Factors that influence decomposition (week 2, lesson 1)

The rate of decomposition

The speed at which a body transforms from a fresh whole body to complete skeletonisation

What factors contribute to the rate of decomposition

Extrinsic factors (external/environment)

Intrinsic factors (intrinsic/individual)

The Cadaver Island

A continuous relationship between decomposition factors and the body

- Energy

- Moisture

- Dead insects and plant material

- Energy and mineral nutrients

- Insect puparia and exuvia

- Fly and maggot migration

- Faecal matter from insects, scavengers, predators and grazers

- Feathers from avian scavengers and predators

What are the main things affecting rate and pattern of decomposition

- Resource quality (body)

- Decomposer community (bacteria and scavengers like insects)

- Physiochemical environment

Extrinsic factors

Temperature

Temperature is the BIGGEST influencing factor on the rate of decomposition

Bodies decay best in warm damp environments

> Van't Hoff's 'rule of 10' - chemical reactions increase in speed up to 3x with every 10°C increase in temp - up to a max of 40-50°C, when enzymes are denatured

Hot and warm weather vs cold weather

Hot/warm weather

• Maggots and flies thrive in warm weather (maggot mass <24hrs)

• A body can become skeletonised in 2 - 4 weeks

Cold weather

• Maggot action slowed outside the body, but fine in body cavities

(generate their own heat)

• Mould can develop

• Not necessarily weather - hot/cold microclimates can exist (freezer, next to radiator, sheltered attic etc.)

Access by insects

- Insects are very important agents of decomposition, most important PMI estimation post-mortem

/ Insects are attracted by the odour/VOCs - if odour is covered/hidden in some way, decomposition may be retarded

- Blowflies colonise during fresh and bloat stages, dermestid beetles in the advanced decay stage/Maggots consume the tissues of the body - aid physical destruction

• Indoor vs outdoor environments

Case study: Leah Questin, can maggots get through zips to bodies in suitcases?

Background: she was murdered by her boyfriend & stored in a suitcase in countryside. Her body was kept whilst he emptied her bank.

Crucial points

- Entomology evidence was crucial in understanding the PMI and the fact her body had been moved

- Pushed question as to whether blow flies were present before her body entered suitcase or if they had ability to go through zips

> scientists have since found they can

Moisture/Humidity/Rainfall

- Decomposition requires moisture/humidity to progress

- Dry environments retard decomp

- Water and rain can help to liquefy the body - speeds up decomposition

- Can rehydrate mummified remains - kick-start bacterial decomposition again

- However, water can physically wash away maggots and retard their destruction of the body

Sun/shade

- Exposure to sunlight - can warm remains and promote bacterial decay

- Insects avoid laying eggs in areas exposed to direct sunlight because eggs are vulnerable to desiccation and UV exposure

- Insects lay eggs just under skin or under covering

- Exposure to sun can cause bleaching, cracking, 'weathering' of bone

Burial environment

Composition

> Moisture content/drainage

> pH

> Oxygen

> VOCs release

> Temperature

> Microbial profile

Particle size (how big the particles of the soil are)

> sandy soil - loose particles so decomposition will move away from the body, dehydrating it & leading to mummification

> clay soil - retains moisture, has lack of oxygen moving through, stops BOCs moving between particles - slows decomp

Depth

> deeper has fewer microbial communities, harder for BOCs to escape lower down, less oxygen and colder as further from sunlight so slows decomp

Coverings, wrappings, coffins

What promotes and retards decomposition in a burial environment

Promotes (when oxygen, BOCs & moisture can move more freely):

- Well aerated soils

- Coarse textured

- Free draining soils

- Acidic sands and gravels: poor survival of bone in sandy, acidic soils

- Sites featuring concentrations of 'sarcosaprophagous' microorganisms:

> Graveyards

> Manure dumps

> Cess pits

Retards:

- Poorly drained soils - moisture retention

- Clay-based soils - small particle size

- Poor aeration - anaerobic bacteria

- Adiopocere formation and preservation of soft tissue

Burial depth

- Decomposition is up to 4x slower at greater depths

- Temperature is lower

- Access by insects/scavengers is reduced

- Coffins retard decomposition

- Acidic soils accelerate decomposition

- Exposure of remains in shallow burials is common→ differential decomposition

- Limits release of gases/VOCs

Coffins

- Coffins can act as physical barriers to insects

- Except Megaselia scalaris ('coffin flies') that burrow down to > 0.5m depth and get through cracks in coffin

- Soil detritivores: earthworms, beetles

Cast iron coffins:

- Delays onset of putrefaction by decades (if correctly sealed)

- Soft tissues and hair present after >100 years

- Adiopocere present

- Clothing preserved in very good condition

- Preservation of internal organs including heart, kidneys, liver

Example: Colonel William Shy was estimated to have been dead only 2-6 months

Submersion in water

- Temperature is cooler but much more constant compared to diurnal temperature experienced in air on land surface

- Insects can only access exposed body parts, once bloat has occurred

- Oxygen is depleted - aerobic bacteria need oxygen - can't respire underwater

- Decomposition rate slows by half in water

- Marine and freshwater scavengers contribute to destruction of the body

> less access when body sinks but will resurface in bloat stage

- Chemical composition important: pH, salinity etc.

- Mechanical destruction due to tides,

currents, scavengers, debris

- Water influences the transportation of bodies and bones

- Postmortem submersion interval (PMSI)

Hanging above ground

- A body left hanging will decompose more slowly than one lying on the ground as suspended above so less interaction with insects/scavengers & no interaction between body and soil

- No dark place underneath the body which is favoured by insects

- Maggots may fall off or be washed off by

rain

- More difficult for some scavengers to

access the remains

- Body fluids drain away - gravity and with also hanging in the air, these may lead to drying of the body

- Differential decomposition

Scavengers

- Scavengers break up the body, pulling apart ligaments, muscle, damaging bone to get to the bone marrow - mechanical decomposition

- Different depending on location - badgers, foxes, coyotes, racoons, rodents

- Marine scavengers: crustaceans, fish, eels, molluscs

- Domestic scavengers: cats eat nose and mouth tissues, dogs eat genitals and face (in home situations)

Dismemberment/fragmentation

- Started destructive process already

- Increase surface area to volume ratio than whole body

- More exposed flesh for oviposition

- Limbs may mummify as have much lower fat content and higher muscle content as well as no kick start at beginning from gut bacterial populations

Desiccation - 'Drying'

- Browning of the skin/membranes due to

drying/exposure to heat or air

- Skin retreats

- Hair and nails DO NOT grow

- Desiccation of the extremities can happen first - differential decomposition

- Body composition and surface area to volume ratio

- Drying of the eyes = Tache noir

Intrinsic factors

Body size

- Surface area to volume ratio

> Large S.A. to volume ratio (i.e. small body) is more likely to lead to dehydration, desiccation & mummification

> Small S.A. to volume ratio (larger body) → faster decomposition

- Obesity - fat will initially help & speed up decomposition but fat can prevent moisture loss and slow decomposition

- Very thin people - more likely to desiccate/mummify

- Infant remains infants who are yet to be weaned (still breast/bottle fed) do not have the same intestinal bacteria/gut microbes - decomposition is slower - infant remains may mummify

Clothing/covering

Clothing or wrapping can slow decomposition:

• Prevents easy access by insects

• Excludes oxygen

• Prevents access by scavengers

But, it can accelerate decomposition:

• Acts as insulation - can increase/maintain high temps for enzyme activity

- Depends on the types of material

> Synthetic

> Natural

> Absorbency

> Weave

Trauma

- Wounds allow entry of air and insects into the body - speed up decomposition

- Scent of blood attracts insects more quickly

- Blowflies less attracted to artificial orifices than natural ones

- But, severe blood loss from trauma can deprive gut bacteria of food, and can slow bacterial colonisation of the body

Burning

- Sterilises skin surface and dries underlying tissues - unsuitable for bacterial growth

- But destruction of skin allows access to unaffected internal tissues

- Reduces likelihood of insect oviposition

- If temperature is high enough, body will be carbonised, and organic matter lost

> In that respect, destruction is accelerated

- Limits PMI estimation and identification

Disease

- Septicaemia (blood infection) - higher amounts of bacteria spread throughout bloodstream - faster decomposition

- Anaemia - low red blood cell counts - less food for bacteria - slower decomposition

- Fever - higher body temp just before death - can accelerate decomposition

Drugs

- Certain drugs have been shown to have an effect on decomposition rate

> Influences insect activity

> Alters the physiological conditions at the time of death e.g., raised body temperature - impacts PMI estimation

- Cocaine in blood stream and tissues - speed up action of insects

- Morphine slows decomposition - underestimation of PMI by 24 hours is possible

- Medications?

Other factors

More research needs to be done on the possible effect of:

• Stress - adrenaline/cortisol in blood?

• Diabetes - higher blood sugar levels

• Diet -Vegan vs meat eating

• Menstruation/pregnancy - raised body temp

• Modern forensic issues' specific to human lifestyle, habits, and culture

Difficult to achieve = Human taphonomy facilities (HTFs)

Summary of factors that accelerate vs deceleration decomposition

All these factors don't happen in isolation, still have to account for multiple factors

Promote:

- unrestricted oxygen

- Warmer temps

- Better access for insects

- Trauma as better access to body

- Higher fat content

- Blood infections

- Fever or stress just before death

- body resting on soil/exposed to air

- scavengers

- Dismembering

Slow:

- depleted oxygen

- cold temperatures

- dry atmospheres

- absence of insects

- intact body

- large SA:V (small/thin body)

- body buried or underwater

- absence of scavengers

Interesting cases

Differential decomposition

- Body parts decompose at different rates

- Can lead to confusing estimations

- No method in isolation

Highly influenced by the deposition environment:

> Mummification = dry environments leads to preservation particularly at the limbs

> Adipocere formation = wet environments leads to preservation

> Exposure to elements - Accelerated changes

> Exposure to scavengers/insects - Accelerated changes

Mass graves

- Create their own microbe environment

- Bodies buried in close proximity to other bodies so this influences

- Bodies decompose at different rates depending on their condition at burial, method of burial, soil conditions in & around grave

> bodies in middle of the mass of bodies are more preserved

Mass graves: top, middle and bottom level

1. More decomposition seen at top of top layer

> higher temps

> Closer to the surface = aerobic

> Greater exposure to insects/scavengers/disturbance

2. More decomposition seen at the periphery of the middle layer rather than the centre

> Greater contact with soil at edges

> Higher levels of moisture in the centre

> Less insulation

3. Lowest level of decomposition seen in the bottom layer = greater levels of preservation

> More compact

> Pressure from above

> Percolation of decomposition fluid

> Retains moisture

> Greater depth

> Reduced oxygen - anaerobic

> Reduced access for insects/scavengers

Disaster taphonomy

- Disasters are often traumatic to the body, 'disaster taphonomy' can be seen as a continuum from survival to complete disintegration

- Primary and secondary factors that affect the preservation/state of the body

- Disaster forces are more variable in intensity and duration than 'normal' ones, it is difficult to predict taphonomic outcomes of a specific disaster

> e.g. disasters involving high speed and flammable products result in burned and highly fragmented human remains. Fragmentation occurs before burning - leaving disassociated, fragmented and burned remains

> Compared to a house fire where fragmentation occurs after burning - burned but associated remains