Name ________________________________________ Date ____________________ Period _____
Stable Isotopes in Forensics
Investigators use elemental variations to unearth new leads.
By Tim De Chant
Thursday, October 18, 2012
Who is ‘Saltair Sally’?
In October 2000, a pair of duck hunters in Utah stumbled into a murder
mystery. As they walked along the south shore of the Great Salt Lake — just
100 feet from Interstate 80—they found buried in a shallow grave a plastic bag
containing a white sock, an oversized t-shirt, a woven blue choker necklace, 12 bones,
and a human skull. Missing was any sort of identification. Police gathered what clues
they could from the remains of "Saltair Sally," named after a resort near where her
remains were found. The body was badly decomposed, dental records didn't reveal
anything, and a composite sketch and description of her provided no valuable
information. The case went cold.
Seven years later, there were still no leads in the case. Desperate for a break, the state
medical examiner released a sample of Saltair Sally's long, blonde hair to be tested by
stable isotope analysis, a new forensic technique that had been introduced in the years
since Saltair Sally had been discovered.
Every molecule in our bodies—including those found in hair—are made up not just of
different elements, but of different ratios of stable isotopes of those elements. Take
hydrogen, for example. In its most common form, it has one proton and one electron.
There are also two less common isotopes, deuterium and tritium, which have one and
two neutrons, respectively, in addition to their proton and electron. Deuterium is useful
to forensic scientists. It is naturally occurring and very stable, meaning it is found in water
in varying amounts and those variations depend on the source of the water.
Oxygen–18 Clues
Lesley Chesson, an analytical chemist, at IsoForensics in Salt Lake City, the company
that received the hair sample, was contacted to see if she would analyze the hair—a
long length of the hair—looking at hydrogen and oxygen to see: Was she local? Did she
move into the area? If she did, where was she from prior to her death?" Such clues
would give investigators valuable information as they continued to search for the
victim's identity.
To see how that's possible, let's follow a raindrop from a cloud over
the Pacific Ocean to Saltair Sally's strand of hair. When those clouds
rain, the heavier, oxygen-18 containing water molecules will fall out
first. That typically happens near the coast. As the rain cloud moves
inland, it's constantly losing molecules with oxygen-18, and its
raindrops become isotopically lighter and lighter. Since our drinking
water comes from rainwater, people near the coasts drink water with more oxygen-18
atoms in it than people living inland. Those atoms eventually become a part of our
tissues, like hair.
If Saltair Sally had been in Salt Lake City in the weeks preceding her death, the hair
closest to her scalp would reflect the isotopic signature of Salt Lake City's local water
Name ________________________________________ Date ____________________ Period _____
supply. If she had been in, say, Seattle close to the Pacific instead, her hair's isotopic
composition would contain more oxygen-18, giving investigators a valuable clue.
"We analyzed the hair sample," Chesson says. "It looked like within the two years leading
up to her death, she had moved at least three or four times, and it seemed she was
making this sort of repeating pattern. She was in a region consistent with Salt Lake City
and the Intermountain West, and then she was moving someplace more towards the
northwest. She did this a couple of times in the years leading up to her death."
Armed with this new information, detectives refocused their investigation on the regions
Chesson and her colleagues had suggested. Still, it wouldn't be until August 2012 that
they received a break in the case.
More than Water
Hair isn't the only tissue scientists can analyze for clues.
Fingernails are nearly identical in composition to hair, and like
hair, they leave an isotopic timeline that remains unchanged
until it gets cut off. In fact, every part of our bodies has
potentially exploitable isotopic signatures. Though hydrogen
and oxygen in hair and fingernails are often the first to be
analyzed, other isotopes and body tissues can provide
different types of information, says Wolfram Meier-Augenstein,
a professor and principal scientist at the James Hutton Institute
in Aberdeen, Scotland.
Carbon and nitrogen are two other elements commonly used by forensic
scientists. Like hydrogen and oxygen, carbon and nitrogen are found
throughout our bodies. But instead of recording the water supply,
Carbon reflect people's diets. Carbon in our bodies is largely derived
from plant tissues, which get their carbon from CO2 in the atmosphere.
Carbon isotopes are concentrated differently depending on which type
of photosynthesis a plant uses. Wheat, rice, and sugar beets use what's
known as C3 photosynthesis. Their cells take CO2 directly from the
atmosphere to convert to sugar. Corn, grain, and sugar cane use a
different photosynthetic pathway known as C4, which has an additional
enzyme that concentrates CO2 before handing it off to Rubisco, which
begins the carbon fixing process. The added step in C4 plants increases their carbon-13
levels relative to C3 plants. In North America, where corn is common in diets, people's
tissues tend to have high carbon-13 concentrations.
"We don't find a needle in a haystack. We reduce the haystack to a manageable size."
Nitrogen isotope levels depend on whether people are omnivorous, vegetarian, vegan,
or otherwise. Each step up the food chain enriches the ratio of nitrogen-15 to nitrogen14 by 3.4‰ (per mille). That means the tissues of a person who is vegan will have less
nitrogen-15 than the tissues of someone who eats mostly meat.
Unlike hair and fingernails, most tissues do not record in linear fashion where a person
was or what they ate. "While the signature in hair will change relatively rapidly, the
signature in other tissues, bone for instance, will change very, very slowly. The signature
in teeth won't change at all," Meier-Augenstein says.
Name ________________________________________ Date ____________________ Period _____
Chemically Identical, Isotopically Distinct
Analyzing human tissue isn’t the only thing we use stable isotopes for. Meier-Augenstein
frequently deals with drug-related cases, including one in the United Kingdom where a
man was initially arrested on the street for possessing five tablets of MDMA, or ecstasy.
The police secured a search warrant and searched his place, and lo and behold, in a
gym bag in a closet, they found a huge plastic bag with thousands of ecstasy tablets.
The suspect denied knowing of the tablets, instead blaming it on a friend. Though the
tablets looked and were chemically similar to the five found on the suspect, police
didn't feel it was enough for a solid conviction. That's where stable isotopes came in.
These tablets were analyzed isotopically, and lo and behold, at a 95-plus percent
confidence level, they were a match. Confronted with this new evidence, the suspect
admitted his guilt.
Drug-related cases aren't the only type where stable isotope forensics can augment
traditional chemical analysis. Today, many products are chemically identical, even if
they are from separate factories. Take, for example, white paint chips found on a crime
scene or traces of explosives used in a terrorist attack. Evidence from the crime scene
may chemically match those found in a suspect's home, but stable isotope analysis
could reveal that they were made in separate factories. If that were a key piece of
evidence, the isotopic analysis could be enough to keep an innocent person out of
prison.
Stable isotopes can also distinguish genuine products from counterfeits. The liquor
industry, which is rife with fakes and mislabeled products, has found isotopic analysis to
be particularly useful. Wine may be intentionally mislabeled as a better vintage, or a
cheap single-malt whiskey could be hawked as an upscale brand. By comparing a
suspected counterfeit with an original sample, stable isotopes can help investigators
unmask the fraud.
Isotopic Filters
Meier-Augenstein recommends viewing each stable isotope as a filter. In our globalized
world, a John Doe could have come from anywhere. Investigators start looking for clues
close to where the victim was found, but if nothing turns up, they could end up
combing through every missing persons list in the world.
Stable isotopes help narrow that search. Deuterium and oxygen-18 from a victim's hair
or fingernails "can exclude 80 or 90 percent of the world," Meier-Augenstein notes. A
nitrogen-15 analysis of the victim's muscle tissue could reveal that he was a vegetarian,
another useful clue. And heavier isotopes such as strontium leech from rocks into
groundwater, eventually making their way into our bones and teeth.
Together, all of these clues narrow the field of potential
matches, greatly simplifying things for detectives. "We don't
find a needle in a haystack," Meier-Augenstein says. "What
we do, in an ideal circumstance, is we reduce the haystack
to a manageable size."
Name ________________________________________ Date ____________________ Period _____
What the Future Holds
While stable isotopes have proven themselves useful, they aren't staples of forensic
science—yet. Part of the problem is cost. Stable isotope analysis isn't cheap. Preparing
samples takes lots of time and involves a host of costly chemicals. Most samples today
are run through mass spectrometers, which are large, expensive, and often
temperamental. Finally, interpreting the data requires an expert. These obstacles aren't
insurmountable, but they're not insignificant.
Naming ‘Saltair Sally’
Salt Lake Unified Police announced on August 7, 2012 that, with the help of stable
isotope analysis, they had identified Saltair Sally. Her name was Nikole Bakoles. The
cyclic pattern of travel between Salt Lake City and Seattle recorded in Saltair Sally's hair
matched information provided in Bakoles's missing persons report, which had been filed
in 2003. A DNA test confirmed the match. Bakoles, who was 20 at the time of her death,
was last seen in March 2000, when she was living in a hotel in a southern suburb of Salt
Lake City with her boyfriend and young child. In the preceding years, she had traveled
to Seattle occasionally to visit family members, a habit which was clearly recorded in
the isotopic composition of her hair. Without that information, it's likely Saltair Sally would
still be a cold case.
Given where Bakoles's remains were found and the manner in which they were
disposed, police suspect foul play. Stable isotopes haven't led to an arrest yet, Chesson
says, "but we did help finally put a name to a person, which was really pretty cool."
Name ________________________________________ Date ____________________ Period _____
Topic: Stable Isotopes in Forensics
Three options: ① KWL ② Questions ③ Defining terms
Only choose 2 to complete
Fill in the KWL Chart below while reading the article, Stable Isotopes in
① Directions:
Forensics. There should be a minimum of 3 statements/questions in each.
K
What I Know…
W
I know that isotope is a change of neutrons that cause the
element to way more or less.
I know that forensic is a way that the application of
scientific methods and techniques is related to
investigating a crime.
I know that stable isotopes are non-radioactive form of
atoms.
I wonder why carbon reflects on peoples diet.
I wonder why carbon isotopes vary
I wonder why teeth don't change
overtime like hair and nails.
What I Wonder…
L
What I Learned…
②
I learned that most tissues do not record in a linear
fashion where a person was or what they ate.
I learned that carbon in our bodies is largely derived from
plant tissues, which get their carbon from CO2 in the
atmosphere.
I learned that stable isotopes can help identify a person
based on the test.
Directions: Answer the questions while reading the article.
1. In hydrogen’s most common form, how many protons and electrons does it
have? 1 proton and 1 electron
2. What are the names of the other two less common isotopes of hydrogen?
deuterium
a. _______________________________________
tritium,
b. _______________________________________
Name ________________________________________ Date ____________________ Period _____
3. Why do the oxygen-18 containing water molecules fall out of the rain clouds
first?
Oxygen-18 containing water molecules fall out of the rain clouds first
because they are heavier.
4. If Saltair Sally’s hair shows less oxygen-18 what valuable clue would that tell
investigators?
Shows that she moved around a
lot and there wasn't a bunch of
water in her hair.
5. Carbon isotopes show what detail about a person?
Carbon isotopes are concentrated differently depending on which type
of photosynthesis a plant uses and reflects on diets due to the amount of isotopes a
person consumed.
6. Since Pennsylvania is in North America, we will have high levels of which carbon
isotope? Circle the one below:
Carbon-12
Carbon-13
Carbon-14
7. Nitrogen isotope levels show what detail about a person?
Nitrogen isotope levels depend on whether people are omnivorous, vegetarian,
vegan, they determined what you eat.
8. Which tissue, mentioned above, in our body, won’t change at all, therefore,
leaving behind a detailed signature?
The signature teeth won't change
at all.
9. In the two drug related examples mentioned, how do stable isotopes help
convict or not convict a person.
Stable isotope analysis could reveal that they were made in separate factories. If
that were a key piece of evidence, the isotopic analysis could be enough to keep
an innocent person out of prison.
10. How do stable isotopes help narrow the search in a missing person’s case?
Allow you to run tests to figure
out an identity.
Name ________________________________________ Date ____________________ Period _____
Read through the article and highlight words that you are not familiar
③ Directions:
with. Then, choose 3-5 of those words from the reading, write them down below.
Look up the definition for each of the words you listed and write it next to the word.
WORD
proton
neutron
electron
atoms
molecule
DEFINITION
an atomic particle that occurs in
the nucleus of every atom and
carries a positive charge equal in
size to the negative charge of an
electron.
an uncharged elementary particle
that has a mass nearly equal to
that of the proton and is present
in all known atomic nuclei except
the hydrogen nucleus.
a negatively charged subatomic
particle that can be either bound
to an atom or free
The smallest part of a substance
that cannot be broken down
chemically
The smallest particle of a
substance that has all of the
physical and chemical properties
of that substance