms
in what type of materials is the highest transfer of diatoms observed
give three examples of materials
open weave and rough textured materials
e.g linen, acrylic, viscose
do diatoms persist well
why
yes because they are small and have a strong silica cell wall making them resistant to degradation
what is meant by hydrogen peroxide fixing of diatoms
to preserve and prepare diatoms for examination
treat with hydrogen peroxide to remove organic matter and make the silica cell wall more visible under the microscope
what affects the level of transfer and persistence of diatoms from their water source to clothing or bodies
the species morphology (shape)
not all diatoms transfer an equal amount
what are the limitations of using diatoms as trace evidence (4)
- SEM is good but slow
- secondary transfer
- they can come from other sources than drowning
- there is a need for complex reference libraries as there are 200,000 species = a lot of time and effort
what is a foraminifera
where is this used in industry
what does this increase
a single celled organism = a type of microfossil
most live on the sea floor and they have an external ‘shell
in the form of limestone
increasing their use as a source of trace evidence
how big are foraminifera
can grow up to 18cm but most are less than 1mm in size
what two things are emerging in making the analysis of diatoms easier and quicker
automated AI/Machine learning systems = for identification workflows
molecular barcoding = for trace and identification
allowing diatom analysis to become more accessible so we don’t need experts
what are the three microscopy methods useful in diatom analysis
transmission light
polarised light
SEM
what can the shell of a foraminifera be made of (4)
calcite
aragonite
sediment particles
proteins
what is a phytolith
what is it made of
a plant microfossil found to persist after the death and decay of plants where it is released into soil
silica - mainly silicon dioxide
what is the typical refractive index of a phytolith
1.41 - 1.47
where are phytolith’s normally used in forensics
tracing human and plant interactions
used alongside soil and other environmental trace evidence
what is pollen
what makes pollen readily available
a powder that contains male gametophytes of seed producing plants
a single anther can produce 50-250,000 pollen grains depending on the species
give three ways pollen can be dispersed
wind
water
animals (bees)
how big is a particle of pollen and how far can it travel
2-100 micrometre
can travel up to 2km from parent plant
what makes pollen persistent (2)
they have a hard coating to protect them as they are transported
they have excellent adhesion properties to clothes, hair, soil, vehicles, and even in the stomach
what is the study of pollen in forensics called
forensic palynology
what makes pollen identifiable to a particular plant
surface texture and features
give 5 things make pollen good for trace evidence
- small size
- vast amount
- resistant to destruction
- ability to be dispersed easily
- identifiable features
what are the two limitations for using pollen as trace evidence
- the lack of awareness of it’s value so people don’t handle or identify well
- limited national or international databases of pollen species relating to locations
when a pollen sample is taken what must also be taken
a reference sample from the surrounding area
what normally result in pollen evidence becoming contaminated
the lack of skilled people being aware of the sample quality
what are the 3 stages in the workflow of pollen
chemically processed to be prepared for analysis
SEM - surface analysis but time consuming
Semi-automated TLM and fluorescence microscopy = quicker alternative to SEM
what is an emerging method for the analysis and identification of pollen samples
molecular barcoding = the use of short DNA sequences to identify and differentiate individual samples
