Concentrations of two toxic ‘forever chemicals’ in England’s rivers have fallen by almost a third over a decade, Environment Agency figures show, although the total amount remaining in the environment is likely to be unchanged.

Data published on Thursday show river concentrations of PFOS fell by 30% and PFOA by 29% over the past 10 years. Levels in freshwater fish dropped by 49%. The declines have been attributed to tighter restrictions introduced after evidence linked the chemicals to harm to human health and the environment.

The distinction between lower concentrations and less pollution overall is important. The agency’s report acknowledges that these exceptionally persistent chemicals have been diluted and washed into the sea, rather than destroyed.

PFOS was all but banned in the UK in 2010, followed by PFOA in 2020. Research beginning two decades ago linked them to tissue damage in animals and increased rates of serious health conditions, including testicular cancer.

Dr David Megson, reader in environmental forensics at Manchester Metropolitan University, welcomed the findings: “It's brilliant to see how far we have come in the last 10 years.”

But the regulatory challenge extends well beyond those two compounds. There are thought to be about 15,000 other PFAS, the wider family known as forever chemicals, with roughly 200 frequently used. First developed in the US in the 1930s, PFAS became useful in products such as frying pans and firefighting foam because of their resistance to oil and water and their electrical properties.

The agency says uncertainty remains about the toxicity of many PFAS, but argues that its findings strengthen the case for regulating them collectively rather than individually. The chemicals industry has long opposed that approach, citing limited or absent evidence of toxicity for other PFAS and vital applications, including life-saving medical equipment.

The agency now regularly tests for 60 other PFAS. Earlier this month, the government announced plans to monitor levels in people’s bodies. Old landfill and industrial sites have been major sources of contamination in rivers such as the Mersey.

Megson said further work was needed and that the report provided a foundation for investigations to make polluters pay for damage they had caused. Destroying the chemicals remains difficult: high-temperature incineration is one of the few permanent methods, and only two suitable sites currently exist in the country.