Corpse decomposition

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Common wild pig (boar) corpse decomposition timelapse

Decomposition is the process in which the organs and complex molecules of animal and human bodies break down into simple organic matter over time. In vertebrates, five stages of decomposition are typically recognized: fresh, bloat, active decay, advanced decay, and dry/skeletonized. [1] Knowing the different stages of decomposition can help investigators in determining the post-mortem interval (PMI). [2] The rate of decomposition of human remains can vary due to environmental factors and other factors. [3] Environmental factors include temperature, burning, humidity, and the availability of oxygen. [3] Other factors include body size, clothing, and the cause of death. [3]

Contents

Stages and characteristics

The five stages of decomposition—fresh (autolysis), bloat, active decay, advanced decay, and dry/skeletonized—have specific characteristics that are used to identify which stage the remains are in. [4] These stages are illustrated by reference to an experimental study of the decay of a pig corpse. [1]

Fresh

A fresh pig carcass Example of a pig carcass in the fresh stage of decomposition.jpg
A fresh pig carcass

At this stage the remains are usually intact and free of insects. The corpse progresses through algor mortis (a reduction in body temperature until ambient temperature is reached), rigor mortis (the temporary stiffening of the limbs due to chemical changes in the muscles), and livor mortis (pooling of the blood on the side of the body that is closest to the ground). [5]

Bloat

A bloated pig carcass Example of a pig carcass in the bloat stage of decomposition.jpg
A bloated pig carcass

At this stage, the microorganisms residing in the digestive system begin to digest the tissues of the body, excreting gases that cause the torso and limbs to bloat, and producing foul-smelling chemicals including putrescine and cadaverine. [6] Cells in tissues break down and release hydrolytic enzymes, and the top layer of skin may become loosened, leading to skin slippage. [7] : 153–162  Decomposition of the gastrointestinal tract results in a dark, foul-smelling liquid called "purge fluid" that is forced out of the nose and mouth due to gas pressure in the intestine. [7] : 155  The bloat stage is characterized by a shift in the bacterial population from aerobic to anaerobic bacterial species. [8]

Active decay

A pig carcass actively decaying Example of a pig carcass in the active decay stage of decomposition.jpg
A pig carcass actively decaying

At this stage, the tissues begin to liquify and the skin will start to blacken. Blowflies target decomposing corpses early on, using specialized smell receptors, and lay their eggs in orifices and open wounds. [8] The size and development stage of maggots can be used to give a measure of the minimum time since death. [9] : 251–252  Insect activity occurs in a series of waves, and identifying the insects present can give additional information on the postmortem interval. [10] Adipocere, or corpse wax, may be formed, inhibiting further decomposition. [9] : 16–18 

Advanced decay

A pig carcass in a stage of advanced decay Example of a pig carcass in the advanced decay stage of decomposition.jpg
A pig carcass in a stage of advanced decay

During advanced decay, most of the remains have discolored and often blackened. Putrefaction, in which tissues and cells break down and liquidize as the body decays, will be almost complete. [1] A decomposing human body in the earth will eventually release approximately 32 g (1.1 oz) of nitrogen, 10 g (0.35 oz) of phosphorus, 4 g (0.14 oz) of potassium, and 1 g (0.035 oz) of magnesium for every kilogram of dry body mass, making changes in the chemistry of the soil around it that may persist for years. [8]

Dry/skeletonized remains

The dry and skeletonized remains of a pig carcass Example of a pig carcass in the dry decay stage of decomposition.jpg
The dry and skeletonized remains of a pig carcass

Once bloating has ceased, the soft tissue of remains typically collapses in on itself. At the end of active decay, the remains are often dried out and begin to skeletonize. [1]

Environmental factors

Temperature

The climate and temperature in which a corpse decomposes can have great effect on the rate of decomposition; [11] higher temperatures accelerate the physiological reactions in the body after death and speed up the rate of decomposition, and cooler temperatures may slow the rate of decomposition. [11]

In summer conditions, the body can decompose to bones in nine days. [12] Warm climates can mean that finger prints cannot be obtained after four days, [13] and in colder climates or seasons they may remain for up to fifty days after death. [13] [14]

Humidity

The amount of moisture in the environment in which a corpse decomposes also has an effect on the rate of decomposition. [11] Humid environments will speed up the rate of decomposition and will influence adipocere formation. [11] In contrast, more arid environments will see corpses dry up faster and decompose more slowly. [11]

Oxygen availability

Whether the corpse is in a more anaerobic or aerobic environment will also influence the rate of decomposition. [2] The more oxygen there is available the more rapid decomposition will take place. [15] This is because the microorganisms required for decomposition require oxygen to live and thus facilitate decomposition. [15] Lower oxygen levels will have the opposite effect. [15]

Burial

Burial postpones the rate of decomposition, in part because even a few inches of soil covering the corpse will prevent blowflies from laying their eggs on the corpse. The depth of burial will influence the rate of decomposition as it will deter decomposers such as scavengers and insects. [2] This will also lower the available oxygen and impede decomposition as it will limit the function of microorganisms. [15] The pH of the soil will also be a factor when it comes the rate of decomposition, as it influences the types of decomposers. [16] Moisture in soil will also slow down decomposition as it facilitates anaerobic metabolism. [11]

Wet environments

Submersion in water typically slows decomposition. The rate of loss of heat is higher in water and the progression through algor mortis is therefore faster. Cool temperatures slow bacterial growth. Once bloat begins, the body will typically float to the surface and become exposed to flies. Scavengers in the water, which vary with the location, also contribute to decay. [17] Factors affecting decomposition include water depth, temperature, tides, currents, seasons, dissolved oxygen, geology, acidity, salinity, sedimentation, and insect and scavenging activity. [18] Human remains found in aquatic surroundings are often incomplete and poorly preserved, making investigating the circumstances of death much more difficult. [19] If a person has drowned, the body will likely initially submerge and go into a position that has been named "the drowning position." This position is when the front of the body is face down in the water, with their extremities reaching down towards the bottom of the body of water. Their back is typically slightly arched down and inwards. This position is important to note as when this occurs in shallow water their extremities may drag across the bottom of the body of the water, leaving injuries. [20] After death, when a body is submerged in water a process called Saponification occurs. This is the process in which adipocere is formed. Adipocere is a wax-like substance that covers bodies created by the hydrolysis of triglycerides in adipose tissue. This occurs mainly in submersion, burial environments or areas with lots of carbon but has been noted in marine environments. [21]

Other factors

Body size

Body size is an important factor that will also influence the rate of decomposition. [22] A larger body mass and more fat will decompose more rapidly. [22] This is because after death, fats will liquify, accounting for a large portion of decomposition. [22] People with a lower fat percentage will decompose more slowly. [22] This includes smaller adults and especially children. [22]

Clothing

Clothing and other types of coverings affect the rate of decomposition because it limits the body's exposure to external factors such as weathering and soil. [2] It slows decomposition by delaying scavenging by animals. [2] However, insect activity would increase since the wrapping will harbor more heat and protection from the sun, providing an ideal environment for maggot growth which facilitates organic decay. [2]

Cause of death

The cause of death can also influence the rate of decomposition, mainly by speeding it up. [23] Fatal wounds like stab wounds or other lacerations on the body attract insects as it provides a good spot to oviposit and, as a result, could increase the rate of decomposition. [23]

Experimental analysis of decomposition on corpse farms

Corpse farms are used to study the decay of the human body and to gain insight into how environmental and endogenous factors affect progression through the stages of decomposition. [8] In summer, high temperatures can accelerate the stages of decomposition: heat encourages the breakdown of organic material, and bacteria also grow faster in a warm environment, accelerating bacterial digestion of tissue. However, natural mummification, normally thought of as a consequence of arid conditions, can occur if the remains are exposed to intense sunlight. [24] In winter, not all bodies go through the bloat stage. Bacterial growth is much reduced at temperatures below 4 °C. [25] Corpse farms are also used to study the interactions of insects with decaying bodies. [8]

Related Research Articles

<span class="mw-page-title-main">Forensic entomology</span> Application of insect and other arthropod biology to forensics

Forensic entomology is a branch of forensic science that uses insects found on corpses to help solve criminal cases. This includes studying the types of insects commonly found on cadavers, their life cycles, their presence in different environments, and how insect assemblages change with decomposition.

Rigor mortis, or postmortem rigidity, is the fourth stage of death. It is one of the recognizable signs of death, characterized by stiffening of the limbs of the corpse caused by chemical changes in the muscles postmortem. In humans, rigor mortis can occur as soon as four hours after death. Contrary to folklore and common belief, rigor mortis is not permanent and begins to pass within hours of onset. Typically, it lasts no longer than eight hours at "room temperature".

<span class="mw-page-title-main">Decomposition</span> Process in which organic substances are broken down into simpler organic matter

Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is essential for recycling the finite matter that occupies physical space in the biosphere. Bodies of living organisms begin to decompose shortly after death. Animals, such as earthworms, also help decompose the organic materials. Organisms that do this are known as decomposers or detritivores. Although no two organisms decompose in the same way, they all undergo the same sequential stages of decomposition. The science which studies decomposition is generally referred to as taphonomy from the Greek word taphos, meaning tomb. Decomposition can also be a gradual process for organisms that have extended periods of dormancy.

<span class="mw-page-title-main">Taphonomy</span> Study of decomposition and fossilization of organisms

Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term taphonomy was introduced to paleontology in 1940 by Soviet scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms from the biosphere to the lithosphere.

Putrefaction is the fifth stage of death, following pallor mortis, livor mortis, algor mortis, and rigor mortis. This process references the breaking down of a body of an animal post-mortem. In broad terms, it can be viewed as the decomposition of proteins, and the eventual breakdown of the cohesiveness between tissues, and the liquefaction of most organs. This is caused by the decomposition of organic matter by bacterial or fungal digestion, which causes the release of gases that infiltrate the body's tissues, and leads to the deterioration of the tissues and organs. The approximate time it takes putrefaction to occur is dependent on various factors. Internal factors that affect the rate of putrefaction include the age at which death has occurred, the overall structure and condition of the body, the cause of death, and external injuries arising before or after death. External factors include environmental temperature, moisture and air exposure, clothing, burial factors, and light exposure. Body farms are facilities that study the way various factors affect the putrefaction process.

Adipocere, also known as corpse wax, grave wax or mortuary wax, is a wax-like organic substance formed by the anaerobic bacterial hydrolysis of fat in tissue, such as body fat in corpses. In its formation, putrefaction is replaced by a permanent firm cast of fatty tissues, internal organs, and the face.

A body farm is a research facility where decomposition of humans and animals can be studied in a variety of settings. The initial facility was conceived by anthropologist William M. Bass in 1981 at the University of Tennessee in Knoxville, Tennessee, where Bass was interested in studying the decomposition of a human corpse from the time of death to the time of decay. The aim was to gain a better understanding of the decomposition process, permitting the development of techniques for extracting information such as the timing and circumstances of death from human remains. Body farm research is of particular interest in forensic anthropology and related disciplines, and has applications in the fields of law enforcement and forensic science. Numerous purposes exist for these research facilities, yet their main purpose is to study and form an understanding of the decompositional changes that occur with the human body. By placing the bodies outside to face the elements, researchers are able to get a better understanding of the decomposition process. This research is then used for medical, legal and educational purposes. Following the outdoor research, skeletal remains are cleaned and curated in permanent known skeletal collections open for research. Such collections are critical for testing and developing new identification methods.

<span class="mw-page-title-main">Post-mortem interval</span> Time that has elapsed since a person has died

The post-mortem interval (PMI) is the time that has elapsed since an individual's death. When the time of death is not known, the interval may be estimated, and so an approximate time of death established. Postmortem interval estimations can range from hours, to days or even years depending on the type of evidence present. There are standard medical and scientific techniques supporting such an estimation.

<i>Calliphora vomitoria</i> Species of fly

Calliphora vomitoria, known as the blue bottle fly, orange-bearded blue bottle, or bottlebee, is a species of blow fly, a species in the family Calliphoridae. Calliphora vomitoria is the type species of the genus Calliphora. It is common throughout many continents including Europe, Americas, and Africa. They are fairly large flies, nearly twice the size of the housefly, with a metallic blue abdomen and long orange setae on the gena.

<span class="mw-page-title-main">Skeletonization</span> Remains of an organism after soft tissues have broken down after death

Skeletonization is the state of a dead organism after undergoing decomposition. Skeletonization refers to the final stage of decomposition, during which the last vestiges of the soft tissues of a corpse or carcass have decayed or dried to the point that the skeleton is exposed. By the end of the skeletonization process, all soft tissue will have been eliminated, leaving only disarticulated bones.

Forensic entomological decomposition is how insects decompose and what that means for timing and information in criminal investigations. Medicolegal entomology is a branch of forensic entomology that applies the study of insects to criminal investigations, and is commonly used in death investigations for estimating the post-mortem interval (PMI). One method of obtaining this estimate uses the time and pattern of arthropod colonization. This method will provide an estimation of the period of insect activity, which may or may not correlate exactly with the time of death. While insect successional data may not provide as accurate an estimate during the early stages of decomposition as developmental data, it is applicable for later decompositional stages and can be accurate for periods up to a few years.

<i>Muscina</i> Genus of flies

Muscina is a genus of flies that belongs to the family Muscidae, currently consisting of 27 species. They are worldwide in distribution and are frequently found in livestock facilities and outside restrooms. The most common species are M. stabulans, M. levida, and M. prolapsa. Muscina flies commonly breed in manure and defecate on food, which has been linked to the spread of some disease and illnesses. The occurrence of Muscina larvae on dead bodies has led to their regular use in forensic investigations, as they may be used to estimate the time of death. Research have shown the prevalence of certain species of Muscina flies as vectors of diseases such as poliomyelitis.

<span class="mw-page-title-main">Microbiology of decomposition</span>

Microbiology of decomposition is the study of all microorganisms involved in decomposition, the chemical and physical processes during which organic matter is broken down and reduced to its original elements.

<span class="mw-page-title-main">Carrion insects</span> Insects associated with decomposing remains

Carrion insects are insects associated with decomposing remains. The processes of decomposition begin within a few minutes of death. Decomposing remains offer a temporary, changing site of concentrated resources which are exploited by a wide range of organisms, of which arthropods are often the first to arrive and the predominant exploitive group. However, not all arthropods found on or near decomposing remains will have an active role in the decay process.

Decomposition in animals is a process that begins immediately after death and involves the destruction of soft tissue, leaving behind skeletonized remains. The chemical process of decomposition is complex and involves the breakdown of soft tissue, as the body passes through the sequential stages of decomposition. Autolysis and putrefaction also play major roles in the disintegration of cells and tissues.

<span class="mw-page-title-main">Forensic mycology</span>

Forensic mycology is the use of mycology in criminal investigations. Mycology is used in estimating times of death or events by using known growth rates of fungi, in providing trace evidence, and in locating corpses. It also includes tracking mold growth in buildings, the use of fungi in biological warfare, and the use of psychotropic and toxic fungus varieties as illicit drugs or causes of death.

<span class="mw-page-title-main">Necrophage</span> Organism that consumes dead animal matter

Necrophages are organisms that obtain nutrients by consuming decomposing dead animal biomass, such as the muscle and soft tissue of carcasses and corpses. The term derives from Greek nekros, meaning 'dead', and phagein, meaning 'to eat.' Mainly, necrophages are species within the phylum Arthropoda; however, other animals, such as gastropods and Accipitrimorphae birds have been noted to engage in necrophagy.

The necrobiome has been defined as the community of species associated with decaying remains after the death of an organism. The process of decomposition is complex. Microbes decompose cadavers, but other organisms including fungi, nematodes, insects, and larger scavenger animals also contribute. Once the immune system is no longer active, microbes colonizing the intestines and lungs decompose their respective tissues and then travel throughout the body via the circulatory and lymphatic systems to break down other tissue and bone. During this process, gases are released as a by-product and accumulate, causing bloating. Eventually, the gases seep through the body's wounds and natural openings, providing a way for some microbes to exit from the inside of the cadaver and inhabit the outside. The microbial communities colonizing the internal organs of a cadaver are referred to as the thanatomicrobiome. The region outside of the cadaver that is exposed to the external environment is referred to as the epinecrotic microbial communities of the necrobiome, and is especially important when determining the time and location of death for an individual. Different microbes play specific roles during each stage of the decomposition process. The microbes that colonize the cadaver and the rate of their activity are determined by the cadaver itself and the cadaver's surrounding environmental conditions.

The stages of death of a human being have medical, biochemical and legal aspects. The term taphonomy from palaeontology applies to the fate of all kinds of remains of organisms. Forensic taphonomy is concerned with remains of the human body.

<i>Necrodes littoralis</i> Species of beetle

Necrodes littoralis, also known as the short sexton beetle, is a species of carrion beetle of the genus Necrodes, found in countries across Europe. As a carrion beetle, it feeds on decaying vertebrate remains and maggots. This species' feeding behaviors make it an important asset to forensic entomology.

References

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  12. ↑ Australian Museum (22 October 2020). "Decomposition - Body Changes". Australian Museum. The time taken for a body to decompose depends on climatic conditions, like temperature and moisture, as well as the accessibility to insects. In summer, a human body in an exposed location can be reduced to bones alone in just nine days.
  13. 1 2 Weise, Elizabeth (9 November 2017). "The dead can unlock iPhones, offering possible clues to a killer's plan after memories go". usatoday.com. Retrieved 25 September 2024. A study done in 2016 at Oak Ridge National Laboratory found that both iris and fingerprint biometric data could be obtained from bodies up to four days after death in warmer seasons and for as many as 50 days in winter.
  14. ↑ Bolme, David (2016). "Impact of environmental factors on biometric matching during human decomposition". 2016 IEEE 8th International Conference on Biometrics Theory, Applications and Systems (BTAS). 2016 IEEE 8th International Conference on Biometrics Theory, Applications and Systems (BTAS), Niagara Falls, NY, USA, 2016, pp. 1-8, doi: 10.1109/BTAS.2016.7791177. pp. 1–8. doi:10.1109/BTAS.2016.7791177. ISBN   978-1-4673-9733-9.{{cite book}}: |website= ignored (help)
  15. 1 2 3 4 Miguel, Michelle A.; Kim, Seon-Ho; Lee, Sang-Suk; Cho, Yong-Il (2021). "Impact of Soil Microbes and Oxygen Availability on Bacterial Community Structure of Decomposing Poultry Carcasses". Animals. 11 (10): 2937. doi: 10.3390/ani11102937 . ISSN   2076-2615. PMC   8532636 . PMID   34679958.
  16. ↑ Haslam, Tamsin C. F.; Tibbett, Mark (2009). "Soils of Contrasting pH Affect the Decomposition of Buried Mammalian ( Ovis aries ) Skeletal Muscle Tissue". Journal of Forensic Sciences. 54 (4): 900–904. doi:10.1111/j.1556-4029.2009.01070.x. PMID   19486250. S2CID   34909759.
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