Eliminate uranium from the food chain: are they


image: Katie Dunlap, MS ’21, in the greenhouse with recently planted sunflower seedlings.
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Credit: Credit: L. Wasylenki.

Portland, Oregon, USA: For decades, mining companies have been digging up uranium in the American Southwest. Today, the remains of these mines dot the landscape, particularly in the Navajo Nation in northeastern Arizona. Mine tailings and dust still circulate through the ecological system, spreading radioactive particles on soils, waterways and homes.

This radioactive dust is absorbed by plants and spreads through leaves and shoots. Grazing animals like sheep, a common livestock eaten by the Navajo, eat the contaminated plants and incorporate the radioactive material into their tissues. Thus, exposure to uranium is more concentrated throughout the food chain.

A new study presented at the 2021 annual meeting of the Geological Society of America’s Connects examines how chronic exposure to uranium in the food chain could be reduced. Professor Laura Wasylenki, Northern Arizona University, presents the work of her former graduate student Katherine Dunlap, where they examined how root fungi might alter uranium uptake in plants.

Plants take up elements, including uranium, from the soil and spread the material from “root to shoot,” Wasylenki explains. The animals that graze the plants then ingest the uranium, where it accumulates in the tissues. The Navajo community raises sheep, which are an important source of food and part of their cultural heritage. Uranium stored in sheep travels up the food web to humans.

Wasylenki says almost nothing is known about the role of fungi in the uptake of elements by plants. “We saw an experimental paper saying that the fungi caused plants to take in more uranium in total, but only in the roots – it was not carried in the shoots or leaves of the plants.”

She explains that among grazers, some tear off the entire plant to nibble on it, while others (like sheep) tear off the tops of the plants. Wasylenki and Dunlap wanted to test if there was a way to stimulate the growth of good fungi and sequester uranium underground. “So at least you would help reduce uranium consumption from the guys who just cut the tops off.” [of the plants]Wasylenki notes.

The team grew sunflowers with and without symbiotic root fungi (called arbuscular mycorrhizal fungi). In particular, they were curious as to how soil mineralogy and the presence of fungi would influence uranium uptake by sunflowers. An artificial soil (Turface) with no uranium present was used in the pots, and a layer of clay-rich material was added. Uranium was added at a known concentration when the plants were watered.

When they looked at uranium concentrations in plant tissue, they found that the presence of fungi decreased the spread of uranium from roots to shoots. They also found that the presence of a layer of clay in the soil increased uranium uptake in plants. Wasylenki hypothesizes that “uranium would sorb onto clay surfaces, retaining it there, so that it would have a longer residence time around the roots.” She adds that while the more uranium was taken up in clay-rich soils, less was carried throughout the plant – more was stored in the sunflower root system.

Wasylenki notes that their sample size for the initial experiment was small, but intends to expand testing with a larger sample size and various soil types. The team notes that this work is an important first step in understanding whether fungi can help mitigate uranium exposure for grazing animals, which eventually find their way through the human food chain, especially for those of the Navajo community.

Laura Wasylenki, University of Northern Arizona, aura.w@nau.edu
Document n ° 134-8: Can root fungi disrupt trophic transfer of uranium from soil to plants, sheep, and the Navajo people?
Tuesday, October 12, 9:50 a.m. PDT
Session 132: T26. Environmental geochemistry and health: https://gsa.confex.com/gsa/2021AM/meetingapp.cgi/Session/51664

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The Geological Society of America, founded in 1888, is a scientific society made up of members of academia, government, and industry in more than 100 countries. Through its meetings, publications and programs, the GSA fosters the professional growth of its members and promotes the geosciences in the service of humanity. Based in Boulder, Colorado, United States, the GSA encourages cooperative research among earth, life, planet, and social scientists, fosters public dialogue on geoscience issues, and supports all levels of teaching of earth sciences.


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