In 2020, shortly after Winslow and Laura Robinson bought a farm in Maine, they were surprised to learn that sewage sludge had been used as fertilizer on that land decades earlier, leaving behind chemicals known as 'forever chemicals' that remained in the soil.

Chemically contaminated American farmland

Maine farmers were at the forefront of revealing this problem affecting farmland across the country; sewage sludge from wastewater treatment plants has been widely used on farms since the 1970s, both to divert it from landfills and to provide cheap fertilizer for farmers.

These materials are also sold under the name 'biosolids' in some garden supply stores as home fertilizer, and you may be using them in your own garden without knowing. However, this sewage can contain high levels of perfluoroalkyl and polyfluoroalkyl substances (PFAS), which are called 'forever chemicals' because they do not degrade and can migrate from soil into food. Although the implications of these compounds in food are not fully understood, they have been linked to liver disease, cancer, and other illnesses.

Search for a lower-cost method

In the context of removing these harmful forever chemicals, a new study by Yale University published in the Proceedings of the National Academy of Sciences (PNAS) proposes a low-cost method for farmers to address this issue while also contributing to the fight against climate change.

Current methods for treating soil contaminated with PFAS are extremely costly—sometimes up to one million dollars per acre—and are typically used only in specific sites such as airports or military bases, as they require soil excavation and removal. Therefore, cleaning millions of acres of American farmland this way is not practical or feasible.

Noah Planavsky, a professor of geochemistry at Yale University specializing in soil health, decided to work on this problem after learning details from farmers. Planavsky says: 'Farmers were deeply worried about this, and they felt they were not getting accurate information, facing a huge problem while being ignored or manipulated and misled.'

Growing crops that absorb toxins

The study tested a simple approach for treating contaminated soil: farmers grow crops known to quickly absorb PFAS, such as hemp and sunflowers. Farmers also add crushed alkaline rocks to the soil to raise the pH, which helps plants absorb larger amounts of chemicals. When the crops are harvested, they are subjected to very high temperatures in the absence of oxygen, which breaks down PFAS compounds.

Planavsky says: 'Although they are called forever chemicals—because they are extremely stable and durable—they can be destroyed at high temperatures, a well-documented fact.' The process produces biochar, which can be returned to the soil to help capture more forever compounds.

Reducing pollution levels to safe limits within a decade

Scientists estimate that this method could, in some cases, reduce pollution levels to safe limits within a decade.

Another challenge is that sewage sludge is still used on some farms in most states. It is not surprising that its use has been widespread historically; Laura Robinson, an organic farmer in Maine who participated in the Yale study, says: 'Farmers barely cover their expenses; farming is not very profitable. So if you are offered free fertilizer for vast hay fields, it is natural to accept, especially since authorities were assuring its safety.'

Is the cost of treatment and purification reasonable?

The scientists' method is much cheaper (a vast cost difference) compared to other methods used to remove forever chemicals, and it has an added benefit: adding crushed rock to the soil helps capture carbon dioxide.

It is worth noting that Planavsky also conducts research on this type of carbon removal—known as 'enhanced rock weathering'—and co-founded a startup called Lithos that separately works on using rock dust on other farms.

Theoretically, revenue from selling carbon removal credits could fund soil treatment for forever chemicals. Planavsky says: 'We need to remove billions of tons of carbon dioxide to meet our climate goals. There is also scientific consensus that PFAS in the food system raises real public health concerns on a broad scale... and I think most people agree that funding for these two issues is insufficient.'

* Fast Company magazine.