Several methods were used to assess the samples including pXRF, stable isotopes from bone collagen as well as hydroxyapatite from bone and tooth enamel. Applicable to the majority of the samples analyzed was a non-destructive process by which the crania of both collections were analyzed using a Bruker Tracer III-SD portable energy dispersive X-ray fluorescence (pXRF) spectrometer. Trace elements of interest in this study are those which replicate calcium, as described previously in Chapter 4. The primary advantage of pXRF is its non-destructive elemental identification. While this in itself provides an effective geochemical survey (Pessanha et al. 2009), for the purpose of this study the results obtained through pXRF analysis were compared to results from collagen and bone apatite analysis from 23 of the 38 human osteological samples that presented viable results from the Kroeber collection; additionally, 56 samples of tooth enamel apatite are also included, 12 of which are affiliated with viable bone samples. While stable isotope analysis was first used in a human dietary study by Vogel and van der Merwe (1977; van der Merwe 1982), pXRF and the earlier stationary XRF spectrometer surveys of human remains in dietary studies is relatively new. Parker and Toots (1970) examined human bone using an electron microprobe. From their experiment they deduced that strontium in fossil bone was indicative of the salinity of water that either the marine or terrestrial animal had
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been exposed to in life (Parker & Toots 1970:930). Schoeninger (1979) had used elemental analysis in a dietary study in Chalcatzingo, Mexico; atomic absorption spectrometry was used to analyze chemically treated and pulverized remains. From this study Schoeninger (1979:306) determined that there was a differentiation in diet based on status during the Formative Period and that individuals interred with jade offerings had the lowest strontium levels, interpreted to have had the highest consumption of meats. Sillen and Kavanagh (1982) mention X-ray spectrometry twice in their review of the literature related to strontium and its relation to paleodietary studies; neither instance involved human sampling. Kyle (1986) incorporated a combination of X-ray diffraction spectrometry and X-ray fluorescence (XRF) spectrometry to analyze the bones of a small sampling (n=47) of individuals who lived in Papua New Guinea between AD 1000 and 1700. Samples were cleaned, pulverized, and then dried; next they went through a two-stage series of chemical processing before they were fused at 1000°centigrade in a platinum crucible (Kyle 1986:404). Samples were then analyzed using XRF spectrometry. The results suggested that seafood was a primary component of this island diet, but that diagenesis as well as contamination from clay soils around archaeological remains needed to be considered in any future analysis of this type (Kyle 1986). Sillen (1992) again demonstrated an interest in strontium (Sr) and calcium (Ca) relation, this time in a specimen of Australopithecus robustus; however, he started with a combination of repetitive chemical treatments of cortical bone. Furnace and flame atomic absorption spectrometry was then used to measure the Sr and Ca in the chemically-reduced supernatant and Sillen (1992) determined that A. robustus was likely an omnivore based on the Sr and Ca signatures of the bone. Pate and Hutton (1988) used X-ray fluorescence spectrometry to determine total elemental composition of soil samples from archaeologically-rich sites near the Murray River in Australia, still not delving into use on the
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human remains. Such is an overview of the early history of the exploration for trace elements in human bone.
In a study comparing pXRF spectrometry results to those of stationary XRF spectrometers, Pessanha et al. (2009) determined that equivalent conclusions were reached for nearly all of the elements in their sample. The only trace element which demonstrated compromised results using the pXRF equipment as compared to stationary XRF in their study was the element lead (Pb) (Pessanha et al. 2009). In northwestern Peru, lead ore is found associated with other metal ores such as copper (Cu) and silver (Ag) (Patterson 1971). Copper, silver, and gold artifacts are present, to some extent, in each of the cultures considered in this study. While hammered gold appears as early as 600 BC, tools of hammered native copper appear first around 400 BC (Engel 1966; Patterson 1971). By AD 200, smelted copper appeared in Moche artifacts (Patterson 1971). There is one cranium in the Smithsonian collection included in this study that revealed a band mark across the forehead that may have resulted from copper leaching from a head ornament. Several other individuals appear to have had copper discs placed in their mouths, indicated from discoloration associated with such a cultural practice. Reuer et al. (2012) explained that the development of the railroad in 1893, leading to increased activity in regional mining and the resultant smelting processes, has caused the lead, arsenic, and cadmium contaminations that pose a substantial health risk today in the mountains east of the capital, Lima, but this should be of no consequence to any of the areas under study. The possibility of diminished results for Pb is also noted in the discussion which follows the statistical interpretations of the data.
The Bruker Tracer III-SD handheld elemental analyzer was setup first in the research lab of Christopher Philipp, a Collections Manager in the Department of Anthropology at The Field
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Museum of Natural History in Chicago. Philipp worked with me in conjunction with P. Ryan Williams, Associate Curator and Section Head of the Integrative Research Center of The Field Museum. It was Williams who worked to facilitate the approval for both this trip and a prior trip seven months earlier when sampling for stable isotope testing was done. Using a tripod, the pXRF was positioned so samples were processed by X-ray fluorescence exposure while safely cradled in bases of either foam or fabric, depending upon the state of preservation of each object. A two-minute exposure of each cranium was replicated in at least two areas from each; if results from the two varied greatly, a third exposure was performed on another area of the cranium.
Since interest was the trace element composition, the tube settings used were high volt: 178; filament: 209; HV Adc: 40; filament Adc: 11. The pulse length was set for 200 and the pulse period was set at 254. All other settings were retained during the regular downtimes of changing batteries or leaving for the night. Using the original numbers assigned to each sample from its home institute, the sample numbers were typed into the system using the Bruker AXS analytical software before each individual exposure.
Timing was set for two minutes, and while one sample was processing I began the staging of the next sample, setting it up for photography and recording of any osteological information such as sex or cranial vault modification which had not been included in the dataset that I had been provided. The Field Museum portion of the sample includes 52 males, four of which did not provide skulls for the trace element analysis, 33 females, and 30 undetermined juveniles and subadults. Age groups for the Kroeber collection are broken down to juveniles (3- 10 years), subadults (11-19 years), young adults (20-34 years), mature adults (35-49 years), and old adults (50+ years).
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Figure 6.1 Drawer of skulls from The Field Museum collection
Figure 6.2 Bruker Tracer III pXRF attached to laptop
After two and one-half days of testing samples at The Field Museum, I drove to the Smithsonian Museum Support Center in Suitland, Maryland, where this same process was performed on 98 crania made available to me by David Hunt, Forensic Anthropologist and Collections Manager in the Department of Anthropology for the Smithsonian National Museum
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of Natural History. I had made prior trips to both the museum in Washington, D. C. and the Museum Support Center in Suitland, meeting with Hunt on several occasions. While I had his support for proceeding with stable isotope sampling on a portion of the museum’s vast Peruvian collection, approval for destructive analysis was never granted by the committee overseeing such applications. Since pXRF analysis does not involve any destruction of the sample, approval for this sampling was by David Hunt himself, without need of going before a committee.
Figure 6.3 Several Smithsonian samples photographed and awaiting pXRF
In two long days I processed 98 samples of the collection. This portion of the sample includes 48 males, 47 females including one subadult, one adult of undetermined sex, and two juveniles, sex undetermined. Age determinations for this collection were also less robust so only juveniles (3-10 years), subadults (11-19 years), and young adults (20+ years) represent the approximations from notations. An in-depth forensic study of the entire Peruvian cranial collection is needed in order to ascertain age approximations beyond the simple juvenile, adolescent, and adult categories that these remains are relegated to currently.
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Figure 6.4 Skulls representing variety of sex and age variables
Once back at the Laboratory for Archaeological Science at the University of South Florida, each of the samples was assigned a USF number. Both the original museum numbers and the corresponding USF numbers were entered into an Excel spreadsheet and the data produced by the Bruker AXS analytical software was populated into the appropriate cells of the pXRF spreadsheet. These data build the primary case for interpreting diet for these specific individuals in the four specific coastal Peruvian habitats during the temporal realms known as the Early Intermediate Period and the Middle Horizon. Categories of variables were then added to the database for valley, cemetery, age, and sex of the samples.