Restoring Soil Health Low-Cost Solution: Removing ‘Forever Chemicals’ from Farmlands

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A Yale-led team has developed a strikingly cheap way to clean "forever chemicals" out of farmland — using crushed rock and homemade charcoal instead of costly excavation or incineration.

A Yale-led research team has proposed a less expensive — and more environmentally friendly — method for removing certain “forever chemicals” from millions of acres of farmland in the United States and around the world. The new process, which is based on data from agricultural sites in Maine. They say it has the potential to address two connected environmental challenges: remediating per- and polyfluoroalkyl substances (PFAS) that have contaminated agricultural land for decades and scaling up the use of enhanced weathering to remove carbon dioxide from the atmosphere.

Just as important, the new approach allows previously contaminated cropland to once again be used for an agricultural purpose — unlike current remediation methods. “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 in Yale’s Faculty of Arts and Sciences and the son and brother of farmers. He is also a faculty member of the Yale Center for Natural Carbon Capture and principal investigator for a new study published in the journal Proceedings of the National Academy of Sciences which describes the new method.

How PFAS Ended up on America's Farms

PFAS, also known as “forever chemicals,” are a class of toxic, man-made chemicals that have been used for decades in hundreds of products, from dental floss and lipstick to frying pans and pizza boxes. PFAS are ubiquitous in the United States, having made their way into groundwater and soil, and then eventually croplands. Only in recent years have scientists begun to understand the full scope of PFAS contamination not just nationally but worldwide.

“Though this study is U.S.-focused, based on the available data, PFAS are a challenge globally,” said Jake Thompson, an associate researcher in the Planavsky Lab and first author of the study. He is a postdoctoral researcher in Yale’s Department of Earth & Planetary Sciences.

“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.

Breaking Down “Forever Chemicals”

New Solutions to the PFAS Problem

How did contamination of “forever chemicals” become so widespread? For years, individuals and factories would flush PFAS into their local sewer system, as part of wastewater. Because forever chemicals don’t decay, they made their way into sewage sludge, which was marketed to farmers as a natural fertilizer.

That cycle continued for decades, until scientists and public health officials began raising concerns. PFAS, which accumulate in the body over time, have been linked to certain cancers, fertility problems, and immune response issues. The state of Maine, where forever chemicals were found in milk from a dairy farm in 2016, banned the application of sewage sludge on agricultural land in 2022. (Perfluorooctanoic acid [PFOA], the most widely studied PFAS, was classified as a human carcinogen in 2023, according to the National Institutes of Health.)

Thompson estimated that 1.2 million hectares (2.96 million acres) of U.S. cropland may be significantly impacted by PFAS.

Meanwhile, current remediation options for farmland have been limited — and expensive.

Farmers can excavate the contaminated soil, for instance, or use machines to essentially burn the soil. The cost for such remediation is $800,000 to $1.6 million per hectare, meaning the bill for removing PFAS from American farmland would run to $8 trillion.

How the New Two-Step Process Works

The Yale-led remediation model requires only a fraction of that cost. It is based on two of the most well-known PFAS — perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS).

The system’s first step involves spreading a thin layer of crushed, alkaline rock to the area. This raises the soil’s pH level, which, in turn, accelerates the removal of PFOS from the soil via plants growing there.

The next step is to create “biochar” — a specialized form of charcoal — from the harvested plants, which destroys both PFOS and PFOA chemicals. This is done by heating the plants with either a large, stationary machine or a smaller, mobile unit.

Researchers estimate that remediation using this new model costs $1,460 per hectare. Since the process would be repeated each year for up to 20 years, the total cost would be just over $29,000 per hectare — which includes compensation for the farmer’s lost income during treatment.

The system also has the added benefit of removing carbon dioxide — a greenhouse gas and main contributor to climate change — via enhanced weathering of the crushed rock applied to the soil and biochar generated from biomass. At a national scale, the system could remove 10.5 million metric tons of carbon dioxide per year, the researchers estimate.

“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,” Thompson said.

The research project recently received a Yale Planetary Solutions Impact Accelerator (PSIA) grant. The grants, recently introduced by Yale Planetary Solutions and Yale Ventures, provide mentorship and commercialization guidance to transformative projects that aim to address the root causes of environmental challenges.

Original Article: Integrated thermal and phytoremediation of agricultural soils impacted by PFAS; Proceedings of the National Academy of Sciences; DOI:10.1073/pnas.2600786123

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