In the last decade or so we have experienced a revolution in archaeological science, and one of the most exciting aspects of this is the extraordinary level of detail that we can glean from everyday objects. But while we are constantly pushing the boundaries of what we can discover from archaeological remains, we are also constantly reminded of the constraints we still face. This dichotomy is well evidenced in a study, recently published in the journal Analyst, on the detection of opioids in archaeological contexts.
In this study, a team from the University of York and the British Museum developed a technique to extract poppy alkaloids from oil residues. To test this technique archaeologically, they were fortunate that radiography of a sealed base-ring juglet from Cyprus, curated at the British Museum, had shown that it was likely to contain some residue from its original contents. This provided the unique opportunity to finally test the theory that these types of containers – widely traded across the eastern Mediterranean during the late Bronze Age – were used to transport opium. The link was originally proposed based on the fact that their shape resembles the capsule of an opium poppy, but this theory began to fall into doubt when numerous studies tried, and failed, to detect opiate residue in these juglets.
These previous studies almost all attempted to detect the morphine alkaloid – the most abundant alkaloid produced by the poppy plant, and the one that causes its narcotic effects. But artificial ageing experiments, carried out by both this current research team and other past studies, have shown that morphine degrades quickly. Hence, it is unlikely to remain preserved archaeologically. The poppy plant produces over 40 different alkaloids, though, several of which – including papaverine and thebaine – are more resistant than morphine to degradation, and are unique to the opium poppy. It was these alkaloids that the recent research concentrated on.
Portions of the juglet’s contents were successfully removed and were first assessed for the presence of lipids – or fats – as the residue was oily in nature. Based on its fatty-acid profile, the substance was determined to be most likely plant-based. Although the specific plant could not be identified due to molecular alterations brought about by degradation, certain oils – such as castor oil or those formed from brassicas – could be ruled out, while some others – such as poppyseed oil – fit the profile more closely.
In order to determine whether the oil was indeed derived from poppies, the alkaloids released by the plant needed to be separated from the rest of the substance. Developing a technique using modern poppyseed oil, the team then applied this methodology to the archaeological samples from the Cypriot juglet. Using mass spectrometry to analyse the different chemicals, papaverine and thebaine were both detected – although both in fairly low levels.
These results definitively linked base-ring juglets with opiates, finally confirming a theory first proposed in the 1960s. The team was not able to determine the exact opiate substance, though, and it could be that the vessel contained poppyseed oil rather than opium. If this was the case, it could be that the poppyseed oil was used in anointing rituals or in a perfume.
This is an amazing achievement that has helped shed light on not only the ancient use of opiates but the possible function of base-ring juglets as well. But it also highlights the difficulty of replicating the method. As the research team notes, the opiate alkaloids were only detected in very low levels from a jar that had, unusually, remained sealed; this means that using the technique successfully on pottery sherds – or even on vessels that remain whole but unsealed – could be extremely hard. As is common with newly developed techniques, it can feel a little bit like one step forward, two steps back. But if we have learned anything over the past few years regarding advancements in archaeological science, it is that while we may not be able to answer every question out there, we get closer and closer with each subsequent study, and researchers will keep on trying until they have exhausted all possibilities.
Professor Jane Thomas-Oates, Chair of Analytical Science at the University of York and the supervisor of the researcher, Dr Rachel Smith, who pioneered this study, highlighted this determination. She said, ‘We were able to establish a rigorous method for detecting opiates in this kind of residue, but the next analytical challenge is to see if we can succeed with less well-preserved residues.’ The paper outlining the study and its results can be accessed for free at https://pubs.rsc.org/en/content/articlepdf/2018/an/c8an01040d
This article appeared in CA 345.
