But some of these same features worry environmental health specialists because traces of the chemicals linger and have been detected in the bloodstream of a large segment of the population, although typically at low levels. In some cases, detectable levels of the older class chemicals have been declining as major manufacturers have developed alternatives they say are safer.

Some researchers cite lingering concerns about a chemical spill more than a decade ago. The health of residents of Parkersburg, W.Va., is still monitored related to a spill of an older form of PFAS from a nearby chemical plant. A class-action lawsuit accused DuPont, which owned the plant, of knowingly contaminating the residents’ groundwater, and the company faces new accusations, in a separate report being issued Friday by the nonprofit Environmental Working Group, that it is not living up to the terms of a court settlement.

Mr. Samples, from DuPont, which is based in Delaware, disputed any suggestion that it was not complying with those terms.

But Dr. Paul Brooks, who helped conduct a study in the West Virginia case that found probable links between the chemical and health issues like thyroid disease and kidney cancer, said DuPont needed to do more to ensure that local residents were participating in the monitoring program. He said he was not convinced that the alternative chemicals that DuPont and other companies were selling would eliminate the health threat.

“When you have something that is a first cousin or brother-in-law to a chemical that we are certain is carcinogenic, you have to somehow prove that it is safe before you use it — that it is not injurious,” he said. “You just have to be cautious.”

Some environmental scientists point to a chemical called GenX as an example of a newer but questionable alternative. Some studies have linked GenX to short-term symptoms like eye and skin irritation in humans, as well as liver damage in animals. Mr. Samples, of DuPont, which manufacturers GenX, said that the tests involved exposing animals to levels so concentrated that they were intended to cause health complications. He also said the chemical was used in industrial settings, not as an ingredient in consumer products.

Still, environmental and health specialists are urging consumers to avoid products containing PFASs “whenever possible.”

“It’s likely they’re going to have some health effects, it just may take us a while to figure out what it is,” said Thomas F. Webster, a professor of environmental health at Boston University’s school of public health who was an author of a paper seeking more scrutiny of PFASs. “It might take five or 10 years to really do the research.”