Profiling of human burned bones: oxidising versus reducing conditions

An overview of the heat-induced changes of the chemical composition of bone from fresh to calcined

When bone is exposed to thermal stress, the chemical composition changes. This affects bone tissue regeneration after surgery, and these changes can also aid in reconstructing ante-, peri-, and post-mortem events in forensic investigations and past activities on cremation practices in archaeology. However, to date, no complete overview exists on the chemical composition of both fresh and thermally altered bone. Therefore, we aimed (i) to present the chemical composition of fresh bone and (ii) to present an overview of heat-induced chemical changes in bone under both reducing and oxidizing conditions. From the overview, it became clear that some chemical changes occur at a consistent temperature, independent of exposure duration, meaning there is a temperature threshold. However, the occurrence of other chemical changes appeared to be more inter-experimentally variable, and therefore, it is recommended to further investigate these changes.

Medico-legal scene investigation in the case of burned bodies - a systematic review

A judicial on-site examination is essential for the correct analysis of a forensic case, particularly when there has been a fatal fire, as heat-related changes to bodies make identification by the forensic pathologist and other specialists difficult along with estimating the post-mortem interval and determining the precise cause and manner of death. We systematically reviewed all relevant articles dating from 2003 to 2022 in the PubMed database with a view to updating recommendations on how best to proceed. Our recommendations highlight the importance of a multidisciplinary team approach involving various forensic specialists.

Half a century of systematic research on heat-induced colour changes in bone - A review

Skeletal human remains presenting heat-induced changes have been a focus of study for a long time. However, there is still a long way to go for the anthropologists to be able to fully interpret and understand these changes. Heat-induced colour modifications are one of the least understood phenomena in bone, displaying a variety of exceptions (e.g., tints of yellow, orange, blue, green, pink, and red) to the expected colour variations that bone can produce when exposed to high temperatures (i.e., ivory, brown, black, various shades of grey, and white). In addition to these, there is a lack of uniformization in the literature regarding the methods to determine the exact colourations observed and the nomenclature used, giving way to subjective descriptions. However, commitment to more objective and reliable methods is visible in more recent research. In this review, we compiled data published in the literature throughout the years to portray the state of the art regarding the potential of heat-induced colour changes for inferring the circumstances of death and the applicability of these methods in the legal framework.

Temperature-specific spectral shift of luminescing thermally altered human remains

Human bone has shown to have luminescent properties that remain throughout the phases of cremation, with the exception of fully carbonized bone, when excited with a narrow band light source. During this research, an alternate light source (420-470nm, peak at 445nm) was used to visualize and investigate latent details relevant for forensic investigations of human remains recovered at fire scenes. As fire is a destructive force, it induces a vast variety of physical and chemical alterations to all components of the bone, making the subsequent analysis and interpretation of burned human remains challenging. A spectral shift in emission bandwidth, from green to red, was previously observed when the exposure temperature increased from 700 to 800 °C. This spectral shift was reproduced on a total of 10 human forearms, divided into 20 segments, by burning at 700 °C and 900 °C in an ashing furnace. The shift of emission bandwidth caused only by an increase in temperature was furthermore investigated by colorimetric analysis, proving the spectral shift to be significant. By easily quantifying the spectral shift, substantiation is provided for the use of this technique in practice to improve the interpretation of heat induced changes of bone.

Differentiating present-day from ancient bones by vibrational spectroscopy upon acetic acid treatment

Acetic acid treatment for an accurate differentiation between ancient and recent human bones was assessed using Raman and FTIR-ATR spectroscopies. Each set of skeletal samples was analysed by these techniques, prior and after chemical washing, in order to determine the variations in bone´s chemical composition and crystallinity. Bone samples were collected from several independent sources: recent bones burned under controlled experimental conditions or cremated, and archaeological (XVII century and Iron Age). The effect of acetic acid, expected to impact mostly on carbonates, was clearly evidenced in the spectra of all samples, particularly in FTIR-ATR, mainly through the bands typical of A- and B-carbonates. Furthermore, as seen for crematoria and archaeological samples, acetic acid was found to remove contaminants such as calcium hydroxide. Overall, acetic acid treatment can be an effective method for removing carbonates (exogenous but possibly also endogenous) and external contaminants from bone. However, these effects are dependent on the skeletal conditions (e.g. post-mortem interval and burning settings). In addition, this chemical washing was shown to be insufficient for an unequivocal discrimination between recent and archaeological skeletal remains. Based on the measured IR indexes, only cremated bones could be clearly distinguished.

Burned and buried: A vibrational spectroscopy analysis of burial-related diagenetic changes of heat-altered human bones

OBJECTIVES

The analysis of burned human remains can be very challenging due to heat-induced alterations. Occasionally, human bones present these coupled with diagenetic changes, offering even more of a challenge, since there is a lack of studies regarding interactions between both taphonomic phenomena. With this study, we aimed to assess and document the effects of inhumation on the chemical composition of both unburned and burned human skeletal remains.

MATERIALS AND METHODS

We buried, for 5 years, four groups of human bone samples comprising unburned bones and bones experimentally burned at 500, 900, and 1050 °C. Periodic exhumations were carried out to collect bone samples to be analyzed through Fourier transform infrared spectroscopy in attenuated total reflectance mode, in order to calculate four chemical indexes: (1) crystallinity index (CI); (2) type B carbonates to phosphate index (BPI); (3) total carbonates (A + B) to carbonate B ratio (C/C); and (4) OH to phosphate ratio (OH/P).

RESULTS

After inhumation, CI and C/C of unburned bones and bones burned at 500 °C, and BPI of bones burned at 1050 °C did not vary significantly. However, the remaining indexes showed both relevant increments and reductions throughout observations, depending on burning temperature and index.

DISCUSSION

Our results suggest that diagenesis can have an effect in bone's molecular composition. However, these effects do not seem to significantly affect the conclusions that can be taken from the analysis of infrared bone spectra, at least in the case of inhumations with a duration of 5 years or less.

In-Situ Anaerobic Heating of Human Bones Probed by Neutron Diffraction

The first neutron diffraction study of in-situ anaerobic burning of human bones is reported, aiming at an interpretation of heat-induced changes in bone, which were previously detected by vibrational spectroscopy, including inelastic neutron scattering techniques. Structural and crystallinity variations were monitored in samples of the human femur and tibia, as well as a reference hydroxyapatite, upon heating under anaerobic conditions. Information on the structural reorganization of the bone matrix as a function of temperature, from room temperature to 1000 °C, was achieved. Noticeable crystallographic and domain size variations, together with O-H bond lengths and background variations, were detected. Above 700 °C, the inorganic bone matrix became highly symmetric, devoid of carbonates and organic constituents, while for the lower temperature range (<700 °C), a considerably lower crystallinity was observed. The present pilot study is expected to contribute to a better understanding of the heat-prompted changes in bone, which can be taken as biomarkers of the burning temperature. This information is paramount for bone analysis in forensic science as well as in archeology and may also have useful applications in other biomaterial studies.

Vibrational spectroscopy to study ancient Roman funerary practices at the "Hypogeum of the Garlands" (Italy)

The “Hypogeum of the Garlands” is a sepulchral site, recently found in Grottaferrata (Lazio, Italy), dating back to the first-second century AD. Two sarcophagi were discovered inside, hosting the human remains of Aebutia Quarta, a rich Roman woman, and her son Carvilius Gemellus. While the body of Carvilius is exceptionally well-preserved, following its embalming and perfect sealing of the sarcophagus, in the case of Aebutia only the bones were preserved because of the sarcophagus’s seal breaking down, although she was covered with perfectly preserved flower garlands. Embalming of the body was a rare ritual in the Imperial Roman times when corpses were more often cremated. The remains of Aebutia showed possible traces of heating. Burned bones from a third individual were discovered on the chamber’s floor and preliminary anthropological survey showed that this individual was a male of 40–50 years old. Here, a combination of spectroscopic techniques, including non-destructive inelastic neutron scattering and Raman spectroscopy, and minimally destructive Fourier transform infrared spectroscopy, were applied to the analysis of these bone samples to give information about ancient Roman funerary practices. The temperature and burning conditions were thus determined, showing that Aebutia Quarta was exposed to mild temperatures (200 °C) only in the upper part of the body, while the third individual was likely cremated as its bones were exposed to temperatures up to 900 °C in quasi-anaerobic conditions.

These boots are made for burnin': Inferring the position of the corpse and the presence of leather footwears during cremation through isotope (δ13C, δ18O) and infrared (FTIR) analyses of experimentally burnt skeletal remains

Cremation is a complex mortuary practice, involving a number of activities of the living towards the dead before, during, and after the destruction of the bodily soft tissues by fire. The limiting information concerning these behavioral patterns obtained from the pyre remains and/or cremation deposits prevents the reconstruction of the handling of the corpse during the burning process. This pioneering study tries to determine the initial positioning of the corpse in the pyre and assess whether the deceased was wearing closed leather shoes during cremation through isotopic (δ¹³C, δ¹⁸O) and infrared (ATR-FTIR) analyses of experimentally burnt pig remains, used as a proxy for humans. The results obtained show that both the position of feet on or within the pyre and the presence of footwears may moderately-to-highly influence the oxygen isotope ratios of bone apatite carbonates and the cyanamide content of calcined bone in certain situations. By forming a protective layer, shoes appear to temporarily delay the burning of the underlying pig tissues and to increase the heat-shielding effect of the soft tissues protecting the bone mineral fraction. In such case, bioapatite bone carbonates exchange oxygen with a relatively more ¹⁸O-depleted atmosphere (due to the influence of lignin-derived oxygen rather than cellulose-derived oxygen), resulting in more pronounced decrease in the δ¹⁸O_carb values during burning of the shoed feet vs. unshoed feet. The shift observed here was as high as 2.5‰. A concomitant isotopic effect of the initial location of the feet in the pyres was also observed, resulting in a top-to-bottom decrease difference in the δ¹⁸O_carb values of shoed feet of about 1.4‰ between each deposition level tested. Finally, the presence of cyanamide (CN/P ≥ 0.02) seems to be indicative of closed footwear since the latter creates favorable conditions for its incorporation into bone apatite.

Estimation of the post-mortem interval in human bones by infrared spectroscopy

In forensic anthropology, there is an inherent difficulty in estimating the post-mortem interval (PMI). This study aimed to assess whether there is a correlation between changes in the bone mineral component and the PMI estimation. Samples of femur and humerus from 80 identified individuals with known post-mortem interval were analyzed. Infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR) was applied for this analysis, several indices having been obtained from the infrared bands most representative of the bone's relative contents in carbonate and phosphate. Specific relationships between sex/age and PMI were attained: for larger PMIs, there was an increase in the amount of B-type carbonate (BPI), A-type carbonates (API), and in the carbonate/phosphate (C/P) ratio, and a decrease of the crystallinity index (CI) and in the carbonate ratio (C/C). Two particular infrared indices (CI and C/C) were identified as the most suitable for post-mortem interval estimation, especially in females, controlling the effects of sex and age (in the statistical analysis).

The impact of moderate heating on human bones: an infrared and neutron spectroscopy study

This study aims to analyse human bones exposed to low/medium temperatures (200-650°C) under experimentally controlled conditions, both oxidizing and reducing, using complementary optical and neutron vibrational spectroscopy techniques. Clear differences were observed between the aerobically and anaerobically heated bones. The organic constituents disappeared at lower temperatures for the former (ca 300°C), while they lingered for higher temperatures in anaerobic environments (ca 450-550°C). Unsaturated non-graphitizing carbon species (chars) were detected mainly for anaerobically heated samples, and cyanamide formation occurred only at 650°C in reducing settings. Overall, the main changes were observed from 300 to 400°C in anaerobic conditions and from 450 to 500°C in aerobic environments. The present results enabled the identification of specific spectroscopic biomarkers of the effect of moderate temperatures (less than or equal to 650°C) on human bone, thus contributing to a better characterization of forensic and archaeological skeletal remains subject to heating under distinct environmental settings. In particular, these data may provide information regarding cannibalism or ancient bone boiling and defleshing rituals.