PFAS chemicals have been identified in synthetic turf, according to lab tests performed on several samples of the artificial grass that were shared with The Intercept. The presence of the chemicals, members of a class that has been associated with multiple health problems, including cancer, adds to growing concerns about the grass replacement that covers many thousands of acres in parks, schools, professional sports stadiums, and practice fields around the U.S.

In one set of tests, the PFAS chemicals were detected in the plastic backing of two samples of the turf. In another, in which the “blades” of the artificial grass were analyzed, scientists measured significant levels of fluorine, which is seen as an indication of the presence of the chemicals.

“We’re seeing unexplained levels of fluorine-based compounds in all of the eight samples of turf grass blades we’ve looked at,” says Jeff Gearhart of the Ecology Center, a nonprofit environmental research group based in Michigan that tested the turf blades. The samples of the blades that tested positive for fluorine were made by two different companies, Shaw Industries and Turf Factory Direct.