Publication date: November 2019
Source: Journal of Archaeological Science, Volume 111
Author(s): Nathan I. Harmston, Erik J. Linduska, Patrick L. Tomco
Stable isotopic analysis (SIA) of incremental dental tissues from archaeological specimens provides unique insight into the paleoecology of animals utilized by humans in the past. Unfortunately, many archaeological specimens are too fragile to survive the mechanical processes necessary to accurately identify and sample incremental dental tissues. Polymethyl-methacrylate (PMMA) is an organic polymer often used to encapsulate and strengthen archaeological specimens for the sectioning, grinding, and polishing necessary to identify incremental tissues. The effects of PMMA embedding on stable carbon and nitrogen isotopes in dental enamel and dentin has not been assessed previously and may be relevant whenever stable isotopic analysis of carbon and nitrogen is to be conducted. We embedded five caribou (Rangifer tarandus) tooth halves in PMMA, sampled these halves and the corresponding non-embedded tooth halves. We found that PMMA embedding has no noticeable effects on the nitrogen values of embedded specimens. PMMA embedding decreased the δ13C values of whole teeth powder by an average of −6.5‰ and increased %C by an average of 8.7%.
We then tested two methods to mitigate the impact of PMMA embedding on dental carbon 1) acetone baths to dissolve the PMMA before SIA, and 2) acetone baths combine with a modified Longin method for collagen extraction to remove PMMA prior to SIA. We found that three, four and five acetone baths appear to be equally efficient at removing PMMA introduced carbon from embedded specimens. Acetone baths reduce the standard error of δ13C values of whole tooth dental powder, including enamel, dentin, and cementum, in both embedded and non-embedded specimens. Both methods were successful at reducing the effects of PMMA embedding; however, the most efficient mitigation of PMMA effects on whole tooth carbon was found in collagen extracts coupled with acetone baths. This information may be helpful in future stable isotope assessments of PMMA-encapsulated dental tissues.