The invisible chemicals, called PFAS, were first developed in the 1940s to resist water and heat and are now used in items such as non-stick pans, textiles, fire suppression foams and food packaging.
But the indestructibility of PFAS, per- and polyfluoroalkyl substances, means the pollutants have built up over time in the air, soil, lakes, rivers, food, drinking water and even our bodies.
There have been growing calls for stricter regulation for PFAS, which have been linked to a range of serious health issues including liver damage, high cholesterol, reduced immune responses and several kinds of cancer.
To find out PFAS contamination in locally caught fish, a team of researchers analyzed more than 500 samples from rivers and lakes across the United States between 2013 and 2015.
The median level of PFAS in the fish was 9,500 nanograms per kilogram, according to a study published in the journal Environmental Research.
Nearly three quarters of the detected “forever chemicals” were PFOS, one of the most common and hazardous of the thousands of forms of PFAS.
Eating just one freshwater fish equalled drinking water with PFOS at 48 parts per trillion for a month, the researchers calculated.