Some paper and bamboo straws contain so-called “forever chemicals” that could make them a less-than-ideal alternative to plastic, researchers have found.

Scientists in Belgium recently tested dozens of straws from supermarkets, retail stores and fast-food restaurants in the country, and found that the majority contained PFAS — a family of synthetic chemicals used in the manufacture of consumer products because they can resist stains, grease and water.

The researchers sampled 39 brands of straws made of paper, bamboo, glass, stainless steel and plastic. Of those, 27 were found to contain PFAS, though the concentrations were low.

The results were published Thursday in the journal Food Additives and Contaminants.

PFAS, an acronym for per- and polyfluoroalkyl substances, are often referred to as “forever chemicals” because they linger almost permanently in air, water and soil. They are frequently detected in food wrappers, cosmetics, carpet, furniture and textiles such as raincoats or workout clothes.

Of the straws tested in the study, those made of paper were the most likely to contain PFAS: The chemicals were detected in 18 out of 20 brands. Four out of five bamboo straws sampled contained PFAS, compared to three out of four plastic straws and two out of five glass straws. All five stainless steel straws analyzed were PFAS-free.

Previous research in the U.S. has also detected PFAS in paper and other plant-based straws, among many other types of cookware and packaging.

Exposure to PFAS can be associated with low birth weight, high cholesterol, thyroid disease and an increased risk of kidney and liver cancers, but researchers are still learning about these health risks and aren’t sure which levels of exposure are problematic.

Thimo Groffen, an author of the new study and environmental scientist at the University of Antwerp, said it’s not clear whether the manufacturers of the straws he analyzed are intentionally adding PFAS as a waterproof coating. Other possibilities, he said, are that PFAS accidentally