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Recent Advancements in Forensic Anthropology: Decomposition Research by…
Recent Advancements in Forensic Anthropology: Decomposition Research
by Daniel J Wescott
Abstract / Introduction
Decomp research is primary focused on estimating the postmortem interval (PMI), detecting clandestine remains, and interpreting context of the scene
Primary focus: Lab based identification of skeletal remains
Develop methods of estimating biological characteristics such as age at death and sex
The desire of knowledge of decomp has also increased fields other than anthropology: entomology, pathology, tox, chemistry
Decomp work in anthropology
Gross morphological changes, regional variation, intrinsic/extrinsic influences, grave soil ecology, vegetations, scavenger aid in PMI, detection of clandestine remains, and scene/trauma interpretation
Other fields have put emphasis on chemical changes and insect/microbiological diversity associated with decomp
The purpose of the article to review some of the advances in decomp research & how they can be applied to forensic anthropology
Fundamental Shifts in Decomposition Research
Decomposition Facilities
Provide interdisciplinary opportunities to conduct semi-controlled actualist research to test specific hypotheses using human samples with known PMI
Allows for longitudinal studies for researchers to gain a better understanding of specific factors that control the patterns / rate of decomp (disease, trauma, antibiotics, body size, etc)
Rely heavily on human donation which has sky rocketed in the past decade - Will open doors to broader studies as diversity of donations increases
Interdisciplinary research
Other fields of forensics have begin to focus their research on understanding decomp to develop more precise methods for estimating PMI and detecting concealed remains
Also has applications for public health, disaster managements, livestock carcass disposal, and more
Carrion ecology
Allows researchers to examine the spatial & temporal effects of carrion on soil nutrients, microbes, plants, arthropods, and vertebrates
Carrion provides a large variety of scavengers with a nutrient rich resources that has been conceptualized as a "cadaver decomp island"
Understanding how necrophagous species attach to carrion, their path of succession, and how the environment affects them is key to understanding decomp
Technological Advancements
Advancements in metagenomics have helped microbial species to be identified at the genus level and their function during decomp
Geophysical resistivity and hyperspectral imaging have increased abilities to detect clandestine graves
Quantifying gross decomposition
Early research focused on describing decomp based on stages and rates of decay in days
Reed study: fresh, bloat, decay, dry
Galloway study: Fresh, early decomp, advanced decomp, skeletonization, extreme decomp
Later research showed that there's unclear demarcations between stages and considerable variation in progression of decomp due to outside conditions: Vass studies (29,30)
Vass studies introduced accumulated degree-days (ADD) which is the sum of the average temps since decomp: Advantage of using ADD is that it includes chronological time & temp and can hypothetically be used across different regions and seasons
Recent Research
Gleiber et al.: Accumulated decomp score (ADS) that uses component scoring of traits based on gross observations
Improved understanding of extrinsic factors
The rate at which decomp occurs is dependent on a number of intrinsic and extrinsic factors
Abiotic extrinsic factors
Influence the ambient temp, acidity, availability of water, and partial pressure of oxygen
Temperature
Has a major influence on chemical rxns, the proliferation and metabolism of microbes, and the growth/development of necrophagous arthropods
Studies 13, 38, 41-43 in the review highlight these factors and decomposition
Rodriguez and Bass (26): Decomp generates heat that can cause ambient temperature near the body to be higher
Water
Can increase or decrease the rate of decomp depending on quantity, pH, and other factors (studies 38, 44-46)
Optimal water content can increase microbe growth
Carter et. al: Soil moisture was one of the primary factors affecting rate of decomp in buried remains (47)
Moisture plays a role in desiccation/mummification and formation of adipocere (byproduct of lipid degradation)
Lennartz: Skin loses moisture rapidly during the first 1000 ADD but becomes mummified at ~10% moisture content (51)
Decomp of submerged bodies is generally slower
Decomp stages in aquatic environments are categorized: fresh submerged, early floating, early floating decay, advanced floating decay, sunken
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pH and oxygen
pH has the greatest influence on chemical rxns during decomposition
Surface decomp is alkaline due to aerobic conditions
Studies 30 and 38
Burials are commonly more acidic
Lower pH can enhance the growth of fungi/plant activity
Decomp is generally more rapid in the presence of oxygen
Study 38
Biotic extrinsic factors
Arthropods
Flies and beetles: major contributors to biomass reduction
Tomberlin et al.: Entomological activity can be divided into pre- and post- colonization intervals (16)
Pre-colonization: Phases when carrion is available and then detected and lasts until it is accepted or rejected as a resource
Post-colonization: Period of consumption and dispersal phases (good predictor of the minimum PMI)
Large scavengers
Studies usually focus on the role of scavengers in the removal of soft tissues, disarticulation, and scattering
Vultures usually consume a lot of soft tissues but do not scatter remains more than a few meters from the original place (Studies 90, 93, 94, 98)
Haglund: Human population density can play a role in if scavengers exploit carrion (99)
Pharr: Permanent waterbodies near carrion may be necessary for larger scavengers (94)
Microbes
Microbial decomp community diversity and function change during decomp in a predictable way
Cobaugh et al.: In buried remains, the microbe community changed during active decay with an increase in aerobic bacteria which switched to anaerobic after active decay (55)
Bacteria produce byproducts that can cause bloating and affect the pH of the body and local scavengers and plants
Can manipulate the behavior insects to attract and develop certain species: Study 22, 65, 66
Applications of Decomposition Research
Detection of clandestine remains
Vegetation & Fungi
Studies suggest vegetation composition can be used to detect clandestine graves (26, 100-102)
Carter and TIbbett: Presence of post-putrefaction fungi on graves in wooded areas may also be used in grave detection
Surface remains: Release of fluids will initially kill surrounding vegetation. Over time, pioneer plants can colonize the grave soils
Eventually plant composition will once again become similar to what it once was: Time is important!
Remote sensing (imagery)
Can provide a rapid and cost effective method for determining high probability areas during initial search (106,107)
Kalacska et. al: Found via remote sensing that mass graves in a tropical environment have a distinct spectral signature based on response to decomp products
Isaacks: Remote sensing with near-infrared sensors could be used to locate surface decomp for up to 2 years based on differences in the surrounding area and the CDI
Cadaveric fluid seeps into the soil and causes it to be organically rich, which produces a signature NIR
Detection dogs and VOCs
VOCs = Volatile organic compounds
Produced during soft tissue decomp and responsible for the smell of decomp
Human remain detection (HRD) dogs can detect VOCs
Carabollo: Examining the type and abundance of compounds in the odor profile can be used to distinguish each stage of decomp
Dekerisschieter et al.: VOCs of decomp in urban settings differs from open air outdoor sites, and pollutants can cause background noise in the profile thats difficult to separate
Postmortem Interval (PMI)
PMI estimation is elusive because of considerable unpredictability and because most studies only focus on unique settings or used animal surrogates
Henssge and Madea: Any method for estimating PMI needs to fill the following criteria: Quantitative measurement, mathematical description, taking into account influencing factors quantitatively, declaration of precision, and proof of precision on independent materials
Megyesi et al.: Method uses quantitative measure, mathematical description, considers temperature on quantitative measure, and provides a quantitative measure of error
Vass: Meets all the criteria except for providing an error rate
Future Needs / Conclusions
Future needs
Research on decomp is still in its scientific infancy
Some problems are that there are limited datasets available for study and comparison
Lack of standardized nomenclature, multi-regional comparative studies, and true inter- and trans- disciplinary research
Most important to decomp research is the need for greater use of theory in decomp research and development of trans-disciplinary theory
General need to gain a basic understanding of decomp ecology instead of focusing on the wide variety of factors that could influence the rate
Conclusions
There is now a greater understanding of the complexity of decomp and the variability caused by numerous variables that affect decomp patterns
While research has demonstrated the unpredictability of decomp, it still holds promise for developing better methods for the detection of remains, interpretation of scenes, and estimation of the PMI
Because of this uncertainty, many anthropologists are still unsure about interpreting decomp to estimate PMI: More research needs to be completed