A growing problem of modern industrial agriculture is the accumulation of ‘forever chemicals’ like PFAS in the soil. But now, researchers have developed a three-part plan involving hemp plants to draw it out of the soil—one that they say will cost a fraction of regular toxic clean up, and remove CO2 while they’re at it.
For decades, groups of persistent synthetic chemicals like PFAS have been used to make a range of products including food-contact materials, so accumulating in our bodies, and then our waste—which often becomes fertilizer. This has created a situation where swathes of farmland is now straining under a toxic load. Some farms in US states like Maine have even been forced to shut down because their soils exceeded safe limits for crop production and consumption.
The new study proposes that the solution to this industrial threat is plants, rock dust and biochar. The research, led out of Yale University, developed a pollution remediation model based on available data from farms in Maine and looked at two types of PFAS: PFOS and PFOAS. They first considered what would happen if they applied basalt rock dust to the soil, a common approach for sequestering carbon dioxide—but which also changes the pH in ways that makes chemicals more mobile in the soil.
While that might sound counterintuitive to the goal, it makes chemicals like PFAS more available for uptake by plants—like the hemp and perennial grasses the researchers tested in the study. They modeled the effects of this plant growth, and then also looked at what would happen if the cuttings were turned into biochar, the heat in this process being a way to neutralize the toxicity of the chemicals. As a final step, they considered scattering this biochar product across other particularly contaminated farmlands as a method to trap forever chemicals and stop them from entering run off and further polluting other ecosystems from farms.
The application of the rock dust was found to increase uptake of PFOS via plants, accelerating the decline of this chemical in the soil by between 20 and 40 percent. The effects weren’t as strong for PFOAS, but PFOS are considered the bigger regulatory priority, the researchers say.
If the uptake plants were recycled into biochar and spread over contaminated farmland, this would immobilize enough PFAS to reduce the runoff of these chemicals by 95%. Overall, they found that these combined solutions could limit PFAS levels in US soils to below the thresholds of concern within a decade. The double-whammy of rock dust and biochar would also remove 10.5 million metric tons of carbon dioxide annually if these remediation methods were scaled up cross-country.
Conventional clean-up methods would involve excavating and burning a huge quantity of farmland soil: this huge endeavour would cost an estimated $1.6 million per hectare, ultimately amounting to $8 trillion ultimately. Meanwhile, the researchers calculate that their approach would cut that per-hectare annual cost to a fraction—just $1,460.
The study focused on the US, but its authors are keen to emphasize its rest-of-the-world relevance. In Europe 50% of sewage sludge—about 10 millions tons—produced annually is spread over farmland; China applies the same amount to its soils. In the UK that figure is 70%. PFAS is likely to keep accumulating in soil, but their solution to this problem is “broadly applicable,” the researchers say.
“We outline a path that allows farmers to continue to work their land while restoring soil health.”
Planavsky et. al. “Integrated thermal and phytoremediation of agriculturalsoils impacted by PFAS.” PNAS. 2026.
Image: ©Anthropocene Magazine
