Pollutants known as "forever chemicals," which do not degrade in the environment, accumulate in the body, and may be toxic, have been found in high concentrations at thousands of sites across the UK and Europe, according to a major mapping project.

Perfluoroalkyl and polyfluoroalkyl substances (PFAS), a family of about 10,000 chemicals valued for their nonstick and detergent properties, have been found in water, soils, and sediments from a variety of consumer products, firefighting foams, waste, and industrial processes, according to the map.

What are PFAS' effects? 

Two PFAS have been linked to a number of health issues. Kidney and testicular cancer, thyroid disease, ulcerative colitis, high cholesterol, and pregnancy-induced hypertension have all been linked to PFOA. Perfluorooctane sulfonic acid (PFOS) has been linked to reproductive, developmental, liver, kidney, and thyroid dysfunction.

PFAS has been linked to immunotoxicity at low levels.

Where were the substances discovered? 

The substances have been discovered at approximately 17,000 locations throughout the United Kingdom and Europe. PFAS have been found in high concentrations of more than 1,000 nanograms per liter of water at approximately 640 sites, and above 10,000ng/l at 300 sites.

“These sorts of concentrations raise concerns with me,” said Prof Crispin Halsall, an environmental chemist at Lancaster University. “You have the risk of livestock gaining access to those waters and [then PFAS is] in the human food web.”

Halsall says there are also risks involving people “accessing wildlife as food sources like fishing and wildfowl”.

The map shows that Belgium has the highest levels of pollution, with PFAS concentrations in groundwater reaching 73m ng/l near 3M's (Multinational conglomerate company) PFAS manufacturing site in Zwijndrecht, Flanders.

Residents within 15 kilometers (10 miles) of the site have been advised not to eat any eggs laid in their gardens and to avoid eating homegrown vegetables. Meanwhile, 70,000 people living within a 5-kilometer radius of the plant have been offered a PFAS blood test.

3M says it will clean up the site and has "signed an agreement with the Flemish region... for an investment of €571 million" (£503 million). It has also announced plans to exit PFAS manufacturing "and work to discontinue the use of PFAS across its product portfolio by the end of 2025".

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The highest levels of PFAS were found in a discharge from a chemicals plant on the River Wyre, above Blackpool, in the United Kingdom. According to data from Defra's Centre for Environment, Fisheries, and Aquaculture Science, fish in the river contain high levels of PFAS, with flounder containing up to 11,000ng/kg.

Prof Ian Cousins, an environmental scientist at Stockholm University, stated that sites with readings greater than 1,000ng/kg should be "urgently assessed" in order to be remedied. “At [highly] contaminated sites, local authorities should consider testing to ensure that PFAS levels are safe in local produce. This would help determine if local health advisories and publication campaigns to discourage regular consumption of wild fish, shellfish, free range eggs … are needed,” he added.

Halsall explained that “PFAS in groundwater is a big problem because if that groundwater is abstracted for farming, or more importantly for humans as a water source, then you’ve got PFAS in your drinking water and it’s very difficult to remove.”

PFAS water contamination 

The map shows that drinking water sources in the UK have been contaminated with PFAS, but water companies claim that the chemicals do not make it into the final tap water because it is either blended with another source to dilute the PFAS or removed through a specialized treatment process.

Data obtained by The Guardian and Watershed from water companies and the Environment Agency show that since 2006, approximately 120 samples of drinking water sources have contained concentrations of PFOS or PFOS above the 100ng/l level - the point at which the Drinking Water Inspectorate's (DWI) guidelines state that water companies should take action to reduce it before supplying it to people's homes. The DWI guideline limit was much higher until 2009, at 3,000ng/l.

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In the United States, the Environmental Protection Agency has established a health advisory limit of 0.004ng/l for PFOA and 0.02ng/l for PFOS in drinking water.

The Environmental Protection Agency of Denmark requires that drinking water contain no more than 2ng/l of the sum of four PFASs.

According to Rita Loch-Caruso, a toxicology professor at the University of Michigan, drinking water limits for PFAS are continuing to be reduced in response to growing evidence about their health effects. "We're finding health effects at increasingly low concentrations - in the single digits," she explained.