Researchers Seek to Develop New Tools to Remove PFAS from Agricultural Soil and Nearby Groundwater via The Freshwater Collaborative of Wisconsin

For years, Wisconsin farmers have applied biosolids—a byproduct of wastewater management — to their fields. The process reduces the need for commercial fertilizers, conditions the soil, and reduces the amount of biosolids going into a landfill.

Unfortunately, biosolids may be a major source of per- and polyfluoroalkyl substances (PFAS). These hazardous chemicals are used widely in household products and manufacturing, and they accumulate in biosolids.

Is Biochar a Solution to PFAS Leaching?

Five years ago, UW-Green Bay faculty began investigating whether land application of biosolids would result in PFAS leaching into groundwater. They received funding from the Freshwater Collaborative to partner with faculty and students from UW-Madison, UW-Platteville and UW-Stevens Point to investigate the issue.

“Not only did the grant provide funding to do the research, but the project was a learning experience in how to collaborate with faculty at different universities,” says Michael Holly, an associate professor at UW-Green Bay who specializes in agricultural waste management.

The team confirmed that use of biosolids can result in PFAS leaching at concentrations hazardous to human health. They also learned that biochar — a charcoal-like substance made by burning organic material such as forestry waste — may mitigate contamination. As part of the project, undergraduates from the four universities tested woodchip-based biochar to determine its effectiveness in adsorbing PFAS from soil.

The results were published by the American Chemical Society in January 2024.

The Freshwater Collaborative awarded a second grant in 2023 so the team could test biochar filter media on a working agricultural field. Holly and his colleague Kpoti Gunn, an assistant professor at UW-Green Bay, partnered with a local farmer who has been using biosolids on his fields. The research team installed moisture sensors and soil water sampling tools on his fields last summer.

“The first year, we observed the fields without the application of biochar,” Gunn says. “The goal this year is to prepare the field along with the farmer, apply biochar, and compare the results.”

Water samples collected from the field are sent to UW-Milwaukee to test PFAS levels. Holly and Gunn are collaborating with Yin Wang, associate professor at UW-Milwaukee, who recently received a two-year grant from the U.S. Department of Defense to identify a more efficient approach of removing PFAS from water.

Students Receive Water-Quality Training

Andrew Votis, a senior at UW-Green Bay, has worked with Gunn for the past year and a half. This spring, he is helping to set up and implement the crop plan for the research plot. The research has provided professional training for his future career and also has personal meaning.

“My wife and I run a dairy farm north of Green Bay in the Coleman-Peshtigo area, so my background made me a natural fit for the project,” he says.

Votis will graduate in summer 2025 with a degree in Environmental Engineering Technology, and he appreciates the practical skills he’s developed while conducting undergraduate research at UW-Green Bay.

“My work with Dr. Gunn has strengthened my ability to communicate with various groups, manage a team, as well as increased my understanding of the intricacies of research projects,” he says.

Jonna Rosenthal participated in the research last summer as part of the Freshwater@UW Summer Research Opportunities Program, also funded by the Freshwater Collaborative. Rosenthal is a senior at Smith College in Massachusetts where they have studied the effects of ocean acidification and salt-water contamination. They wanted to work on freshwater systems and were particularly interested in emerging contaminants such as PFAS.

“It was incredibly rewarding to collaborate with the faculty at UW-Green Bay,” they say. “I attend a small liberal arts school, so I had no experience with scientific work at a research institution. It was amazing to have access to analytic equipment and other esteemed scientists with whom I could collaborate.”

Jonna Rosenthal and Kpoti Gunn install moisture sensors in a field to help measures PFAS levels.

Rosenthal graduates in May 2025 and will begin work as an environmental scientist with AECOM, a global infrastructure consulting firm. They will research groundwater contamination.

“This work includes testing and monitoring sediments and groundwater, a skill that I developed during my collaboration with Dr. Gunn,” they say.

The project has already trained 13 undergraduates, and two graduate students are conducting research for their thesis. Another Freshwater@UW Scholar will join Votis on the project this summer.

What they learn could identify practical solutions to PFAS leaching — and give farmers a cost-effective tool for protecting groundwater near their fields.

Written by Heidi Jeter, Freshwater Collaborative.