Soil: types and composition; Collection and preservation of soil evidence; Forensic examination of soil: particle size distribution, turbidity test, microscopic examination and density gradient analysis

1. SOIL
EXAMINATION

2. SOIL

3. ORIGIN OF SOILS
PHYSICAL DISINTEGRATION
• It predominates in dry and cold
environments where the heating and
cooling of the
• abrasion by water, ice, or wind
CHEMICAL DECOMPOSITION
• alter the structure of the parent material by
chemical reactions
• More pronounced in hot and wet climatic
regions
(1) Hydration (water molecule binds to mineral)
(2) Hydrolysis (water molecule splits and the
hydrogen is replaced by a cation from mineral
structure)
(3) Dissolution (water dissolves some minerals)
(4) oxidation-reduction ( minerals rich in Fe,Mn,S)
Weathering : The process of Soil formation by physical and chemical
breakdown of the earth’s rocks

4. FACTORS AFFECTING
COMPOSITION OF SOILS
1. Parent Material
2. Climate
• Precipitation: water is required for
all the major chemical reactions
during the weathering process
• Temperature: soil formation reaction
rates doubles for every 10 degree
increase in temperature.
• influences organic matter content
through plant growth and
decomposition.
3.Topography
 Topography influences
formation, loss, and various
properties of the soil.
 steep slope (erosion)
 low-lying areas (soil
accumulation)

5. FACTORS AFFECTING
COMPOSITION OF SOILS
4.Biota
• Plants: organic matter
accumulation, profile mixing,
biogeochemical weathering,
nutrient cycling, and
aggregate stability
• Animals: Facilitate movement
of Water , enhance plant
nutrient availability
(earthworm)
• Humans :anthropogenic soil
alteration practices
5. Time
• 100 or even 1000 years for soil to
develop, making it extremely difficult
to measure soil formation processes
over time.

6. SOIL

7. SOIL
O=Decaying organic matter
(Humus)
A(Topsoil)=Humus and Mineral
particles
E=Sand and Silt
B=Leached Clay and Mineral
(subsoil)
C=Partially broken up rock
R=solid Rock Layer

9. Physical
Properties
• Soil Texture
• Soil Color
• Soil Density
Chemical
Properties
• pH
• Plant
Nutrients
• Soil Carbon
• Soil Salinity
and
Sodicity
Biological
Properties
• Flora
• Fauna
PROPERTIES OF SOILS

10. Soil Texture (Physical property)
 Clay: capacity to retain water due to the extremely small pore size, which
causes water to move very slowly in clay soils.
 Silt: more numerous compared to sand particles in the same volume of soil.
susceptible to wind and water erosion.
 Sand : visible to the naked eye , relatively large pores in between individual
particles ( poor water-holding properties)

11. SOIL

12. Soil Colour(Physical property)
Munsell color chart which recognizes different soil types by color. There are
three main components of soil color:
(1) hue is the soil’s resemblance to red or yellow,
(2) value describes the relative darkness and lightness of the soil
(3) chroma is how weak or strong a color appears.
 humus (organic material) adds a dark brown, almost black appearance
 Iron is an important contributor to soil color i.e. red (Fe2o3 ferric oxide =Red,
Feo (ferrous oxide ) =Grey, Fe(OH)3 ferric oxyhydroxide = Yellow)

13. How to Identify the Color of Soil Using the Munsell Soil Color Book

14. 12/19/2022
B.Sc. Forensic Physics SEM V
14

15. 12/19/2022
B.Sc. Forensic Physics SEM V
15
Case 1
 The complainant in a civil action alleged that a contractor had dumped soil from a
highway project on to his private property.
 6 specimens of soil from various locations were collected.
 To examined to determine which one of the soil samples did not originate from
the same location as the other five.

16. 12/19/2022
B.Sc. Forensic Physics SEM V
16
Case 2 (Homicide)
 In the early spring, the body of a young adult
female was seen floating down the East River
near midtown Manhattan.
 At autopsy it was determined that the victim had
been shot with a handgun.
 It was discovered that the dead woman was in
the process of attaining a divorce from her
estranged husband (suspect).
 Evidence: water-stained men’s right shoe in the
suspect’s bedroom closet.
 To determine whether QS1(sand from suspect
shoe) matched with KS1(Known sample from
beach i.e. crime scene).

17. 12/19/2022
B.Sc. Forensic Physics SEM V
Ions through XRD

18. 12/19/2022
B.Sc. Forensic Physics SEM V
Case 3 (Homicide)
 A young woman was found on a beach lying supine in the sand. She was
killed by a blunt force trauma to the head. Her van was on the beach next to
her.
 Three days after the victim’s body was found a suspect, who lived close to
the beach, was arrested.
 To determine whether QS2,QS4(sand from suspect’s van) or
QS1,QS3,QS5,QS6 (Clothing) matched with KS1(Known sample from
beach i.e. crime scene).

19. 12/19/2022
B.Sc. Forensic Physics SEM V
19

20. 12/19/2022
B.Sc. Forensic Physics SEM V
Case 4 (Homicide)
 A female who had been running on a roadway in Central Park (CP) was found
close to death in an isolated area. She had been struck in the head with a
large rock and dragged several hundred feet into a ravine where she was
further brutalized. After the attack, it is believed she managed to travel a short
distance and then collapsed from her injuries. She lay bleeding until the
morning, when she was discovered by some passersby.
 To determine whether Questioned aggregate soil specimens S3, S4, and
S5 (sand from suspect’s clothing) and soil samples S2 and S2A
(victim’s clothing ) matched with S1 and S7 (Known sample from crime
scene).

21. 12/19/2022
B.Sc. Forensic Physics SEM V
21

22. Soil Density(Physical property)
 Particle density mass of a unit of soil
solids divided by the volume of the soil
solids only(2.60 to 2.75 mg/m3)
 3.0 mg/m3 or more =low in organic
matter
 1.3 mg/m3 = high organic matter
content.
 Bulk density :mass of the dry soil
divided by the volume of the soil (pore
space)
 porosity, or the percentage of total pore
space.
 macropores (larger than 0.8 mm) and
micropores (smaller than 0.8 mm).

23. CHEMICAL PROPERTY
pH (Chemical property)
• pH is a term that
measures the hydrogen
ion (Hþ) activity in the
soil
• vegetable crops grow at
a soil range with a pH of
5.5-7.0.
• Alkaline = calcitic
limestone, burned lime,
wood ashes
• Plant Nutrients
Plant Nutrients (Chemical property)

24. CHEMICAL PROPERTY
Soil Carbon
(Chemical property)
• Soil organisms obtain
carbon either by
breaking down organic
materials or from the
carbon dioxide in the air.
Soil Salinity and
Sodicity (Chemical property)
• Soil salinity = the amount of
dissolved salts in the soil solution
(the aqueous phase in the soil).
(Process=salinization)
• (Acidic nature)
• Sodicity = amount of sodium that is
present in the soil.
• (Alkaline nature)

25. Biological properties

26. FORENSIC RELEVANCE OF SOIL
• Soil as a Powerful Contact Trace
• Soil Is Highly Individualistic
• Soil Is Easy to Characterize: Large and Trace Amounts
• Soil Has a High Probability of Transfer and Retention
• Soil Can Quickly Be Collected, Separated, and Concentrated
• Soil Is Nearly Invisible

27. FORENSIC EXAMINATION OF SOIL
R=as per the Crime
• D=Sketch ,Photography,
note on map soil collection
location
• C=Time, samples that
appear different or out of
place ,surface baseline
samples, Volume, suspect’s
or victims clothing’s or
footwear, Document
evidence
• P= moist samples

28. • Aim: Observe the colour of the soil as such and after drying in oven at 105oC
• Sample Preparation:Set of sieves( ranging in size from ASTM No.5 to 200)
range size)
• Removal of Blood from Blood Stained Soil (0.85% Nacl solution)
• Observations Apparatus: Stereo-microscope capable with high magnification
range.
• colour of soil particles after drying at 105oC.
• nature of particles as- geometrical shape, black particles (coal dust, black
minerals), red particles (brick dust, red ash, iron oxide or metal oxide),
colourless particles (quarts grains, colourless mineral fragments), green
particles of vegetation (grass, leaf fragments, seeds, moulds, fungi, micro-
organism etc.
• traces of foreign materials as -dung cloth fibres, glass fragments, hair, wooden
particles etc.
FORENSIC EXAMINATION OF SOIL
(MICROSCOPIC EXAMINATION )

31. FORENSIC EXAMINATION OF SOIL
 Soil examination generally starts with a visual comparison and microscopic
analysis, gathering information on characteristics such as structure, texture,
colour and organic matter content. (Typically usuaing a stereo binocular
microscope).
• conventional soil characteristics such as particle size distribution and pH may
require about 1 g of soil.
• comparison to Munsell soil colour charts care has to be taken in its applicability in
forensic casework.
• In a study of 73 soil samples, multiple colorimetric features such as colour after
air-drying, after wetting, after organic matter decomposition, after iron
oxide removal and after ashing were used.
• 70% differentiated by air-dried samples
• 97% differentiated by air-dried samples along with other combinations
• 99.5% differentiated by air-dried samples and other combinations along with
particle size distribution
• soil colour analysis with increased resolving power, e.g. the Minolta CM2600d
spectrophotometer.

33. FORENSIC EXAMINATION OF SOIL (PH
MEASUREMENT OF SOIL SAMPLE)
 Dissolve weighed quantity ( one gm of soil sample in 100 ml distilled water
and stir thoroughly. Filter it. Take the filtrate and measure the pH value.
 Similarly, measure the pH values for control soil sample in the same
conditions and compare with suspect soil sample.

34. • Moisten a small portion of soil with water and then add a small drop of
concentrated hydrochloric acid (HCl) on it. Observe the nature of reaction as-
bubbles (insoluble carbonates such as chalk, dolomite or lime stone) and colour
(yellow colour indicates Fe confirmed potassium ferrocynide which turns green)
FORENSIC EXAMINATION OF SOIL (MICROSCOPICAL
OBSERVATION WITH CHEMICAL REGENTS)

35. • Apparatus: Set
of sieves
(ranging in size
from ASTM No.5
to 200), Motor-
driven sieve
shaker,
Analytical
balance,
Standard
Weights
FORENSIC EXAMINATION OF SOIL (PARTICLE SIZE
DISTRIBUTIONS)

36. FORENSIC EXAMINATION OF SOIL (PARTICLE
SIZE DISTRIBUTIONS)

37. FORENSIC EXAMINATION OF SOIL
• Particle size (physical property) because of transfer and selective
persistence the particle size distribution may be altered.
• For example, sand may not be retained on a shoe or a vehicle as readily as
clay, but the sand fraction will still be present in the control sample.
• The ‘field’ conditions at the time the soil is collected (as a control or contact
trace), the pre-treatment of the soil prior to sieving and the form of
sieving (wet or dry) may also influence the particle distribution.
• The Malvern Mastersizer 2000 laser granulometer, for example, offers rapid
and precise sizing of particles in the range 0.02–2000 μm for a variety of
sample types, including soils, unconsolidated sediments, dusts, powders and
other particulate materials. It is possible to use this technique for sample
weights of just 50 mg,

38. https://www.youtube.com/watch?v=XAklcalCW-8

39. • Take an exactly weighed quantity (one gm) of soil sample from sieve fractions dried at
105oC in a alumina crucible and keep it in a muffle furnace.
• Heat it at temperature between 750-800 oC for 1 hr. And then, cool it to room
temperature. Reweigh accurately and record the loss in weight and change in color on
ignition.
FORENSIC EXAMINATION OF SOIL (IGNITION
TEST)

40. FORENSIC EXAMINATION OF SOIL (DENSITY
DISTRIBUTIONS OF SOIL PARTICLES)

41. FORENSIC EXAMINATION OF SOIL (DENSITY
DISTRIBUTIONS OF SOIL PARTICLES)

42. FORENSIC EXAMINATION OF SOIL (DENSITY
DISTRIBUTIONS OF SOIL PARTICLES)