The class-action lawsuit and thousands of personal injury claims that followed were, in many ways, a triumph for the plaintiffs. In total, DuPont and its spinoff company Chemours wound up paying more than $1 billion as a result of the litigation. Yet in the more than two years I have been writing about these chemicals, the crisis that at first seemed limited to those two specific compounds has turned into a much larger and messier conundrum. That’s because, while they were phasing out PFOS and PFOA, many of the companies were also phasing in replacement chemicals that recent research in lab animals has shown pose some of the very same problems. It’s unclear what these chemicals will do to people, which is precisely the problem.

When DuPont introduced GenX, in 2009, the company promoted it as a sustainable alternative to PFOA. The new chemical, which is based on a chain of six rather than eight carbons, does exit the human body more quickly than PFOA. But like PFOA, GenX is a “forever chemical,” expected to persist on the planet long after humans are gone. According to studies DuPont submitted to the E.P.A., GenX had many of the same effects on lab animals that PFOA did, including changes in the size and weight of animals’ livers and kidneys, alterations to their immune responses and cholesterol levels, weight gain, reproductive problems and cancer.

I found those studies about GenX in an E.P.A. database almost two years ago. Since then, GenX has been detected in the drinking water of more than 200,000 people in North Carolina. Their water comes from the Cape Fear River, where another factory first owned by DuPont and later Chemours emitted its chemical waste for years. GenX has also recently been found in the groundwater near the same West Virginia plant that caused the PFOA contamination. Testing is underway to see whether it is also in drinking water there.

While researchers are now turning their attention to the health effects of GenX, it will take years to amass enough information to fully understand it. Even if scientists were to quickly catalog its effects, GenX is only one chemical. Recent water testing near the same Chemours plant in North Carolina found that GenX made up a small portion of the PFAS chemicals. Other related compounds have yet to be named, let alone studied or regulated.

Up to this point, we have treated these mystery chemicals with a bizarre optimism: that despite the similarities, somehow they won’t cause the same problems that their close relatives do. Combined with our longstanding federal policy of requiring definitive proof of environmental dangers before taking action, this way of thinking has led to lots of regrettable substitutions. One is underway now as the Department of Defense is phasing out firefighting foams containing PFOS and PFOA, which have caused contamination near military bases and airports, and phasing in foam that contains other PFAS chemicals.

Firefighting foam that doesn’t contain any of the PFAS chemicals, which a growing number of entities around the world are beginning to adopt, is part of the solution. The approach Washington State is taking — banning the entire class of compounds, instead of just one — presents another. Washington’s new laws won’t make it any easier to clean up the extensive mess we’ve already made. Nor can they undo the exposure people have already had or address the health problems that has caused. But by tackling the whole class of dangerous compounds together, the state has shown a way out of the endless contamination cycle for the rest of us, who keep hoping for the best and getting the worst.