The so-called "forever chemicals" are a broad class of substances that have been used over the last seven decades in a huge variety of industrial applications. They are technically known as per- and polyfluoroalkyl substances, or PFAS, and their crucial characteristic is that they are very stable. This makes them super useful but has led to growing concerns about how these molecules impact human health and the environment.

A review of current studies on forever chemicals has now been published in Science. It looks at what we know about PFAS and finds that we actually know very little. There are more than 8,000 compounds in this class of chemicals so understanding their detailed properties and their effects when they accumulate in water, soil, and human tissues is an enormous undertaking.

“One of the biggest findings is that there is much that we don’t know. There are a lot of data gaps and unknowns when it comes to these compounds, just because of the sheer size of this compound class,” lead author Dr Marina Evich from the Environmental Protection Agency, told IFLScience.

“We end up with some kind of patchwork data with some of the compounds we know quite a bit about, especially the ones we call legacy PFAS and then others we don’t even know the structure of these compounds much less the toxicological endpoints.”

A lot of the unknowns are due to the confidential business nature of the synthesis of these substances, given their industrial use – from fire-retardant foams to stain-proof textiles and jet engine blades. Some classes have molecules with a huge mass range, with the smallest being about five times the mass of caffeine and the largest being 100 times bigger.

“We don’t know what we don’t know. It is very difficult to look for a compound if we don’t know it exists. It’s difficult to study the toxicology if we don’t know the structure of it,” Dr Evich told IFLScience. “It would be useful to the community to know more in general; which compounds are being manufactured? What are the quantities they are being manufactured in? what are the uses for these compounds?"

Some of the most famous PFAs at the center of environmental scandals have been phased out and replaced by different compounds but it is not certain that they are necessarily safer due to the clear lack of knowledge on these substances. Remediation efforts to clean the environment are being employed but they are only just beginning, so there is a need for longer-term strategies.

“I think one of the biggest concerns with these compounds is that they are so stable. They are really not going anywhere. They are going to be around longer than we are going to be around,” Dr Evich told IFLScience.

“Maybe one place we can start is by prioritizing uses. These PFAS are in very high demand and have properties that consumers particularly enjoy. These compounds repel both oil and water, and everybody loves that sort of technology. Right now there are more than 200 diverse applications for them. They are used in fast-food containers coating, in anti-staining fabrics, some carpets, upholstery, clothing. They are used in electronics, etc. By prioritizing uses we mean that we don’t need to use them for everything as well as starting to seek alternatives.”