Effects of applied consolidants on the stable isotope values of bone collagen and bioapatite: implications for the use of treated bones as reliable paleoenvironmental proxies

Carbon, nitrogen, and oxygen stable isotopes from bones and teeth are valuable indicators of ancient diets, ecosystems, environments, and climates. Inherent in these analyses is the need to have pristine remains unaltered by glues or consolidants commonly used in museum and academic collections (i.e. human-induced alterations). This study examined the effects of applying and removing polyvinyl acetate/alcohol (PVAc), methyl methacrylate resin (Acryloid/Paraloid), polyvinyl butyral resin (Butvar), cellulose nitrate (Amboird, Celluloid, Duco Cement), and the sublimating polymer cyclododecane (CDD). Consolidants were applied to a modern whale rib and seal femur, then removed with various solvents and drying methods. ATR-FTIR and GCMS results indicate that consolidants can be removed successfully below limits of detection. Carbon, nitrogen, and oxygen stable isotopes were compared across treatment groups and controls. Nitrogen and carbon isotopes in collagen and bioapatite are unaffected by consolidant treatment and removal. Oxygen isotope values are unaffected in bioapatite phosphates, but oxygen from bioapatite carbonates did show non-systematic alteration after consolidant application. The notable exception is the sublimating CDD which did not alter any stable isotope values. These results suggest that labile oxygen-bearing side groups (e.g. -OH) may be susceptible to exchange with consolidants in the presence of solvents, while the stronger covalent bonds in organic molecules, phosphates, and carbonates are less susceptible. This bodes well for other types of consolidant-treated or resin-embedded samples whose isotopes serve as valuable paleoenviromental proxies, such as conodonts, carbonates (e.g. speleothems, shells), or tree rings. However, use of oxygen isotopes from treated materials with labile side groups (e.g. certain preserved biofilms, bioapatites) should be considered with caution. Using CDD or other sublimating solvents as a temporary consolidant for excavation, transport, or embedding is a viable alternative that may avoid oxygen isotope alteration.