Zinc isotope variations in archeological human teeth (Lapa do Santo, Brazil) reveal dietary transitions in childhood and no contamination from gloves

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.

Zinc isotopes from archaeological bones provide reliable trophic level information for marine mammals

“…Most non-diet related factors, such as sex and age of an animal, have so far shown no effect on the isotope values and relative isotopic variability in body tissues 23 , 24 . Provenance, on the other hand, appears to affect the Zn isotope compositions of terrestrial vertebrates, though it remains unclear to what extent 13 , 16 , 25 . Provenance is known to play an important role for bulk δ 15 N and δ 13 C studies in marine food webs 26 but has until now not been studied for δ 66 Zn.…”

Trophic position of Otodus megalodon and great white sharks through time revealed by zinc isotopes

“…Samples were typically measured at least twice with mean analytical repeatability of <0.02‰ (2 SD, n = 235). Reference material NIST SRM 1400 was prepared and analysed alongside the samples and had δ 66 Zn values (+0.92 ± 0.03‰, n = 28) as reported elsewhere 13 , 54 demonstrating complete Zn elution during column chromatography. Reference materials and samples show a typical Zn mass-dependent isotopic fractionation, i.e., the absence of isobaric interferences, as the δ 66 Zn vs. δ 67 Zn and δ 66 Zn vs. δ 68 Zn values fall onto lines with slopes close to the theoretic mass fractionation values of 1.5 and 2, respectively (Supplementary Data 1 ).…”

Combining collagen extraction with mineral Zn isotope analyses from a single sample for robust palaeoecological investigations

“…The same steps were then repeated with additional HCl precleaning of the glass beakers and tubes and personnel wearing vinyl gloves rather than nitrile gloves, as commonly used in our laboratory. Such practice is a crucial consideration as vinyl gloves have been shown to have a lower Zn contamination potential than nitrile gloves (Jaouen et al 2020). Hydrochloric acid glass cleaning steps involved filling beakers and tubes with 2 M highpurity HCl for 24 h and subsequently rinsing them with ultrapure water to remove any Zn.…”

“…All samples were measured at least twice with a mean sample reproducibility of ± 0.01‰ (2 SD). NIST SRM 1400 was analysed alongside the samples with δ 66 Zn values, as reported elsewhere (Jaouen et al, 2016b(Jaouen et al, , 2020Bourgon et al 2020;McCormack et al 2021). SRM reference material and samples show a normal Zn mass-dependent isotope fractionation, i.e.…”