About 20m acres of cropland in the United States may be contaminated from PFAS-tainted sewage sludge that has been used as fertilizer, a new report estimates. PFAS, or per- and polyfluoroalkyl substances, are a class of about 9,000 compounds used to make products heat-, water- or stain-resistant. Known as "forever chemicals" because they don't naturally break down, they have been linked to cancer, thyroid disruption, liver problems, birth defects, immunosuppression and more. Dozens of industries use PFAS in thousands of consumer products, and often discharge the chemicals into the nation's sewer system. The analysis ... is an attempt to understand the scope of cropland contamination stemming from sewage sludge, or biosolids. Regulators don't require sludge to be tested for PFAS or closely track where its spread, and public health advocates warn the practice is poisoning the nation's food supply. Sludge is a byproduct of the wastewater treatment process that's a mix of human excrement and industrial waste, like PFAS, that's discharged from industry's pipes. EPA records show over 19bn pounds of sludge has been used as fertilizer since 2016 in ... 41 states. It's estimated that 60% of the nation's sludge is spread on cropland or other fields annually. The consequences are evident in the only two states to consistently check sludge and farms for PFAS contamination. In Maine, PFAS-tainted fields have already forced several farms to shut down.