As one of the birthplaces of the industrial revolution, the River Mersey in northern England is no stranger to pollution flowing into its waters. Now it's got a new problem: monitoring shows the amount of forever chemicals, also known as PFAS, entering the Mersey catchment area is among some of the highest in the world.

In this episode we speak to water scientist Patrick Byrne at Liverpool John Moores University in the UK about why so many per- and polyfluoroalkyl substances (PFAS), are still making it into our rivers, many from sources that are lying hidden. Identifying these sources of pollution, can help prioritise how to clean them up.

This episode was produced by Mend Mariwany, Katie Flood and Gemma Ware. Sound design and mixing by Michelle Macklem and theme music by Neeta Sarl. Read the full credits for this episode and sign up here for a free daily newsletter from The Conversation.

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• You can be exposed to PFAS through food, water, even swimming in lakes – new maps show how risk from ‘forever chemicals’ varies
• Australia has banned 3 ‘forever chemicals’ – but Europe wants to ban all 14,000 as a precaution
• How I tracked the biggest hidden sources of forever chemical pollution in UK rivers – new study