Eating just one portion of freshwater fish — such as a catfish, trout, or salmon — could expose people to a tremendous amount of harmful chemical compounds, a new study warns.

Researchers with the Environmental Working Group have discovered high levels of so-called “forever chemicals” in fish caught in U.S. lakes and rivers. Their study found that eating just a single serving of freshwater fish could equal a month’s worth of drinking water laced with PFAS at level high enough to be harmful to consumers.

PFAS – or perfluoroalkyl substances – are a group of more than 9,000 different chemicals, some of which are already banned or highly restricted. Manufacturers often use them in non-stick cookware, food packaging, stain repellents, coatings, and fire-fighting foams.

The chemicals in PFAS are nearly impossible to destroy. They can accumulate in animals throughout the food chain and also contaminate everything from drinking water to food and personal care products. PFAS can build up in our bodies and never break down. Studies have found them in the blood of virtually everyone, including newborn babies.

Studies have also linked very low doses of PFAS in drinking water to the suppression of the immune system, weakening the effectiveness of vaccines, and increasing risk of certain cancers. Researchers believe PFAS can also increase cholesterol, reproductive and developmental problems, and other health issues.

Environmental Working Group (EWG) scientists discovered that the average amounts of PFAS in freshwater fish throughout the U.S. were 280 times greater than forever chemicals detected in some commercially caught fish. The findings estimate that eating a single freshwater fish caught in a lake or river could cause PFAS exposure equal to consuming store-bought fish daily for an entire year.

“People who consume freshwater fish, especially those who catch and eat fish regularly, are at risk of alarming levels of PFAS in their bodies,” says study lead author David Andrews, Ph.D., a EWG senior scientist, in a media release. “Growing up, I went fishing every week and ate those fish. But now when I see fish, all I think about is PFAS contamination.”

Which forever chemicals are hiding in freshwater water?

Study authors say the most common forever chemical found were PFOS, or sulfonic acid, averaging roughly three in four of total PFAS detections.

“These test results are breathtaking,” adds Scott Faber, EWG’s senior vice president for government affairs. “Eating one bass is equivalent to drinking PFOS-tainted water for a month.”

Consuming freshwater fish contaminated with PFOS can cause “significant” increases in blood serum levels of the forever chemical, the researchers say. Even occasional consumption of freshwater fish could raise PFOS levels in the body.

“The extent that PFAS has contaminated fish is staggering,” explains Nadia Barbo, a graduate student at Duke University and lead researcher on this project. “There should be a single health protective fish consumption advisory for freshwater fish across the country.”

Researchers analyzed data from more than 500 samples of fish filets collected between 2013 and 2015. The average level of total PFAS in the filets was 9,500 nanograms per kilo, with an average of 11,800 nanograms per kilo in fish from the Great Lakes.

“PFAS contaminate fish across the U.S., with higher levels in the Great Lakes and fish caught in urban areas,” says study co-author Tasha Stoiber, Ph.D., an EWG senior scientist. “PFAS do not disappear when products are thrown or flushed away. Our research shows that the most common disposal methods may end up leading to further environmental pollution.”

Who’s contaminating American waterways?

Freshwater fish are an important source of protein for many Americans, but PFAS contamination threatens those who cannot afford to buy seafood from the grocery store.

“Identifying sources of PFAS exposure is an urgent public health priority,” says Stoiber.

The researchers estimate that there may be more than 40,000 industrial polluters of PFAS in the United States. These include manufacturing facilities, municipal landfills, wastewater treatment plants, and airports. Contaminated water has spread PFAS to soil, crops, and wildlife — including fish.

“For decades, polluters have dumped as much PFAS as they wanted into our rivers, streams, lakes and bays with impunity. We must turn off the tap of PFAS pollution from industrial discharges, which affect more and more Americans every day,” notes EWG’s Faber.

Testing has revealed that nearly all fish in American rivers and streams are contaminated with PFAS in the parts-per-billion range – even greater than parts per trillion. Although the most recent tests have found decreasing PFAS levels, freshwater fish are still showing high levels of the chemicals.

“The EPA needs to move swiftly to set regulations for the industries most likely to be dumping PFAS into the environment. Downstream communities especially have suffered the consequences of unregulated PFAS discharges for far too long,” Faber concludes.

The findings are published in the journal Environmental Research.

South West News Service writer Stephen Beech contributed to this report.