TRACE METAL AND RARE EARTH ELEMENT CHEMISTRY OF MODERN HUMAN BONE

Bone is a mineralized connective tissue that has a remarkable ability to incorporate a whole range of elements and ions into its mineral matrix. Trace elements in bone can provide medical, biological, anthropological, and/or geographic origin information. While the majority of research has focused on the incorporation of a select group of elements (Ca, F, Sr, Pb, K, Mg, Zn, and Na), little information exists on the abundance and incorporation of most geologically informative trace and rare earth elements (REE). As a result, our current model for trace element incorporation into bone is limited. Trace element incorporation into bone is a result of both dietary and geological inputs, and metabolic processes that may concentrate or biopurify essential elements, while depleting nonessential or toxic elements. This study is the first to quantify the abundance of a large suite of transition metals, trace elements, and rare earth elements in human bone collected from femoral heads following hip replacement surgery. We establish a coefficient of incorporation and a ratio of incorporation, which we apply to determine: (1) the degree of biopurification of trace elements in bone compared to a geological input, Upper Continental Crust (UCC); (2) if the variation in trace element concentrations is related to biomolecular selection, or follows geochemical principles such as ion substitution related to ion radius; (3) which elements are biologically regulated due to their covariance with zinc, a known metabolically controlled nutrient; and (4) which elements maintain their geological composition when incorporated into bone and therefore may be useful tracers for geographical provenance, biominieralization, archeology, paleodiet reconstruction and/or forensic science. We find that many transition metals (Co, Fe, Sc, Ti, Cr) as well as strontium correlate with zinc concentrations, indicating biological regulation of these elemental concentrations in bone. For elements with no relationship to zinc (e.g. Ba, Pb, V, REEs), incorporation into bone can occur according to predictable physiochemical parameters including ionic radius, valence state, and solubility. REEs, in particular, show minimal fractionation during incorporation into bone and may provide the best proxy for geographical provenance studies.