Archaeological wood degradation at the site of Biskupin (Poland): Wet chemical analysis and evaluation of specific Py-GC/MS profiles

• We investigated 3000 year old oak wood from the Biskupin site.
• We collected complementary results by wet chemical analyses and Py(HMDS)-GC/MS.
• Depletion in carbohydrates was quantitatively assessed in degraded samples.
• Short side chain lignin Py products and cyclopentenones are indexes of wood decay.
• Abundance of lignin monomers and levoglucosan indicate good preservation of wood.

Eight samples of ca. 3000 year old oak wood from the Biskupin site and a piece of sound oak (Quercus sp.) wood were analysed. The degradation state of archaeological oak wood was investigated using two analytical approaches: classical wet chemical analysis and analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS) with in situ silylation. The results were compared with those obtained for sound oak wood.Chemical analysis provided information on the amount of wood components. Their alteration at a molecular level was investigated by Py-GC/MS, highlighting how degradation can affect the formation of primary and secondary wood pyrolysis products.The results showed that the chemical changes in the wood material in the eight samples examined had different entities and extents with comparison to sound oak wood. Samples taken from the external parts of the fragments had undergone a significant loss in polysaccharide components, whereas the internal parts were in a relatively good state of preservation. Evaluation of the relative amounts of pyrolysis products deriving from holocellulose and lignin highlighted that specific categories of compounds, such as lignin monomers and anhydrosugars, can be taken as an index for good preservation of wood components.These results will be used to evaluate the effectiveness of the in situ conservation strategy by repeating the analyses on these samples after some years and comparing the results.