The role of stable isotopes in human identification: a longitudinal study into the variability of isotopic signals in human hair and nails

Abstract

Recent natural catastrophes with large-scale loss of life have demonstrated the need for a new technique to provide information for disaster victim identification when DNA methods fail to yield the identification of an individual, or in other situations where authorities need to determine the recent geographical life history of people. The latter may be in relation to the identification of individuals detained on suspicion of terrorism or in relation to people-trafficking or smuggling. One proposed solution is the use of stable isotope profiling (SIP) using isotope ratio mass spectrometry (IRMS). Exploiting the link between the isotopic signal of dietary components and the isotopic composition of body tissue, the aim of this study was to refine a non-invasive method of analysing human material such as scalp hair and fingernails using SIP and to assess the degree of natural variability in these profiles. Scalp hair and fingernail samples were collected from British and non-British volunteers at Queen's University Belfast every 2 weeks for a minimum of 8 months. Samples were analysed using IRMS to determine their isotopic composition for 13C, 15N, 2H and 18O. The results of this longitudinal study yielded information on the natural variability of the isotopic composition of these tissues. The data demonstrate the relatively low degree of natural variation in the 13C/15N isotopic abundance of scalp hair and fingernails whilst greater variations were recorded in the hydrogen and oxygen values of the same samples. The 15N and 18O values of nail are noticeably more variable than that of scalp hair from the same subject. A hypothesis explaining this trend is put forward based on the faster rate of formation of hair than of nails. This means that there is less time for the compounds forming hair to be affected by biochemical processes that could alter their isotopic signature.

Tracking human travel using stable oxygen and hydrogen isotope analyses of hair and urine

“…teeth 15,16 ). Few studies have investigated the combined values of dD and d 18 O in organic tissues; 17,18 however, technical developments have streamlined this type of analysis for organic samples [19][20][21] such that these analyses are becoming increasingly routine.…”

“…17,18,22 In animal populations it is generally assumed that animals and the plants or animals that they eat draw on similar sources of water; thus, the d 18 O and dD values of an animal's diet and drinking water should vary in parallel. 1,2,18 However, when an animal's diet includes items expected to have dissimilar d 18 O and dD values from drinking water (e.g.…”

“…Subsequently, interpretation of d 18 O and dD values in organic tissue samples becomes even more complicated when applied to modern human populations. 17 Isotopic analyses have a rich history in the human anthropological literature; [23][24][25][26][27] including the use of inorganic 18 O from teeth and bone to track past human movements. 28,29 Studies of modern humans are confined to organic tissues that can be non-invasively sampled (e.g.…”

“…[30][31][32][33][34][35] However, there is a growing interest in tracking modern human movements via values of hair and nail d 18 O and dD. 17 Studies of this type could find a wide variety of forensic applications; for example, establishing the likelihood of reported travel or location of origin. 1,17 Studies using organic d 18 O and dD values to track the movements of modern humans are required to consider the multiple sources of oxygen and hydrogen to nail and hair tissue, and the kinetics by which oxygen and hydrogen isotope signatures change.…”

“…17 Studies of this type could find a wide variety of forensic applications; for example, establishing the likelihood of reported travel or location of origin. 1,17 Studies using organic d 18 O and dD values to track the movements of modern humans are required to consider the multiple sources of oxygen and hydrogen to nail and hair tissue, and the kinetics by which oxygen and hydrogen isotope signatures change. In many human populations foods are non-locally grown and may derive from a huge range of geographical origins (e.g.…”