The impact of freezing temperatures on soft tissue and microbial decomposition using human and porcine remains: a pilot study

Environmental factors such as temperature, vertebrate and invertebrate activity and microbial succession patterns are important variables driving the decomposition process. However, the effects of low temperatures, specifically freezing on how a body decomposes are less understood. This pilot project aimed to determine the taphonomic effects of freezing on morphological changes during decomposition and the microbiome in an Australian context. Two human donors (one frozen, one non-frozen) and two frozen and two non-frozen Sus scrofa (pig) carcasses (n = 4) were allowed to decompose on the surface of woodlands for 12-weeks during summer 2017. Visual morphological changes were recorded, and microbial swabs were collected at regular intervals and analysed via real-time PCR to assess differences in bacterial community structure. Results indicated clear differences in decomposition patterns between frozen and non-frozen remains. Frozen remains were slow to enter ‘early’ decomposition but first to skeletonise. Microbial results suggest that patterns in community structure between bacteria may indicate if a body has been frozen at or around the time of death. This research suggests that quantifying the microbiome present during the fresh and early stages of decomposition and noting observations of an outside-in decomposition pattern may be a useful tool in identifying if remains have experienced extreme cold temperatures at the time of death. This knowledge could improve approaches to PMI estimation, particularly if the remains have experienced a freeze-thaw event after death.