Lecture 19 - Advanced Evidence Types Part 2 Flashcards
1
Q
What are diatoms?
A
- Diatoms are a type of phytoplankton, which is a eukaryotic algae
- Generally between 2-500μm in diameter with a silica cell wall
- Most of them sit in the 200-300 range.
- Unique in the their biology
- Cells are made of silica
- Take in over 6.5 billion tonnes of silicon every year
- ~200,000 species making up a significant proportion of the Earth’s biomass
- Nearly half of the organic material found in the ocean
- Contribute significantly to sequestering carbon and producing oxygen
- Found near or in bodies of water.
- Can be used to estimate place and TOD depending on where and how it’s found.
2
Q
Why are diatoms great for the planet?
A
- Diatoms fix 10-20 Gigatonnes of CO2 every year through photosynthesis!
- In the process of them fixing it they produce 20-50% of the oxygen we breathe.
- As a result, vital for the long-term sequestration of carbon for a long period of time
- Vital part of the oceanic food chain
- They take in nitrogen in as well.
- They are consumed by animals and then when those animals die they fall to the bottom of the ocean with a load of carbon hidden. Carbon that has been taken out of the atmosphere, the long term removes it from the ocean. This then gets compressed and reconverted into oil and gas over a long period of time.
3
Q
Diatoms
History
A
- First suggested in 1861 by W.A. Guy that diatoms would enter the body during drowning- Hofmann detected them in lung fluid in 1896
- By 1942 shown to be transferred to multiple organs, in the blood, via the lungs during drowning and regularly being used to identify drowning victims by the 1960s
- 1990s showed the development of the ‘diatom rule’ - A significant number of diatoms must be present while preforming diatom test before coming to any final conclusion
- At least need to be 10-20 diatoms present as a general rule.
4
Q
Diatoms as forensic trace evidence
A
- Many cases where victims died due to other reasons than drowning but diatoms are still found present which is controversial.
- Consumed in foodstuffs
- Inhaled in low quality cigars
- Contamination of equipment
- Contamination of autopsy equipment through cleaning is a problem.
- Anything that is processed with water in anyway could contain diatoms
5
Q
Why are diatoms an excellent form of trace evidence?
A
- Diverse group of species with small size range which makes their entry inside the body organs feasible.
- Hard silica cell wall is resistant to the chemical changes - Helps in recovering of intact structure of diatoms from body or clothes.
- Can exist inside and outside the body
- Even when the organs have been putrified you’ll still find diatoms in there.
- Their growth corresponds to certain specific parameters of the environment - Analysis therefore allows cause and site of death to be concluded.
- Wide range of study has been done on the taxonomy of diatoms due to which these species are easy to identify and trace.
- Around 20,000 species have been identified.
- Small so the can sit on top of the body, on clothes or other items meaning they can easily be transferred.
6
Q
Taxonomy and chemistry of diatoms
A
- Classing of diatoms is now a complex process with the evolution of molecular understanding -
- Contain unique silica cell walls known as frustule made up of two valves
- Mechanism of transferring and transporting silica is unknown but they have a unique biochemistry that isn’t repeated anywhere else
- Defined by their shape and their porous valve and the number of those.
- Unique biochemistry makes them interesting.
7
Q
Analytical workflow of diatoms
A
- The primary concern is to identify them so this will involve some chemical processing.
- Different chemical extraction approaches
- Hydrogen peroxide, acid or alkali seperation in order to break them down and take it own.
- Then using a basic transition microscope to count the number of diatoms.
- Identify the ones there
- Move to SEM so you can see the detail within them. SEM has the resolution required to obtain the desired detail.
- There is a possibility to be able to do this with a light microscope but the standard at the moment is to use SEM.
8
Q
Transfer and persistance of diatoms
A
- Highest transfer to open weave and medium-rough textured materials e.g Linen, acrylic, viscose material.
- Seasonal variation has to be taken into account.
- Species morphology affects the level of transfer and persistence from a water source to clothing or footwear.
- Not all diatoms will be transferred, smoother surface ones will transfer less.
- They transfer and persist quite easily as they are small.
- Lowest transfer was to things like nylon, lycra and pvc which is smoother and tighter weave.
9
Q
Limited entrainment of diatoms
A
- Striae
- Raphe
10
Q
Successful entrainment of diatoms
A
- Spines
- Pores & aerolae
11
Q
Annie Börjesson
Case study of diatoms
A
- Annie Börjesson - Found dead on Prestwick Beach 4th December 2005
- Assigned a suicide but the mother didn’t believe this.
- If it was death by suicde then the diatoms found form freshwater environments shouldnt have been found.
- This suggest she was killed elsewhere and then moved to this location.
12
Q
Stenges pond attacl
Case study of diatoms
A
- Two young boys fishing in 1991 on a pond in Connecticut attacked at knife point, bound with duct tape, beaten with a baseball bat and dragged into pond to drown by group of teenagers.
- No fingerprints on baseball bat, no other apparent evidence to link suspected teenagers to the crime scene except mud on trainers.
- Diatoms extracted from mud on trainers of suspects, victims and also from a reference sample of the mud at the pond to compare.
- 25 species of diatom identified in common on all samples - population ratio also compared for 3 of the species which also matched between all samples increasing discrimination certainty.
- The species in common wasn’t sufficient enough to make a link between them because in the area other water sources like lakes could have contained those same species. This is why the population ratio was helpful.
- Convicted May 1992
13
Q
Diatoms caveats and future research?
A
- Cross contamination and secondary transfer is a big issue
- Automated AI/Machine Learning systems are emerging as processes able to speed-up identification workflows enabling the usage of diatoms as trace evidence to become more widely adopted.
- Molecular barcoding combined with big-data approaches is also emerging as an exciting new field for rapid tracing and identification.
- All these require complex reference libraries of samples and data to be collected and maintained marking seasonal and geographic locations which is a big job.
- SEM to analyse them is slow.
14
Q
Foraminifera as Trace Evidence
A
- Early observation by Robert Hooke in Micrographia (1665).
- 1/6th of Earth’s surface covered in microfossil-bearing sediment and marine limestone used widely in building and industry increases their potential as forensic trace evidence.
- Limited usage to date as trace evidence.
- SImilar to diatoms in the fact that they have a hard outer shell.
- Limestone is used a lot so we are taking them out of the environment so they could be traced.
15
Q
What are foraminiferas?
A
- Single celled organisms - the majority live on the sea floor and have an external ‘shell’
- Can grow up to 18cm but majority are less than 1mm in size.
- Shell can be made up of calcite, aragonite, sediment particles or proteins.
- Often referred to as microfossils and they sediment and produce limestone when they’ve been compressed and when they’ve hardened.
