France, May 15 -- For decades, residents living near the Arkema and Daikin chemical factories near the southern city of Lyon believed they were safe. But after discovering alarmingly high levels of toxic forever chemicals (PFAS) in their blood, hundreds of alleged victims are filing complaints against the companies in what could become the largest lawsuit of its kind in Europe.

Per- and polyfluoroalkyl substances (PFAS) are found in everyday products such as cosmetics, pesticides, food packaging and non-stick coatings.

They're often referred to as "forever chemicals" because they can stay in the human bloodstream for years.

Studies have shown that exposure to these chemicals can lead to metabolic disorders, decreased fertility in women...