What they are: PFAS (pronounced “pea-fass”) are synthetic compounds that have been linked to serious health problems. The federal government has been criticized for moving too slowly to find polluted sites and protect the public.
What it means: PFAS is an acronym that stands for “per- and polyfluoroalkyl substances.”
Why they’re called “forever chemicals”: Because of how difficult it is for the human body or the environment to break them down into less harmful material. They have been found widely in water, soil and human blood.
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Where they come from: Private companies created them, and found uses for them because they don’t break down. They have been used in nonstick pans, and applied to paper and fabric to make them resistant to water, grease and stains. They have been used to reduce machine friction and in firefighting foam. Manufacture of some forms has slowed, but thousands of new and relatively untested PFAS varieties have been introduced.
Health effects: Depending on dosage, PFAS affect growth, learning and behavior of infants and older children. Exposure may lower a woman’s ability to get pregnant, block important natural hormones, increase cholesterol levels, weaken the immune system, and increase risk of cancer and other diseases of the liver, kidneys and pancreas.
How they spread: People are most likely to be exposed by drinking water contaminated by manufacturers and heavy users of PFAS. A 2016 Harvard study found drinking water for 6 million people is contaminated. Highest levels were in drinking water near industrial sites, military fire training areas and wastewater treatment plants.
How they’re regulated: A federal health advisory was set at 70 parts per trillion in drinking water in 2016, but a 2018 report from the leading federal toxicology agency said the level was up to five times too high times too high to protect infants and fetuses. Few states have enforceable standards. Home filtration systems are available.
[Editor's note: This story has been updated to reflect a correction. The original misstated the scale of the difference between the federal health advisory for PFAS of 70 parts per trillion and that of the leading federal toxicology agency, the Agency for Toxic Substances and Disease Registry.]