Cadmium is an especially nasty toxic metal- a quick look at Wikipedia shows that the exposure is wide-spread and potentially fatal conditions result. Studying uptake and subsequent release of Cd by bone is a part of the quest for methods to treat people already exposed; development of environmentally acceptable HA-based filters to sequester Cd is another. The article cited below contributes to the on-going efforts to understand how Cd is absorbed, and how it can be controlled.
Theoretical and Experimental Studies of Substitution of Cadmium into Hydroxyapatite
Joice Terra1, Gabriela Gonzalez2, A. M. Rossi1, J.G. Eon3, D. E. Ellis4
Abstract (J. Phys. Chem. Chem. Phys. 2010)
Substitution of cadmium into bulk hydroxyapatite Ca(10-x)Cdx(PO4)6(OH)2 (CdHA: x= 0.12, 1.3, 2.5) is studied by combining X-ray diffraction data from synchrotron radiation, infra-red spectroscopy (FTIR) and density functional theory (DFT) calculations. Energetic and electronic analyses are carried out for several configurations of Cd substitution for Ca at both cationic sites. Rietveld analysis shows preferential occupation of Ca2 site by cadmium. FTIR data suggest a non-negligible covalent character of Cd-OH. The much-discussed cation site preference for substitution is determined on the basis of relaxed-lattice energetics, and interpreted in terms of chemical concepts; theory indicates that the Ca2 site is clearly favored and such preference is related to the more covalent character of this site compared to that of site1.