Isotope analysis of tooth enamel from Papcastle site
J.A. Evans, H. Sloane and A. Lamb
NIGL report
2014
Introduction
A tooth enamel and bone sample from Roman aged male was submitted to NIGL for isotope
analysis by Mr Don O’Meara.
Methodology.
Preparation of tooth enamel for Sr isotope analysis
In a clean laboratory, the samples were first cleaned ultrasonically in high purity water to
remove dust, rinsed twice, put in di-ionized water on a hotplate at 50°C for an hour and
rinsed twice and then dried. They were then weighed into pre-cleaned Teflon beakers. The
samples were mixed with 84Sr tracer solution and dissolved in Teflon distilled 8M HNO3.
The samples were converted to chloride using 6MHCl and strontium was collected using
Dowex resin columns.
Strontium was loaded onto a single Re Filament following the method of (Birck, 1986) and
the isotope composition and concentrations were determined by Thermal Ionisation Mass
spectroscopy (TIMS) using a Thermo Triton multi-collector mass spectrometer. The
international standard for 87Sr/86Sr, NBS987, gave a value of 0.710250 ± .000006 (n=8, 2)
during the analysis of these samples. Blank values were in the region of 100pg. Data are
presented below.
The chemical preparation and isotope analysis of oxygen in structural carbonate
For the isotopic analysis of phosphate carbonate oxygen approximately 3 milligrams of
prepared enamel was loaded into a glass vial and sealed with septa. The vials are transferred
to a hot block at 90°C on the GV Multiprep system. The vials are evacuated and 4 drops of
anhydrous phosphoric acid are added. The resultant CO2 was collected cryogenically for 14
minutes and transferred to a GV IsoPrime dual inlet mass spectrometer. The resultant isotope
values are treated as a carbonate. 18O is reported as per mil (‰)(18O/16O) normalized to the
PDB scale using a within-run calcite laboratory standard (KCM) calibrated against SRM19,
NIST reference material and were converted to the SMOW scale using the published
conversion equation of (Coplen, 1988): SMOW=(1.03091 x 18O VPDB) +30.91. Analytical
reproducibility for this run of laboratory standard calcite (KCM) is 0.09‰ (1 σ, n=6) for
18OSMOW and ± 0.04‰ (1s, n=6) for 13CPDB. The apatite carbon value (δ13C(ap) ‰ VPDB) is
converted to the equivalent collagen values (δ13C(coll) ‰ VPDB ) using the equation of O’Regan et
al 2008.
The carbonate oxygen results 18OSMOW(c) are converted phosphate values18OSMOW(p) using
the equation of Chenery et al 2012: (18OSMOW (p) = 1.0322*18OSMOW (c) – 9.6849) and these
are converted to drinking water using the equation of (Daux et al., 2008) ( DW =
1.54*18OSMOW(p) -33.72) . The calculation of drink water values involves considerable
uncertainties (Pollard et al., 2011) and the values should be used as guidance.
Collagen Extraction and C & N analysis
Collagen was extracted following the method of (Brown et al., 1988) and M.P. Richards
(pers. com.). Approximately 0.5-1.0g of each bone was cleaned thoroughly in distilled water
and placed in polypropylene test tubes with 8 ml of 0.5 M HCl in the fridge for at least 48
hours to demineralise. The demineralising solution was discarded and the remaining solid
collagen was rinsed 3 times in deionised water, placed into glass test tubes and solubilised in
a solution of pH3 HCl at 70ºC in a hot block for 48 hours. The solutions were filtered using
an 8μm Ezze filter to remove solids before freeze drying. Two aliquots from each collagen
sample were weighed into small tin capsules for analysis. Analysis of carbon and nitrogen
isotopes was by Continuous Flow Isotope Ratio Mass Spectrometry (CFIRMS).
The
instrumentation is comprised of an Elemental analyser (Flash/EA) coupled to a
ThermoFinnigan Delta Plus XL isotope ratio mass spectrometer via a ConFlo III interface.
δ13C and δ15N ratios were calibrated using an in-house reference material M1360p (powdered
gelatine from British Drug Houses) with expected delta values of –20.32‰ (calibrated
against CH7, IAEA) and +8.12‰ (calibrated against N-1 and N-2, IAEA) for C and N
respectively. The 1 reproducibility for mass spectrometry controls in this batch of analysis
were 15N = ± 0.06‰ and 13C = ± 0.07‰. The results are given below.
Results
Sample
Sr
ppm
87
86
Sr/ Sr
δ13C(ap)
‰
VPDB
δ13C(coll) ‰
VPDB
δ18OC ‰
VSMOW
δ18OP ‰
VSMOW
drinking water estimate
RHB-B 125
72.56
%C
0.71093
C/N
at
%N
32.4
-10.79
11.1
3.4
-17.1
d13C PDB
-19.5
+27.49
18.7
-4.9
d15N AIR
11.2
The data provide no evidence that this individual is not of local origin. Both the strontium
and oxygen isotope composition from the tooth enamel of this individual is consistent with a
childhood spent in the Lake District. These values are not unique and so these results do not
rule out other areas with similar characteristics. The oxygen isotope value of δ18OP ‰ = 18.7
is central to the range of value from the western, higher rainfall area of Britain (Evans et al
2012). The rocks that crop out in the Lake District could generate higher values in the
biosphere (Evans et al 2010) but such values are modified by high rainfall and proximity to
the coast, so the strontium isotope composition of 0.71093 consistent with a Lake District
origin. The carbon and nitrogen isotope analysis the bone reflect an adult diet that was
typical of British individuals and plots within the dietary field of Roman individuals from
Britain (Chenery et al 2010.) We suggest this individual was of local origin.
References
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Chronology.Chem. Geol. 56, 73-83.
Brown, T. A., Nelson, D. E., Vogel, J. S., and Southon, J. R., 1988. Improved
collagenextraction by modiefied Longin method. . Radiocarbon 30, 171-177.
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isotope evidence for diet and mobility in Roman Gloucester, UK, J. Arch Sci. 37, 150-163.
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isotope relationship between the phosphate and structural carbonate fractions of human
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variation in archaeological human tooth enamel excavated from Britain." Journal of
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O’Regan, H.J., Chenery, C., Lamb, A., Stevens, R., Rook, L., Elton, S.E., 2008. Modern
macaque dietary heterogeneity assessed using stable isotope analysis of hair and bone., J.
Hum. Evol. 55, 617-626.
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the conversion of dental enamel 18O values to 18OW to determine human mobility,
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Contact.
Don O'Meara
Environmental Specialist
Wardell Armstrong LLP
Cocklakes Yard
Carlisle
Cumbria
CA4 0BQ
Tel: 01228 564820
Fax: 01228 560025
www.wardell-armstrong.com