Understanding the process of decomposition is extremely important and aids in criminal investigations, especially when attempting to estimate the post mortem interval (PMI). Although several studies have been conducted on the decomposition patterns in surface remains, much less is known about this process in buried remains. By quantifying decomposition rates, factors influencing decomposition and research on the process of decomposition can be standardised and validated in a South African setting.
The aim of this study was to record decomposition stages and rates of buried remains and to compare it to that of remains decomposing on the surface. Twenty five pigs (Sus scrofa; 45-80 kg) were buried and excavated at different post mortem intervals [7 days (1 week), 14 days (2 weeks), 33 days (1 month), 92 days (3 months) and 183 days (6 months)]. Stages of decomposition were scored according to separate categories for different anatomical regions based on standardised methods, and photographed. The point values for each region were added to determine the total body score (TBS), which represents the stage of decomposition for each pig. When studying decomposition, accumulated degree days (ADD) are effective in standardising the effect of variables (i.e., temperature) that influence the decay process. It also enables researchers to replicate experiments and compare results. In this study, ADD were used to measure the rate of decomposition and to compare decomposition rates between buried and surface remains.
Results indicated that early stages of decomposition occured rapidly for both surface and buried remains within 7-33 days. Differences in the degree of decay were especially noticeable with the buried, 7 day interval pigs that displayed variations in discolouration in the lower abdomen and trunk. Between 14 and 33 days, buried pigs displayed common features associated with the early stages of decomposition, such as discolouration and bloating. The pigs then reached a stage of advanced decay where little change was observed in the next ±90-183 days after internment. Similar patterns of decomposition were observed for surface remains with rapid decay during the early stages of decay where after a plateau phase was reached during advanced decay. However, as expected, the surface remains reached higher TBS scores during similar intervals.
In this study, the decomposition rates of buried remains were mostly influenced by being buried at an average depth of 0.75 m which could have resulted in lower in-soil temperatures and limited insect activity at a depth of 0.75 m on the remains. Also, adipocere presented itself on the remains with the 33 day PMI pigs, the 92 day PMI pigs and 183 day PMI pigs. Adipocere is capable of degrading over a prolonged period which reduces the rate of decay in a conducive environment (i.e., burial in soil).
Overall, surface and buried pigs decompose with similar patterns, but buried pigs decompose at a much slower rate, reaching lower TBS values relative to similar PMIs in surface remains. This suggests that burial does have a significant effect on the rate of decomposition. Results from this study suggest that when using TBS guidelines on buried remains in the Central Highveld region of South Africa, buried remains will have, on average, a lower TBS score (7.4) than surface remains within a similar post mortem interval.