PFAS

per- and polyfluoroalkyl substances

PFAS are synthetic 'forever chemicals' that resist breaking down and build up in the body, which they reach mainly through drinking water.

PFAS are a class of thousands of synthetic chemicals built around the carbon-fluorine bond, the strongest single bond in organic chemistry. That bond is why they are called forever chemicals: they do not meaningfully break down in the environment or in the body, so ongoing low-level intake builds body burden over time instead of washing out. Their original jobs were non-stick coatings, stain and water repellents, and firefighting foam. They now turn up in soil, in water, and in roughly 99 percent of US adult blood. PFOA and PFOS are the most studied; PFOA is classified by IARC as carcinogenic to humans. In the home, PFAS is a source-water contaminant, meaning it enters the supply upstream rather than from your pipes, so the point of agency is the water you drink and the filter on it. For the mechanism, thresholds, and what actually removes it, see the full PFAS page.