Crystal clear: Vibrational spectroscopy reveals intrabone, intraskeleton, and interskeleton variation in human bones

Vibrational spectroscopy is a valuable tool for the study of burned skeletal remains. Nonetheless, most investigations have been focused on a limited number of samples as well as on faunal bones rather than human bones. Conclusions based on those investigations may lack representativeness, namely about the intrabone, intra- and interskeleton variability of several chemometric indices. We aimed to investigate this issue on a large sample of human bones.

Powder samples were collected from 168 bones from four human skeletons. The sampling targeted 47 long bones, 72 short bones, and 49 tarsal bones as well as different bone regions in a total of 638 powder samples. Bones were experimentally burned in an electric muffle furnace for two hours to maximum temperatures ranging from 400°C to 1000°C. Another 623 burned samples were then collected totaling 1261 samples subjected to FTIR-ATR analysis. The CI, BPI, C/C, and OH/P indices were calculated.

An important intrabone, intra- and interskeleton variation was observed, especially for the BPI. The CI, C/C, and OH/P indices revealed much less variation so site-specific sampling may not be as critical in these cases. Clear differences between our results and those from previous investigations were observed, namely on the temperature increment evolution of the CI and C/C indices.

The relatively large heterogeneity, especially at the intrabone level, is possibly the consequence of microstructural bone differences. The dissimilarities observed between our investigation and other published studies are probably due to the fact that the samples used here came from human rather than faunal bones. Also, our samples were buried previously to the experimental burning so this may also partly explain our contrasting results, since previous research was mostly performed on fresh bone. Future inferences based on vibrational spectroscopy analyses should take into account the possible effect of all these sources.