The FDA found 'forever chemicals' in meat, seafood, and chocolate cake sold in grocery stores. Here's how worried you should be.

• An FDA investigation found evidence of a class of toxic chemicals in samples of meat, seafood, and chocolate cake.
• The chemicals in question, known as PFAS, have been associated with cancer, liver damage, and developmental issues.
• The FDA said the samples are "not likely to be a human health concern," but the agency did find concerning levels of PFAS at a dairy farm in New Mexico.
• Scientists are still working to determine the source of PFAS in our food supply.
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The rules of healthy eating used to be simple, at least in theory: Consume fewer processed items, avoid sugar, and keep your meals balanced. But scientists are slowly uncovering a hidden threat that's complicating this narrative.

A recent investigation from the US Food and Drug Administration (FDA) found evidence of a class of manmade chemicals that have been linked to cancer in numerous foods sold in mid-Atlantic grocery stores, including samples of meat, seafood, and chocolate cake.

Read more: Dangerous foods that could raise your risk of developing cancer

The chemicals in question - per- and polyfluoroalkyl substances, or PFAS - became popular in the United States around the 1940s, when manufacturing companies realized PFAS could resist heat, grease, stains, and water.

Though many PFAS have been phased out of the manufacturing industry, they still lurk in drinking water and consumer goods such as food packaging, carpets, leather, textiles, and non-stick cookware. In addition to their ties to cancer, PFAS are associated with liver damage and developmental issues.

Since PFAS rarely break down in the environment, they can linger in water and air for thousands of years, landing them the nickname "forever chemicals." Consuming or inhaling them means they could stay in the body for life.

The FDA said the food samples aren't a health concern - with one exception

The FDA investigation, conducted in October 2017, tested for 16 types of PFAS in the mid-Atlantic region, which the agency defined as West Virginia, Ohio, Virginia, Kentucky, Tennessee, North Carolina, Washington, D.C., Maryland, and Delaware.

After taking more than 90 samples from grocery stores, the agency found trace amounts of PFAS in pineapples and sweet potatoes. It also found higher amounts of these "forever chemicals" in meat, seafood, chocolate milk, and chocolate cake.

The samples of meat and seafood - which included ground turkey, steak, hot dogs, lamb chops, chicken thighs, tilapia, cod, salmon, shrimp, and catfish - all showed levels of PFAS that exceeded warning levels set by the US Environmental Protection Agency (EPA). The warning levels apply to drinking water and groundwater, not food.

Though the chocolate cake showed the highest amounts of PFAS (17,640 parts per trillion), it contained a variation that hasn't been evaluated by the EPA.

The FDA provided Business Insider with an advanced copy of its overview of the investigation, which states that the sampled food items are "not likely to be a human health concern."

The overview did point out, however, that samples from a dairy farm near an Air Force base in New Mexico showed concerning levels of PFAS in 2018.

The farm's groundwater and silage (grass fed to animals) had been contaminated with PFAS, causing cows to ingest the compound. The FDA estimated that it could take one-and-a-half years to remove PFAS from a cow that had been exposed to the contaminant for just 30 days.

Samples of milk taken from the dairy farm showed levels of PFOS that were 35 times greater than the EPA's health advisory threshold.

"Based on a safety assessment, samples were determined to be a human health concern and all milk from the farm was discarded," the FDA said in its overview.

The EPA has issued a health advisory about certain types of PFAS

There are nearly 5,000 varieties of PFAS, but the EPA has only established a health advisory for two types: PFOA and PFOS.

These chemicals represent "the most concerning" varieties of PFAS, said David Andrews, a senior scientist at the watchdog Environmental Working Group (EWG).

The EPA considers drinking water with PFOA or PFOS levels that exceed 70 parts per trillion to be a human health risk. Their advisory is not a legal regulation, but serves as a warning to state agencies and public health officials.

When it comes to toxic chemicals, the EPA tends to be more cautious than most environmental groups, waiting for considerable bodies of scientific evidence before making a health determination.

"It took decades of study before we really understood how potent [PFAS] are," Andrews told Business Insider. "We have to give up the assumption that all of these chemicals are perfectly safe ... These chemicals are concerning and we should eliminate as much [exposure to them] as possible."

Scientists are still trying to find the source of 'forever chemicals' in our food

There are a few theories as to why PFAS have turned up in our food supply, but scientists are still working to determine the most likely cause.

One possibility could be food packaging. In December 2018, a watchdog report found evidence of PFAS in paper to-go boxes and a sandwich wrapper product at Whole Foods Market.

That same year, Washington became the first US state to ban PFAS from food packaging, including microwave popcorn bags and fast food wrappers. A few months later, San Francisco banned PFAS from single-use food containers, utensils, napkins, plates, straws, trays, and lids.

When biodegradable packaging containing PFAS gets composted, the chemicals can ultimately be fed to plants, which are later consumed by humans.

Another possible scenario, Andrews said, is demonstrated by the contaminated milk samples near the Air Force base in New Mexico. In the 1970s, the US Department of Defense began using firefighting foam that contained PFAS during training exercises and emergency responses. By 2018, the department reported that at least 90 Air Force, Army, and Navy bases had PFAS-contaminated groundwater that exceeded the EPA's acceptable levels.

The EPA has also detected PFAS in the local water systems in Colorado, Michigan, Pennsylvania, New York, and North Carolina. When this contaminated water is applied to fields, it can wind up poisoning our food supply.

Andrews said the "common assumption" in the scientific community is that most humans are exposed to PFAS through food. But there's plenty more to learn.

"[The FDA investigation is] really just scratching the surface," he said. "It opens up many more questions than answers."