University of Wisconsin–Milwaukeearchaeolab.anthro.uwm.edu/.../docs/J.Richards_SAA_2015.docx · Web viewSoil Science Society of America Journal 76(4):1436-1445. Radu, Tanja and

Using PXRF Technology to Aid in the Recovery and Analysis of Human Remains

John D. Richards, University of Wisconsin-MilwaukeeCatherine R. Jones, University of Wisconsin-Milwaukee

ABSTRACT

Excavation and analysis of human remains from the Milwaukee County Institution Grounds Cemetery (MCIG) provided an opportunity to test the effectiveness of portable X-ray fluorescence (pXRF) as both a field and laboratory tool. During the fieldwork portion of the project, excavations exposed soils that visual inspection suggested might harbor a concentration of toxic materials. PXRF was used on site to determine the nature of the potential toxins and determine the risk factor associated with continued excavation. Subsequent laboratory analysis used the pXRF analyzer in two separate instances. First, elemental composition of excavated soil samples was identified to determine background levels of soil constituents that might produce diagenetic changes in human skeletal remains. Second, the MCIG excavations recovered multiple instances of commingled human remains representing multiple individuals. This paper reports the results of a pilot study to use pXRF as an aid in identifying commingled bones from MCIG interments as belonging to specific individuals.

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Presented in Symposium " People That No One Had Use for, Had Nothing to Give to, No Place to Offer: The Milwaukee County Institution Grounds Poor Farm Cemetery", 80th Annual Meeting of the Society for American Archaeology, San Francisco, CA, April 15-19, 2015

Introduction

This paper reports a very preliminary study of the use of a portable X-ray

fluorescence (pXRF) analyzer as an aid to the excavation and analysis of human remains.

The use of handheld XRF analyzers in archaeology continues to increase as costs go

down and instrumentation improves (Liritzis and Zacharias 2011). Within the limits of

instrument design parameters, some modern handheld XRF units are now capable of

achieving results comparable to bench mounted laboratory units (Hunt and Speakman

2015). However, any number of cautionary tales exist pointing out the pitfalls of treating

these devices as the scientific equivalent of a point-and-shoot digital camera (e.g.,

Shackley 2010; Shugar and Mass 2012a, Richards 2015). As Shugar and Mass (2015b)

note the uncritical use of these instruments can easily produce bad data and spurious

interpretations. Recently, Speakman and Shackley (2013) have characterized this as “silo

science” that is neither reproducible nor comparable on an inter-laboratory basis. Lest we

be accused of building yet one more such silo, we wish to be very clear concerning the

goals of the study reported here. Specifically, the exercise was intended as a

methodological experiment to evaluate the applicability of pXRF technology within a

particular archaeological context; i.e, excavation and analysis of a late nineteenth and

early twentieth century pauper cemetery. Our goal was to generate information that

would allow us to design a comprehensive analytical protocol tailored to the specifics of

the MCIG sample. Thus, no claim is made that our results represent a useful data set

relating to the elemental composition of the artifacts or the human bone subjected to

analysis. However, we do think the results are informative regarding the potential

applicability of future, more intensive, detailed analyses of the materials presented here.

Richards and Jones-pXRF at MCIG

During the course of the MCIG project, the analyzer was used in the field to test soils

containing potentially contaminated deposits. Laboratory use included analysis of soils

and selected artifacts as well as analysis of human remains directed toward sorting out

commingled human bone.

Methods

The artifact analysis reported here used a Niton XLt analyzer utilizing factory

calibrations and operated in bulk soil mode. The instrument was controlled by a computer

and three readings of 180 second duration were recorded for each artifact. The Niton

analyzer returns elemental values in parts per million.

Soils were analyzed using a Bruker Tracer IIIv+ analyzer. The instrument was

operated at settings of 40Kv and 30 micro-amps with Bruker’s “green” beam filter” (6

mil Cu/1 mil Ti/12 mil Al) installed. Three readings of 180 seconds each were recorded

for each sample. The instrument was operated by hand in the field but was controlled by

a laptop computer in the laboratory. All soils were analyzed wet and un-processed.

Human bone was analyzed using the Bruker analyzer also. The instrument was

operated at 15Kv and 28 micro-amps under vacuum and without a filter. Three readings

of 180 seconds duration were recorded at three separate sites on each bone. Results were

exported to Microsoft Excel using Bruker’s S1PXRF and Artax software.

Soil and Artifact Analysis

A benefit of pXRF is the ability to conduct rapid field examinations of soils and

sediments as a component of field investigations. As a result, pXRF units have been used

by geologists as well as archaeologists in order to aid stratigraphic interpretation

(Colombo et al 2011), assist in site survey (Hayes 2013), provide a first approximation of

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soil composition (McLaren 2012; Zhu, Weindorf, and Zhang 2011), or as an initial test to

screen for the presence of heavy metals or toxic compounds (Radu and Diamond 2009).

During the 2013 MCIG excavations, an exposed coffin was observed associated with a

bright blue soil deposit (Fig. 1). Since blue soils do not occur naturally in southeastern

Wisconsin, excavators were reasonably concerned that they had encountered a pocket of

contaminated soil. Excavators at Dubuque’s Third Street Cemetery (Lillie and Mack

2015) also noted the presence of bluish soils but considered the coloration the result of

particular kinds of molds. However, at MCIG, the immediate area was cordoned off and

excavation of the associated burial was halted until the pXRF unit could be brought to the

site. Tests produced the spectrogram shown in the slide (Fig. 2) and the crew and

Principal Investigator breathed a sigh of relief to see that the deposit was not radioactive

or worse. However, it was clear that the deposit did contain elevated levels of arsenic so

excavators took special care removing the nearby burial (Lot# 10569).

Subsequent comparisons to adjacent soils as well as soils from other parts of the

cemetery suggests that low levels of arsenic are typical of many locations in the cemetery

but the 10569 deposit did not appear to have spread too far from its point of origin (Fig.

3). The genesis of this deposit remains unknown. It should be noted that the four soil

samples analyzed were coffin fill collected from the pelvic region of burials identified in

the field as female. Consequently, arsenic levels in these deposits may not be typical of

undisturbed cemetery soils.

Selected grave goods were analyzed in the laboratory as an aid to preliminary artifact

analysis. Items included an upper denture, a partial denture, two metal finger rings, and a

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piece of what appears to be slag. All were recovered from within excavated coffins. Only

the dentures are reported on here.

Late nineteenth century and early twentieth century dentures were manufactured from

a compound patented as Vulcanite by Charles Goodyear (Fig. 4). Basically a mixture of

natural rubber and sulfur, Vulcanite revolutionized denture production. When the

Goodyear Dental Vulcanite Company (the same firm still manufacturing tires) chose to

no longer enforce its patent, dentures became commonly available at affordable prices

(Wynbrant 2000). The MCIG specimens appear to be typical examples of vulcanite

dentures with an elemental composition including high relative levels of sulfur. Mercury

present in the dentures is likely the result of the use of vermillion to color the naturally

black vulcanite a more pleasing shade of reddish pink.

Human Remains

Previous studies have successfully tested the applicability of portable X-ray

fluorescence analysis (pXRF) on known single adult populations (Perrone et al. 2014;

Gonzalez-Rodriguez and Fowler 2013). Peronne et al. reported an analysis of 20 sets of

human remains consisting of forensic specimens recovered as in-flesh and skeletonized

surface finds as well as a single inhumation. The analysis was directed toward

determining if elemental variation was greater between individuals than within

individuals. Results suggest that little or no intra-skeletal variation was present in the

Perrone et al. sample. Peronne et al. conclude that pXRF may be a viable technique to aid

in re-associating individuals in small-scale commingling scenarios.

The Gonzalez-Rodriguez and Fowler study examined five medieval stone coffin

burials using pXRF to derive elemental ratios for 23 bones from each skeleton. The

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authors report a high success rate in correctly assigning individual bones to specific

burials. Results are suggested to support the use of the method as a screening tool prior to

confirming association by DNA analysis.

Both studies offer the hope that pXRF analysis can be used to confidently sort and re-

associated commingled human bone. However, as Peronne et al. note, neither study was

designed to consider the potential effects of diagenetic processes on inhumed remains.

This is a potentially confounding issue as post-mortem diagenetic changes in elemental

concentrations can be profound (e.g. Price et al. 1992). In the case of the MCIG

Cemetery we suspect that significant diagenetic alteration of bone may have occurred as

a result of ground water infiltration, deposition of industrial and medical wastes,

compaction of overlying sediments, and episodic inundation and desiccation due to

changes in the local water table. Consequently, the present study was intended to

determine if a pXRF analysis of human bone would be an effective aid to the sorting of

commingled human bone in the diagenetically complex environment of the MCIG

Cemetery.

Data Set

The analysis was conducted on 15 skeletal lots from the 2013 excavations at the

cemetery (fig. 5). Burials included are unidentified and undated so may span the entire

period of cemetery use from 1882 to 1925. As noted in earlier presentations, a burial

register was kept for the cemetery but no map keyed to ledger entries has yet been found.

In addition, removal of grave tags, incomplete record keeping, episodic disturbances and

consequent reburial preclude association of burial locations with individuals listed in the

burial register. Biological analysis was conducted for all remains to allow estimation of

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an age range and sex in accordance with established methods (Buikstra and Ubelaker

1994; Spradley and Jantz 2011; White et al. 2012).

Sample Selection

During the 2013 excavations, portions of the cemetery were highly saturated with

ground water. As noted, this can have a significant diagenetic affect on human bone, so

lots were chosen that appeared to be relatively dry at the time of excavation. However,

excavations revealed also that the portion of the cemetery excavated in 2013 harbors a

perched water table and it is likely that fluctuating water levels may have inundated all

burials at one or more points in time.

Three control lots and five commingled burials consisting of adult and subadult

remains were chosen for analysis. Control lot 10293 represents a middle adult probable

male and lot 10737 consists of a middle adult female adult interment (Fig. 6). Both

burials were relatively complete and were recovered from dry sediments. These lots are

typical of the majority of burials recovered during the 2013 excavations at the site. The

third control lot consisted of a human skeleton previously purchased from a biological

supply house as a teaching aid. The five commingled sets of human remains include

mixed interments with established MNIs of between 2-6 individuals. These lots likely

result from the disposal of medical cadavers, and were selected for varying complexity of

commingling and potential for positive re-association.

The commingled burials of Lots 10097/10137 and Lots 10707/10881represent the

simpler commingled burials recovered from the site. These burials involved the interment

of one or two individuals whose skeletons remained discrete enough in situ to be quickly

and confidently re-associated in the field. These field associations were confirmed by

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laboratory analysis. While separated by analysts into individual skeletons, the remains

shared a diagenic environment that may have tended to obscure individual elemental

signatures. Lots 10097/10137 include a middle adult male west-east interment clearly

delineated from a second middle adult male east-west interment. Lots 10707 and 10881

consist of a young adult probable male extended interment pushed to the side of the

coffin to make space for a disarticulated juvenile adolescent and other miscellaneous

commingled bone.

The commingled burials of Lots 10342/10429/11021, Lots 10525/11052, and Lots

10669/11042/11043 represent the more complex commingled burials present at

the site (Fig. 8). These burials involved the interment of multiple individuals as

well as disassociated disarticulated bone and medical waste. Laboratory analysis

of the commingled lots separated some articulated bones into analytical units

termed Element Sets (ES). Lots 10342, 10429, and 11021 include two disparate

middle adult male torsos and two right leg inclusions. Lot 10525 consists of

disarticulated skeletal sections that could be matched to two included rib cages.

Lots 11042, and 11043 represent a middle adult male and juvenile adolescent

heavily mixed with commingled bone and medical waste and disturbed by

installation of a water pipe.

Of particular interest are two sets of subadult remains included in the commingled

lots chosen for analysis. Lot 10881 contains a full adolescent skeleton with missing

cranium and arms, while Lot 11042 contains a compatibly aged set of adolescent arms. If

these lots can be positively re-associated, it would indicate that bones from one individual

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were interred in multiple locations throughout the site. This would have significant

impact on future research with the commingled remains from the 2013 excavation.

Methods

Bones evaluated in the study include cranial, scapula, humerus, ulna, innominate,

femur, and tibia elements. Prior to analysis each bone was cleaned with water and air-

dried. This was followed by a second cleaning with 100% denatured alcohol. Each bone

was scanned at three sites for 180 seconds apiece and results averaged to produce the

final data set. Readings were analyzed as raw net intensity values and were not calibrated

to Bruker’s mudstone standard. Thus, results do not represent elemental concentrations in

parts per million. Net intensity values were averaged and subjected to principal

components analysis using the software package XLSTAT.

Results

The analyzer returned useful values on 14 elements including arsenic, calcium, copper,

iron, magnesium, manganese, nickel, phosphorus, rubidium, tin, strontium, zinc, and

zirconium. This resulted in a data set of 485 readings. Following removal of missing data,

reading sets were averaged to produce a final data set of 71 readings.

Control Lots

The two MCIG control lots appear to separate from one another (Fig.9). Lot 293 clusters

more closely but this may be an artifact of a greater number of data points. When the

reference skeleton is added to the analysis, there is a clear separation between the

reference skeleton data points and the MCIG samples (Fig 10). However, the MCIG

samples no longer separate out from one another but instead form two mixed clusters.

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This suggests that the influence of diagenesis increases as the number of data sets

increases.

Complete Data Set

When all MCIG samples are included in the analysis the only data set easily

distinguished from the main point cloud is the reference skeleton (Fig 11). Note that Lot

10293 continues to form a discrete set of data points although these are not clearly

separated from adjacent data points.

Lot 10881 and Lot 11042

The two subadult skeletal assemblages (Fig. 12) do not appear to group together although

they do form relatively discrete clusters. When evaluated against the entire data set (Fig.

13), including Lot 10707, recovered from the same coffin that harbored Lot 10881,

overlap decreases markedly suggesting that these remains represent two individuals.

Commingled Lots

Data points representing commingled Lots 10525 and 11052 (Fig. 14) are widely

distributed and do not appear to sort out from one another or from the main point cloud.

This appears to be true also for commingled Lots 10666, 11042, and 11043. Lots 10342,

10429, and 11021 cluster tightly and exhibit considerable overlap making confident re-

association difficult.

Elemental Ratios

Ratios calculated for this study included Sr/Ca and Zn/Fe. Lead was in low frequency in

all samples so a Pb/Ca ration was not calculated. When PCA scores for Lot 10293, Lot

10737, and the reference skeleton are plotted (Fig. 17), all three samples do seem to sort.

Curiously, the reference skeleton is less tightly clustered by this procedure. A biplot of

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the averaged PCA scores for the same ratios continues to distinguish the reference

skeleton as well as Lot 11052 but the remaining lots are more closely clustered (Fig. 18).

Conclusions

The very preliminary assessment presented here suggests that it is possible to distinguish

individual bone sets in the MCIG sample using pXRF. As in previous studies, intra-

skeletal variation does not appear to be a significant factor. Not surprisingly, the clearest

distinction is between the reference skeleton used as a control and the MCIG burials. This

is likely due to a lack of diagenetic effects on the control skeleton and/or its different

recovery context. This highlights the difficulty of deriving confident re-associations of

commingled remains in diagenetically complex environments. We are guardedly

optimistic that it may be possible to sort commingled remains in the MCIG sample by a

combination of pXRF and careful archaeological and osteological analysis. However, our

pilot study has taught us several important lessons. First, if low energy elements are

targeted under vacuum, the need to eliminate or minimize any air gap between the

analyzer lens and the surface of the analyzed bone may preclude analysis of small or

irregularly shaped elements thus reducing the potential pool of possible re-associations.

Second, confident re-associations using this method will require collection of a much

larger set of elemental readings per bone per commingled assemblage. Third, any future

study of the MCIG human remains must also target a more comprehensive suite of

elements with results calibrated to a specific reference standard. Finally, at a minimum of

30 minutes per analyzed bone, collection of a truly representative data set may take a

very long time indeed.

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References Cited

Buikstra, Jane E., and Douglas H. Ubelaker1994 Standards for Data Collection from Human Skeletal Remains. Ed. Jane Buikstra and Douglas Ubelaker. Arkansas Archaeological Survey.

Colombo, C, S Bracci, C Conti, M Greco and M Realini2011 Non‐invasive approach in the study of polychrome terracotta sculptures: employment of the portable XRF to investigate complex stratigraphy. X‐Ray Spectrometry 40(4):273-279.

Gonzalez-Rodriguez, J., and G. Fowler2013 A study on the discrimination of human skeletons using X-ray fluorescence and chemometric tools in chemical anthropology. Forensic Science International 231(1-3): 407.e1–407.e6.

Hayes, Katherine2013 Parameters in the use of pXRF for archaeological site prospection: a case study at the Reaume Fort Site, Central Minnesota. Journal of Archaeological Science 40(8):3193-3211.

Hunt, Alice MW and Robert J Speakman2015 Portable XRF analysis of archaeological sediments and ceramics. Journal of Archaeological Science 53:626-638.

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Twenty-First Century City. University of Iowa Press.

Perrone, Alexandra, Janet E. Finlayson, Eric J. Bartelink, and Kevin Dennis Dalton2014 Application of Portable X-ray Fluorescence (XRF) for Sorting Commingled Human Remains. In Commingled Human Remains, edited by Bradley J. Adams and John E. Byrd, pp. 145–165. Academic Press, Amsterdam.

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McLaren, Timothy I, Christopher N Guppy, Matthew K Tighe, Nicola Forster, Peter Grave, Leanne M Lisle and John W Bennett2012 Rapid, nondestructive total elemental analysis of vertisol soils using portable X-ray fluorescence. Soil Science Society of America Journal 76(4):1436-1445.

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Radu, Tanja and Dermot Diamond2009 Comparison of soil pollution concentrations determined using AAS and portable XRF techniques. Journal of Hazardous Materials 171(1):1168-1171.

Richards, John D.2015 Online Review: Handheld XRF for Art and Archaeology. American Journal of Archaeology 119.1.

Shackley, M Steven2010 Is there reliability and validity in portable X-ray fluorescence spectrometry (PXRF). The SAA Archaeological Record 10(5):17-20.

Shugar, A.N. and J.L. Mass, editors2012a Handheld Xrf for Art and Archaeology. Leuven University Press.

Shugar, A.N. and J.L. Mass2012b Introduction. In Handheld Xrf for Art and Archaeology, edited by A. N. Shugar and J. L. Mass, pp. 17-36. Leuven University Press.

Speakman, Robert J and M Steven Shackley2013 Silo science and portable XRF in archaeology: a response to Frahm. Journal of Archaeological Science 40(2):1435-1443.

Spradley, M. Katherine, and Richard L. Jantz2011 Sex estimation in forensic anthropology: Skull versus postcranial elements. Journal of Forensic Sciences 56(2): 289–296.

White, Tim D., Michael T. Black, and Pieter A. Folkens2012 Human Osteology. 3rd ed. Academic Press, Amsterdam.

Wynbrant, James2000 The Excruciating History of Dentistry: Toothsome Tales and Oral Oddities from Babylon to Braces. St. Martin’s Press, New York.

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Fig# Slide#

1 2 Analyzing contaminated soils on site2 3 Contaminated soil spectrogram3 4 MCIG soils compared4 5 Vulcanite dentures5 6 Skeletal assemblages analyzed in study6 7 Lots 10293 and 10737 in situ7 8 Lots 10097 and 10137; 10707 and 10881 in situ8 9 Lots 10669/11042/11043; Lots 10525/11052; and Lots

10342/10429/11021 in situ9 10 PCA of 10293 and 10737 control samples10 11 PCA of all control samples11 12 PCA of all data points12 13 PCA of Lots 10881 and 1104213 14 PCA of Lots 10881, 11042, and 1070714 15 PCA of Lots 10525 and 11051515 16 PCA of Lots 10666, 11042, and 1104316 17 PCA of Lots 10342, 10429, and 1102117 18 PCA of elemental ratios Sr/Ca and Zn/FE for control lots18 19 PCA of averaged elemental ratios Sr/Ca and Zn/FE for all lots

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Documents

University of Wisconsin–Milwaukeearchaeolab.anthro.uwm.edu/.../docs/J.Richards_SAA_2015.docx · Web viewSoil Science Society of America Journal 76(4):1436-1445. Radu, Tanja and