Influence of biological degradation and environmental effects on the interpretation of archeological bone samples with laser-induced breakdown spectroscopy

Laser Induced Breakdown Spectroscopy (LIBS) has emerged in the past decade as a very promising technique for the analysis and characterization of a broad variety of objects of cultural heritage especially bio-archeological samples such as calcified tissues namely teeth and bones. The most important advantages of LIBS from the archeological point of view are its quasi nondestructive nature and its potential for performing in situ measurements. In the present work human calcified tissue samples of recent and archeological bones have been studied via the LIBS technique. The old samples were from three different ancient Egyptian dynasties representing the middle kingdom (1980-1630 BC), the 2(nd) intermediate period (1630-1539/23 BC) and the pre-Roman period (664 BC). Elements normally used to study dietary habits such as strontium, barium, aluminium and lead were analyzed in the obtained LIBS spectra and the interferences of postmortem or diagenic effects due to the burial place were investigated via LIBS analysis of soil samples taken from the same locations where the archeological bones have been buried. The obtained results have demonstrated evidently that conclusions about dietary habits must take into account postmortem effects such as biological degradation and environmental leaching (especially from the surrounding soil). Study of CN and C-2 molecular bands in the obtained LIBS spectra of the bones revealed that these bands have strong intensities in recent bones spectra contrary to the archaeological ones. This is attributed to the degradation of the tissues and has been confirmed by following up calcium to phosphorus ratios in different bone samples.