Diné toxicologist studies effects of uranium on DNA

By Alastair Lee Bitsoi
Navajo Times

SAN ANTONIO, Oct. 24, 2013

Text size: A A A

Monica Yellowhair

U nderstanding that there had been previous studies conducted on the radiological impacts of uranium, Monica Yellowhair has decided to study its chemical nature.

More specifically, the toxicologist, who is a postdoctoral research associate at the University of Arizona, is interested in the effects of uranium on DNA repair.

"Uranium is a naturally occurring heavy metal," said the Kayenta, Ariz. native.

She added that uranium has 16 different isotopes -- variants with different numbers of neutrons -- with uranium 238 being the most abundant isotope.

"The other two isotopes are 235 and 234 and these isotopes make up less than one percent and even though these isotopes make less than one percent, those are the most radioactive isotopes," she said.

This is what Yellowhair told attendees at the 2013 SACNAS National Conference, held on Oct. 3-6 in San Antonio.

SACNAS is a Society for the Advancement of Hispanics/Chicanos and Native Americans in Science. In the Alamo City, Yellowhair served on the panel titled, "Native American Researchers: From the rez to world-class research," and explained her journey into science and her research about uranium.

In her presentation, she added that uranium 235 and 234 are the isotopes mined for use in nuclear reactors and weapons.

"It has five different oxidation states and, as it decays, it emits ionizing radiation in the form of radon gas," Yellowhair said, adding that once uranium is processed it becomes depleted uranium.

She compared processing uranium to eating a pomegranate fruit.

Just as the pomegranate juice must be extracted from the seed pods, the uranium 234 or 235 must be separated from the ore.

Uranium 238 has 60 percent the radioactivity of natural and enriched uranium, with uranium 234 and 235 being used as fuel for nuclear reactors, she said.

Yellowhair also touched on the legacy of uranium mining and milling on the Navajo Nation during the Cold War Era.

According to Yellowhair, prolonged exposure to uranium not only can result in cancer of the stomach, colon, pancreas and prostate, but has also been shown to cause "genotoxic effects like chromosomal aberrations, micronuclei formation, sister chromatid exchanges and DNA damage."

In other words, uranium exposure actually alters the tiny components of individual cells.

"However, these particular types of cancer are not related to ionized radiation exposure," Yellowhair said.

"So, to us, something chemically is happening because when you think of radiation exposure, you think of leukemia and lung cancer."

As a result, a lot of the work she and colleagues have conducted so far looks at the genotoxic effects.

Yellowhair's path as a toxicologist studying the chemical structure of uranium began at Northern Arizona University, where she was both an undergraduate and graduate student.

As an undergraduate, she was exposed to research in the science lab of Diane Stearns, a professor in NAU's Department of Chemistry and Biochemistry.

It was through Stearns, who has published 23 manuscripts and seven reviews and book chapters on metals biochemistry and genetic toxicology, that Yellowhair was introduced to the topic of uranium and other metals.

According to the National Cancer Institute, Stearns has mentored eight Navajo researchers, including Yellowhair, with her research on how metals damage DNA in ways that lead to cancer.

To understand if uranium causes individual strands of DNA to break, Yellowhair, along with Stearns, conducted a simple experiment to see if the metal causes DNA strand breaks in the bacteria E-coli.

And from their experiment, they found in a micrograph, that uranium was, in fact, causing strand breaks.

"Just from the little micrograph that we took of the results, she (Stearns) actually incorporated that into a multimillion grant that eventually became the Partnership for Native American Cancer Prevention," Yellowhair said.

From there, her path in science was paved.

"My future has kind of been brought upon me," Yellowhair said.

Following the establishment of the Partnership for Native American Cancer Prevention, a partnership between NAU and the UA aimed at alleviating the unequal burden of cancer of Native Americans, Yellowhair began graduate study in chemistry at NAU.

The National Institutes of Health and National Cancer Institute continue to fund the Partnership for Native American Cancer Prevention.

Since NAU was awarded the grant from the National Institute of Health, and from presenting her research at national conferences, it was only natural for Yellowhair to begin graduate school.

"It was pretty obvious to go into graduate study," she explained.

Upon graduation with her master's degree, she also was accepted into the University of Arizona's toxicology program and paid nothing from out-of-pocket to get her Doctor of Philosophy.

Tribal scholarships, being named a Sloane Research Fellow, funding from her previous research and writing her own pre-doctoral fellowship at Arizona helped Yellowhair pay for her doctoral degree.

Now as a postdoctoral fellow at the University of Arizona, Yellowhair is looking to identify how biological markers from heavy metals affect Mexican communities impacted by coal and copper mining.

Specifically, she will investigate DNA repair responses in populations highly exposed to uranium.

Once her fellowship is completed, she plans to conduct similar research on the Navajo Reservation -- where there are approximately 1,000 abandoned uranium mines, according to data collected by the U.S. Environmental Protection Agency.

Becoming a scientist was only natural for Yellowhair, given her "curious-observer" mindset.

Her achievements were the reasons why she was invited to the SACNAS conference as a panel speaker.

Yellowhair is Kinyaa'aa'nii (Towering House People Clan) and born for Tódích'ii'nii (Bitter Water People Clan). Her maternal grandfather is Tl'izilani (Manygoats Clan and paternal grandfather is Loka'ii Dine'e.

Back to top ^