FIND-EM Info

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Isoscapes

Everything and everyone is made up of atoms of many elements. These elements - for example, carbon and hydrogen - are the building blocks of our bodies, and can be found in all body tissues. Your hair, bones, and teeth contain abundant carbon and hydrogen, and even low levels of other, rarer, elements like strontium and lead.

Did you know, though, that not all hydrogen atoms are the same? Minor differences in the nucleus cause natural variation in the weight of different atoms of the same element, and these different 'flavors' of an element are called isotopes.

We tend to think of isotopes as associated with bombs, nuclear energy, or radiation, and indeed some are. Most isotopes, however, are not radioactive or dangerous. They are a naturally occuring part of the environment, and have been since the Earth was formed. Lake Monona, Wisconsin, for example, contains about 112 million tons of water. That water contains a little more than 12 million tons of the element hydrogen. Of that, about 5 thousand tons is not the normal, common version of hydrogen but rather the rare isotope hydrogen-2.

Although rare isotopes occur everywhere in nature, their abundance is not the same in all locations. Natural processes sort isotopes and create predictable patterns in their distribution. Water in lakes at high latitudes, for example, has less hydrogen-2 than does water in lakes nearer the equator. We use isotopic measurements of samples collected at different locations together with statistical mapping methods to produce estimates of isotope variation across the USA and other parts of the world. The resulting maps are called 'isoscapes', or isotopic landscapes.

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Forensic Applications

Our bodies grow and replace tissue continuously throughout our lifetimes. As this happens, new tissues are formed from the elements and isotopes taken into our bodies from the local environment. Our food, the water we drink, and even the air we breathe all contribute to the isotopic composition of our bodies. Because the isotopic composition of these elemental sources varies among locations, isotopes in our body are a bit like a biological passport, registering a change each time we move from one location to another.

Many body tissues preserve isotope signatures obtained when they were initially formed for years to decades. The hard enamel coating our teeth, for example, is chemically stable throughout our lifetime, and its isotopic composition reflects the location and environment we lived in during our childhood, when these teeth first formed. Hair, which grows continuously, is more akin to a tape recorder, with each new segment of growth locking in body isotopic signatures as it is growing.

The ability to reconstruct the geographic origin or movements of individuals based on isotope compositions of their body tissues is now used by many law enforcement agencies as an investigative tool. In 2012, police in Utah solved a 12-year-old cold case when isotope measurements of human remains helped point their investigation toward missing people who had traveled to the Pacific Northwest prior to their death. Just this year, isotope evidence contributed to the identification of remains discovered in North Carolina in 1998.

Isotope forensic evidence is different from fingerprints or DNA: it does not provide a unique identification of an individual or location. Instead, it indicates general areas that are more or less likely to be places where an individual has lived in the past. However, isotopes have one key advantage that makes them a great addition to the forensic scientist's toolkit: isotope data can be useful even in no reference sample is available. Fingerprints must be matched to a fingerprint taken from the same individual. DNA samples generally need to be compared to samples from close relatives to make a positive match. For isotopes, however, we can use isoscapes to help us interpret data from forensic samples. This means that even if scientists have never sampled a relative, or even someone living in the same town or county, they can assess whether an individual may have lived there.

This makes isotopes and DNA a great pair, and in fact this is how IDs were made in both cold cases mentioned above. DNA provides very specific identification information, but requires the right reference samples. Without guidance on where to look for potential relatives, the collection of reference data can take a huge amount of time and resources and represent a bottleneck in many cases. Isotope data can help to guide this process, highlighting the most likely locations where an individual might have lived and helping investigators prioritize the collection of DNA reference samples.

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POW/MIA Accounting

More than 82 thousand American armed service members from post-WW I actions remain un-accounted for. Obtaining, identifying, and repatriating the remains of those who perished oversees remains a focus for the families of missing service members, the US military and many non-governmental groups that have taken on this mission.

Discovering and obtaining remains is usually only the first step in the process of accounting for missing service members. Depending on the context of the recovery, positive identification of the individual or individuals recovered can be a major challenge. Forensic scientists use a wide range of contextual clues and records to work toward an identification. In addition to these traditional methods, forensic DNA techniques have led to huge advances in the ability to identify long-missing persons. DNA-based identification requires matching with samples from close relatives, however, and in many cases the search for potential relatives, acquisition of reference samples, and testing represents a major bottleneck in the identification process.

Isotope forensics can assist in this process by guiding and streamlining the search for DNA reference samples. Consider a typical 11-man crew of a B-24 Liberator bomber. If unidentified remains are recovered from a crash site, DNA identification may require finding, obtaining and analyzing reference samples from relatives of up to 11 crew members, assuming the identity of the plane and the crew can be established by other means. This type of un-focused search places a large burden on over-taxed forensic DNA labs and can slow the identification process.

Isotope analysis offers the potential to dramatically reduce this workload and associated delays by focusing the search. Analysis of the isotope composition of teeth from the recovered remains, for example, might indicate that the individual spent his childhood in the southern Great Plains states of Texas and/or Oklahoma. If only two of the 11 crew fit this profile, a simple isotope test will have reduced the DNA testing effort by more than 80%, meaning more cases can be processed to obtain positive identifications faster.

The key to succesfully adding isotope testing to servicemember accounting process is isoscape mapping. Although researchers have learned a lot about isotope distributions, reliable, high-quality maps showing the isotope values found in food and water across the USA don't yet exist. In addition, isoscapes for POW/MIA accounting need to be developed and tested using data from human teeth of known origin. The FIND-EM project will be developing these isoscape maps, using a combination of isotope sampling and GIS-based modeling to map patterns of isotope variation across the USA.

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Donor FAQ

How do I donate my teeth to the study?

If you have had your wisdom teeth extracted and saved your teeth, or if you’re planning to have your wisdom teeth extracted, fill out our survey with some basic life history and contact information. If you qualify for the study, our study coordinator will contact you with instructions for submitting your teeth.

Is there any cost to participate?

There is no cost to you to take part in this study beyond the normal dental care costs already associated with your extraction. Although the project cannot cover the cost of your extraction procedure or associated care, you do have the option to receive a $35 gift card for completing the survey and submitting your extracted teeth.

Is my dentist allowed to give me my extracted teeth?

Yes, according to the Centers for Disease Control and Prevention dental providers are allowed to give extracted teeth to the patient. Some providers may tell you otherwise; in that case you can try pointing your provider to the guidance on the CDC website and telling them that you need the extracted teeth to participate in a humanitarian research study.

My child is having/has had their wisdom teeth extracted. Can they participate?

We can only accept teeth from people 18 years or older. We anticipate our study will continue to collect teeth at least through 2024, and individuals who are not yet 18 are welcome to save their teeth and sign up for the study when they turn 18.

Is any genetic information taken from my teeth?

Your teeth will not be used for any genome sequencing or other genetics studies. The only analyses that will ever be performed on them will be isotopic or elemental chemical analyses.

Will the study provide information about or benefits to my health?

The data collected by the study will not tell us anything about your health or provide any health benefits. We are measuring minor, natural variations in the chemistry of your teeth, which are not associated with health status or outcomes.