Heat-Induced Changes to Porcine Bone at Different Taphonomic Conditions

Abstract

Heat exposure to bone results in physical and chemical alterations thus making victim identification and the circumstances surrounding their death difficult to determine. There is conflict in understanding how the expression of macroscopic heat-induced changes relate to microstructural heat-induced alterations of collagen with specific reference to burnt bone. The aim of this study was to investigate the relationship between heat-induced macroscopic and histological alterations at different taphonomic conditions cremated at different temperatures. The study was done with incrementally heated (300°C, 400°C and 500°C) bones (N=3, experimental n=27; control n=6) at different taphonomic conditions (fleshed, wet/defleshed and dry bone) using a muffle furnace. Bone samples were weighed, and analysed for macroscopic changes (colour, mass loss, fracturing and fragmentation). Post-cremation, 3mm bone blocks were extracted and fixed in 10% neutral buffered formalin, decalcified (10% formic acid) then processed and sectioned. Sections were stained with Sirius Red-Fast Green (SFRG) stain to investigate collagen presence and distribution. Additionally, 1mm blocks were extracted for ground bone sectioning and photomicrographs were taken for micro-fracture assessment. Wet and dry bones cremated at 400°C and 500°C were partially calcined and had more macroscopic and microscopic fractures compared to fleshed bones. Only fleshed and wet bones presented misaligned fragmentation, indicative of plastic deformation. The SRFG stain was shown to reveal both collagenous and non-collagenous proteins; however, with polarized light in combination with SRFG staining it was possible to identify areas of putative collagen even at higher temperatures (400°C and 500°C) in fleshed but not in wet and dry bones. Further studies using more specific approaches to identifying collagen degradation are proposed, in order to understand the mechanisms of fracturing and bone deformation. The present study was able to propose a role for soft tissue and moisture in protecting bone during cremation and provide insights into the biomechanics of thermal alterations of porcine bone. Before application can be made in a human forensic setting, further research in human bone and across more varied conditions is required. This study is seminal to the understanding of both macro and microscopic bone heat-induced changes, a relationship rarely assessed in burnt bone studies.