Chemistry and Trace Elemental Potential in
Paleopathology
The materials we eat, drink, and breath are metabolically transformed during our
lifetimes into chemical markers related to our diet and health. If these markers are able to
survive to the archaeological context, in soil or bone, their chemical content may be
analyzed.
Dietary Analysis
Carbon Isotope Analysis
Nitrogen Isotope Analysis
Calcium and Strontium Analysis
Diagenesis
Pathology
Fluorosis
Lead Poisoning
Miscellanious other poisoning
Trace Elements
are utilized primarily in small doses and involved mainly in
enzymatic functions. Although integral in maintaining life, most of these elements are
toxic if ingested excessively- some at very low levels. Zinc Manganese, Iron, Lead,
Mercury, Cadmium, Strontium, Calcium, and Barium are just a few examples of vital
trace elements.
Elemental analysis took the Paleopathological world by storm in the late 1970s with trace
element values accepted as accurate and unadulterated representation of paleodiets.
Contemporary research is more reserved due to a better appreciation for the sources of
induction of trace elements into bone. Food processing and preparation, cooking utensils,
geological variation, natural bone variation, and diagenic processes can all leave trace
element hallmarks in bone. Contemporary research currently focuses on Alkaline-Earth
elements; Multi-elemental analysis; and Single-element analysis.
Lead Poison
Basics
Ancient populations had little exposure to lead, however, around 5000BC the
utilitarian uses were discovered. It has since been adopted into a kaleidoscope of
applications, dramatically increasing the amount of exposure to this element. Industry
and civilization have both positive and negative facets. One negative is the havoc lead
wrecks on the body. Lead can be ingested, inhaled, or simply transferred through touch.
Unfortunately, the relatively recent introduction has not allowed the human body to
develop a method of dealing with the element. Instead, lead is simply incorporated
directly into the skeletal system. Approximately 95% of the lead introduced into the
body is fixed into the hydroxyapatite crystal of bone. The body takes decades to cleanse
itself of lead fixed into bone, leading to extremely high concentrations of lead over
extended periods of exposure.
Damage
Lead poisoning is most devastating to children, as their minds and nervous
systems are developing at the time of exposure. Even small amounts of lead, for example
a paint chip the size of a finger nail, can have a dramatic affect on a developing child. On
the other hand, adults require larger doses in order for lead poisoning to occur.
Symptoms of lead poisoning include intestinal cramps, nerve paralysis, kidney failure,
and gout.
Low Level Lead Poisoning in Children under Six:
Reduced IQ
Growth
Behavioral Problems
Stunted
Learning Disabilities
Attention Deficit Disorder
Impaired Hearing
Kidney
Damage
High Level Lead Poisoning in Children:
Drastic Mental Retardation
Coma
Death
Adults:
Increased
Blood
Disorders
Pressure
Fertility
Problems
Nerve
Muscle and Joint Problems
Irritability
Memory
Problems
Decreased
Concentration
Archaeological Context
Lead poisoning is not overtly evident in skeletal remains. Black lines may be
found in the oral soft tissue, this practice is only applicable in conditions of immaculate
preservation, such as mummies. Bone weight is another specious indicator. The most
popular method of identifying lead poisoning is chemical analysis.
Lead poisoning seems to be a ubiquitous aspect of development. Each civilization or
generation has succumb to the attractive utility of this element, and they all have borne
the pathology. The interesting aspect of this truth is the ability to trace the source of lead
in poisoned populations. For example, Greco-Roman period was marred by lead
poisoning. The first solid example, exposure to lead is thought to have lead to the
collapse of the Roman empire due to decreased fertility. People in this time period were
exposed to lead leaching into food and water via drinking-water pipes and dishes.
Europe’s Industrial Revolution was accompanied by epidemics of colic, paralysis, and
convulsions. The culprit? Lead poisoning due to heightened industry as well as pewter
cook ware.
Perhaps the most interesting example of lead poisoning comes from the Caribbean
islands. Arthur Aufhderheide realized that both slaves and plantation owners from these
islands had extremely high levels of lead in their bones, but different percentages. He
concluded the different populations were both lead poisoned, only through different
avenues. In an attempt to be vogue, plantation owners and their families imported
ceramics from abroad, all decorated by lead based paint. Obviously, slaves were not
given luxurious plates or cups. Instead, they were exposed to lead via leaching when
distilling rum (sometimes old car radiators).
Miscellaneous Elemental Poisoning
Arsenic Poisoning
Basics
Arsenic is commonly used as a pesticide and preservative in contemporary
populations. The heavy metal is extremely poisonous and pernicious to the human body.
It can be introduced into the body via ingestion, inhalation, or physical exposure. Unlike
other elements, such as lead and fluoride, arsenic is not incorporated into the bone and is
usually excreted soon after imbibed. Poisoning can occur at levels around 0.5-0.9ppm
within muscle tissue or 0.8-3.8mg/100g of hair. Bones of bodies marked as poisoned by
arsenic exhibit between 9.0ppm and 24.0+ppm.
Damage
Arsenic exposure is often manifested first in gastrointestinal, kidney, and liver
problems. Prolonged exposure causes damage to the peripheral nervous system, skin
lesions, and respiratory inflammation.
Archaeological
The pathology which accompanies arsenic poisoning are relegated to the soft
tissue, therefore, evidence in the archaeological record comes only from mummies or
otherwise preserved bodies. Humans who were poisoned by arsenic during their life and
then mummified (intentionally or otherwise) usually exhibit livers with marked lesions,
abnormal kidneys, skin lesions, and assorted other problems.
Archaeological
investigation of arsenic poisoning has been used primarily to validate historical records.
For example, a strong conspiracy theory exists regarding the death of Napoleon. Many
believe his death was precipitated by arsenic poisoning. In order to add credibility to this
theory, strands of Napoleon’s hair have been examined. Unfortunately, there has not
been a uniform agreement in arsenic levels between different strands of hair. Some
indicate levels elevated enough for poisoning, others hardly indicate any problem. In a
similar vein, the remains of the explorer Charles Francis Hall were exhumed in order to
figure out if he died of natural causes, or if he was a victim of an unruly crew. His body
was buried in the Artic, causing rapid freezing and impeccable preservation.
Unfortunately, the soft tissues studied suffered from a similar problems of inconsistency
as those of Napoleon. These inconsistencies are the result of diagenetic problems.
Nitrogen Isotope Analysis
How it Works
The atmosphere has contains two stable Nitrogen isotopes, 14N (99.7 percent of
atmospheric Nitrogen) and 15N (0.3 percent of atmospheric Nitrogen). These isotopes
are metabolized in a similar fashion to Carbon. Nitrogen Isotope Analysis is used
primarily to delineate diet in marine settings.
The Delta 15N ratio of organisms is estimated as follows:
Marine Algae 0ppt
Marine Plants 3-10ppt
Marine Predators 10-15ppt
Marine Apex Predators 15-20ppt
Using these numbers, high values of Delta 15N ratios indicate a diet based on apex
marine predators (ie seals) while low values indicate a diet focused on seaweeds.
This technique is hampered by the ability of some organisms in arid climates to recycle
rather than excrete their urea, the primary source of nitrogen. This practice can skew the
Delta 15N ratio, therefore, this practice is not reliably used in dry coastal regions.
Fluorosis
Basics
In the 1950s, American dentists realized the potential for fluoride to protect teeth
from caries. However, they soon learned that too much of a good thing can be
dangerous. Fluorosis is a condition caused by excessive exposure to or ingestion of the
fluoride ion. Such exposure is most often the result of utilizing drinking water naturally
contaminated with elevated levels of fluoride. Groundwater of North Dakota is notorious
for it’s high level of fluoride, as are many areas of India, Pakistan, China, Sri Lanka, and
the Great Lakes region of East Africa. The concentration of fluoride in ground water can
be so capricious that people using one well may be completely healthy while their
neighbors using a separate well exhibit symptoms.
How It Works
Hydroxyapatite crystal is a major component of the inorganic bone and skeletal
system. A key aspect of this crystal is the hydroxyl ion, an ion whose size and bonding
potential is closely mimicked by the fluorine ion. Thus, the fluorine ions are able to
replace hydroxyl ions and form fluoroapatite crystal, rather than hydroxyapatite crystal.
When compared to hydroxyapatite, fluoroapatite is brittle and more dense.
Dental Fluorosis
The first stage of dental pathology in fluorosis is a loss of the characteristic gleam
on enamel. Next, the dull appearance turns chalky. One of the most diagnostic features
of fluorosis is the yellow to brown mottling of teeth. Fluorine does not stain the teeth,
instead it adversely affects enamel, causing small pits to form across all tooth surfaces.
These pits soon become home to organic matter, producing the cosmetic yellow to brown
spots. Unfortunately, if neglected these pits may increase the likelihood of caries. Dental
pathology on account of fluorosis may occur at levels as low as 0.07mg/kg of
fluoride/body mass a day.
Fluorosis and You
It may seem counterintuitive to be wary of fluoride, a popular additive to many
diets used to protect teeth. One must understand fluorosis is only manifested in people
who ingest large amounts of fluoride for an extended period of time, usually beginning
very early in life. In the initial stages of fluoride supplementation some children
developed mild cases of fluorosis, however, these days supplemented water is kept below
1ppm. The World Health Organization lists levels above 1.5ppm of fluoride as
dangerous to health for children seven years of age and younger. These days dental
hygiene products, including toothpaste, are only about 0.15% fluoride. Therefore, you
should not have to worry about fluorosis from excessive dental hygiene, especially if you
don’t swallow the products.
Skeletal Fluorosis
Fluorosis in the skeleton is characterized by proliferative bone growth, which can
take on several different appearances. The most characteristic forms of growth are large,
flat sheets across entire bones or small lumps dispersed throughout a bone. This growth
is spurred by the unique ability of sodium fluoride to stimulate osteoblast action,
therefore bone production. The impact of fluorosis is usually first seen on cervical
vertebra , followed by the rest of the axial skeleton, and ultimately every bone may be
affected. Bones with excessive fluoride concentration are usually thick, coarse, and
dense with a surface that resembles broken glass when magnified. The proliferative
nature of bone production affects the motion and flexibility of an individual in ways
similar to osteoarthritis. Fluorosis has the most dramatic impact on vertebra, where
ligaments are often ossify to the vertebrae, the vertebrae themselves grow to abnormal
size, and eventually ankylosis occurs from cervical vertebrae on down. This all
contributes to leaving the patient bedridden.
Archaeological Evidence
Advanced fluorosis is often easily identified in skeletal remains. Teeth with a
mottled appearance or chalky enamel are a major indication of the affliction. If such
teeth are found in the same context as bones with massive growth, the evidence is
conclusive. Diagnosis becomes muddled and complicated if the individual is only
partially affected. The proliferative bone formation may resemble Diffuse Idiopathic
Skeletal Hyperostosis, causing differentiation to be contentious. Chemical analysis is one
tactic employed in order to avoid such confusion.
Case Study
Judith Littleton undertook a major research study where she analyzed skeletal fluorosis in
a community from coastal Bahrain. The island has been occupied steadily since 7000BP,
however, the study focuses on individuals who lived 2300-1700BP. At this time,
Bahrainian diets were primarily agriculture based, with some supplement coming from
marine resources. Dr. Littleton was able to diagnose many cases of fluorosis from this
population. She sought out excessive examples of ossification of ligaments and
interosseous membranes as well as stained teeth with obvious etiological origin within
the enamel, rather than post-mortem staining. Only severe cases were accepted in order
to filter out potential arthritic origins for given problems.
Littleton mapped out the bones most commonly exhibiting evidence for fluorosis,
dividing them into male-female and age categories. She realized the thoracic vertebrae
showed the highest prevalence of ossification, followed by the sternum, and associated
other bones. Males were more vulnerable to the affliction relative to females, but both
sexes showed a strong correlation between age and level of disease. The older an
individual, the more likely they were to exhibit severe degrees of skeletal fluorosis
throughout their body. In fact, no bones aged younger than 30 exhibited any fluorotic
pathology, those 30-40 only marginal amounts, and only individuals aged 50 and above
suffered from ankylosis.
Littleton was perplexed because contemporary levels of fluoride in the water do not seem
to be high enough to lead to fluorosis (only 1.5ppm). After comparing the collection with
DISH, Ankylosing Spondylitis, Pagets Disease, and osteoarthritis Littleton decided
fluorosis was culpable. She accounted for the surprisingly small amount of natural
fluoride by taking weather into account. Fluoride levels in the soil and ground water
fluctuate with temperature, precipitation, and so forth. Therefore, the conditions of the
past may have been more conducive to fluoride leaching into water. Additionally, the
arid conditions of Bahrain induce the population into drinking excessive amounts of
water to stay hydrated. In addition, evaporation occurs rapidly. When water evaporates,
fluoride and other trace elements are left behind, therefore the concentration increases.
Diagenesis
How it Works
The processes which allow the inorganic aspect of bone, hydroxyapatite, to fix different
elements into the bone does not stop when an organism dies. Such postmortem
alterations to bone chemistry is referred to as Diagenesis and can dramatically affect the
research if not accounted for. The extent of diagenesis is based on the type of
substrate/pH in which a bone is buried, the water table, temperature, and the levels of
given elements in preexisting soil.
There are a few different strategies which may be utilized in order to combat the problem
of diagenesis. One example is repeatedly washing to remove diagenic strontium, which
has weaker bonds in the bone when compared with biologically bound strontium.
Another technique is to compare the groups only within a population, who should all
share a common level of contamination due to their similar archaeological context.
Carbon Isotope Analysis
How it Works
Predicated on differential carbon fixation by C3, C4, and CAM Plants.
C3 plants convert carbon dioxide to a three carbon molecule. Most trees, shrubs, and
grasses indigenous to temperate or shady environments make up this group of plants.
C4 plants convert carbon dioxide to a four carbon molecule. Grasses from the subtropics,
which grow at high temperatures and in sunny conditions, are the primarily constituent of
this class.
CAM LOOK THIS ONE UP. This group is charazterized by cacti and other succulents,
all of which rarely contribute to the diet and therefore have little affect on dietary
analysis.
The different methods of carbon fixing employed by these plant categories result in
different concentrations in carbon isotope ratios. This ratio is expressed by the Greek
Letter Delta Superscript 13 C and represents 13C/12C ratio. This ratio is expressed in
parts per thousand and is almost always negative. Larger negative numbers usually
convey C3 diets: around -21 parts per thousand; while smaller negative numbers convey
C4 diets: approximately -7 parts per thousand. Mixed diets of both C3 and C4 are
indicated by a ratio around -14ppt. These numbers are based on strict herbivores,
carnivores usually have slightly less negative values- as they get their carbon from that
previously fixed by herbivores.
Archaeological Application
Nikolass van er Merwe pioneered this research technique while studying the adoption of
maize in North American Woodlands. C3 plants are endemic to this region, an
observation supported by Delta 13C values from 5,000 BP which were -21ppt. This
level was relatively constant until around 1200 BP, when Delta 13C began to become
less negative: -18ppt at 1000BP, -14ppt at 800 BP, and finally -10ppt at 500BP. These
gradual changes obviate the adoption of a tropical cultigen, in this case the C4 Maize
plant. This theory is supported by maize in the archaeological context. Interestingly, the
adoption of maize agriculture indicated by this study allowed population density to
increase. The bones used to obtain the Delta 13C values support denser populations, as
the later bones are riddled with pathologies relative to the earlier bones.
Calcium, Strontium, and Barium Analysis
How it Works
The ratio of calcium to strontium or barium fixed into human bone hydroxyapatite is used
to understand the dietary trophic level of past human populations. H. Toots and M.R.
Voorhies developed the calcium/strontium chemical analysis and based it on the
following biological understanding:
Plants absorb Strontium from water
Herbivores consume plants, but have a proclivity toward forming bone with Ca rather
than Sr. This causes a lower Sr level in herbivores than plants.
Further down the trophic line, a carnivore consumes a herbivore. The same preference
for Ca over Sr occurs in all animals, herbivore and carnivore alike. Only the strontium
fixed by herbivores is ingested by carnivores, therefore, much lower amounts of
strontium are available to this next trophic level.
The process continues until the apex predator is reached. Naturally, this organism has the
lowest ratio of Ca to Sr in any given ecosystem.
Quick review, strontium is highest in herbivores (400-500ppm)- next omnivores (150400ppm)- and lowest in carnivores (100-300ppm).
Archaeological Application
Ca/Sr relationship has been used in conjunction with grave goods and position order to
further understand societal ranking systems. Status from the Chalcatzingo site in Mexico
was based on presence or absence of jade on the mortuary context. People buried with
jade objects had the lowest levels of strontium at the site. Those interred in prime
locations within a burial mound at the Middle Woodland Gibson site in Illinois indicated
the same phenomenon. This indicates that higher ranking members of these different
societies benefited from meat rich diets, at least relative to their peers.
Barium
Barium is another element in the second column of the periodic table, larger than both
Strontium and Calcium. The difference in size makes Barium the least attractive option
for fixing into hydroxyapatite (calcium preferred followed by strontium).
relationship is usually around 10ppm Ca, 5ppm Sr, and 1ppm Ba.
The
NEED BIOLOGICAL ANTHROPOLOGY OF THE HUMAN SKELETON book
pages 336-337 for a case study of this