Processes intended to decontaminate noxious liquid landfill waste before it enters rivers and sewers have been found to increase the levels of some of the worst toxic chemicals, a study has shown.

Landfills are well known to be a main source of PFAS forever chemicals – or per- and polyfluoroalkyl substances – but the new study shows that the treatment plants designed to clean up the liquid waste can instead boost the levels of banned PFAS such as PFOA and PFOS, in some cases by as much as 1,335%.

PFAS are a family of about 15,000 human-made chemicals with nonstick properties that are used in a wide range of consumer products and industrial processes. They can take thousands of years to break down in the environment and the handful that have been studied in detail have been found to be toxic, with PFOA and PFOS linked to cancers and other diseases. PFAS pollution is widespread, having been found in the remotest parts of the world, and it is thought every US citizen has it in their blood.