An investigation of taphonomic changes and decomposition rates of remains after exposure to cold environments : a porcine model

Abstract

Many taphonomic studies have concluded that temperature is one of the most influential variables driving decomposition. However, the effect extreme cold treatments, such as freezing, have on the process and rate of decomposition has received little attention. This is presumably because temperatures below zero degree Celsius are believed to slow or stop microbial and invertebrate activity, inhibiting the decomposition process. The few studies present in the literature describing the decomposition process of cold treated remains are mostly international in origin, with no consensus as to whether the decomposition process and rate is even affected by frozen temperatures. The vast majority of these studies have, however, suggested that frozen remains tend to disarticulate at an accelerated rate and are more prone to external decay whereas never-frozen remains exhibit putrefaction from within, or internal decay. Knowledge of how a body decomposes after exposure to extremely cold temperatures is important, particularly as it will assist with the development of methods used to determine the post-mortem interval (PMI) when remains are suspected to have been exposed to these extreme temperatures. To determine if freezing impacts the decomposition of soft tissue and the disarticulation sequence of remains, a 2017 summer and winter field study was conducted in the Hawkesbury region of NSW Australia. Two frozen and two never-frozen Sus scrofa (domestic pig) carcasses were deposited on the grounds surface and left to decompose over a 12-week period each season. Soft tissue changes were recorded and 'scored' and the PMI determined using a previously published method. Bacterial swabs were also collected and analysed via real-time PCR to determine which bacterial communities were present at each stage of decomposition. Results indicate clear morphological differences in decomposition patterns between frozen and never-frozen remains throughout summer, with frozen remains skeletonising faster and decomposing in an 'outside-in' pattern. Winter appears to produce little morphological variation between frozen and never-frozen remains. PMI calculations show that there are clear differences in PMI estimations between frozen and never-frozen remains in early decomposition, however differences become negligible as decomposition progresses. The summer study was validated using human remains at the Australian Facility for Taphonomic Experimental Research (AFTER), where morphologically the human remains decomposed similarly to the summer pigs. Microbial results in both pig and human models show freezing appears to pause microbial activity, however, once remains are allowed to thaw, bacteria experiences rapid growth in frozen remains. Furthermore, patterns are observed between bacteria that may provide an indication as to whether a body has been frozen at or around the time of death. The results of this study contribute to the increasing knowledge of taphonomic factors affecting decomposition in Australian environments.

Date of Award	2017
Original language	English