Decomposition
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Pallor mortis |
Decomposition (or spoilage) refers to the reduction of the body of a formerly living organism into simpler forms of matter. The body of a living organism begins to decompose (as part of a succession) shortly after death. Such decomposition can be simplified in two stages: In the first stage, it is limited to the production of vapors. In the second stage, liquid materials form and the flesh or plant matter begins to decompose. The science which studies such decomposition generally is called taphonomy. Historically, the progression of decomposition of a living organism has been described as taking place in four stages: fresh (autolysis), bloat (putrefaction), decay (putrefaction and carnivores) and dry (diagenesis).
There are environmental influences that will affect decomposition. A body that is exposed to air will decompose more quickly and will have more insect activity. A buried body will decompose eight times slower than a body exposed to air. This is due in part to limited insect activity and possibly lower temperatures. Likewise a body submerged in water decomposes at half the rate of an exposed body. The rate of decomposition depends on the temperature of the water. Cold water will allow slow decomposition and warm water causes faster decomposition. The body is also shielded from insect activity as long as it is submerged.
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[edit] Plant decomposition
- See also: Compost and Anaerobic digestion
Decomposition of plant matter occurs in many stages. It begins with leaching by water; the most labile (easily lost) and soluble carbon compounds are liberated in this process. Another early process is physical breakup or fragmentation of the plant material into smaller bits which have greater surface area for microbial colonization and attack. This process is mostly governed by the soil fauna, such as invertebrates. Following this, the plant detritus, which can consist of cellulose, hemicellulose, microbial products, and lignin, undergoes actual chemical alteration by microbes. Different types of compounds decompose at different rates. For instance, wood contains a component called lignin which is relatively resistant to decomposition and in fact can only be decomposed by certain fungi such as the white-rot fungi. These fungi are thought to be seeking the nitrogen content of lignin rather than its carbon content. Lignin has a very complex chemical structure which slows down the rate of microbial breakdown.
Fungi and bacteria are very important in the decomposition of plants, accounting for approximately 80 to 90 % of the total biomass of the decomposed material (Chapin et al., Principles of Terrestrial Ecosystem Ecology).
In most grassland ecosystems, fire is the primary mode of decomposition, making it crucial in nutrient cycling (DeBano et al. 1998).
The chemical aspects of plant decomposition always involve the release of carbon dioxide.
[edit] 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 gases that are the chief source of the characteristic odor of dead bodies. These gases swell the body.
Scavengers play an important role in decomposition. Insects and other animals are typically the next agent of decomposition, if the body is accessible to them. The most important insects that are typically involved in the process include the flesh-flies (Sarcophagidae) and blow-flies (Calliphoridae). The green-bottle fly seen in the summer is a blowfly. Larger scavengers, including coyotes, dogs, wolves, foxes, rats, and mice may eat a body if it is accessible to them. Some of these animals also remove and scatter bones.
Most decomposers are bacteria or fungi.
[edit] Human decomposition
[edit] Stages
Once death occurs, human decomposition takes place in stages. The process of tissue breakdown may take from several days to years.
[edit] Fresh
The fresh stage of decomposition occurs during the first few days following death. There are no physical signs of decomposition during this time. However, homeostasis of the body has ceased to function which allows cellular and soft tissue changes to occur because of the process of autolysis, the destruction of cells and organs due to an aseptic chemical process. At this point, the body enters algor mortis, the cooling of the body's temperature to that of its surroundings. When the body’s cells reach the final stage of autolysis, an anaerobic environment is created. This allows the body’s normal bacteria to breakdown the remaining carbohydrates, proteins, and lipids. The products from the breakdown create acids, gases, and other products which cause volatile organic compounds (VOCs), and putrefactive effects. According to Science Direct, VOCs are produced during the early stage of human decomposition.[1][citation needed]
[edit] Putrefaction
Odor, color changes, and bloating of the body during decomposition are the results of putrefaction. The lower part of the abdomen turns green due to bacteria activity in the cecum. Bacteria break down hemoglobin into sulfohemoglobin which causes the green color change. A formation of gases enters the abdomen which forces liquids and feces out of the body. The gases also enter the neck and face, causing swelling of the mouth, lips, and tongue. Due to this swelling and disconfiguration of the face, identification of the body can be difficult. Bacteria also enter the venous system causing blood to hemolyze. This leads to the formation of red streaks along the veins. This color soon changes to green, through a process known as marbelization. It can be seen on the shoulders, chest and shoulder area, and thighs. The skin can blister and have a serous fluid inside. The skin also becomes fragile, leading to skin slippage, making it difficult to move a body. Body hair comes off easily. The color change of the discoloration from green to brown marks the transition of the early stage of putrefaction to the advanced decompositional stages.
[edit] Black putrefaction
After the body goes through the bloating stage it begins the black putrefaction stage. At this point the body cavity ruptures, all of the abdominal gases begin to escape and the body darkens from its greenish color. These activities allow for a greater invasion of scavengers, and insect activity increases greatly. This stage ends as the bones become apparent, which can take anywhere from 10 to 20 days after death depending on region and temperature. This period is also dependent on the degree to which the body is exposed.
[edit] Butyric fermentation
After the early putrefaction and black putrefaction phases have taken place, the body begins mummification, in which the body begins to dry out. The human carcass is first mummified, and then goes through adipocere formation. Adipocere (grave wax) formation refers to the loss of body odor and the formation of a cheesy appearance on the cadaver. Mummification is considered a post-active stage because there is less definite distention between changes and they are indicated by reduced skin, cartilage, and bone. Mummification is also indicated when all of the internal organs are lost due to insect activity.
[edit] Dry decay
When the last of the soft-tissue has been removed from the body, the final stage of decomposition, skeletonization, occurs. This stage encompasses the deterioration of skeletal remains, and is the longest of the decomposition processes. Skeletonization differs markedly from the previous stages, not only in length, but in the deterioration process itself.
The strength and durability of bone stems from the unique protein-mineral bond present in skeletal formation; consequently, changes to skeletal remains, known as bone diagenesis, occur at a substantially slower rate than stages of soft-tissue breakdown. As the protein-mineral bond weakens after death, however, the organic protein begins to leach away, leaving behind only the mineral composition. Unlike soft-tissue decomposition, which is influenced mainly by temperature and oxygen levels, the process of bone breakdown is more highly dependent on soil type and pH, along with presence of groundwater. However, temperature can be a contributing factor, as higher temperature leads the protein in bones to break down more rapidly. If buried, remains decay faster in acidic-based soils rather than alkaline. Bones left in areas of high moisture content also decay at a faster rate. The water leaches out skeletal minerals, which corrodes the bone, and leads to bone disintegration.[2]
[edit] Insect activity
Substances produced during the fresh stage attract a variety of insects. Many of the Diptera insects begin to lay their eggs on the body during this stage, especially the Calliphoridae. There is also considerable insect activity by the insects that live in the soil around the body.
During putrefaction the majority of the insects begins with the Calliphoridae, and include Formicidae, Muscidae, Sphaeroceridae, Silphidae, Lepidoptera, Hymenoptera, Sarcophagidae, Histeridae, Staphylinidae, Phalangida, Piophilidae, Aranae, Sepsidae, and Phoridae. Again, there is also considerable insect activity by the soil-inhabiting arthropods.
There is considerable insect activity during black putrefaction. Some of the insects that can be found living in the body are the Calliphoridae larvae, Staphylinidae, Histeridae, Gamasid mites, Ptomaphila, Trichopterygidae, Piophilid larvae, Parasitic wasps, Staphylinid larvae, Trichopterygid larvae, Histerid larvae, Ptomaphila larvae, Dermestes, Tyroglyphid mites, Tineid larvae, and the Dermestes larvae. Some insects can also be found living in the soil around the body such as Isopoda, Collembola, Dermaptera, Formicidae, Pseudoscorpiones, Araneae, Plectochetos, Acari, Pauropoda, Symphyla, Geophilidae, and Protura. Finding these insects is what was found on a body in Australia. The types of insects will differ based on where the body is, although Diptera larvae can be found feeding on the body in almost all cases.
Insects that can be found on the body during mummification include most of the same insects as in putrefaction stage, but also include Acarina, Nitidulidae, Cleridae, Dermestes caninus, and Trogidae. The main soil-inhabiting arthropods include Dermaptera and Formicidae.
At the dry decay stage commonly found insects include Sphaeroceridae, Acarina, Nitidulidae, Cleridae, Dermestes caninus, Trogidae, Tyroglyphid mites, and the Tineid larvae. The soil-inhabiting arthropods are Collembola, Dermaptera, Heteroptera, Coleoptera and their larvae, parasitic Hymenoptera, Formicidae, Diptera larvae, Psuedoscorpiones, Aranae, Plectochetos, Acari, Pauropoda, Symphyla, Geophilidae, Protura, and Aphididae.
[edit] Importance to forensics
- Further information: Forensic entomological decomposition
Various sciences study the decomposition of bodies. These sciences fall under the general rubric of forensics, because the usual motive for study of the decomposition of human bodies is to determine the time and cause of death, for legal purposes:
- 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.
- Forensic anthropology is the branch of physical anthropology that studies skeletons and human remains, usually to seek clues as to the identity, race, and sex of their former owner.
The University of Tennessee Forensic Anthropology Facility (better known as the Body Farm) in Knoxville, Tennessee has a number of bodies laid out in various situations in a fenced-in plot near the medical center. Scientists at the Body farm study how the human body decays in various circumstances to gain a better understanding into decomposition.
[edit] Case study
According to a preliminary investigation of insect colonization and succession on remains in New Zealand, results on decay and colonization revealed the following. In the open field habitat, the environment had a daily average maximum temperature of 19.4 degrees Celsius and a daily minimum temperature of 11.1 degrees Celsius. The average rainfall in this study averaged 3.0 mm/day for the first 3 weeks. According to the preliminary investigation of insect colonization and succession, around days 17-45, the body began to start active decay. During this stage, the successions started with Calliphora stygia, which lasted until the 27th day. The larvae of Chrysomya rufifacies are present between the 13th and 47th day. The H. rostrata, larvae of Lucilia sericata, Psychodidae family, and sylvicola are present relatively late in the post decay.
In the coastal sand-dune habitat, the weather conditions are described as the warmest with an average daily maximum temperature of 21.4 degrees Celsius and minimum of 13.5 degrees Celsius. The daily average rainfall is recorded as 1.4 mm/day during first 3 weeks. Due to the weather conditions of this environment, the post-decay time interval, beginning 6 to 15 days after death, is greatly reduced from the average. This stage last till the skeletal stage which exceeds the 124 day experimentation time. Insects obtained late in the post-active stage include the Callihora quadrimaculat, adult Phaeroceridae, Psychodidae and Piophilidae (no larvae from this family were obtained in recovery).
In a native bush habitat, the recorded daily average maximum and minimum temperatures were 18.0 and 13.0 degrees Celsius, respectively. The average rainfall in this habitat was recorded at .4 mm/day. After the bloat stage, which lasted until the seventh day, the post active decay began around the 14th day. In this habitat, the H. rostrata, Phoridae adult, Sylvicola larvae and adult are the predominant species remaining on the body during the pre-skeletonization stages.
[edit] Factors affecting decomposition
- Further information: Environmental effects on forensic entomology
The rate and manner of decomposition in an animal body is strongly affected by a number of factors. In roughly descending degrees of importance, they are:
- Temperature
- The availability of oxygen
- Prior embalming
- Cause of death
- Burial, and depth of burial
- Access by scavengers
- Trauma, including wounds and crushing blows
- Humidity, or wetness
- Rainfall
- Body size and weight
- Clothing
- The surface on which the body rests
- Foods/objects inside the specimens digestive tract (bacon compared to lettuce)
The speed at which decomposition occurs varies greatly. Factors such as temperature, humidity, and the season of death all determine how fast a fresh body will skeletonize or mummify. A basic guide for the effect of environment on decomposition is given as Casper's Law (or Ratio): when there is free access of air a body decomposes twice as fast than if immersed in water and eight times faster than if buried in earth.
The most important variable is a body's accessibility to insects, particularly flies. On the surface in tropical areas, invertebrates alone can easily reduce a fully fleshed corpse to clean bones in under two weeks. The skeleton itself is not permanent; acids in soils can reduce it to unrecognizable components. This is one reason given for the lack of human remains found in the wreckage of the Titanic, even in parts of the ship considered inaccessible to scavengers. Freshly skeletonized bone is often called "green" bone and has a characteristic greasy feel. Under certain conditions (normally cool, damp soil), bodies may undergo saponification and develop a waxy substance called adipocere, caused by the action of soil chemicals on the body's proteins and fats. The formation of adipocere slows decomposition by inhibiting the bacteria that cause putrefaction.
In extremely dry or cold conditions, the normal process of decomposition is halted — by either lack of moisture or temperature controls on bacterial and enzymatic action — causing the body to be preserved as a mummy. Frozen mummies commonly restart the decomposition process when thawed, whilst heat-desiccated mummies remain so unless exposed to moisture.
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 produce much of decomposition and quite commonly mummify if kept in even moderately dry conditions.
Embalming is the practice of delaying 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 "fixing" cellular proteins, which means that they cannot act as a nutrient for bacteria, and killing the bacteria themselves. In sufficiently dry environments, an embalmed body may end up mummified and it is not uncommon for bodies in dry vaults to remain preserved to a viewable extent after decades, such as the murdered civil rights activist Medgar Evers. Another case of this would be the body of Vladimir Lenin, who was kept submerged in a special tank of fluid for decades, almost perfectly preserved. Bodies submerged in peat bog may become naturally "embalmed", arresting decomposition and resulting in a preserved specimen known as a bog body. The body of Evita Peron was kept perfectly preserved for many years, and as far as is known, may still be so (her body is no longer on display as it once was). 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 slower) but would not restore a natural appearance without extensive reconstruction and cosmetic work, and is largely used to control the foul odours due to decomposition.
[edit] See also
[edit] References
- Statheropoulos, M, Agapiou, A., Spiliopoulou, C., Pallis, G.C., and Sianos, E. "Environmental aspects of VOCs evolved in the early stages of human decomposition." Science of The Total Environment. 385(2007): 221-227.
- Eberhardt, Terry L., and Elliot, D. A. "A Preliminary investigation of insect colonisation and succession on remains in New Zealand." Forensic Science International 176(2008): 217-223.
- Kulshrestha, Pankaj, and Satpathy, D.K. "Use of beetles in forensic entomology." Forensic Science International 120(2001): 15-17.
- Schmitt, Aurore, Cunha, E., and Pinheiro, J.. Forensic Anthropology and Medicene: Complementary Sciences Frome Recovery to Cause of Death. 1st ed. Totowa, NJ: Humana Press, 2006.
- Haglund, William D., and Sag, M. H.. Forensic Taphonomy: The Postmortem Fate of Human Remains. 1st ed. Boca Raton: CRC Press, 1997.
- Smith, K. G. V.. A Manual of Forensic Entomology. 3rd. Ithaca, N.Y.: Cornell University Press, 1986.
- Eberhardt, Terry L., and Elliot, Douglas A. A preliminary investigatio of insect colonisation and succession on remains in new Zealand. University of auckland, department of chemistry, forensic science programme, 2006. Forensic science international 176 (2008) 217-223
