Even if you remove yourself from the scene of the crime, you can’t always take the crime scene out of you.
As our nails and hair grow, they carry clues about our health: medical professionals can examine them for signs of illness or poor nutrition. They can also contain traces of the chemicals we’ve touched or ingested long ago—including enriched uranium used in nuclear power or weapons. Researchers from the University of Missouri have demonstrated (paywall) that different ratios of the radioactive element in hair and nails can distinguish people who have handled the material recently from those who haven’t.
Uranium is a naturally occurring element found in food and water in amounts that are safe for human consumption. In its natural state, uranium is found in the isotopes U-235 and U-238; the numbers indicate the amount of neutrons in each atom. Because uranium is relatively massive for an atom, its atom breaks down over time, which gives off energy. In nature, this process happens really slowly—”over hundreds of years, or even longer,” says John Brockman, a chemist at the University of Missouri and lead author of the paper. The energy from this slow decay process gives off is not enough to harm us, generate significant electrical power, or build weapons.
To boost the amount of energy from decaying nuclear energy at any given time, you have to split the atom by hitting it with another neutron—a process called fission. Fission works best with U-235 rather than U-238. Scientists can enrich natural uranium to make sure there are more U-235 atoms than U-238 atoms in a given chunk of it. “That allows you to make fuel for a nuclear reactor or some other application,” Brockman says.
Uranium can stay in our systems for a long time—regardless of whether we encounter it in a natural or unnatural setting. Brockman and his colleges tested the hair, fingernails, and toenails of people who work in the Oak Ridge National Lab in Tennessee and handle enriched uranium on a regular basis. They compared the levels of uranium found in these samples to similar hair and nail samples taken from a control group in Missouri. They discovered that although the overall concentration of uranium was similarly low in both groups, the ratio of U-235 to U-238 differed significantly.
People who handle non-natural uranium had trace amounts of the chemical with either high or low ratios of U-235 to U-238 compared to the control group. That, Brockman explains, is because when making enriched uranium, which has a high ratio of U-235 to U-238, you end up making a lot more uranium with a lower proportion of the slightly lighter isotope.
The bottom line: an abnormal ratio of the isotopes likely means the sample came from a person who handled enriched uranium in the last year.
It’s a measure that could be useful in uncovering illicit handling of uranium. For example, you could use it to determine if someone was smuggling enriched uranium across international borders. Or, you could test lab workers in countries supposed to shut down their nuclear weapons program to see if they were illegally continuing to work with enriched uranium.
Brockman and his colleagues only compared U-ratios in 13 different people; the study was more of a proof-of-concept than an actual detection plan. Next, they plan on looking at analyzing historical samples from people who have been exposed to higher levels of enriched uranium to better understand exactly how long traces of it linger in the body.