A team of Yale University researchers has developed a lower-cost method for removing PFAS from contaminated farmland while also capturing carbon dioxide from the atmosphere, offering what they say could be a practical alternative to existing remediation techniques.
The approach, detailed in a new study published in Proceedings of the National Academy of Sciences, combines soil treatment with carbon removal technologies to address two environmental challenges at once. Researchers say the process could allow contaminated farmland to remain in agricultural use during remediation, unlike many existing cleanup methods that require land to be taken out of production.
The research is based on data from agricultural sites in Maine, where PFAS contamination linked to the historical use of sewage sludge as fertilizer has affected farms. The researchers estimate that approximately 1.2 million hectares of U.S. cropland may be significantly contaminated with PFAS.
PFAS, or per- and polyfluoroalkyl substances, are a group of persistent synthetic chemicals used for decades in products ranging from non-stick cookware and food packaging to cosmetics.
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“There is an obvious need for new tools to help farmers affected by ‘forever chemicals’ contamination,” said Noah Planavsky, a professor of Earth and planetary science at Yale University and principal investigator of the study, in a statement. “We outline a path that allows farmers to continue to work their land while restoring soil health.”
Current options for remediating PFAS-contaminated farmland are both disruptive and expensive, the researchers noted. Excavating contaminated soil or using high-temperature treatment can cost between $800,000 and $1.6 million per hectare, they said, placing nationwide cleanup costs in the trillions of dollars.
The proposed alternative begins by applying a thin layer of crushed alkaline rock to contaminated fields. Raising the soil’s pH accelerates the uptake of one of the most common PFAS compounds, perfluorooctanesulfonic acid (PFOS), by plants growing on the site.
The harvested plant material is then converted into biochar, a charcoal-like material produced by heating biomass under controlled conditions. According to the researchers, this process destroys both PFOS and another widely studied PFAS compound, perfluorooctanoic acid (PFOA).
The team estimates the treatment would cost about $1,460 per hectare each year. Repeated annually for up to 20 years, the total remediation cost would exceed $29,000 per hectare, including compensation for farmers’ lost income during treatment.
Researchers also say the system offers climate benefits. Enhanced weathering from the crushed rock, combined with biochar production, removes carbon dioxide from the atmosphere. On a national scale, the approach could remove an estimated 10.5 million metric tonnes of carbon dioxide annually.
“Though this study is U.S.-focused, based on the available data, PFAS are a challenge globally,” announced Jake Thompson, a postdoctoral researcher in Yale’s Department of Earth and Planetary Sciences and the study’s lead author, in a statement. “This issue — the contamination of agricultural land with PFAS — disproportionately hurts small farmers and organic farmers, who used fertilizers with PFAS before the full extent of the problem was known.”
Thompson said the approach could give affected farmers a practical means of restoring contaminated land.
“This is a real pathway to actually give farmers in this situation some agency over their land and leave the soil in better condition than it was before,” he added.
The project recently received a Yale Planetary Solutions Impact Accelerator grant to support commercialization efforts. The research was also supported by the Schmidt Family Foundation and the U.K.’s Natural Environment Research Council.
