Abstract
Zinc (Zn) isotope ratios of dental enamel are a promising tracer for dietary reconstruction in archeology, but its use is still in its infancy. A recent study demonstrated a high risk of Zn contamination from nitrile, and latex gloves used during chemical sample preparation. Here we assess the potential impact of the use of such gloves during enamel sampling on the Zn isotope composition of teeth from a population of early Holocene hunter gatherers from Lapa do Santo, Lagoa Santa, Minas Gerais, Brazil. We first examined the amount of Zn and its isotopic composition released from the gloves used in this study by soaking them in weak nitric acid and water. We compared Zn isotope ratios obtained from teeth that were sampled wearing nitrile, latex or no gloves. Finally, we performed a linear mixed model (LMM) to investigate post hoc the relationship between the gloves used for sampling and the Zn isotope variability in dental enamel. We found that the gloves used in this study released a similar amount of Zn compared to previous work, but only in acidic solution. Zn isotope ratios of teeth and the LMM identified no sign of significant Zn coming from the gloves when teeth were handled for enamel sampling. We hypothesize that Zn in gloves is mostly released by contact with acids. We found that the main source of Zn isotope variability in the Lapa do Santo population was related to the developmental stage of the tooth tissues sampled. We report identical results for two individuals coming from a different archeological context. Tooth enamel formed in utero and/or during the two first years of life showed higher Zn isotope ratios than enamel formed after weaning. More work is required to systematically investigate if Zn isotopes can be used as a breastfeeding tracer.
Highlights
Geochemists performing ion exchange column chromatography for Zn isotopes (66Zn/64Zn expressed as δ66Zn value) are well aware of contamination issues
While the blanks assessed during ion exchange column chromatography can detect contamination in the clean lab, these blanks cannot account for any Zn contamination occurring during tooth handling, enamel sampling or during dilutions performed prior to Zn isotope analyses
In a third test (TEST 3), we indirectly explored post hoc the contamination through nitrile and latex gloves used during the sampling of the Lapa do Santo teeth
Summary
Geochemists performing ion exchange column chromatography for Zn isotopes (66Zn/64Zn expressed as δ66Zn value) are well aware of contamination issues. While the blanks assessed during ion exchange column chromatography can detect contamination in the clean lab, these blanks cannot account for any Zn contamination occurring during tooth handling, enamel sampling or during dilutions performed prior to Zn isotope analyses. The sampling procedure should not involve any direct contact between the sampled enamel and the gloves, as the experimenter should hold the tooth by the root–if formed and/or preserved–, and use tweezers to collect the chunks of enamel. This contact may happen, especially when the experimenter is not aware of the risk of contamination or for teeth without any formed or preserved roots
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