Title:
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Stable isotope analyses of keratin for human provenance : implications for forensic science
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This research explores the application of carbon, nitrogen, oxygen and hydrogen
isotopic analysis of modem human hair and nail tissues for forensic purposes. Carbon
and nitrogen isotopic signatures are transferred from the environment to plants and to
human tissues through trophic levels, therefore reflecting the diet. Oxygen and
hydrogen isotopes are closely linked to the geographical location of the individuals
through precipitation. drinking water and food products. The use of carbon, nitrogen,
oxygen and hydrogen isotopic analysis of "hair and nail tissues can therefore be applied
to diet-reconstruction and geo-localisation of individuals, which has been widely used
on older human remains. Hair and nail are ideal tissues for obtaining a precise temporal
archive of diet and location due to their known and relatively constant growth rates. The
high keratin content of these tissues (between 65 and 95% by weight) enables analysis
of small sample sizes, without prior chemical purification, which makes them ideal
matrices in forensic investigations where sample size is often a limiting factor. The easy
and non• invasive sampling of hair and nail tissues enables the transfer of this
application to living humans, which has been the focus of forensic scientists for several
years.
In this study, hair and nail samples were collected from 134 volunteers from
Reading (UK) with known diet and geographical movements. A total of 43 hair samples
and 74 fingernail samples were also collected from volunteers living in Kenya, whose
recent travel record was known. A total of 17 hair samples and 10 fingernail samples
were also collected from a group of27 individuals claiming to be of Somalian origin but
who could have been Kenyan, as part of the British Human Provenance Project. These
samples were compared to the two reference groups from Reading and Kenyan
volunteers in order to assess their likely area of origin, and to determine their diet.
The results obtained in this study confirm the potential of carbon and nitrogen
isotopic analysis of modem human hair and nail tissues in discriminating between the
different levels of protein intake of omnivore, ovo-lacto-vegetarian (OL V) and vegan
diets. Through the largest dataset analysed so far (mostly from Europe and Kenya), this
research confidently reports the effect of location on δ13C, δ 2H and δ 180 values of
human tissues. Hair and nail δ13C values show significant differences between locations
with diverse proportion of C3/C4 food product intake (USA and Kenya versus Europe),
while locations such as Kenya, Australia and Turkey show significantly enriched 02H
and δ180 values than locations at higher latitudes such as Spain, France, Germany and
the United-Kingdom. The level of location discrimination is however increased by a
simultaneous combined approach of δJ3C and δ2H analysis, which enables the
determination of the likely area of origin of samples from uncertain location to a greater
extent than the isotope ratio pairs (δ13C- δ15N, δ2H- δ18O).
This study also presents a unique dataset of a series of hair and nail samples
from the same individual (n=74 for δ13C and δ 15N and n=60 for δ 2H and δ 18O), showing
strong correlations between these two tissues.
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