Provenancing humans: the real uncertainty of stable isotope data
Stable isotope profiling is a relatively new technique within the field of human identification. It allows forensic investigators to deduce information pertaining to an individual’s geographical provenance, recent movements, and even dietary intake. Human identification requires the development of new methods able to overcome the issues associated with traditional techniques such as the degradation of DNA samples in aqueous environments, and the extreme fragmentation of skeletal material. Stable isotope profiling is a rapid, cost effective, and accurate technique capable of assisting forensic investigations by focussing resources and providing additional information to the biological profile provided by the anthropologist. Variation in the isotopic composition of local tap water arises as a result of mass-dependent fractionation processes occurring within the hydrologic cycle. These processes occur constantly as water is transported around the globe, and produces distinct isotopic signatures for tap water depending upon geographical location. The isotopic content of tap water is then incorporated into human body tissue via dietary intake, with further fractionation occurring as a result of metabolic processes. Variation in both metabolic rates within the tissues of the same individual, and of tissues belonging to different individuals, will result in differences in the isotopic composition of human material. However, there are very few data available demonstrating intra- and inter- individual variability. This information is of particular use in forensic investigations, as judges will often evaluate the errors associated with a technique before declaring evidence admissible. Barristers also use these data to support or interrogate the statements provided by individuals involved in a case. The primary aim of this research is to quantify the inter- and intra-individual variation associated with human tissue, in particular femoral material. This was achieved by collecting femoral sections from cadavers, and analysing the 13C and 18O content of the carbonate portion. The data collected from this research suggested there is significant variation in the isotopic variability of d18O both within, and between individuals. It also indicated that there was no significant difference between the isotope values obtained from the left and right femora of the same individual, however there was significant variation between a number of samples originating from the same piece of femur. It was possible to link the d18O values obtained from the analysis of bone carbonate to geographical locations using established d18O maps of tap water for the UK. This study utilised a small number of samples, and it is acknowledged that this is only preliminary research. It is essential that a greater number of individuals are sampled, both for bone and hair material, in order draw more accurate and meaningful conclusions from the data.
Stable isotope, Human identification, Provenancing
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