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

Isotopic evidence of high reliance on plant food among Later Stone Age hunter-gatherers at Taforalt, Morocco

The transition from hunting-gathering to agriculture stands as one of the most important dietary revolutions in human history. Yet, due to a scarcity of well-preserved human remains from Pleistocene sites, little is known about the dietary practices of pre-agricultural human groups. Here we present the isotopic evidence of pronounced plant reliance among Late Stone Age hunter-gatherers from North Africa (15,000-13,000 cal BP), predating the advent of agriculture by several millennia. Employing a comprehensive multi-isotopic approach, we conducted zinc (δ66Zn) and strontium (87Sr/86Sr) analysis on dental enamel, bulk carbon (δ13C) and nitrogen (δ15N) and sulfur (δ34S) isotope analysis on dentin and bone collagen, and single amino acid analysis on human and faunal remains from Taforalt (Morocco). Our results unequivocally demonstrate a substantial plant-based component in the diets of these hunter-gatherers. This distinct dietary pattern challenges the prevailing notion of high reliance on animal proteins among pre-agricultural human groups. It also raises intriguing questions surrounding the absence of agricultural development in North Africa during the early Holocene. This study underscores the importance of investigating dietary practices during the transition to agriculture and provides insights into the complexities of human subsistence strategies across different regions.

The Distribution and Biogenic Origins of Zinc in the Mineralised Tooth Tissues of Modern and Fossil Hominoids: Implications for Life History, Diet and Taphonomy

Zinc is incorporated into enamel, dentine and cementum during tooth growth. This work aimed to distinguish between the processes underlying Zn incorporation and Zn distribution. These include different mineralisation processes, the physiological events around birth, Zn ingestion with diet, exposure to the oral environment during life and diagenetic changes to fossil teeth post-mortem. Synchrotron X-ray Fluorescence (SXRF) was used to map zinc distribution across longitudinal polished ground sections of both deciduous and permanent modern human, great ape and fossil hominoid teeth. Higher resolution fluorescence intensity maps were used to image Zn in surface enamel, secondary dentine and cementum, and at the neonatal line (NNL) and enamel-dentine-junction (EDJ) in deciduous teeth. Secondary dentine was consistently Zn-rich, but the highest concentrations of Zn (range 197-1743 ppm) were found in cuspal, mid-lateral and cervical surface enamel and were similar in unerupted teeth never exposed to the oral environment. Zinc was identified at the NNL and EDJ in both modern and fossil deciduous teeth. In fossil specimens, diagenetic changes were identified in various trace element distributions but only demineralisation appeared to markedly alter Zn distribution. Zinc appears to be tenacious and stable in fossil tooth tissues, especially in enamel, over millions of years.

Shark teeth zinc isotope values document intrapopulation foraging differences related to ontogeny and sex

Trophic ecology and resource use are challenging to discern in migratory marine species, including sharks. However, effective management and conservation strategies depend on understanding these life history details. Here we investigate whether dental enameloid zinc isotope (δ⁶⁶Zn_en) values can be used to infer intrapopulation differences in foraging ecology by comparing δ⁶⁶Zn_en with same-tooth collagen carbon and nitrogen (δ¹³C_coll, δ¹⁵N_coll) values from critically endangered sand tiger sharks (Carcharias taurus) from Delaware Bay (USA). We document ontogeny and sex-related isotopic differences indicating distinct diet and habitat use at the time of tooth formation. Adult females have the most distinct isotopic niche, likely feeding on higher trophic level prey in a distinct habitat. This multi-proxy approach characterises an animal's isotopic niche in greater detail than traditional isotope analysis alone and shows that δ⁶⁶Zn_en analysis can highlight intrapopulation dietary variability thereby informing conservation management and, due to good δ⁶⁶Zn_en fossil tooth preservation, palaeoecological reconstructions.

A Neandertal dietary conundrum: Insights provided by tooth enamel Zn isotopes from Gabasa, Spain

The characterization of Neandertals' diets has mostly relied on nitrogen isotope analyses of bone and tooth collagen. However, few nitrogen isotope data have been recovered from bones or teeth from Iberia due to poor collagen preservation at Paleolithic sites in the region. Zinc isotopes have been shown to be a reliable method for reconstructing trophic levels in the absence of organic matter preservation. Here, we present the results of zinc (Zn), strontium (Sr), carbon (C), and oxygen (O) isotope and trace element ratio analysis measured in dental enamel on a Pleistocene food web in Gabasa, Spain, to characterize the diet and ecology of a Middle Paleolithic Neandertal individual. Based on the extremely low δ⁶⁶Zn value observed in the Neandertal's tooth enamel, our results support the interpretation of Neandertals as carnivores as already suggested by δ¹⁵N isotope values of specimens from other regions. Further work could help identify if such isotopic peculiarities (lowest δ⁶⁶Zn and highest δ¹⁵N of the food web) are due to a metabolic and/or dietary specificity of the Neandertals.

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

Diet is a crucial trait of an animal's lifestyle and ecology. The trophic level of an organism indicates its functional position within an ecosystem and holds significance for its ecology and evolution. Here, we demonstrate the use of zinc isotopes (δ⁶⁶Zn) to geochemically assess the trophic level in diverse extant and extinct sharks, including the Neogene megatooth shark (Otodus megalodon) and the great white shark (Carcharodon carcharias). We reveal that dietary δ⁶⁶Zn signatures are preserved in fossil shark tooth enameloid over deep geologic time and are robust recorders of each species' trophic level. We observe significant δ⁶⁶Zn differences among the Otodus and Carcharodon populations implying dietary shifts throughout the Neogene in both genera. Notably, Early Pliocene sympatric C. carcharias and O. megalodon appear to have occupied a similar mean trophic level, a finding that may hold clues to the extinction of the gigantic Neogene megatooth shark.

Longitudinal isotope ratio variations in human hair and nails

Due to the straightforward and non-invasive sampling, ease of transport and long-term storage and access to time-resolved information, determination of element concentrations and isotope ratios in hair and nails finds increasing use. Multi-isotopic information preserved in keratinous tissues allows one to reveal dietary, physiological and environmental influences, but progress in this area is still limited by complicated and time-consuming analytical procedures and challenges in accuracy assessment. In this study, longitudinal distributions of δ³⁴S, ⁸⁷Sr/⁸⁶Sr, ^207,208Pb/²⁰⁶Pb, δ⁶⁶Zn, δ⁵⁶Fe, δ⁶⁵Cu, δ²⁶Mg, and δ¹¹⁴Cd were obtained for hair and nails collected from nine subjects with different age, biological sex, diet and/or place of residence. For S and Zn, the distribution along hair strands revealed a trend towards a heavier isotopic signature from the proximal to the distal end, with a maximum difference within the hair of a single subject of 1.2‰ (Δ³⁴S) and 0.4‰ (Δ⁶⁶Zn). For Fe, Cu, Mg and Cd, a shift towards either a lighter (Cu) or heavier (Fe, Mg and Cd) isotopic composition is accompanied by increasing concentration towards the distal hair end, indicating possible isotope fractionation during deposition or external contamination with a different isotopic composition. Pb and Sr isotope ratios are relatively stable throughout the hair strands despite notable concentration increases towards the distal end, likely reflecting external contamination. The isotopic composition of Sr points to tap water as a probable main source, explaining the relative stability of the ratio for individuals from the same geographical location. For Pb, isotopic compositions suggest tap water and/or indoor dust as possible sources. Similar δ³⁴S, ⁸⁷Sr/⁸⁶Sr, ^207,208Pb/²⁰⁶Pb, δ⁶⁶Zn, δ⁵⁶Fe, and δ⁶⁵Cu observed for hair, fingernails and toenails sampled from the same individual suggest that keratinous tissues are conservative receivers of internal and external inputs and can be used complementary. Seasonal variation in δ³⁴S, ^207,208Pb/²⁰⁶Pb, and δ⁶⁵Cu was observed for fingernails.

Preanalytical errors on zinc concentrations caused by single-use gloves

Preanalytical errors causing specimen contamination with zinc (Zn) are disastrous for routine medical diagnostics or scientific studies. The aim of the study presented here is to simulate contamination possibilities when using single-use gloves. The ability to release Zn into the specimen was tested using nitril (A), vinyl (B) and latex (C) gloves with 15 (14) replications. In our first approach, a 1 × 1 cm piece of the glove's fingertip was incubated for 10 min with serum. Our second approach imitated a very short contact of serum to the glove's material by letting serum run over the glove from a pipette for 3 cm distance into a tube. The effect of gloves' contact to liver tissue was examined using glove C only: a block of liver tissue was touched once at one side producing an experimental fingerprint. Zn was analyzed in serum and liver wet weight (ww) using ICP-MS; the basal serum/liver Zn concentration was set as zero for calculation. The calculated addition of Zn is given as median (p25 - p75). The first approach led to distinct contamination with Zn (in μg/L) being evident from all three types of gloves, but depended markedly from the type of material: A: 176.5 (129.7-204); B: 975.1 (663.6-1164.3); C: 2112 (1685-2516). Imitating a very short contact of serum to the glove's surface resulted in an additional Zn concentration of 105.7 (70.4-168.8), 56.2 (-13.5-121.4) and 955.7 (746-1159) μg/L using gloves A, B and C, respectively. A single fingerprint on liver tissue using glove C resulted an addition of 3995 (861-6435) μg Zn/kg liver ww. The data underline that the dimension of preanalytical contamination of blood and tissue samples for Zn analysis via single-use gloves is relevant for routine diagnostics and scientific studies. Critical steps and possibilities to minimize these effects should be considered seriously for specimen handling in routine laboratory diagnostics as well as in scientific studies to avoid preanalytical errors and, finally, misinterpretation of the data.

Trophic ecology of a Late Pleistocene early modern human from tropical Southeast Asia inferred from zinc isotopes

Tam Pà Ling, a cave site in northeastern Laos, has yielded the earliest skeletal evidence of Homo sapiens in mainland Southeast Asia. The reliance of Pleistocene humans in rainforest settings on plant or animal resources is still largely unstudied, mainly due to poor collagen preservation in fossils from tropical environments precluding stable nitrogen isotope analysis, the classical trophic level proxy. However, isotopic ratios of zinc (Zn) in bioapatite constitute a promising proxy to infer trophic and dietary information from fossil vertebrates, even under adverse tropical taphonomic conditions. Here, we analyzed the zinc isotope composition (⁶⁶Zn/⁶⁴Zn expressed as δ⁶⁶Zn value) in the enamel of two teeth of the Late Pleistocene (63-46 ka) H. sapiens individual (TPL1) from Tam Pà Ling, as well as 76 mammal teeth from the same site and the nearby Nam Lot cave. The human individual exhibits relatively low enamel δ⁶⁶Zn values (+0.24‰) consistent with an omnivorous diet, suggesting a dietary reliance on both plant and animal matter. These findings offer direct evidence of the broad utilization of resources from tropical rainforests by one of the earliest known anatomically modern humans in Southeast Asia.

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

In marine ecology, dietary interpretations of faunal assemblages often rely on nitrogen isotopes as the main or only applicable trophic level tracer. We investigate the geographic variability and trophic level isotopic discrimination factors of bone zinc ⁶⁶Zn/⁶⁴Zn ratios (δ⁶⁶Zn value) and compared it to collagen nitrogen and carbon stable isotope (δ¹⁵N and δ¹³C) values. Focusing on ringed seals (Pusa hispida) and polar bears (Ursus maritimus) from multiple Arctic archaeological sites, we investigate trophic interactions between predator and prey over a broad geographic area. All proxies show variability among sites, influenced by the regional food web baselines. However, δ⁶⁶Zn shows a significantly higher homogeneity among different sites. We observe a clear trophic spacing for δ¹⁵N and δ⁶⁶Zn values in all locations, yet δ⁶⁶Zn analysis allows a more direct dietary comparability between spatially and temporally distinct locations than what is possible by δ¹⁵N and δ¹³C analysis alone. When combining all three proxies, a more detailed and refined dietary analysis is possible.