Late Postmortem Changes

Define decomposition

The disintegration of the body tissues after death due to the arrest of biochemical processes that preserve the integrity of organs, cells, and molecules in the body

Two mechanisms of decomposition:

Autolysis, putrefaction

Stages of decomposition

Autolysis (chemical breakdown); bacteria colonization and migration/propagation in vessels (marbling); hemolysis (hemoglobin degradation) - skin green coloration; skin blister and slough (necrotic tissue - fluid exiting orifices; putrefaction gas (abdomen and scrotum)

Autolysis

Postmortem self-digestion and degradation of the cells and organs by intracellular enzymes; faster in enzyme-rich organs (pancreas, gastric wall, liver)

Steps in autolysis:

Cells stop receiving nutrients and oxygen via blood circulation; when all ATP reserves are depleted, accumulation of waste lactic acid in cell tissues disrupts cell function; enzymes collapse cell nucleus: necrosis

Factors affecting autolysis

Temperature (higher = faster), pH, presence of microorganisms

Putrefaction

Microbial-driven process, primarily driven by anaerobic bacteria, that degrades and liquefies tissues; fall in oxygen concentration and rise in hydrogen ion concentration after death

Signs of putrefaction

Gaseous bloating, dark green to purple discoloration of the skin caused by the breakdown of hemoglobin to sulf-hemoglobin (24-30h starting in the lower abdomen and spreading to chest and extremities after 36-48h), face/tongue swelling, purging of body fluids/gases and bacteria, marbling pattern (decomposition of the blood in the subcutaneous vessels), foul odors

During putrefaction a body releases:

Carbon dioxide, methane, nitrogen, ammonia, sulfuric acid, hydrogen sulfide

Diffusion of gases during putrefaction into the soil/atmosphere is regulated by:

Grave depth and chemical structure and soil texture, moisture, and oxygen

Factors influencing decomposition

Decrease in insect activity and scavengers, decrease in temperature relative to above-ground temperature, soil characteristics influencing pH and bioavailable moisture and oxygen

Buried remains affect on autolysis and putrefaction

No change on underlying chemical and biological mechanisms of decomposition, but particularly hot/dry or cold/dry environments inhibit decomposition and cause mummification

Define mummification

Preservation of a human body through artificial embalming or natural dehydration (extreme cold, heat, or dry conditions), resulting in leather-like skin and preserved soft tissues

How long does mummification take?

Generally, 2-3 months; possible in 2 weeks if left exposed in hot, arid environments of 1-3 months when enclosed

Factors that encourage mummification

Arid and dry environment (dehydration and preservation; inhibits bacteria growth and other decomposing organisms), extreme cold environment (slows decomposition), chemical preservation (certain soil conditions of chemicals in the environment inhibit decomposition), lack of insect activity (restricted or non-existent insect activity)

Natural mummification

Includes mummies from wet environments - bog bodies preserved in wetland pit deposits (acidic peat bogs)

Two types of peat environments:

Ombrotrophic sites (peat bog), minerotrophic sites (fens)

Ombrotrophic sites (peat bogs)

Acidic wetlands (ph: 3.2 - 5), water derived only from precipitation, bodies frequently have well-preserved soft tissue, bones often severely demineralized or sometimes absent

Minerotrophic sites (fens)

Generally alkaline (pH: 5.5 - 7.8), bodies typically skeletonized, commonly in northern Europe

Advantages of mummification in forensics

Fingerprint preservation, soft tissue for various analyses, potential trace evidence (non-skeletal)

Disadvantages in forensics

Postmortem tearing can imitate sharp force trauma

Adipocere

Product of body fat decomposition that results from the processes of hydrolysis and hydrogenation of adipose tissue; can occur in as little as 3 weeks

Saponification

Process of the conversion of fatty tissue to adipocere

What kind of environment promotes adipocere development?

Unoxygenated, alkaline, semi-moist - wet environments: high temperature, high humidity, subcutaneous tissue of high fat content; may be accelerated by bacteria

Hydrolysis

Splits larger molecules into smaller components by adding water to break chemical bonds

Hydrogenation

Chemical reaction that adds hydrogen to unsaturated compounds to produce saturated compounds

Adipocere mechanisms

Fat migration theory, saponification theory, hydrogenation theory

Fat migration theory

Fat disperses into surrounding tissue during decomposition; triglycerides in the fat break down into free fatty acids (oleic acid and glycerol)

Saponification theory

Breaking down fats into fatty acids and glycerol through hydrolysis; creation of insoluble soaps from the fatty acids, comprising only 2 - 35% of the overall adipocere composition

Hydrogenation theory

Dispersion of fatty acids; unsaturated fatty acids that undergo hydrogenation to form saturated fatty acids

Early stage of adipocere formation

Small amount of tissue is undergoing saponification; composition is still similar to adipose tissue; decrease of unsaturated fatty acid content and increased saturated fatty acid content; triglycerides are still detectable at this stage

Intermediate stage of adipocere formation

Increase in palmitic acid and decrease in oleic acid, stearic acid content; triglycerides are also still detectable at this stage

Advanced stage of adipocere formation

Palmitic acid comprising more than 50%; oleic acid reduced and other saturated acids and triglycerides are no longer present

Saponification occurs more often in:

Bodies in the water, in plastic bags, in shallow wet graves; women, children, and obese individuals

Common by-product of lipid (fat) degradation:

A greyish-white substance; can become solid; resistant to further putrefactive changes; the process may preserve the external morphology of the subjects; protective coating preserving underlying tissues

Influencing factors of adipocere

Many microorganisms convert specific acids into adipocere; clothing, damp or moist environment

How is mummification different from adipocere?

Drying of tissues; requires dry airy situations, often but not always warm; thin or very young individuals; occurs where insect activity is prevented or seriously limited

How is adipocere different from mummification?

Saponification, presence of water and lack of oxygen, bacterial activity is present

Decomposition processes that are not autolysis or putrefaction

Activity of aerobic decomposer organisms; weathering processes such as thawing or freezing (temperature-related), shrinking or swelling (moisture-related)

Bone diagenesis

Refers to any chemical, physical or biological change to a bone after its initial deposition

Factors of bone diagenesis

Ground water and sediment, soil pH, weathering, transport by natural or physical forces, plant growth through bones, microbes

How is the term “weathering” used in geology and geomorphology?

Used to describe breakdown of rocks, soils, and minerals through various physical/mechanical, chemical or biological forces

How is the term “weathering” used by paleontologists, archaeologists, and forensic anthropologists in taphonomy?

Used to describe the stage by which bone starts to compositionally and physically break down in response to exposure to its burial or depositional environment

“Weathering”, as opposed to “decomposition”, applies to:

Hard tissue

Potential effects of weathering on physical and/or chemical nature or cortical and/or trabecular bone are numerous:

Cracking/fracturing, flaking, shrinkage, warping, exfoliation (flaking of outer surface), desiccation (extreme dryness), polishing and/or grooving (caused by root and/or animal action), color changes (fungal growth, thermal effects, oxidation from contact with metals or minerals), bleaching

Relevance of weathering:

Distinguish this type of taphonomic alteration from other sources; movement of a bone from its original position, information that osseous weathering can give regarding the postmortem interval (specific to the environment)

Influencing factors of bone weathering:

Intrinsic: taxon (human or non-human), bone type and size; extrinsic: environment, time and events that occurred between death and recovery

Histotaphonomy

Bioerosion only - biological activity; semiquantitative; time-consuming; small portion of the bone analysed

Applications of PMI in forensic investigation

Aid in identification, intelligence, and investigation

Methods for estimating PMI

Insects, carbon dating, ADD / total body score

Decomposition and ADD

Looks at the state of decomposition of the body and assigns scores to it resulting in total decomposition / body score (TBS); TBS with ADD are used to give time since death interval (PMI)

ADD

Accumulated degree days

Stages of decomposition according to Megyesi et al?

Fresh, early decomposition, advanced decomposition, skeletonization

Gross morphological stages of decomposition

Fresh, initial decay - bloating, putrefaction (4 -10 days) - black putrefaction (10 - 20 days), butyric fermentation (20 - 50 days), dry decay

Total Body Score

Take decompositional stages of head and neck, torso, and limbs; place them in order; assign scores - score areas differently according to decompositional changes

Volatile Organic Compounds (VOCs)

Carbon-based chemicals that easily evaporate into the air at room temperature, acting as significant indoor and outdoor air pollutants

VOCs give potential for:

Cadaver detection, search dog training, PMI estimation