PFAS, or per- and polyfluoroalkyl substances, are a class of about 9,000 compounds used to make products heat-, water- or stain-resistant. They are known as "forever chemicals" that are linked to cancer, thyroid disruption, liver problems, birth defects, and more.

Since they don't naturally break down, these chemicals contaminate cropland when they're mixed with sewage sludge. Sludge is a byproduct of treating wastewater and is a mix of human excrement and industrial waste discharged from industrial pipes.

Records from the Environmental Protection Agency show that over 19 billion pounds of sludge have been used as fertilizer since 2016 in the US, and it's estimated that 60% of US sludge is spread on cropland.

These chemicals end up in crops, cattle, water and humans, and the public health toll is unknown. Some PFAS-tainted fields in Maine have had their farms completely shut down.

Advocates say that the health cost of using sludge outweighs the benefits, with sludge being linked to public health problems, contaminated beef, and contaminated drinking water.