From the 2016 Celebrating Excellence | Dr. Fred Andrus says he would never do this to you, but if he pulled one of your teeth, took it to his lab, and dissolved it, he could tell you about where you lived as a child. How? By analyzing isotopes, or variations of chemical elements.
“Isotopes are used to detect everything from steroid use to the paths that medicines and nutrients take in your body,” said Andrus, a professor in the Department of Geological Sciences.
“They can help an ecologist learn how an element cycles through a wetland, or they can help the FBI figure out where a murder victim was born.”
He points to marble samples on his desk.
“We’re using those to detect forged works of art for a museum.”
Most recently, Andrus and Celeste Marie Gagnon, a professor at Wagner University, used isotopes to deconstruct the chemistry of beer—Peruvian beer—in order to explain differences in bone chemistry. Their research was published in the Journal of Archaeological Science: Reports and was covered in an article in Forbes.
For nearly 15 years, Andrus studied climate change in Peru, and in the process he conducted research on water chemistry.
Gagnon also studies ancient Peru, and in the process of doing a forensic study on human skeletons, she noticed something strange.
Typically when two people grow up and live in the same area, they have a similar bone chemistry. But after analyzing the oxygen isotopes in the teeth and bones of some skeletons in the Andes, Gagnon noticed that the bone chemistry of the men did not match the bone chemistry of the women. Her first hypothesis was that they might have ingested different water sources.
She contacted Andrus, knowing he had analyzed water in Peru, and asked him if differences in water source—whether a well, a spring, an irrigation canal, or a river—might explain the difference.
“She and I happened to have some students in Peru, who grabbed some additional water samples,” Andrus said. “And we found differences, but not any that would explain the disparity in the bones.”
After brainstorming, Gagnon and Andrus thought that maybe water wasn’t the difference; maybe it was beer. In Peru, particularly ancient Peru, people drank large quantities of a type of beer called chicha, which is made from maize.
“The beer is made in part by boiling water and corn paste in open containers,” Andrus said. “So the water evaporates a lot, and when you evaporate water, you change its chemistry pretty dramatically.”
In particular, the ratio of light oxygen isotopes to heavy ones severely decreases.
“It takes less energy to evaporate a light molecule than a heavy one,” Andrus said. “So when you heat water, causing evaporation on the surface of the water, you’re removing more of the light molecules and retaining more of the heavy ones.”
This is why, Andrus explains, beer has such a different chemistry from water even though it is largely made of water. Because chicha is boiled in an open container, all of the light molecules that evaporate are lost, and the beer left over is isotopically heavier than the water that was used to make it.
In modern Peru, women are responsible for manufacturing beer, and the researchers hypothesized that in the past this might also have been true, and maybe there were gender disparities in drinking beer as well—which would explain the variations in the bone chemistry.
“It was a plausible hypothesis,” Andrus said, “but we didn’t know the chemistry of chicha. No one had ever bothered to measure it before.”
Not ready to give up, Gagnon and her undergraduate students at Wagner took on the task of making chicha themselves.
“First they tried to make it by mashing up corn and boiling it down in an open container,” Andrus said. “And as a control group, they duplicated the process with just water.”
“They would send the water samples to me, and we would run it through the stable isotope lab,” Andrus said. “When the first waves of data came in, our hypothesis looked plausible: there was a pronounced difference between the plain old water and the developed beer.”
However, in the process of making the beer, Gagnon realized that there might be a difference between her chicha and the real thing. Wanting to double-check her results, she went to Peru and made the beer with a traditional chicha maker. Again, she sent the samples to Andrus, and the results confirmed what they had already found.
“Our analysis showed that the beer likely influences people’s skeletal chemistry—and people in Peru have been drinking beer for millennia,” Andrus said. “So anyone who does forensic research in South America needs to take beer into account when they are analyzing bones.” •