Diatoms, forams, pollen Flashcards
1
Q
What are diatoms?
Where is it found primarily?
What is their size and structure?
How do they work?
How many species and what do they makeup of ocean?
A
- diatoms are a type of phytoplankton which is a eukaryotic algae
- found in bodies of water primarily or near bodies of water e.g. beaches
- between 2-500 um in diameter with a silica cell well (known as frustule made up of two valves. mechanism of transferring and transporting silica is unknown but they have unique biochemistry not found anywhere else)
- most are between 2-300 um range
- they take in over 6.5 billion tonnes of silicon every year, process it and make it into the outside of their shell
- about 200k species making up significant proportion of earths biomass
- nearly half the organic material found in ocean
2
Q
Why are diatoms good for the planet
A
- they fix 10 - 20 gigatonnes of CO2 every year through photosynthesis
- contribute significantly to sequestering carbon and producing oxygen (around 20 - 50 % of oxygen produced on planet)
- they are a vital part of the oceanic food chain
- will be eaten, when animals die, they fall with loads of carbon sequestered
- as a result they are vital for long term sequestration of carbon for a long period of time
3
Q
How were diatoms introduced as trace evidence?
A
1861: first suggested by W.A. Guy that diatoms would enter body during drowning
1896: Hofmann detected them in lung
1942: shown to be transferred to multiple organs, in blood, via lungs during drowning
1960: regularly being used to identify drowning victims
1990: diatom rule where a significant number of diatoms must be present while performing diatom test before coming to any final conclusion (10 - 20)
4
Q
What introduced controversy of using diatoms to detect victims of drowning?
A
- there are cases where victims died not due to drowning but diatoms are still found to be present
- diatoms are:
- consumed in foodstuffs (anything processed with water)
- inhaled in low-quality cigars
- contamination of equipment during collection through any processes through to autopsy if water used to clean
5
Q
When are diatoms a good form of trace evidence?
Why are diatoms a good form of trace evidence? (species, size range, resistivity, putrefied bodies, growth and taxonomy)
A
- when used with care excellent form of trace evidence
- diverse group of species mean can identify something distinguishing or discriminatory if something has come from somewhere based on analysing diatoms
- with small size range which makes their entry inside the body organs feasible (also sit on top of body)
- hard silica cell wall is resistant to the chemical changes – helps in recovering of intact structure of diatoms from body or clothes
- organs get blended with putrefied bodies and only bones left but diatoms can still be recovered even when little other evidence is available
- because identifiable can use them as real distinguishing factors to trace where someone has come from or where the body has been dumped
- 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
6
Q
What can be said about the taxonomy and chemistry of diatoms?
- old
- vs new
- how are they defined
A
- used to be easy naming and identifying them (used to be three classes in 1990’s
- now complex process with evolution of molecular understanding
- defined by shape, porous, number of valves
7
Q
Is there an analytical workflow for diatoms? What is said instead?
A
- no
- try and identify them (test them – number of chemical extraction approaches to take this – hydrogen peroxide fixing, acid, or alkali separation)
- basic transmission light microscope - identify and count them (can start to identify exactly what ones)
- SEM - pick out details compared to light microscope (possibility to do with light but standard is SEM)
8
Q
What can be said about the transfer and persistence of diatoms? (size, highest and lowest transfer, seasonal variation, species morpology)
A
- diatoms are small so transfer and persist onto everything
- highest transfer is onto open weave and medium-rough textured materials (linen, acrylic, viscose)
- lowest transfer - smoother and tighter weave (nylon, PVC, lycra)
- seasonal variation has to be taken into account - more diatoms in march than november
- species morphology affects level of transfer and persistence from water source to clothing/footwear
- not all diatoms guaranteed transfer
- limited entrainment with smoother surface
- more successful entrainment with less smooth surface (pores)
- no consistent transfer across board between different types of diatoms
9
Q
What two case studies have diatoms been used in?
A
- Annie Borjesson found dead on Prestwick beach 4th december 2005
- Stenger’s pond attack - 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 which also matched between all samples increasing discrimination certainty
10
Q
What are the caveats with diatoms?
A
- cross-contamination
- secondary transfer
11
Q
What are two future research areas for diatoms?
What is a caveat?
A
- automated AI/machine learning systems are emerging as processes able to speed up identification workflows enabling the usage of diatoms as TE to become widely adopted
- SEM is good but slow and laboursome
- new methods will use TLM and polarised
- molecular barcoding combined with big-data approaches is also emerging as an exciting new field for rapid tracing and identification
- no longer need diatom expert but - require complex reference libraries of samples and data to be collected and maintained marking seasonal and geographic locations
12
Q
What are forams? (definition, compared to diatoms, size, shell constituents, other names, where are they found, use as TE)
A
- they are single celled organisms of which the majority live on sea floor and have an external shell
- very similar to diatoms as still come with hard outer shell and exist within aqueous environments
- more colourful than diatoms
- have a far broader range of hard outer shells
- can grow up to 15/18 cm but most are less than 1 mm in size
- shell can be made up of calcite, aragonite, sediment particles or proteins
- often referred to as microfossils
- 1/6 of Earth’s surface is covered in micro-fossil bearing sediment and marine limestone is used widely in building and industry (building material can be traced to limestone)
- increases potential as forensic trace evidence
- currently limited usage as trace evidence
13
Q
Explain a case study including forams?
A
- prime minister in Italy was kidnapped and murdered in 1978
- small amount of sand found in car where his body was discovered and on his trousers and shoes
- mineralogy of the sand along with identification of the 18 different types of foraminifera enabled tracing to 150km stretch of shore line
- 92 samples taken along the stretch of beach, enabled narrowing the likely location of where he was kept while kidnapped for 55 days down to an 11km stretch of beach
- foram evidence didn’t ever get used in trial as the 32 people eventually convicted of being involved in his kidnapping and murder denied a link to any beach – but this was proved unlikely due to evidence
14
Q
What are phytoliths? (definition, compared to diatoms, when are they released, composition, their use and their TE use)
A
- plant microfossils made of silica found in some plant tissue and persisting after the death and decay of plants
- similar idea to diatoms in sense made of silica but from plants
- released into soil or sediment after plant death – great forensic potential
- composed mainly of silicon dioxide with a refractive index between 1.41-1.47
- used widely in palaeontology and paleoenvironmental reconstruction to expand archaeobotanical knowledge particularly tracing domestication of plants and tracing plant-human interactions
- can be used alongside wider soil and environmental trace evidence although little/no forensic case evidence of phytoliths alone
15
Q
What is pollen (definition, different types, size and structure, how many pollen grains can single anther produce)
A
- pollen is the powder containing the male gametophytes of seed-producing plants
- it is dispersed in order to reproduce by wind, water, or animals (e.g. bees)
- different forms of pollen are designed in different ways in order to dispersed in different ways depending on environment they live in
- water one really relevant
- generally less than 50μm in diameter (range 2-100μm), often with air bladders (like a little parachute that allows them to float) which allow them to keep aloft in the wind & travel up to 2km from the parent plant
- have a fairly hard coat to protect them as they are transported and are relatively resistant to destruction
- surface texture can be incredibly diverse and identifiable to a particular plant
- a single anther on a plant can produce 50-250,000 pollen grains depending on the plant species
- if only 50 - less likely to be in an environment – might be more of a transfer if direct interaction with plant with body
