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A $1.3 million grant from the Department of Defense's Environmental Security Technology Certification Program will allow University of Arizona researchers to further study how synthetic chemicals known as PFAS move through soil and threaten groundwater.

PFAS, or perfluoroalkyl and polyfluoroalkyl substances, are composed of nearly 3,000 synthetic chemicals and have been widely used in industrial and consumer products since the 1940s, including firefighting foams, paints, food packaging, water-resistant clothing and household cookware. In 2019, the Department of Defense cited a total of 651 military installations that have been impacted by these synthetic chemicals.

At a local level, PFAS not only pose a long-term threat to groundwater quality, but also a long-term challenge to scientists tasked with cleaning them up, explained Bo Guo, the principal investigator of the project and an assistant professor in the Department of Hydrology and Atmospheric Sciences.

"PFAS have been discovered almost everywhere in the world. While toxicological research is still ongoing and very limited data is available, it's clear that these types of chemicals can cause adverse health effects, including cancer, at very, very low concentrations," Guo said. "We are talking about parts per trillion levels."

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"We have the long-term persistence, their presence pretty much everywhere in the environment, and the toxicological impacts from exposure. Those three things together make PFAS very critical emerging contaminants of concern," said Mark Brusseau, a professor in the Department of Environmental Science and co-principal investigator on the project.

PFAS have been discovered at several locations in Southern Arizona, including Davis-Monthan Air Force Base, the Tucson International Airport and local wastewater treatment plants. Guo and Brusseau, along with co-investigators Christopher Higgins from the Colorado School of Mines and James Hatton from Jacobs Engineering, will focus on PFAS found in the portion of the soil subsurface known as the vadose zone, which is the area below the land surface that extends to the groundwater table.

"At many sites, particularly at military bases and industrial sites where they're using PFAS, the concentrations in the soil are very high, often much higher than they are in groundwater," Brusseau said. "We are observing that, at many sites, the soil is a reservoir, like a source zone of PFAS, that can then have long-term potential for contaminating groundwater."

As part of the grant from the Department of Defense, the researchers will have an opportunity to test computer models against undisturbed field soils collected from Davis-Monthan Air Force Base. These validated computer models will ultimately help scientists around the United States predict the movement of PFAS underground and help policymakers develop risk assessments and target remediation efforts.

"It is important to continue studying how PFAS behave underground at these sites, especially in the face of a changing climate and growing competition for water resources here in the Southwest," Guo said.

The University of Arizona is a world leader in water research. In the ShanghaiRanking 2021 Global Ranking of Academic Subjects, UArizona is ranked No. 1 in the nation and No. 2 in the world for its water resources research program.

"One of the most important parts of the University of Arizona's mission as a land-grant institution is to tackle real-world challenges, particularly those that are most pressing in our desert region, like the many threats to the availability and quality of water," said University of Arizona President Robert C. Robbins. "This grant from the Department of Defense will allow us to bring together the incredible faculty expertise we have in hydrology and environmental science to see how we can more effectively identify and remediate areas at risk for groundwater contamination. This work could have an impact well beyond the state of Arizona."