A major mapping project has shown that pollutants known as “forever chemicals” have been found at high levels at thousands of sites across the UK and Europe. Per- and polyfluoroalkyl substances (PFAS) are a family of about 10,000 chemicals that make their way into water, soils and sediments from a wide range of consumer products, firefighting foams, waste and industrial processes. PFAS don’t break down in the environment; they build up in the body and may be toxic. Marco Werman speaks with Leona Hosea, an environmental journalist for Watershed Investigations, a UK-based investigative journalism nonprofit that was involved in the mapping project.