Using Human Mummified Tissue to Determine Postmortem Interval
I conducted an internship with the Forensic Anthropology Center at Texas State (F.A.C.T.S) during the Spring 2015 semester. I worked closely with the director of F.A.C.T.S., Dr. Daniel Wescott, to conduct a study to determine if human mummified tissue can be used to estimate the postmortem interval of an individual. The postmortem interval (PMI) is the time that has passed since the individual died, or time since death. Scientists and medical professionals use varying approaches to estimate the postmortem interval, and there have been numerous studies dealing with PMI research. However, no such studies have been performed to examine if mummified tissue can be used to estimate PMI. This report will discuss the work done at F.A.C.T.S., describe the steps conducted to produce a PMI study with mummified tissue, and discuss the importance of this type of research.
The Forensic Anthropology Center at Texas State (F.A.C.T.S.)
Source: www.txstate.edu/anthropology/facts/labs/farf.htm
F.A.C.T.S. is a research and teaching center located in San Marcos, Texas, the mission of which is to further the forensic anthropology discipline through use of its body donation program, the Forensic Anthropology Research Facility (FARF), the Osteological Research Processing Laboratory (ORPL), and the Grady Early Forensic Anthropology Research Laboratory (GEFARL). F.A.C.T.S. uses its body donation program in conjunction with their laboratories to study human decomposition processes and PMI, among other areas of research.
Bodies donated to F.A.C.T.S. undergo several stages between being placed at FARF, cleaned at ORPL, and ultimately curated at GEFARL. The process of receiving body donations here is as follows: A person agrees to donate their body while they are living or through next of kin. Body donations, which from this point on are referenced using an identification number rather than the decedent’s name, are picked up by F.A.C.T.S. personnel up to a 200-mile radius of San Marcos. Donations can also be transported from anywhere else in the United States by plane. When a body donation is received, it is taken to ORPL for intake and documentation. Staff and volunteers take photos and x-rays of various parts of the body, measure it, and take samples of hair, nails, and blood. The body is then tagged with a donation number and driven to FARF where it is again photographed and left to decompose.
Bodies are placed in various scenarios, depending on the research being conducted at the time. For example, a donation may be placed in the sunlight or in shade to see how either would affect decomposition. After the body has completed the decomposition process, the remains are inventoried and transported back to ORPL, where excess tissue is removed and the bones are cleaned, usually by student volunteers. The bones are then curated and stored at GEFARL for teaching purposes and future research by students and professionals across the world.
F.A.C.T.S. also offers numerous workshops and extensive training for law enforcement, students, and other professionals.
An Idea for Postmortem Interval Research
Determining the postmortem interval is very important, albeit difficult, as it provides forensic anthropologists and other medical professionals with a means to determine how long a person has been dead, which can be critical in the context of a forensic investigation. This information provides law enforcement with crucial information to help better understand the case at hand, such as the cause and manner of death, or to help rule out or include a suspect. As important as estimating an accurate postmortem interval is, it is also very difficult, due to the fact that so many factors are present that go into figuring out how long an individual has been deceased. However, the more research that is conducted in this area provides professionals with a more accurate means to correctly estimate the PMI and thus provide law enforcement with a smaller range of time since death.
Research dealing with the postmortem interval has become more extensive over the years, including studies that replicate and examine numerous variables that happen in real life scenarios. The most accurate research dealing with the postmortem interval takes all variables surrounding the body into account in an uncontrolled environment. One of the earliest postmortem interval studies (Bass et al., 1990) was a simple observation compilation of human decomposition at the Anthropology Research Facility (ARF) at the University of Tennessee-Knoxville. The following variables were tested to determine their effect on decomposition: temperature, insects, whether the body was buried and how deep, animal scavenging, trauma, humidity/aridity, rainfall, body size and weight, whether or not they were embalmed, clothing, terrain, and soil pH. Temperature, insect activity, and burial/depth proved to have the highest effect on the decay rate of a body (Bass et al., 1990).
Although all of these variables will have an effect on how a body decomposes, there are other variables effecting the postmortem interval that require researching. Bass’s study states, “Ambient temperature appears to have the greatest effect on the decay rate of the human body” (Bass et al., 1990). This is important when considering the type of environment the person died in. A body will decompose outdoors very differently in Tennessee compared to Texas (Parks, 2011; Shirley et al., 2011). The low humidity and high temperatures in Texas often leave a body mummified. This is very apparent if one were to take a trip to FARF. The majority of the bodies there are mummified, preventing them from becoming skeletonized and completing the decomposition process.
As mummification in Texas is so prevalent, it is important to take this factor into account when considering the postmortem interval. However, no research using mummified human remains to determine time since death has been conducted. F.A.C.T.S. director Dr. Daniel Wescott presented me with this idea and suggested to me that we perform a study dealing with mummified tissue in relation to the postmortem interval. Excited by the idea that no one had conducted such a study, I was happy to comply. This would be done by collecting samples and measuring the moisture content and ash weights of each one to determine the difference.
The method for determining PMI with unmummified bodies usually follows the literature by Megyesi et al., 2005. Following this method, practitioners can score human remains and rank them in fresh, early, or late decomposition states using accumulated degree days, which are units of an accumulation of energy being put out. To determine the amount of accumulated degree days, the maximum temperature is subtracted from the minimum temperature for each day a body has been exposed and the average is calculated from that (Megyesi et al., 2005).
It is much easier to determine PMI for bodies in the fresh and early stages. When a body becomes mummified, it usually stays that way, making it much more difficult to determine time since death. However, the more accumulated degree days it holds, the older it will be. The question is: is the body newly mummified or much older?
The Study
The first step of our research was to collect the samples. Dr. Wescott and I went to FARF and chose thirty mummified bodies from which to take samples. This process took approximately two hours to complete. The metal cages, intended to prevent animal scavenging, were lifted while one of us cut off roughly three-inch-by-three-inch pieces of mummified skin from each of our designated bodies. The skin was taken from the abdomen area as this is generally where most of the moisture is preserved as a body decomposes. After the sample was removed, we wrapped it in foil to preserve its moisture and placed it in a plastic baggie labeled with its donation number.
Source: moviepilot.com
After the collection of the samples, they would need to go through a series of steps to be dried and weighed to ensure the moisture content was completely gone, as it can be hypothesized that the greater the PMI, the dryer the mummified skin would be. I would therefore see a smaller change in the weights before and after they were burned to ash weight, which will be discussed later.
The procedure for drying the samples are as follows: I brought the samples to a laboratory in the Agriculture Building on the Texas State University campus. Dr. Ken Mix, an assistant professor of soil and crop science, instructed me how to properly use the equipment in the lab. This included cutting each sample into roughly the same size and placing each one in their own tin can. I weighed the tin cans before and after they contained the sample and calculated the difference to determine the weight of each sample. After each one was weighed, I placed the samples in a small drying oven. This would allow for moisture to be removed from the skin. In order to make sure all the moisture was absent, I weighed the samples approximately every two days; once a constant measurement was reached, it was safe to say the moisture content was void. This gave me the opportunity to compare the sample weights before and after they went into the drying oven and gave me an idea of how much total moisture was in the samples. This would later help us determine if the moisture content in mummified skin can be used to determine the postmortem interval.
After the drying process was complete, we decided to burn the samples to ash in order to collect extra data. This was done by placing each sample in a small white crucible. Again, like the tin cans, I had to weigh each crucible before and after it held a sample. This would allow me to measure the weight of the ash after it came out of the kiln. The kiln was a very small furnace that allowed me to burn my samples at a temperature of approximately 800°F. As the kiln was very small, I could only have about nine samples in it at a time. This was a tedious process as I could not label the crucibles, and since the temperature was so high it would remove any Sharpie markings. In order to remain systematic in the process of data collection, I drew maps of the kiln’s interior marking where I had placed each sample. This prevented later confusion as I removed and replaced samples for weighing. When the ash weights were collected, the ash was discarded.
Photograph by the author
Photograph by the author
Results
After inserting the accumulated degree days and ash weight percentages into Excel, we produced this scatter plot graph:
The correlation between the two sets of data was not as strong as we had hoped it would be. To see if there was a better correlation elsewhere, we decided to run four more graphs which are as follows, with the R square value showing the percentage of the variation that is explained by PMI: Difference in Ash Weight, Percent Difference in Ash Weight, Difference in Oven Weight, and Percent Difference in Oven Weight.
Overall, there is not much variation. However, using solar radiation data in the future can help to fine estimating PMI, as solar radiation is a main cause of mummification. By itself, the methods used in this study may not be very predicative, but can add to a model used for estimating PMI by establishing a means to create stronger correlations.
Conclusion
This internship opportunity has been an excellent experience for me. I have always been most interested in estimations of the postmortem interval, and to be lucky enough to participate in research such as this has been amazing. To contribute to research that will further knowledge to help law enforcement and forensic/medical professionals in determining time since death is something that I have always wanted to be involved in. I hope to continue similar postmortem research in graduate school.
Acknowledgements
I would first like to thank Dr. Daniel Wescott for agreeing to take me on as an intern. This was an experience unlike anything I had been a part of before, and I learned a great deal from him. I would also like to give a massive thank you to Dr. Ken Mix for allowing me to use his lab and for patiently answering all of my questions. This project would not have been possible without his help. Thank you to Marilyn Isaacks for kindly agreeing to show me how to use the kiln. Finally, thank you to F.A.C.T.S. for allowing me to use their facility for this study.