Source: DOE/Lawrence
Berkeley National Laboratory
Summary: Experiments
are casting a new light on Egyptian soil and ancient mummified bone samples
that could provide a richer understanding of daily life and environmental
conditions thousands of years ago.
In a two-monthslong research effort that concluded in late
August, two researchers from Cairo University in Egypt brought 32 bone samples
and two soil samples to study using X-ray and infrared light-based techniques
at Berkeley Lab's Advanced Light Source (ALS). The ALS produces various
wavelengths of bright light that can be used to explore the microscopic
chemistry, structure, and other properties of samples.
Their visit was made possible by LAAAMP -- the Light sources for
Africa, the Americas, Asia and Middle East Project -- a grant-supported program
that is intended to foster greater international scientific opportunity and
collaboration for scientists working in that region of the globe.
Samples represent four dynasties, two burial sites
The samples included bone fragments of mummified human remains
that date back 2,000 to 4,000 years, and soil collected from the sites of the
human remains. The remains represent four different dynasties in Egypt: the
Middle Kingdom, Second Intermediate Period, Late Period, and Greco-Roman.
The visiting scientists, Cairo University Associate Professor
Ahmed Elnewishy and postdoctoral researcher Mohamed Kasem, wanted to
distinguish whether chemical concentrations in the bone samples were related to
the individuals' health, diet, and daily lives, or whether the chemicals in the
soil had changed the bones' chemistry over time.
Their work is important for Egypt's cultural heritage and also
for a better understanding of antiquities preservation and the potential
pathways for contamination of these remains. The samples were recovered from
two Egyptian sites -- Saqqara, the site of an ancient burial ground; and Aswan,
the site of an ancient city on the bank of the Nile once known as Swenett -- by
Cairo University archaeologists.
"The bones are acting like an archive," said Kasem,
who has studied ancient bone chemistry since his Ph.D. studies, dating back to
2011. He has used a chemical-analysis technique involving laser ablation, in
which a short laser pulse blasts away a small volume of material from a sample.
Then, emitted light from this little blast is analyzed to determine what elements
are present.
"We have found lead, aluminum, and other elements that give
us an indication of the environment and the toxicity of that time," he
said. "That information is stored right in the bones."
Differentiating soil vs. bone chemistry
What's tricky is to sort out how the elements got in the bone.
"There might be some diffusion of elements from outside to inside the
bones, and effects from bacteria, humidity, and other effects. It is difficult
to separate this -- to know if it is coming from the surrounding soil. So we've
been trying different techniques."
Kasem added, "So many factors affect the preservation. One
of them is how long the bone has been buried in soil and also the state of the
bone and the different types of soil." Differences in embalming techniques
could also affect the preservation of the bone and the chemistry they find in
the X-ray studies. "There are different qualities in the materials, like
the cloth and the resins they used to embalm," he said.
While the ancient Egyptians didn't use aluminum in
metal-working, researchers have found that they used potassium alum, a chemical
compound containing aluminum, to reduce cloudiness in drinking water. And the
concentrations of lead were likely due to the lead that Egyptians used to polish
pottery.
The latest studies are focused on samples including slices from
the head of femur bones and from the femur shafts to see whether one sample
type may be more prone to contamination from surrounding soil than the other
type, for example. Femur bones are the strongest bones in the human body and
run from the knees to the hips. The head, at the top of the femur, has spongier
bone material than the core of the shaft.
The researchers worked with ALS research scientists Hans Bechtel
and Eric Schaible to carry out experiments at three different beamlines.
Schaible assisted the researchers with a technique known as small-angle X-ray
scattering (SAXS), which they used to analyze the nanoscale patterning of
collagen, an abundant human protein.
X-ray scans reveal collagen patterns
A single scan of the bone cross-sections, which measured up to 3
to 5 centimeters across and about half a millimeter in thickness, took two to
six hours to complete and provided a detailed 2D map showing how the collagen
was organized within the bone.
These images can be compared with modern bones to better
understand whether and how the collagen degraded over time, and can possibly
tell us about an individual's health.
"Collagen is one of the main building blocks of the
body," Schaible said. "It's found in skin, bones, internal organs,
eyes, ears, blood vessels -- it's one of the main things we're made of. When we
shine X-rays through the collagen, the X-rays are scattered and the pattern of
scattering that they make can tell us a lot about how well-preserved and
well-organized the collagen is."
Though there is much analysis ahead to interpret the data taken
from the samples, Schaible said that the collagen assemblies generally aren't
as well ordered in the ancient samples as in healthy modern bones.
"It's very exciting to be involved in this project, and to
learn about the journey these mummies have been on, in life and after
death," he said.
Infrared light shows bone chemistry, mineral concentrations
The infrared studies at the ALS show the chemical distribution
and concentration of the minerals and organic materials present in the bones.
"One of the main obstacles was in how to prepare the
samples," said Elnewishy. It is difficult to cut thin cross-sections from
such delicate material.
Schaible contacted a specialized lab at UC Berkeley's Earth and
Planetary Science Department, which aided in slicing the samples. For the
thinnest sections and the most fragile samples, the bone was suspended in epoxy
resin and then sliced.
Plans for new experiments
Elnewishy said there are plans to also conduct related
experiments at SESAME (Synchrotron-light for Experimental Science and
Applications in the Middle East), a scientific light source in Jordan that
opened up to experiments in 2017. SESAME was built through a cooperative
venture by scientists and governments in the region.
He noted that what the team learns about cultural heritage and
preservation of samples through its experiments could potentially benefit the
collections of the Grand Egyptian Museum in Giza, which is expected to open in
2020 and will host more than 100,000 Egyptian artifacts.
The Advanced Light Source is a U.S. Department of Energy Office
of Science User Facility. LAAAMP is a joint program of the International Union
of Pure and Applied Physics and the International Union of Crystallography, and
is supported by the International Council for Science Grants Program.
Berkeley Lab's Theresa Duque and Cindy Lee contributed to this article.
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