Science Notes – Hidden in the soil: assessing the chemical composition of graves

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Soil from this Anglo-Scandinavian burial in Hungate, York, was analysed to see what its chemical composition could tell us about the grave. (PHOTO: Dr Matthew Pickering)

In the early days of archaeology, human remains were often treated as an afterthought, deemed unable to tell us much about past populations. As we are well aware today, though, this could not be further from the truth, and in more recent decades the study of human bones has become a major component of archaeological research. But, despite this skeletal success, there is another key aspect of burials that remains relatively under-researched: the grave soil.

While some facets of soil analysis have become more commonplace – such as the identification of pollens or other plant materials that may shed light on the surrounding environment at the time of burial – for the most part this is new and uncharted territory. Yet the first exploratory research projects are now beginning to examine what soil analysis can and cannot tell us about interments.

Chemical analysis of the burial environment has the potential to offer a wealth of information. Soil from around the torso and pelvis can be used to assess the contents of an individual’s stomach and intestines, potentially leading to the identification of their last meal, signs of parasitic infection, or their microbiome (the community of micro-organisms that lived inside them). The technique could also be used to help identify organic grave goods that may have disintegrated with time. And it could be used to discern the location and position of human remains that have completely degraded into the soil, at the same time giving us a better understanding of the environmental conditions that lead to such destruction.

In an effort to lay some of the foundations for this promising avenue of research, a study – carried out as part of the InterArChive project by researchers from the University of York, and recently published in the Journal of Archaeological Science – assessed the soil from two graves from Hungate, York. One dated to the city’s Roman occupation, and the other to York’s Anglo- Scandinavian period. During the excavation, the team took soil samples from around different areas of each grave, specifically concentrating on key anatomical locations, such as the head, pelvis, and feet. To be able to identify chemical characteristics unique to each grave, they also took samples from the grave-fill immediately above the skeletons, as well as from other locations on the site that were not near any burial.

Through different chromatography methods that separated out the various chemical components of each soil sample, the team was able to the identify some characteristics that were unique to the burials. In both instances, elevated levels of triacylglycerols (TAGs) were identified. As these are a primary component of animal fats, it is believed that they were derived from decomposed adipose (fat) tissue – an idea that was supported by the fact that the largest concentrations of TAGs were found in the area of each individual’s torso.

High concentrations of cholesterol were also present. Cholesterol is a significant component of archaeological bone, so this is not an unexpected find, but its identification does raise the possibility of its distribution in a grave potentially being used to identify the location and position of human remains that have not survived. Much more work needs to be done in this area, however, before such analysis can become a viable technique.

In addition to cholesterol, coprostanol – a chemical compound formed from cholesterols in the gut of many animals, including humans – was identified. Its presence is often used as a biomarker for faecal matter. Logically, then, in the Anglo-Scandinavian grave, coprostanol was found in samples taken from around the pelvic region, probably signifying the decomposition of the gastrointestinal tract. In the Roman grave, however, high levels of coprostanol were discovered throughout the soil. These are probably due to contamination from the Anglo-Scandinavian cesspit that was located near the burial. It is believed that seepage from this pit significantly contributed to the accelerated decalcification and subsequent decomposition of some of the bones.

Overall, this study was able to provide a detailed analysis of the chemical components of each grave, highlighting the fact that the soil is, as the paper outlining these results notes, ‘a valuable unexploited archive of information’. Further research into this area will only continue to expand this methodology, and it is likely that sometime in the future, grave soil will be considered as important an archaeological resource as the skeletons buried within it.

This article appeared in CA 346.

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