Decomposition

Decomposition or rot is the process by which dead

One can differentiate abiotic decomposition from biotic decomposition (biodegradation). The former means "the degradation of a substance by chemical or physical processes", e.g., hydrolysis; the latter means "the metabolic breakdown of materials into simpler components by living organisms",^[2] typically by microorganisms.

Animal decomposition

Decomposition begins at the moment of death, caused by two factors: autolysis, the breaking down of tissues by the body's own internal chemicals and enzymes, and putrefaction, the breakdown of tissues by bacteria. These processes release compounds such as cadaverine and putrescine, that are the chief source of the unmistakably putrid odor of decaying animal tissue.^[3]

Prime decomposers are

Five general stages are typically used to describe the process of decomposition in vertebrate animals: fresh, bloat, active decay, advanced decay, and dry/remains.[9] The general stages of decomposition are coupled with two stages of chemical decomposition: autolysis and putrefaction.^[10] These two stages contribute to the chemical process of decomposition, which breaks down the main components of the body. With death the microbiome of the living organism collapses and is followed by the necrobiome that undergoes predictable changes over time.^[11]

Fresh

Among those animals that have a heart, the fresh stage begins immediately after the heart stops beating. From the moment of death, the body begins cooling or warming to match the temperature of the ambient environment, during a stage called algor mortis. Shortly after death, within three to six hours, the muscular tissues become rigid and incapable of relaxing, during a stage called rigor mortis. Since blood is no longer being pumped through the body, gravity causes it to drain to the dependent portions of the body, creating an overall bluish-purple discoloration termed livor mortis or, more commonly, lividity. Depending on the position of the body, these parts would vary. For instance, if the person was flat on their back when they died, the blood would collect in the parts that are touching the ground. If the person was hanging, it would collect in their fingertips, toes and earlobes.^[12]

Once the heart stops, the

Visible changes caused by decomposition are limited during the fresh stage, although autolysis may cause blisters to appear at the surface of the skin.^[14]

The small amount of oxygen remaining in the body is quickly depleted by cellular metabolism and aerobic microbes naturally present in respiratory and gastrointestinal tracts, creating an ideal environment for the proliferation of anaerobic organisms. These multiply, consuming the body's carbohydrates, lipids and proteins, to produce a variety of substances including propionic acid, lactic acid, methane, hydrogen sulfide and ammonia. The process of microbial proliferation within a body is referred to as putrefaction and leads to the second stage of decomposition known as bloat.^[15]

If insects have access, maggots hatch and begin to feed on the body's tissues.^[9] Maggot activity, typically confined to natural orifices, and masses under the skin, causes the skin to slip, and hair to detach from the skin.^[17] Maggot feeding, and the accumulation of gases within the body, eventually leads to post-mortem skin ruptures which will then further allow purging of gases and fluids into the surrounding environment.^[15] Ruptures in the skin allow oxygen to re-enter the body and provide more surface area for the development of fly larvae and the activity of aerobic microorganisms.^[16] The purging of gases and fluids results in the strong distinctive odors associated with decay.^[9]

Active decay

Active decay is characterized by the period of greatest mass loss. This loss occurs as a result of both the voracious feeding of maggots and the purging of decomposition fluids into the surrounding environment.^[16] The purged fluids accumulate around the body and create a cadaver decomposition island (CDI).^[19] Liquefaction of tissues and disintegration become apparent during this time and strong odors persist.^[9] The end of active decay is signaled by the migration of maggots away from the body to pupate.^[15]

Advanced decay

Decomposition is largely inhibited during advanced decay due to the loss of readily available cadaveric material.^[16] Insect activity is also reduced during this stage.^[17] When the carcass is located on soil, the area surrounding it will show evidence of vegetation death.^[16] The CDI surrounding the carcass will display an increase in soil carbon and nutrients such as phosphorus, potassium, calcium and magnesium;^[15] changes in pH; and a significant increase in soil nitrogen.^[20]

Dry/remains

As the ecosystem recovers from the disturbance, the CDI moves into the dry/remains stage, which is characterized by a decrease in the intensity of the disturbance and an increase in the amount of plant growth around the affected area. This is a sign that the nutrients and other ecological resources present in the surrounding soil have not yet returned to their normal levels.

During this stage, it is important to monitor the ecosystem for any signs of continued disturbance or ecological stress. The resurgence of plant growth is a positive sign, but it may take several years for the ecosystem to fully recover and return to its pre-disturbance state.^[16] All that remains of the cadaver at this stage is dry skin, cartilage, and bones,^[9] which will become dry and bleached if exposed to the elements.^[17] If all soft tissue is removed from the cadaver, it is referred to as completely skeletonized, but if only portions of the bones are exposed, it is referred to as partially skeletonized.^[21]

Factors affecting decomposition of bodies

Exposure to the elements

A dead body that has been exposed to the open elements, such as water and air, will decompose more quickly and attract much more insect activity than a body that is buried^[22] or confined in special protective gear or artifacts.^[23] This is due, in part, to the limited number of insects that can penetrate soil^[24] and the lower temperatures under the soil.^[25]

The rate and manner of decomposition in an animal body are strongly affected by several factors. In roughly descending degrees of importance,^[26] they are:

• Temperature;
• The availability of oxygen;
• Prior embalming;
• Cause of death;
• Burial, depth of burial, and soil type;
• Access by scavengers;
• Trauma, including wounds
  and crushing blows;
• Humidity, or wetness;
• Rainfall;
• Body size and weight;
• Composition;
• Clothing;
• The surface on which the body rests;
• Foods/objects inside the specimen's
  digestive tract (bacon compared to lettuce
  ).

The bodies of newborns who never ingested food are an important exception to the normal process of decomposition. They lack the internal microbial flora that produces much of decomposition[34] and quite commonly mummify if kept in even moderately dry conditions.^[35]

Anaerobic vs aerobic

Aerobic decomposition takes place in the presence of oxygen. This is most common to occur in nature. Living organisms that use oxygen to survive feed on the body.

Embalming is the practice of delaying the decomposition of human and animal remains. Embalming slows decomposition somewhat but does not forestall it indefinitely. Embalmers typically pay great attention to parts of the body seen by mourners, such as the face and hands. The chemicals used in embalming repel most insects and slow down bacterial putrefaction by either killing existing bacteria in or on the body themselves^[37] or by fixing cellular proteins, which means that they cannot act as a nutrient source for subsequent bacterial infections.^[38] In sufficiently dry environments, an embalmed body may end up mummified and it is not uncommon for bodies to remain preserved to a viewable extent after decades.^[39] Notable viewable embalmed bodies include those of:

• Eva Perón of Argentina, whose body was injected with paraffin, was kept perfectly preserved for many years, and still is as far as is known (her body is no longer on public display).^[40]
• Vladimir Lenin of the Soviet Union, whose body was kept submerged in a special tank of fluid for decades and is on public display in Lenin's Mausoleum.^[41]
  • Other
    cults of personality such as Mao Zedong, Kim Il Sung, Ho Chi Minh, Kim Jong Il and most recently Hugo Chávez have also had their cadavers preserved in the fashion of Lenin's preservation and are now displayed in their respective mausoleums
    .
• Pope John XXIII, whose preserved body can be viewed in St. Peter's Basilica.
• formalin before burial in a dry vault from which he was later removed and placed on public display at the San Giovanni Rotondo.^[42]

A body buried in a sufficiently dry environment may be well preserved for decades. This was observed in the case for murdered civil rights activist Medgar Evers, who was found to be almost perfectly preserved over 30 years after his death, permitting an accurate autopsy when the case of his murder was re-opened in the 1990s.^[43]

Bodies submerged in a peat bog may become naturally embalmed, arresting decomposition and resulting in a preserved specimen known as a bog body. The generally cool and anoxic conditions in these environments limits the rate of microbial activity, thus limiting the potential for decomposition.^[44] The time for an embalmed body to be reduced to a skeleton varies greatly. Even when a body is decomposed, embalming treatment can still be achieved (the arterial system decays more slowly) but would not restore a natural appearance without extensive reconstruction and cosmetic work, and is largely used to control the foul odors due to decomposition.^[38]

An animal can be preserved almost perfectly, for millions of years in a resin such as amber.^[45]

There are some examples where bodies have been inexplicably preserved (with no human intervention) for decades or centuries and appear almost the same as when they died. In some religious groups, this is known as incorruptibility. It is not known whether or for how long a body can stay free of decay without artificial preservation.^[46]

Importance to forensic sciences

Various sciences study the decomposition of bodies under the general rubric of forensic science because the usual motive for such studies is to determine the time and cause of death for legal purposes:

• Forensic taphonomy specifically studies the processes of decomposition to apply the biological and chemical principles to forensic cases to determine post-mortem interval (PMI), post-burial interval as well as to locate clandestine graves.
• Forensic pathology studies the clues to the cause of death found in the corpse as a medical phenomenon.
• Forensic entomology studies the insects and other vermin found in corpses; the sequence in which they appear, the kinds of insects, and where they are found in their life cycle are clues that can shed light on the time of death, the length of a corpse's exposure, and whether the corpse was moved.^[47][48]
• physical anthropology that studies skeletons and human remains, usually to seek clues as to the identity, age, sex, height and ethnicity of their former owner.^[49][50]

Wood decomposition is a complex process involving fungi which transport nutrients to the nutritionally scarce wood from outside environment.[53] Because of this nutritional enrichment, the fauna of saproxylic insects may develop^[54] and, in turn, affect dead wood, contributing to decomposition and nutrient cycling in the forest floor.^[54] Lignin is one such remaining product of decomposing plants with a very complex chemical structure, causing the rate of microbial breakdown to slow. Warmth increases the speed of plant decay by roughly the same amount, regardless of the composition of the plant.^[55]

In most

The chemical aspects of plant decomposition always involve the release of carbon dioxide. In fact, decomposition contributes over 90 percent of carbon dioxide released each year.^[55]

Food decomposition

This section needs expansion with: information from the main article. You can help by adding to it. (July 2010)

The decomposition of food, either plant or animal, called spoilage in this context, is an important field of study within

Spoilage of food is attributed to contamination from microorganisms such as bacteria, molds and yeasts, along with natural decay of the food.[56] These decomposition bacteria reproduce at rapid rates under conditions of moisture and preferred temperatures. When the proper conditions are lacking the bacteria may form spores which lurk until suitable conditions arise to continue reproduction.^[56]

Rate of decomposition

The rate of decomposition is governed by three sets of factors—the physical environment (temperature, moisture and soil properties), the quantity and quality of the dead material available to decomposers, and the nature of the microbial community itself.^[57]

Decomposition rates are low under very wet or very dry conditions. Decomposition rates are highest in damp, moist conditions with adequate levels of oxygen. Wet soils tend to become deficient in oxygen (this is especially true in

The quality and quantity of the material available to decomposers is another major factor that influences the rate of decomposition. Substances like sugars and amino acids decompose readily and are considered labile. Cellulose and hemicellulose, which are broken down more slowly, are "moderately labile". Compounds which are more resistant to decay, like lignin or cutin, are considered recalcitrant.^[57] Litter with a higher proportion of labile compounds decomposes much more rapidly than does litter with a higher proportion of recalcitrant material. Consequently, dead animals decompose more rapidly than dead leaves, which themselves decompose more rapidly than fallen branches.^[57] As organic material in the soil ages, its quality decreases. The more labile compounds decompose quickly, leaving an increasing proportion of recalcitrant material. Microbial cell walls also contain recalcitrant materials like chitin, and these also accumulate as the microbes die, further reducing the quality of older soil organic matter.^[57]

See also

• Cadaverine
• Chemical decomposition
• Ecosystem
• Humus
• Leachate
• Microbiology of decomposition
• Peat (turf)
• Putrescine
• Staling

References

External links

Look up decomposition, spoilage, or perishable in Wiktionary, the free dictionary.

• How to Revive Dying or Dead Plants: 10 Easy Steps for Snake Plant
• Media related to Decomposition at Wikimedia Commons
• 1Lecture.com – Food decomposition (a Flash animation)

Preceded by Death

Stages of human development Decomposition

Succeeded by Skeletonization