Corpse decomposition
Decomposition is the process in which the
Stages and characteristics
The five stages of decomposition—fresh (aka 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
At this stage the remains are usually intact and free of insects. The corpse progresses through
Bloat
At this stage, the
Active decay
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
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
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 will speed up the rate of decomposition as it accelerates the physiological reactions in the body after death.[11] Cooler temperatures will slow the rate of decomposition.[11] Sunlight availability will also influence the temperature and, as a result, influence decomposition.[11] When there is more sunlight available this will facilitate decomposition whereas shaded areas can slow down decomposition.[11]
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 dry up faster but will overall 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.[12] This is because the microorganisms required for decomposition require oxygen to live and thus facilitate decomposition.[12] Lower oxygen levels will have the opposite effect.[12]
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.[12] The pH of the soil will also be a factor when it comes the rate of decomposition, as it influences the types of decomposers.[13] 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.[14] Factors affecting decomposition include water depth, temperature, tides, currents, seasons, dissolved oxygen, geology, acidity, salinity, sedimentation, and insect and scavenging activity.[15] Human remains found in aquatic surroundings are often incomplete and poorly preserved, making investigating the circumstances of death much more difficult.[16] 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.[17] 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.[18]
Other factors
Body size
Body size is an important factor that will also influence the rate of decomposition.[19] A larger body mass and more fat will decompose more rapidly.[19] This is because after death, fats will liquify, accounting for a large portion of decomposition.[19] People with a lower fat percentage will decompose more slowly.[19] This includes smaller adults and especially children.[19]
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.[20] 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.[20]
Experimental analysis of decomposition on corpse farms
References
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- ^ ISBN 9781439821923.
- ^ ISSN 0261-3077. Retrieved 2019-07-14.
- ^ ISBN 9781119141402.
- ISBN 9781420008869.
- ^ S2CID 132436926.
- ^ PMID 34679958.
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- PMC 6474513. Retrieved April 5, 2023.
- . Retrieved April 5, 2023.
- ^ . Retrieved 2022-04-14.
- ^ S2CID 7928207.
- ^ Blakinger, Keri (2018-02-23). "Learning about decomposition at the body farm in San Marcos - HoustonChronicle.com". www.houstonchronicle.com. Retrieved 2019-07-14.
- PMID 28284436.