18 Human Bones as Archaeological
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Samples Changes Due to Contamination and Diagenesis A.
El-Kammar , 1
R. G . V. Hancock , and Ralph O. 2
Allen
3
Faculty of Science, Cairo University, G i z a , Egypt Department of Chemical Engineering & Applied Chemistry, and the S L O W P O K E Reactor Facility and the Department of Chemical Engineering and Applied Science, University of Toronto, Toronto, Ontario, Canada M 5 S 1A4 Department of Chemistry, University of Virginia, Charlottesville, VA 22901 1
2
3
While the inorganic matrix of human bones can survive, it can also be contaminated by the soil in which it was buried. Instrumental neutron activation analysis and X-ray fluorescence can be used to detect levels of contamination. Microscopic studies show that voids in the inorganic matrix can be filled with new mineral deposits that have resulted from diagenesis and contamination.
H U M A N
B O N E S
B E C O M E
A R C H A E O L O G I C A L S A M P L E S
because an i n o r g a n i c
m i n e r a l phase (poorly c r y s t a l l i n e hydroxylapatite) develops i n association w i t h organic m a t e r i a l such as collagen a n d l i p i d s i n the h u m a n b o d y (I). A f t e r b u r i a l , the organic m a t e r i a l g r a d u a l l y decomposes a n d leaves b e h i n d the i n o r g a n i c m i n e r a l phase. T h e r e is a great v a r i a b i l i t y i n the rate at w h i c h the organic fraction i n b o n e decreases. T h i s v a r i a b i l i t y is especially p r o n o u n c e d i n b u r i e d b o n e . A l t h o u g h m o d e r n bones contain about 3 5 % (by weight) organic m a t e r i a l , b u r i e d bones o b t a i n e d as archaeological samples can contain a n y w h e r e b e t w e e n 0 % a n d 3 5 % organic m a t e r i a l . M a n y studies have b e e n d i r e c t e d at u n d e r s t a n d i n g the changes that occur i n the organic p o r t i o n of b u r i e d b o n e (2); h o w e v e r , the i n o r g a n i c c o m p o n e n t s o f b o n e c a n also b e affected b y b u r i a l . O n e goal o f this s t u d y was to investigate some archaeological bones to show h o w the i n o r g a n i c c o m p o n e n t s w e r e affected b y b u r i a l . T h e archaeological bones investigated 0065-2393/89/0220-0337$06.00/0 © 1989 A m e r i c a n C h e m i c a l S o c i e t y
In Archaeological Chemistry IV; Allen, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.
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CHEMISTRY
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w e r e a l l from E g y p t a n d r e p r e s e n t e d ages r a n g i n g f r o m the P r e d y n a s t i c (ca. 5500 B . P . ) to the R o m a n (ca. 2000 B . P . ) periods. Some of the samples w e r e from m u m m i e s that w e r e p r o t e c t e d f r o m d i r e c t contact w i t h soils. O t h e r bones h a d b e e n b u r i e d . A n o t h e r goal of these studies was to investigate the value of two types of analysis (instrumental n e u t r o n activation analysis a n d X - r a y fluorescence) for the r a p i d screening of b o n e samples to d e t e r m i n e t h e i r state of c o n t a m i n a t i o n . T h e i d e a that the inorganic composition of b o n e c o u l d y i e l d i n f o r m a t i o n about ancient h u m a n diet has b e e n p u r s u e d for over a decade (3, 4). T h e s e studies have s h o w n that soil c o n t a m i n a t i o n can complicate a n d e v e n i n v a l idate the i n t e r p r e t a t i o n of trace e l e m e n t data o b t a i n e d b y a n a l y z i n g archaeological bones ( 5 - 7 ) . If o n l y the surface of a b o n e s p e c i m e n w e r e c o n t a m i n a t e d b y the s o i l , t h e n i t m i g h t b e possible to clean the surfaces before analysis (5). P r o b l e m s of sample c o n t a m i n a t i o n can be o v e r c o m e b y d e t e r m i n i n g w h i c h trace e l e ments are least affected b y the soils a n d the diagenesis of the bones t h e m selves. F o r e x a m p l e , S r a n d Z n have b e e n f o u n d to b e less sensitive to soil c o n t a m i n a t i o n t h a n several other elements. T h r o u g h the studies of ancient bones, the t h e o r y has e v o l v e d that the S r concentration i n b o n e is i n v e r s e l y p r o p o r t i o n a l to the p r o t e i n o r meat intake i n the h u m a n diet. A l t h o u g h S r is generally f o u n d at l o w levels i n meat (as c o m p a r e d to plants), the Z n levels i n meat are h i g h (8). R h e i n g o l d et al. (9), u s e d this information to demonstrate that the concentration of Sr a n d Z n i n the bones of m o d e r n animals depends u p o n diet. R e s e a r c h w i t h animals fed c o n t r o l l e d diets has b e e n suggested to d e t e r m i n e w h e t h e r a series of trace elements c o u l d be u s e d to p r o v i d e a m u l t i d i m e n s i o n a l p a t t e r n analysis that w o u l d d i s c r i m i n a t e b e t w e e n different diets (10). Because o f the w e l l - r e c o g n i z e d p r o b l e m s of diagenesis a n d c o n t a m i n a t i o n , the q u e s t i o n of u s i n g trace elements to obtain i n f o r m a t i o n o n diet remains u n c e r t a i n . T h e r e have b e e n n e w proposals o n h o w to obtain a d d i tional i n f o r m a t i o n from archaeological bones. Taylor a n d coworkers (11, 12) have p r o p o s e d u s i n g C a as a means of d a t i n g bones that have b e e n b u r i e d (or p l a c e d i n caves) d e e p e n o u g h to s h i e l d t h e m from the cosmic ray b o m b a r d m e n t . T h e i n t r o d u c t i o n of " m o d e m " m a t e r i a l into ancient samples can seriously affect the accuracy of the isotopic data. To k n o w the r e l i a b i l i t y of the p r o p o s e d C a d a t i n g p r o c e d u r e , it is i m p o r t a n t to k n o w the extent to w h i c h diagenesis can i n t r o d u c e m o d e r n C a into the m i n e r a l matrix of ancient bones. F o r b u r i e d bones, m o d e r n C a c o u l d b e i n t r o d u c e d b y recrystallization of the hydroxylapatite. T h i s recrystallization involves exchange w i t h C a i n the e n v i r o n m e n t or the filling of voids (left b e h i n d as the organic components w e a t h e r away) b y n e w C a - c o n t a i n i n g minerals. These studies w e r e also d i r e c t e d at o b s e r v i n g the m e c h a n i s m for this t y p e of c o n t a m i n a t i o n or exchange w i t h one of the major components. 4 1
4 1
In Archaeological Chemistry IV; Allen, R.; Advances in Chemistry; American Chemical Society: Washington, DC, 1989.
18.
E L - K A M M A R ET AL.
Human Bones as Archaeological
Samples
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Materials and Methods M o d e r n h u m a n b o n e samples w e r e analyzed to test the i n s t r u m e n t a l n e u t r o n activation analysis ( I N A A ) a n d to h e l p establish more c o m p l e t e i n f o r m a t i o n o n the natural levels of several trace elements i n m o d e r n bones. T h e m o d e r n bones i n c l u d e d seven samples of cortical b o n e a n d 16 samples of cancellous bone (eight of w h i c h w e r e defatted). A l l samples w e r e o b t a i n e d from femoral heads. T h e data o b t a i n e d for these 23 samples a n d a further d e s c r i p t i o n of the I N A A t e c h n i q u e have b e e n r e p o r t e d elsewhere (13). F o r the p u r p o s e of c o m p a r i s o n w i t h the archaeological bone samples, this data obtained b y u s i n g the same I N A A t e c h n i q u e is s u m m a r i z e d i n this chapter. T h e archaeological bones i n c l u d e d eight samples from m u m m i e s i n the c o l l e c t i o n of the R o y a l O n t a r i o M u s e u m (Toronto, Canada). T h r e e of these samples w e r e about 3200 years o l d (from N a k h t ) , one was about 3700 years o l d (from George), a n d four w e r e from R o m a n p e r i o d m u m m i e s a n d w e r e about 4000 years o l d . F i v e samples of h u m a n bones that h a d b e e n b u r i e d i n the soil w e r e collected at archaeological sites o n the eastern side of the N i l e D e l t a at T e l - R o b a . O n e sample was a n a l y z e d from each of the f o l l o w i n g periods: the P r e d y n a s t i c p e r i o d (ca. 5500 B . P . ) , the early D y n a s t i c p e r i o d (4000-3000 B . P.), the later D y n a s t i c p e r i o d (3000-2000 B . P.), a n d the R o m a n p e r i o d (ca. 2000 B . P . ) . I n a d d i t i o n , one tooth from an early D y n a s t i c p e r i o d (ca. 4000 B.P.) grave at T e l - R o b a was also analyzed. T h e s e five samples w e r e all c l e a n e d to r e m o v e surface contamination b y a d r i l l fitted w i t h a carbo r u n d u m a b r a d i n g bit. F o r one R o m a n p e r i o d sample there was e v i d e n c e of a fire above the grave and some soil was fused to the bone. I n an earlier p a p e r (13), the I N A A p r o c e d u r e was d e s c r i b e d a n d c o m p a r e d to the c h e m i c a l analysis of b o n e b y u s i n g i n d u c t i v e l y c o u p l e d p l a s m a e m i s s i o n spectroscopy ( I C P E S ) . T h e I C P E S t e c h n i q u e r e q u i r e d dissolution of the ashed sample before analysis, b u t otherwise the techniques p r o v e d to be q u i t e comparable. I n this study, some of the samples w e r e a n a l y z e d by u s i n g X - r a y fluorescence ( X R F ) to d e t e r m i n e w h e t h e r there was adequate sensitivity for the study of contamination i n archaeological bone. F o r the I N A A p r o c e d u r e , d r i e d samples (100-600 mg) w e r e p l a c e d i n p o l y e t h y l e n e vials a n d i r r a d i a t e d for 1-3 m i n i n the S L O W P O K E Reactor at the U n i v e r s i t y of Toronto (flux of ΙΟ" η c m " s" ). T h e Ρ was m e a s u r e d w i t h the Ρ (η, α) ^ A l reaction. To measure the actual concentration of P, the same samples w e r e i r r a d i a t e d a few days later u n d e r i d e n t i c a l conditions w h i l e w r a p p e d i n c a d m i u m foil (14). T h i s step a l l o w e d for a correction i n samples for w h i c h there was significant A l contamination. A l t h o u g h the I N A A p r o c e d u r e c o u l d p r o v i d e a clear i n d i c a t i o n of soil c o n t a m i n a t i o n , the cor rections w e r e large w h e n e v e r b a d l y c o n t a m i n a t e d soils w e r e e n c o u n t e r e d . If soil c o n t a m i n a t i o n was expected, the d r i e d bone samples w e r e a n a l y z e d b y X - r a y fluorescence. T h e analysis was p e r f o r m e d w i t h a w a v e l e n g t h d i s 11
2
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p e r s i v e X - r a y spectrometer ( X R D - 7 0 0 , D i a n o C o r p o r a t i o n ) , a n d calculations w e r e c a r r i e d out w i t h a f u n d a m e n t a l parameters p r o g r a m (Corset). F o r bones that h a d b e e n b u r i e d i n contact w i t h the soil, a scanning e l e c t r o n microscope ( S E M ) (JSM-35) was u s e d to examine the samples. A K e v e x X - r a y system (Si(Li) detector a n d associated analytical programs) was u s e d to p r o v i d e semiquantitative analysis o f particles o b s e r v e d w i t h the S E M . T h i s analysis, along w i t h the crystal m o r p h o l o g y , w e r e u s e d to identify the minerals i n the b o n e samples. X - r a y d i i r a c t i o n w i t h C u - K r a d i a t i o n ( N i filter) p r o v i d e d i n f o r m a t i o n o n the minerals i n the b u l k b o n e samples. P o w d e r patterns w e r e o b t a i n e d w i t h a P h i l l i p s diffractometer. Downloaded by EAST CAROLINA UNIV on June 26, 2014 | http://pubs.acs.org Publication Date: July 1, 1989 | doi: 10.1021/ba-1988-0220.ch018
a
Results and Discussion W i t h the n e u t r o n activation p r o c e d u r e , the m e a s u r e m e n t of Ρ is r e l i a b l e o n l y w h e n there is v e r y little A l (
