Carry out techniques used to examine soil, pollen and diatom evidence in forensic investigation
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Course
Unit 9 - Environmental Forensics
Institution
PEARSON (PEARSON)
A report explaining the scientific techniques and the value of this type of evidence. Observation sheet for practical assessment.
This assignment was graded a distinction piece, so guarantees a good grade
There are many sampling techniques of soil which are
important to match a soil sample to a crime scene to find an
offender and therefore link them to the scene. Soil comes in
many types, it consists of inorganic and organic matter.
Organic matter contains humus, which appears when an
animal or plant dies. Inorganic matter however consists of
mineral grains. However, it can come fully dried, partially
saturated and or fully saturated. Edaphic factors are
physical, chemical and biological properties in soil, like the
structure and pH. Edaphic factors are what affects organism diversity within soil.
As previously mentioned, soil comes in many types. Firstly is Podzols, which are acidic.
percolating water forces the components in the soil to move downwards. (The soil
components are gradually filtered through a porous component. Additionally, the water will
dissolve and cause the organic materials in the soil to leech. Podzols discourage organisms
from living within it as the cold climate and acidity repels them.
Next is Brown Earths, it contains humus (organic material) which is crumbly. This
decomposes organic material very fast, as it contains large amounts of bacteria. Additionally,
with this soil, the pH increases further down into the soil.
Another soil is Rendzina, it's made mostly of calcareous (alkaline soil). Rendzina occurs
when limestone is present in soil, and encourages organism activity. Gley soil is a bluey grey
colour. It creates anaerobic conditions as water fills up free spaces in the soil and causes a
lack of oxygen.
Soil Sampling techniques (brushing & sieving):
There are various ways to collect soil. However it cannot be contaminated or any evidence
within it, like bodily fluids or blood. Soil with trace evidence must be analysed separately, so
it prevents any evidence being missed. Another point is soils from indoor environments, the
most effective collection method would be a vacuum. Whereas for outdoor environments, a
teaspoon may be used to collect the soil and place it inside a plastic vial. If a sample is to be
collected off a body, extra care must be taken so no evidence is contaminated. Different
spoons will be used each time, so trace evidence in the soil cannot be mixed together and
lost. Therefore this prevents any evidence from being made inadmissible when presented in
court.
The sieving method is the most common method to sample soil types in entomology. It
involves using six layers of sieves, and placing soil into the sieve. Then the sieve is shaken
to allow the soil to pass through. Then, using the survive with the largest soil amount, this
will determine the soil particle size. Usually, this method is used for gravel and sand.
,There are three ways which soil can be classified. The first being sandy, it has a particle size
between 0.05 mm - 2 m. Sand is the easiest of the soil types to view under a low
magnification microscope like a light microscope. Silt is a very fine substance. Its particle
size is between 0.002 mm - 0.05 mm. It can be seen through low magnification microscopes,
although it may not be clear. Lastly, is clay, the finest of the three. Clay has a particle size of
less than 0.002 mm.
When sieving soils, protective equipment must be used to maintain health and safety. Lung
damage can occur when sieving, as breathing in the dust can cause severe complications.
Usually, a face mask will be worn to avoid inhaling the dust.
The next method of sampling soil is brushing. Using various dense bristle brushes can
collect small amounts of soil found on clothing and inside pockets. Brushing will be used if
the soil amount is small, meaning it cannot be sieved. Samples taken using the brushing
method can either be placed inside small universals, then when brought to the lab can be
wiped onto a glass slide and looked under a microscope.
Soil Analytical Techniques (cartography, photography, recording of soil profile & pH,
microscopy work for colour, grain size and texture):
There are various ways to analyse soil including structure, sediment and colour. These
various characteristics can create different samples to analyse. There are many different
profiles that soil can help to determine. For example, how long a skeleton has been buried
based on how long it has laid on the ground for.
Colour is an important way of determining soil history. If soil appears white, it suggests the
soil contains lime or that liquid was passed through it. Grey and black soil could suggest
signs of soil moisture. Colour is great for forensic analysis, as it conclusively links samples
together. Like, if a type of soil was found at a crime scene, and the colour was analysed
under a microscope to link it to a suspect whose clothes contained that same soil. This
means a conclusive link has been made between a potential offender to the case.
Munsell Colour System is another distinguishing method for soil colour. This is where the
soil type is determined by its hue and value of soil colour. This can be used alongside the
sieving method to help further determine the particle size of the soil, and then can be linked
to its colour. However, the colour system can be misinterpreted by its colour hues, as people
could view it differently. Therefore, multiple opinions are needed to conclude the opinion of
the soil colour. The colour chart is very affordable and quick to evaluate soil.
Microscopic analysis can be done on soils to analyse its mineral structure. One strength to
microscopic analysis is that it requires minimal sample preparation. Additionally, using
microscopy makes it easier to use, as it's equipped with user interfaces. All results will be
shown digitally, meaning that the data collected from the evidence can be moved between
devices, and many copies can be made. This is also a strength to Microscopy, as it means
the examination records and data from analysing the evidence cannot be lost, and therefore
shown in court.
, However, with Microscopy comes some complications. Electron microscopy is very
expensive and cannot be transported. Therefore, only fully equipped establishments will be
equipped with such complex equipment. Additionally, electron microscopy requires training,
whilst it is easier to use compared to other equipment, the analyst must be trained in the
components of the microscope to avoid complications. Another limitation is that microscopy
is a lengthy process, meaning results cannot be produced quickly. This could be an issue, if
the evidence being analysed may be definitive evidence to link the suspect to the scene,
therefore this cannot happen in the time frame which the court expects.
Soil can help to raise questions of how long a body has decomposed in the ground for, which
can be affected by pH levels. Acidic soils mean decomposition will happen slower as there
are less organisms. Like podzol soil, organisms aren’t encouraged due to its acidity. You can
compare this to alkali soils like Rendzina. This soil type allows for an abundance of
organisms, which therefore, will make decomposition happen faster. Another way soil pH
can be shown is in flowers. Hydrangeas will change colour depending on the soil they are in,
alkaline soil will make the flower turn pink, whereas acidic soil will turn the flower blue. For
forensic analysts, this is a critical natural indicator of the type of soil in the area, as it can
help to confirm an affecting rate of decomposition.
Once the evidence collected from the scene has been collected and transported to the
laboratory, each sample must be separated from the victims samples and offender samples,
they must also be examined by different analysts. Tests like determining mineral content can
be done. Using a density gradient tube is where soil samples are added to liquid. Once the
soil has been suspended, its soil profile will be analysed. If soil is stuck to garments or
clothing, the entire piece of clothing will be packaged and a photograph and written account
must be made. Then the item of clothing must be left to air dry. A strength to Density
Gradient Tubes is that the results appear instantly. This method will compare the soils pH,
size distribution and can compare the soils density. Therefore, it can conclude the soil type
almost instantly once the examination has concluded.
Cartography is another soil analytical technique, it friends measurements and evidence from
a map. With soil, cartography is used to show different kinds, and the location which the
crime was committed in. The soil properties will be documented to show how it links to one
another. Additionally, it helps link satellite scenes, if a tyre had specific soil on it which was
highlighted on a cartography evidence map at a scene.
However, cartography risks human error, which can lead to incorrect map measurements.
This can significantly impact the image of what the scene looks like, and the soils at the
scene. Therefore, it may present inaccurate and distorted examples of evidence of location
and the soil in the location. This can impact a court case so crucially as the incorrect
representation of the crime scene will therefore change the soil expectations which should
link to the location but no longer will. If this were to occur, it can evidently affect the case as
the evidence may not now be connected to the offender, so justice cannot be served to the
victim.
Photography is used in environmental forensics to document soil types and how the soil was
initially discovered at the scene. Photography is the main form of scene documentation, as it
shows visual evidence of how the scene was prior to any collection of evidence and
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