In 2015 Andrea Amico returned from vacation to four large yellow envelopes on her kitchen table — one for each family member.

The letters contained blood tests sent from her state health department in the US. "As soon as I saw the envelopes… I just got this pit in my stomach," Amico recalled.

A year before, she had discovered a news article about a drinking well in Portsmouth, New Hampshire, that had been closed after it was found to contain high levels of per- and polyfluoroalkyl substances — known as PFAS. The well was located right beside her husband's office and children's daycare.

The tests revealed what Amico had feared. The family had elevated levels of the chemicals in their blood and her young daughter was most exposed. "It was devastating," said Amico.

The Portsmouth well contained PFOS, a toxic chemical found in a type of firefighting foam. The levels were 12 times above the US Environmental Protection Agency's recommended guidelines at the time and 600 times above current standards.

The chemical was traced to a former air force base near the city which had used the foam for training purposes. It had leached into the soil and contaminated groundwater.

PFOS is part of a family of around 15,000 synthetic chemicals called PFAS. They are known as 'forever chemicals' because they don't naturally break down and can take thousands of years to degrade.

With a unique ability to resist heat, water and dirt, they're widely used in a huge range of consumer and industrial products. These chemicals are found in everything from waterproof outdoor clothes, makeup, and stain-resistant carpets to medical devices, semiconductors and wind turbines.

PFAS spread easily through water and air,

© Deutsche Welle