Lecture 19 - Advanced Evidence Types 2

Question 1

what are 5 types of environmental trace evidence we looked at

Answer 1

diatoms
pollen
foraminifera
phytoliths
soil

Question 2

what is a diatom

Answer 2

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

Question 3

why are diatoms good for the planet (2)

Answer 3

take in carbon and produce oxygen

part of the ocean food chain

Question 4

how many species of diatom are there

Answer 4

approx 200,000

Question 4

why is the use of diatoms in forensic investigation controversial

Answer 4

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

Question 5

how big are diatoms and what are they made of

Answer 5

2-500 micrometre in diameter

composed mostly of a silica cell wall - a bacteria cell

Question 6

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

Answer 6

to suggest the victim drowned

diatoms are said to enter the body upon drowning

Question 7

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

Answer 7

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

Question 8

give three other ways than drowning diatoms may enter the body

Answer 8

consumption of food - particularly seafood

inhaled in low-quality cigars

contamination of equipment used in evidence collection

Question 9

what makes diatoms ‘unique’

Answer 9

they have a biochemistry that has not been seen elsewhere

they have a mechanism of transporting and transferring silica

Question 10

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

Answer 10

• 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

Question 11

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

Answer 11

a frustule - made up of two valves

Question 11

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

Answer 11

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

Question 12

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

Answer 12

seasonal variation

Question 12

what is meant by acid/alkali treatment of diatoms

Answer 12

use of an acid to dissolve the organic material surrounding them

alkali treatment to remove any remaining impurities

helps obtain pure diatoms

Question 13

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

give three examples of materials

Answer 13

open weave and rough textured materials

e.g linen, acrylic, viscose

Question 14

do diatoms persist well

why

Answer 14

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

Question 15

what is meant by hydrogen peroxide fixing of diatoms

Answer 15

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

Question 16

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

Answer 16

the species morphology (shape)

not all diatoms transfer an equal amount

Question 16

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

Answer 16

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

Question 17

what is a foraminifera

where is this used in industry

what does this increase

Answer 17

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

Question 17

how big are foraminifera

Answer 17

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

Question 17

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

Answer 17

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

Question 18

what are the three microscopy methods useful in diatom analysis

Answer 18

transmission light
polarised light
SEM

Question 19

what can the shell of a foraminifera be made of (4)

Answer 19

calcite
aragonite
sediment particles
proteins

Question 20

what is a phytolith

what is it made of

Answer 20

a plant microfossil found to persist after the death and decay of plants where it is released into soil

silica - mainly silicon dioxide

Question 21

what is the typical refractive index of a phytolith

Answer 21

1.41 - 1.47

Question 22

where are phytolith’s normally used in forensics

Answer 22

tracing human and plant interactions

used alongside soil and other environmental trace evidence

Question 23

what is pollen

what makes pollen readily available

Answer 23

a powder that contains male gametophytes of seed producing plants

a single anther can produce 50-250,000 pollen grains depending on the species

Question 24

give three ways pollen can be dispersed

Answer 24

wind
water
animals (bees)

Question 25

how big is a particle of pollen and how far can it travel

Answer 25

2-100 micrometre

can travel up to 2km from parent plant

Question 26

what makes pollen persistent (2)

Answer 26

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

Question 27

what is the study of pollen in forensics called

Answer 27

forensic palynology

Question 28

what makes pollen identifiable to a particular plant

Answer 28

surface texture and features

Question 29

give 5 things make pollen good for trace evidence

Answer 29

1. small size
2. vast amount
3. resistant to destruction
4. ability to be dispersed easily
5. identifiable features

Question 30

what are the two limitations for using pollen as trace evidence

Answer 30

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

Question 31

when a pollen sample is taken what must also be taken

Answer 31

a reference sample from the surrounding area

Question 31

what normally result in pollen evidence becoming contaminated

Answer 31

the lack of skilled people being aware of the sample quality

Question 32

what are the 3 stages in the workflow of pollen

Answer 32

chemically processed to be prepared for analysis

SEM - surface analysis but time consuming

Semi-automated TLM and fluorescence microscopy = quicker alternative to SEM

Question 32

what is an emerging method for the analysis and identification of pollen samples

Answer 32

molecular barcoding = the use of short DNA sequences to identify and differentiate individual samples