The Environmental Protection Agency is proposing that nine PFAS, also known as "forever chemicals," be categorized as hazardous to human health.

The EPA signed a proposal Wednesday that would deem the chemicals "hazardous constituents" under the Resource Conservation and Recovery Act.

For the agency to consider a substance a hazardous constituent, it has to be toxic or cause cancer, genetic mutation or the malformations of an embryo. The full list of the nine substances can be found here.

The agency cited various studies in which forever chemicals were found to cause a litany of "toxic effects" in humans and animals, including, but not limited to cancer, a decreased response to vaccinations, high cholesterol, decrease in fertility in women, preeclampsia, thyroid disorders and asthma, the EPA said.

Short for "per-and polyfluoroalkyl substances," PFAS cover thousands of man-made chemicals. PFAS are often used for manufacturing purposes, such as in nonstick cookware, adhesives, firefighting foam, turf and more.

PFAS have been called "forever chemicals" because they break down very slowly and can accumulate in people, animals and the environment. Last summer, a study by the U.S. Geological Survey found that the man-made chemicals are present in nearly half the country's tap water supply.

The survey tested for 32 types of PFAS, though there are more than 12,000, the USGS said, and they can pose a health threat even at very small amounts.

In June, the chemical manufacturer 3M said it would pay about $10 billion in lawsuit settlements to help detoxify water supplies across the country, after plaintiffs claimed the company's firefighting foam and other products were responsible for contaminating tap water with PFAS.

The proposed rule will be open for public comment once it is uploaded to the Federal Register, under docket number EPA-HQ-OLEM-2023-0278.