“Eco-friendly” paper drinking straws contain long-lasting and potentially toxic chemicals, a new study has concluded.

In the first analysis of its kind in Europe, and only the second in the world, Belgian researchers tested 39 brands of straws for the group of synthetic chemicals known as poly- and perfluoroalkyl substances (PFAS).

PFAS were found in the majority of the straws tested and were most common in those made from paper and bamboo, found the study, published in Food Additives & Contaminants.

PFAS are used to make everyday products, from outdoor clothing to non-stick pans, resistant to water, heat and stains. However, they are potentially harmful to people, wildlife and the environment. They break down very slowly over time and can persist over thousands of years in the environment, a property that has led to them being known as “forever chemicals.”