Thames Water pilot shows surge in toxic forever chemicals

Pilot tests for a Thames Water recycling scheme have shown levels of a toxic ‘forever chemical’ rising to 13 times the legal limit. The multimillion-pound project aims to combat drought by pumping treated sewage into the River Thames to replace water abstracted during low-flow periods.

Technical notes indicate that the recycling system significantly increased levels of perfluorooctane sulfonate (Pfos), a type of per- and polyfluoroalkyl substance (PFAS) and suspected carcinogen. These chemicals are known as ‘forever chemicals’ because they do not break down in the environment. Standard wastewater treatment plants are not currently designed to filter or destroy them.

The proposed system involves abstracting up to 75 million litres of water a day from the Thames at Teddington and replacing it with treated sewage from the Mogden treatment plant. However, test results suggest the scale of sewage input may make it difficult for the water to meet current legal standards for pesticides and forever chemicals.