Lecture 19 - Advanced Evidence Types 2 Flashcards

1
Q

what are 5 types of environmental trace evidence we looked at

A

diatoms
pollen
foraminifera
phytoliths
soil

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2
Q

what is a diatom

A

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

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3
Q

why are diatoms good for the planet (2)

A

take in carbon and produce oxygen

part of the ocean food chain

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4
Q

how many species of diatom are there

A

approx 200,000

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4
Q

why is the use of diatoms in forensic investigation controversial

A

there have been many cases where a victim died due top something other than drowning but diatoms were found present

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5
Q

how big are diatoms and what are they made of

A

2-500 micrometre in diameter

composed mostly of a silica cell wall - a bacteria cell

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6
Q

how are diatoms typically related to being a type of trace evidence

A

to suggest the victim drowned

diatoms are said to enter the body upon drowning

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7
Q

what was introduced in the 90s relating to the use of diatoms as trace evidence

A

the diatom rule = a significant number of diatoms must be present while preforming diatom test before conclusions are made

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8
Q

give three other ways than drowning diatoms may enter the body

A

consumption of food - particularly seafood

inhaled in low-quality cigars

contamination of equipment used in evidence collection

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9
Q

what makes diatoms ‘unique’

A

they have a biochemistry that has not been seen elsewhere

they have a mechanism of transporting and transferring silica

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10
Q

give 5 reasons why diatoms are a good form of trace evidence

A
  • 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
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11
Q

what is the silica cell wall of a diatom also known as

A

a frustule - made up of two valves

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11
Q

what is included in the analytical workflow of diatoms (4)

A

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

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12
Q

what is an environmental conditions that needs to be taken into account when analysing diatoms

A

seasonal variation

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12
Q

what is meant by acid/alkali treatment of diatoms

A

use of an acid to dissolve the organic material surrounding them

alkali treatment to remove any remaining impurities

helps obtain pure diatoms

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13
Q

in what type of materials is the highest transfer of diatoms observed

give three examples of materials

A

open weave and rough textured materials

e.g linen, acrylic, viscose

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14
Q

do diatoms persist well

why

A

yes because they are small and have a strong silica cell wall making them resistant to degradation

15
Q

what is meant by hydrogen peroxide fixing of diatoms

A

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

16
Q

what affects the level of transfer and persistence of diatoms from their water source to clothing or bodies

A

the species morphology (shape)

not all diatoms transfer an equal amount

16
Q

what are the limitations of using diatoms as trace evidence (4)

A
  1. SEM is good but slow
  2. secondary transfer
  3. they can come from other sources than drowning
  4. there is a need for complex reference libraries as there are 200,000 species = a lot of time and effort
17
Q

what is a foraminifera

where is this used in industry

what does this increase

A

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

17
Q

how big are foraminifera

A

can grow up to 18cm but most are less than 1mm in size

17
Q

what two things are emerging in making the analysis of diatoms easier and quicker

A

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

18
Q

what are the three microscopy methods useful in diatom analysis

A

transmission light
polarised light
SEM

19
what can the shell of a foraminifera be made of (4)
calcite aragonite sediment particles proteins
20
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
21
what is the typical refractive index of a phytolith
1.41 - 1.47
22
where are phytolith's normally used in forensics
tracing human and plant interactions used alongside soil and other environmental trace evidence
23
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
24
give three ways pollen can be dispersed
wind water animals (bees)
25
how big is a particle of pollen and how far can it travel
2-100 micrometre can travel up to 2km from parent plant
26
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
27
what is the study of pollen in forensics called
forensic palynology
28
what makes pollen identifiable to a particular plant
surface texture and features
29
give 5 things make pollen good for trace evidence
1. small size 2. vast amount 3. resistant to destruction 4. ability to be dispersed easily 5. identifiable features
30
what are the two limitations for using pollen as trace evidence
1. the lack of awareness of it's value so people don't handle or identify well 2. limited national or international databases of pollen species relating to locations
31
when a pollen sample is taken what must also be taken
a reference sample from the surrounding area
31
what normally result in pollen evidence becoming contaminated
the lack of skilled people being aware of the sample quality
32
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
32
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