A Scoping Review on Factors Affecting Cadaveric Decomposition Rates
Lai Poh Soon1*, Khoo Lay See1, Nazni Wasi Ahmad2, Kharmila Abdullah3 and Ahmad Hafizam Hasmi4
1Department of Forensic Medicine, Hosp Kuala Lumpur, Malaysia
2Department of Forensic Entomology, Institute of Medical Research (IMR), Malaysia
3Department of Forensic Pathologist, University of Science Islamic Malaysia (USIM), Malaysia
4Department of Forensic Medicine, Hosp Kuala Lumpur, Malaysia
Submission: February 02, 2017; Published: March 09, 2017
*Corresponding author: Lai Poh Soon, Forensic Scientific Officer, Department of Forensic Medicine, National Institute of Forensic Medicine, Hospital Kuala Lumpur Jalan Pahang 50586 Kuala Lumpur, Malaysia, Tel: +60174709068; Email:email@example.com
How to cite this article: Lai P S, Khoo L S, Nazni W A, Kharmila A, Ahmad H H. A Scoping Review on Factors Affecting Cadaveric Decomposition Rates. J Forensic Sci & Criminal Inves. 2017; 2(2): 555584.DOI:10.19080/JFSCI.MS.ID.555584. DOI: 10.19080/JFSCI.2017.02.555584
Introduction: The importance of the determination of cadaveric decomposition rate is to enable the forensic pathologist and forensic scientist in estimating the time since death also known as post-mortem interval. There are many factors affecting the cadaveric decomposition rate including environmental factors and non-environmental factors. This scoping review is to explore the relationship between the delaying or accelerating factors and the decomposition rate. Methods: It was conducted using framework suggested by Arksey and O'Maley. Comprehensive search was performed to identify published works and literatures. Inclusion criteria for the search were articles in English published from 2007 to 2016 and related to taphonomic study as well as the decomposition process and/or rate.
Results: A total of 2,893 titles were extracted from electronic databases and other resources and 41 articles were selected based on inclusion criteria. The variables and decomposition rates were generally varied between studies. Accelerating factors were mostly related to higher temperature including the summer season, rainy season, urban and desert area, sun-exposed on ground area, burning effect, enclosed vehicle as well as exposure to insects and scavenger activities. Decelerating factors often relied on the effect of the lower temperature such as winter season, deep coastal marine, underwater, highland and shaded area. It might also depend on the burial effect and other physical barriers by using heavy clothing, wrapping, lime and cement as well as the chemical barrier likewise the organophosphate (OP) pesticide etc.
Conclusion: There were emerging evidences on the affecting factors of the decomposition rate, although it was still very limited in tropical countries including Malaysia. Findings of this scoping review demonstrated that insect activities and temperature were the main factors affecting the overall decomposition rates except in the presence of physical barriers which might have contributed some variations to the decomposition rates.
Abbreviations: OP: Organophosphate; MOH: Ministry of Health; IMR: Institute of Medical Research; USIM: University of Science Islamic Malaysia; NMRR: National Medical Research Registry Malaysia; MREC: Medical Research and Ethics Committee; ADD: Accumulated Degree Days; TBS: Total Body Scoring System; ADD: Accumulated Degree Days
Post-mortem interval can be estimated using several methods such as entomological study, post mortem changes and taphonomic study, biochemistry of tissues or body fluids from the cadaver etc. The importance of the determination of cadaveric decomposition rate is to enable the forensic pathologist and forensic scientist in estimating the time since death also known as post-mortem interval. With estimation of postmortem interval, the investigating officer could narrow down the search of witness and suspects for a scene of crime or during the death investigation. There are many factors affecting the cadaveric decomposition rate including environmental factors and non-environmental factors. Environmental factors including weather (temperature, humidity etc.), indoor or outdoor, burial or underwater or above ground. Non-environmental factors including body mass/size, wrapping or unwrapped, clothing or unclothed and entomological effects.
There are factors delaying decomposition indicated by M Lee Goff  in which divided into physical, chemical and climatic barriers. A body buried in the soil does not decompose as quickly as one exposed on the surface due to the physical barriers. In a similar manner, a body enclosed in a sealed casket or placed into some form of sealed container will also exhibit a delayed decomposition. Embalming process is specifically and chemically designed to prevent the decomposition of the body, with natural body fluids being drained and replaced with various preservative fluids. Insecticides will not permanently delay the colonization of the body by insects. With regards to the climatic factors, at temperatures below 6oC most insect activity ceases but may resume once temperatures rise above this threshold. Wind speed in excess of 16 km/h will inhibit insect flight. Rainfall may also serve as a temporary barrier. Under conditions unfavourable for the colonisation of insects, such as concealment, low temperature or mummification, mites might become the most important or even the only arthropods on a dead body.
Zhou and Byard  have also describing the factors accelerating decomposition including exogenous and endogenous factors. Exogenous factors included exposure to elevated environmental temperatures, both outdoors and indoors, exacerbated by increased humidity or fires. Situations indoor involved exposure to central heating, hot water, saunas and electric blankets. Deaths within motor vehicles were also characterized by enhanced decomposition. Failure to quickly or adequately refrigerate bodies may also lead to early decomposition. Endogenous factors included fever, infections, illicit and prescription drugs, obesity and insulindependent diabetes mellitus. When these factors or conditions are identified at autopsy less significance should, therefore, be attached to changes of decomposition as markers of time since death. Therefore, the present review will explore the relationship between the delaying or accelerating factors and the decomposition rate. It is hoped that these findings will support future research on the decomposition changes and its affecting factors that might not been well-established to assist in the postmortem interval estimation especially the homicidal cases.
The design of the study is scoping review. Scoping review aims to map rapidly the key concepts underpinning a research area and the main sources and types of evidence available especially when an area is complex or has not been reviewed comprehensively before. For the purpose of this topic, the scoping review is performed to identify the affecting factors, determine the indicators for decomposition rates and study relationships between both factors and decomposition rates. In this review, cadaver refers to the dead human bodies or animal carcasses that are left to the decomposition process whilst decomposition rate is defined as the time relapse from the first decomposition stage (fresh) to the final decomposition stage (skeletonisation) which based on the TBS scoring system or any of the observational systems. The 5 stages of the scoping review York Framework by Arskey and O'Maley include "Identifying the research questions", "identifying relevant studies", "study selection", "charting the data" and "collating, summarising and reporting the results" Consultation with reviewers from Ministry of Health (MOH), University of Science Islamic Malaysia (USIM) and Institute of Medical Research (IMR) are also conducted to enhance the review work undertaken by the research team members. The study was registered under the National Medical Research Registry Malaysia (NMRR) and the protocol was approved by the Medical Research and Ethics Committee (MREC) Malaysia (ID: NMRR-16-2310-33318).
The purpose of performing the scoping review was to conduct a comprehensive search to identify primary studies (published work) and reviews. The research team members adopted a strategy for searching the evidence using different sources which included electronic databases and relevant research websites such as ProQuest, PubMed and Wiley. The searches also involved online journal articles and books focusing on taphonomic study in Forensic Science and Forensic Medicine. The researchers decided to set the coverage of the review based on the time span and language of the articles. Inclusion criteria for the search were articles in English from year 2007 till 2016 and studies that are consistent with research questions related to taphonomic study as well as the decomposition process and/ or rate are studied. The commencement date of 2007 was chosen in order to cover the recent 10 years findings and it was felt that the evidence on the decomposition rate was limited especially in Asian countries including Malaysia. Titles, abstracts and document text for eligibility were examined independently by the researchers. All type of studies were included in the search strategy. Unpublished articles or those written in the language other than English were excluded due to the cost and time that would be required to translate those documents. Studies that were irrelevant such as purely entomological methods and/or biochemical methods used were excluded. Key terms used in the search of articles were shown in Table 1 and Table 2.
The study selection is based on the objectives of the study. The review is focused on documents related to the factors including environmental and non-environmental factors affecting cadaveric decomposition rates. Based on the eligible abstracts, copies of full articles were retrieved. The full articles is checked by the researchers as to whether appeared to answer the research questions of the study. Selected full articles were then read by the researchers in order to select the final full articles for the review.
General and specific information about the studies is charted which include authors(s), year of publication, types of affecting factors, objectives or aims of the study, country of study location, study population/sample, sample size including comparison group (if any), methods/instruments and indicators used in the study and findings that were relevant to the objectives of the review.
The characteristics of the results from the selected articles from various countries are described based on the design, types and outcomes of each study. The findings of the review were presented in table. Table of evidence on the factors affecting the cadaveric decomposition rates and their relationships with measurements and indicators that are used to describe the various approaches or methods to determine the decomposition rate. Limitation of several studies and research gaps are also identified in order to generate useful knowledge on the taphonomy and post-mortem interval estimation.
Table 3 shoed a total of 2,893 titles were extracted from the selected electronic databases and other resources using the search terms. As portrayed in Figure 1, 59 abstracts were included after the initial screening process and the rest were excluded as they were irrelevant with regards to the decomposition changes or rates, non-English articles, and duplicates. Among these 41 articles met the inclusion criteria in the review, environment factors and non-environmental factors were studied with total of 20 articles and 17 articles respectively. The rest of 4 articles were focus on mixed factors. The studies in this review were equally focus on both environmental factors and non-environmental factors. Most of the environmental aspects surveyed the climate factors especially the temperate/tropical climate, dry and wet/ rainy seasons, habitats/locations and burial effect. Additionally, researchers emphasize to explore the non-environment factors including the scavenger or insect effect, clothing, wrapping, lime or cement effect, burning effect. Countries of origin of the studies included Malaysia, Europe (United Kingdom, Italy, Germany, Poland, Romania, and Belgium), America (United States, Canada, Colombia, and Brazil), Middle East (Saudi Arabia, Egypt, and Kuwait), South Africa, Australia and China.
All the articles in this review were using animal carcasses as subjects except Jeong Y et al.  using human cadavers to study on scavenger effects during summer season. Majority (26 articles) using swine / pig carcasses as subjects, followed by rabbit carcasses (10 articles) and minority were using monkey and other animal carcasses. The measurement of indicators for each studies were primarily on the comparison of time taken to different decomposition stages, however, some researchers were also using total body scoring (TBS) system in 6 articles as the decomposition scoring methods. Part of the studies utilised different approaches such as decomposition changes by observation, mass/weight loss, first colonisation of insects, insect richness, insect residency time, insect succession patterns and taxa variation. In this review, there were 14 full text articles, out of the 41 selected articles, available online and free for open access. The list of these articles was elucidated in a summary format as shown in the Table 4. In terms of environmental factors focusing on temperate climate variables, the decomposition rate have remarkably slowed down during winter season compared to the other three seasons. According to Meyer J et al. , summer season with greater temperature have enhanced the decomposition rate from triple to septuple to reach the dry remains or skeletonisation stage which consistent with the findings by Wang J et al. .
Some articles reported an extreme difference between summer and winter seasons whereby pig carcasses reached the dry stage within 8 days but still maintained in bloating stage at Day 133 . Although first insect colonisation started after 15 weeks during winter season, the bacteria activity have actively occurred throughout the first 5 weeks of decomposition at low temperature. However some have reported pig carcasses reached the skeletonised stage at Day 60 in winter season compared to summer season at Day 27 with all the soft tissues completely lost by decomposition. There was no significant difference among spring, summer and fall seasons, yet faster decomposition rate and higher insect richness were encountered during summer season followed by spring and fall seasons for both pig and rabbit carcasses. Rabbit carcasses which were in smaller size consumed 21days and 28days to reach the dry stage compared to 26days and 42days for pig carcasses during summer and spring seasons respectively. In some equatorial or tropical countries [7,8], the wet or rainy season have caused the more rapid decomposition compared to dry season. It showed common decomposition rate for both seasons during the fresh and bloated stage, however the conversion of later decaying stages till the dry stage was relatively faster during the wet or rainy season.
Animal carcasses subjected to different habitats and localities would present different decomposition changes and insect colonisation. Although there was no significant difference of decomposition in a lake and a stream area, time taken to reach skeletonised stage of pig carcasses was three times longer (61 days) compared to in semi-rural area (21 days) according to the Colombian locality located over 2600 m above sea level. Canadian articles have reported that anoxic condition (very low oxygen level) under deep coastal marine environment would delay the skeletonisation as much as five times compared to moderately low oxygen level (22 days), however, it has taken only 4 days under submergence sea environment in the Strait of Georgia . Also there would be a delay of 5 days in insect colonisation causing the delay of skeletonisation in indoor condition compared to outdoor environment. Voss SC et al. [12,13] have investigated into the enclosed vehicle environment in which they found that the higher temperature inside the vehicle have enhanced the decomposition rate by 3 to 4 days. In the Middle East taphonomic study of rabbit carcasses, researchers have reported that decomposition rate in urban area and desert area was double up. It has taken 5 days to reach the dry stage compared to coastal area and agricultural area (13 days). Silahuddin SA et al.  has encountered the similar results whereby rabbit carcasses undergone faster decomposition rate in rural or pasture area compared to jungle area and highland area.
Faria LS et al.  has also complied with their findings by using pig carcasses whereby insects bred more abundantly in the pasture area compared to forest area. Furthermore, sun-exposed carcasses underwent greater variation in fauna compared to shaded carcasses whilst more abundant on meadow compared to on the floor. From the burial factor perspective by using the total body scoring system, time taken to reach skeletonised stage with score of 30/35 TBS was within 42 days compared to period of 10 days for the ground control rabbit carcasses . It was four times slower decomposition rate due to the burial factor and the SPSS analysis showed that the burial factor was significant in affecting the TBS score. Troutman L et al.  reported that deep and core buried subjects of burial were even more significantly slower than those of the shallow and mid-outer buried subjects. According to Simmons T et al.  stated that ground and buried rabbit carcasses that have been accessed by insects activity were scored 26/30 TBS after 300 and 400 accumulated degree days (ADD) respectively. In terms of non-environmental approaches, rabbit carcasses did not show significant difference among types of clothing. Combination of burial and type of clothing factors also was not significant.
However, pig carcasses have shown unclothed carcasses decomposing faster than clothed carcasses and presence of clothing markedly prolonged the wet decay stage as well as had larger visible maggot masses which moved more freely and took longer to be dried out. Clothing was the minor importance compared to the insect assemblages and body mass factor. Spicka A et al.  mentioned that animal carcasses of a mass less than 20 kg decomposed more rapidly than larger carcasses. Insect exclusion carcasses were delayed at least two times to reach dry stage of decomposition (10 days) compared to the exposed carcasses (26 days). It was reported similarly with the presence of scavenging effects by King KA et al . Nevertheless, physical barriers such as usage of wrapping, lime and cement had significantly more important than clothing effect. Ahmad A et al.  had reported that wrapping delayed the arrival of all fly species encountered the monkey carcasses, with the delay up to maximum 13 days. Cemented pig carcasses showed areas of mummification at the abdomen within a general context of initial putrefaction at the third month and showed wide adipocere formation after 6 months . After 17 months of burial, unlimed carcass exhibited disintegration of soft tissue on the torso and skeletonised extremities and skull whilst limed pigs displayed liquefying soft tissue at the torso and head with skeletonised extremities .
Moreover, application of quicklime instigated an initial acceleration of decay. Microscopic changes may be delayed in presence of concrete and lime but not totally eliminates all the aerobic bacteria. On the other hand, burning pig carcasses greatly accelerated decomposition in contrast to unburnt carcasses. Physical modifications following burning such as skin discolouration, splitting of abdominal tissue and leathery consolidation of skin eliminated evidence of bloat and altered micro ambient temperatures . It was supported by Vanin S et al.  whereby burning effect doubled up the decomposition rate compared to unburnt carcasses. In contrary, burning effect was still not statistically significant as examined by four of local and foreign researchers for both pig and rabbit carcasses. In certain rare condition which happened occasionally, Lynch- Aird J et al.  reported that hanging pigs reached advanced decomposition stages sooner, but lagged behind during the early stages. This delay is believed to result from lower variety and quantity of insects. Pig carcasses had undergone only partial decay even 40 days following organophosphate (OP) pesticide pirimiphos-methyl poisoning whilst the control remains reached the skeletal stage by 19 days post-killing . They stated that only the lower parts of the test carcasses were obviously decayed, whilst their upper parts remained unchanged.
Based on the evidence in this review, there were emerging literatures for the past 10 years reporting the factors, including environmental and non-environmental, affecting the cadaveric decomposition rates by using animal carcasses in which majority were pigs and rabbits. Several important aspects of these affecting factors within animal carcasses have been identified: Firstly, the affecting factors on the decomposition rate could be further classified into enhancing or accelerating and delaying or decelerating factors which were regularly reported by the published studies . Accelerating factors were mostly related to higher temperature including the summer season (triple to septuple), rainy season, urban and desert area (double), sun- exposed on ground area, burning effect (double), enclosed vehicle as well as exposure to insects (at least double) and scavenger activities (double). Decelerating factors, on the other hands, often relied on the effect of the lower temperature such as winter season (3 - 7 times), deep coastal marine (5 times), underwater (3 times), highland and shaded area. It might also depend on the burial effect (4 times) and other physical barriers to prevent the access of insect activities by using heavy clothing, wrapping, lime and cement as well as the chemical barrier likewise the organophosphate (OP) pesticide etc. However, the variables and decomposition rates were generally varied between studies. There are several reasons for these inconsistent findings including the differences in the study design, sample size, sample type, location of study, choice of comparison groups and methods used to assess the relationship between the affecting factors and decomposition rate.
Some of these studies have implied combination of affecting factors which have made the analysis and comparison more complicated. Secondly, it appeared that the techniques of measurements used to evaluate the decomposition rate were also varied depending on the objectives of the respective studies in this review. Most of the researchers observed and recorded the time taken to reach each of the categorised decomposition stages which was also varied from one another. However, the start point (fresh stage) and the ending point (dry or skeletonised stage) of the decomposition changes were often similar among the studies and permit immediate comparison. Nonetheless, some researchers used different approaches such as time taken for first colonisation of insects, insect richness, insect residency time, insect succession patterns and taxa variation. Moreover, more systematic approaches such as total body scoring system (TBS), accumulated degree days (ADD) system and percentage of weight loss of the carcasses were also used to determine the decomposition rate. Again these were also varied from one another, for example, the maximum scores might be different from each articles and the measurements made at different period or by different point of time or at different ADD values [37-40]. The comparison, hence, might be very complex to certain extend in making inference and conclusion from this review.
Thirdly, findings from this scoping review have demonstrated that insect activities and temperature were the main factors affecting the overall decomposition rates except in the presence of physical barriers which might have contributed some variations to the decomposition rates. Apart from that, Simmons T et al.  have collected data from previous studies and recent experiments in which were then compared using simple conversions across multiple environments. The major effector of change in decomposition rate was the insect presence, regardless of depositional environment, species, or season. Body size of the animal carcasses chosen was only significant when carcasses were accessed by insects. When insects were excluded, while bodies were indoors, submerged, or buried, then decomposition progresses at the same rate regardless of body size. Therefore, early differentiation of the carcass type and body size used by the researchers would definitely make the scoping review more applicable for comparison as the analogue to the human cadavers. This is due to the limitation of the ethics issues which have been extensively discussed for any taphonomic study using human cadavers .
To overcome this problem, researcher are recommended to compute the degree of the affecting factors and report the decomposition rate of animal carcasses in terms of either percentage or tuple order of the delaying effect or enhancing power. It could be also in the form of average TBS per day or ADD per day to tolerate for the application in any carcass type and body size used as the analogue to human cadavers. Finally, this scoping review also found that there was no extensive evidence on the decomposition rate in equatorial or tropical countries including Malaysia. Only a few taphonomy studies in Malaysia was identified which mainly focus in Kedah and Selangor area. However, there were in fact many other studies have been excluded owing to researchers reported only the entomological findings and biochemistry details of the carcasses without correlating with the decomposition rate. The limitation of this study was that the data was collected from certain selected resources without considering unpublished articles especially those minor studies conducted by undergraduate students. Some of the finite values of decomposition rate for each affecting factors were not fully concluded in this study due to the limitation of their study period whereby some of the carcasses might not be fully skeletonised. Therefore, future researches need to be conducted in a systematic ways in order to address the significant factors affecting the decomposition rate and more accurately estimate the postmortem interval in any of the death investigation .
Collaborative research effort between the Ministry of Health, universities and other international agencies is one of the strategies that need to be implemented to provide evidence on the relationship between the affecting factors and the decomposition rate which could be recognised worldwidely later on. Trained professionals are also encouraged to conduct proper extensive studies and actively discuss with their international networking especially during any platform of research presentations. In conclusion, there were emerging evidences on the affecting factors of the decomposition rate, although it was still very limited in tropical countries including Malaysia. Findings of this scoping review demonstrated that insect activities and temperature were the main factors affecting the overall decomposition rates except in the presence of physical barriers which might have contributed some variations to the decomposition rates. It is hoped that these findings will support the planning of future researches in a more systematic and extensive way to enable more accurate estimation of postmortem interval based on the delaying effects and enhancing factors on the decomposition rates .
The authors would like to thank the Director General, Ministry of Health Malaysia for the permission to publish this paper. This scoping review was partially funded by the National Institutes of Health, Ministry of Health Malaysia to prepare for an experimental taphonomic study by using rabbit carcasses in Kuala Lumpur Hospital. The authors would also like to thank Dr. Mohd Shah Mahmood who acting as Director of the National Institute of Forensic Medicine and appreciate all the contributors who have involved directly or indirectly throughout this scoping review.