People living within 10 miles of Heathrow and Gatwick airports have been supplied with drinking water containing increased levels of toxic ‘forever chemicals’ known as PFAS, openDemocracy can reveal.

SES Water, which supplies customers to the north of Gatwick, admitted in documents obtained under the UK’s Environmental Information Regulations that it had detected three such PFAS chemicals (which stands for per- and polyfluoroalkyl substances) in drinking water leaving its treatment works for customers’ taps, each at levels of 15 nanograms per litre of water (ng/l) or below.

Similarly, Thames Water revealed that water at five of the 105 treatment plants it runs within 10 miles of Heathrow was found to contain PFAS quantities in excess of 10 ng/l.

These contamination levels, which may be linked to the use of firefighters’ foam during training exercises, are well below the 100 ng/l limit set in 2021 by the government’s Drinking Water Inspectorate. SES said there were “currently no operational measures, or restrictions, required”, while Thames Water pointed to filtration systems at its facilities – ignoring the fact that the readings in question were taken after water had already been through them.

But the UK is significantly out of step with the EU, whose limit is 20 times stricter. In November last year, 116 global PFAS experts signed a letter stating that the level of 100 ng/l in drinking water that the World Health Organization had proposed in draft guidance for two chemicals, PFOS and PFOA, was too weak.

Campaigner Dr Julie Schneider of the UK’s CHEM Trust campaign group told openDemocracy: “The standards currently in place in the UK are not protective enough. The maximum levels of individual PFAS acceptable in drinking water should be drastically reduced based on the most up-to-date science. A maximum threshold for the sum of all quantifiable PFAS should also be set, as hundreds of PFAS have been detected in surface water.”

Manmade industrial chemicals known collectively as PFAS – or ‘forever chemicals’, because they can take hundreds, thousands or even tens of thousands of years to break down in the environment – have been used extensively since the 1940s. There are approximately 10,000 different types, used in all manner of products: firefighting foams, carpets, textiles, non-stick coatings such as Teflon, car waxes, electronics manufacturing, plastics, cosmetics, and even toilet roll.

When these chemicals enter the environment, they accumulate in soil, water, animals and humans. As chemist and PFAS expert Dr Roger Klein explains: “The problem with PFAS is that they are toxic and don’t degrade. As you drink them, you increase your body burden as many build up in the body over time.”

The PFAS compounds found near Gatwick were called FTAB, PFOS and PFBA. PFBA exposure has been linked to “developmental, thyroid, and liver effects in humans”. Thames Water did not disclose which compounds had been found near Heathrow.

The use of firefighters’ foam has been cited as one possible reason why high levels of PFAS were also discovered in drinking water in Jersey and Cambridge in 2021 and 2022.

Contamination was found to be particularly strong for a group of 88 islanders using a private water supply near Jersey Airport, and ‘forever chemicals’ were subsequently found in their blood at elevated levels.

In Cambridge, The Guardian revealed that water being drawn from a layer of permeable rock close to Duxford Airfield had levels of one type of PFAS, called PFOS, at almost 400 ng/l. Cambridge Water claimed it had reduced the PFAS levels in residents’ drinking water to around 10 ng/l by blending the contaminated water with other sources. However, South Staffs Water, which owns Cambridge Water, has since admitted to openDemocracy that 1,279 properties in Sawston, Hinxton and Stapleford may have received water on three occasions (between January and June 2021) with PFAS levels above 10 ng/l. While it denies that treated water with PFAS above 400 ng/l was ever released it admits: “Before removal from supply, our sampling programme found the highest concentration of PFAS in customer tap water was 131 ng/l.”

The problem of PFAS contamination in drinking water isn’t just confined to areas near airports or airfields, although on the available evidence they do appear to be worst affected. But data for elsewhere in England and Wales is patchy as testing isn’t uniform and the results aren’t made freely available by the water companies. (By contrast, Scottish Water, which supplies most of Scotland’s domestic drinking water, told us: “The sum of PFAS compounds in final treated water samples has not been above 5 ng/l.”)

Exposure to the most studied PFAS (including PFOS and PFOA) has been linked to a vast array of adverse effects, Schneider said, including impacts on the hormonal, immune and reproductive systems, as well as increased risk of developing certain cancers.

The Department of the Environment, Food and Rural Affairs (Defra), which oversees the Drinking Water Inspectorate, said it was “developing proposals” to restrict the use of PFAS in firefighting foam, adding: “UK drinking water standards are of a very high standard and are among the best in the world. Water companies are required to carry out regular assessments and sampling for PFAS to ensure that drinking water remains safe.”

The inspectorate’s threshold in England and Wales only applies individually to known PFAS chemicals, of which there are currently 47, meaning multiple chemicals could be present so long as none of them individually makes up more than 100 ng/l. The US Environmental Protection Agency has proposed going 25 times lower than the UK with a maximum level of 4 ng/l for PFOS and PFOA chemicals individually, while the EU uses a 100 ng/l limit for the overall total of 20 different PFAS substances that can be present in drinking water – meaning its rules are far more stringent than those in Britain.

Dr Roger Klein argues the UK maximum level is “ludicrously high”, while Philippe Grandjean – a former Harvard professor and leading global expert on the adverse effects of PFAS – told openDemocracy his calculations agreed with the US Environmental Protection Agency’s assessment that the “only safe exposure is zero”.

Grandjean outlined the risks, particularly to children: “Our research identified adverse effects at lower and lower levels of exposure. We currently believe the immune system is particularly vulnerable [to the effects of PFAS buildup], and we can see that children and adults respond less favourably to vaccinations and there is a risk that the vaccination may not work. We also know of increased risks of metabolic disease, such as diabetes, obesity and thyroid dysfunction, and decreased fertility, lowered birth weight, and decreased skeletal mineralisation in children.”