Study: Ingredient found in salad bowls and burger wrappers less safe than previously thought

A compostable salad bowl seems like an Earth-friendly way to enjoy a healthy lunch. But the toxic chemicals used in containers like molded-fiber salad bowls, sandwich wrappers, and French fry pouches may be leaching into food despite efforts to make those materials safer, according to the results of a study published in March in the journal Environmental Science and Technology.

The presence of “forever chemicals” in materials used to contain or carry food is far from new. Various formulations of compounds called per- and polyfluoroalkyl substances, or PFAS, are used in materials like pizza boxes, popcorn bags, and paper straws because they’re both water-proof and oil-proof. That means they’re perfect for keeping fake butter or salad dressing from seeping out of microwave popcorn packets and takeout salad bowls, as well as for maintaining structural integrity while protecting a steaming, cheesy pizza.

But PFAS are also toxic. They’ve been linked to testicular and kidney cancers, ulcerative colitis, low birth weights, and even decreased immune response to vaccines.

Because of these health concerns, some forever chemicals used in food materials have been removed from the market in recent years and replaced by polymeric PFAS, compounds thought to be more stable and therefore less likely to get into food.

“The rationale there was that these polymeric PFAS were much safer because they are bigger, they don’t break down, and so the idea [was] that they would not pose a risk,” said Marta Venier, one of the study’s co-authors and an assistant professor in the School of Public and Environmental Affairs at Indiana University. “But this study shows that actually they are not as safe as we thought.”

The troubling cycle in which manufacturers replace one hazardous chemical with another has played out again and again due to lax chemical standards in the U.S., according to environmental health advocates. They say the issue is compounded by the Food and Drug Administration’s reactive approach to regulating food additives. An FDA spokesperson said in a statement that the agency is reviewing the findings of Venier’s paper.

“In general, the FDA reacts when there is an acute problem,” such as issues with product recalls and bacterial contamination, said Maricel Maffini, an independent environmental health and chemical safety consultant. The health effects of chemicals, however, manifest more slowly. “It is ongoing exposures and small amounts over time,” she said. “So it is hard to see — you cannot connect the dots directly.”

How the food industry plays whack-a-mole with PFAS

For the Environmental Science and Technology study, research assistant Anna Shalin spent weeks in 2020 running around the city, asking restaurants for burger wrappers, burrito bowls, salad bowls, donut bags, and sub sandwich wrappers. Promptly after receiving them, she sealed them in individual Ziploc bags and took them back to the University of Toronto lab where she worked. Then the research team shipped samples off for various kinds of analysis, while keeping the remainder.

When the research team re-analyzed the samples two years later, the composition of the PFAS in the bowls and bags had changed. Some of the PFAS disappeared completely — which shouldn’t have been possible. If there’s one thing that shouldn’t change after being stored in a sealed bag in a Rubbermaid bin for two years, it’s a takeaway salad bowl laced with “forever chemicals.” After all, they’re called “forever chemicals” for a reason — they’re seen as practically indestructible.

“Oh, boy, we made a mistake,” Venier said the team thought when they first saw the results. After double-checking, the researchers realized the PFAS that had disappeared were PFAS compounds leftover from the polymerization process that have the right properties to let them escape into the air.

“Our hypothesis is that they actually volatilize. They get out of the food packaging materials, they get into the air. From the air, they get into the dust,” said Venier. “This is something surprising to us and we realized that it might be another route of exposure to PFAS that we didn’t consider before.” Most importantly, experts stressed, the fact that PFAS in these materials can volatilize means they most certainly can migrate into food.

The study found that molded fiber bowls and trays have the most total fluorine — a measure of all of the kinds of PFAS, including short-chain, long-chain, and polymeric versions. That’s troubling, especially because those containers are advertised as compostable and could spread PFAS to crops through that compost. But even more concerning is the amount of PFAS that disappeared from the paper products, like pastry and popcorn bags, which could pose risks to people eating food from the packaging.

Concerns about PFAS toxicity were what prompted the FDA in 2016 to ban the use of “long-chain” PFAS — that is, PFAS that have chains with eight or more fluorinated carbons, which are considered more persistent and toxic than smaller PFAS — in food packaging. Later in the year, several companies assured the FDA they were no longer using long-chain PFAS in their materials.

The ban led the industry to instead use short-chain PFAS compounds that contain chains with fewer than eight fluorinated carbons, like 6:2 fluorotelomer alcohol. That didn’t turn out well, either.

“FDA scientists started to look carefully into the short-chain PFAS, those that were sold to us — to everybody — as the ‘friendly type,’ the less dangerous one, the replacement for the long-chain PFAS,” said Maffini, who has worked with the Natural Resources Defense Council and the Environmental Defense Fund in the past. Then, “scientists quickly realized that there was something that wasn’t working, and that was that the short-chain PFAS can also accumulate in the body; they biopersist.”

In response, the FDA in 2020 secured commitments from companies to phase out the use of short-chain PFAS over the next three years. But the market is now moving towards polymeric PFAS, Venier explained — twisty tangles of carbon chains decorated with fluorines and other atoms, strung together in a repeating pattern like a non-biological strand of DNA. Venier and other experts describe the food industry as playing a chemical game of  whack-a-mole.

“You replace one chemical with another one, which is initially thought to be maybe better,” said Venier. “And then we realize: Oops! It was not any better.”

How does PFAS migrate into food?

Polymers made of PFAS are commonly assumed to be inert; that’s why Teflon is used in everything from nonstick pans to gaskets in weapons-grade uranium plants for the Manhattan project. But the polymers used in food-packaging applications, called “side-chain polymers,” are different.

“Imagine that you are building something with Lego, so you have a building block of a chain. And then on the side you attach little arms that stick out that are fluorinated,” Venier said. While the polymer itself is too big to migrate into food, those arms can become loose and break off into PFAS molecules, which are much more worrisome in terms of consumers’ exposure to PFAS.

Laurel Schaider, a senior scientist at the environmental health research organization Silent Spring Institute, said there’s still research to be done to understand the speed and the extent to which the side chains of the polymers break off from the main part of the polymer. “Some evidence has suggested that that happens sort of slowly over time,” she said. “But the study is suggesting that that isn’t necessarily the case, that substantial amounts of those side-chain PFAS can be breaking off on timescales that are relevant to people’s exposures while they’re using the packaging.”

Multiple experts noted that while there are studies of how much PFAS migrates into food using food simulants, and studies suggest that foods that are hot as well as those high in salt, fat, and acid cause more PFAS migration, no one knows what actually happens during a meal.

One of Schaider’s studies found that people who reported eating microwave popcorn or eating out the day before having their blood taken had higher amounts of PFAS in their blood. But there are so many exposures to PFAS — through clothing and fabrics treated with stain- and water-resistant PFAS, drinking water, and cosmetics — that it’s not only people who eat takeout who have PFAS in their bodies. “In the case of PFAS, we are all part of the experiment,” said Schaider. “Testing by the CDC has found that over 99% of Americans have PFAS in our bodies.”

A Consumer Reports investigation last year showed that several chains that claimed to have PFAS-free packaging still had fluorine signatures coming from their wrappers and bowls.

Burger King, one of the restaurants flagged in the Consumer Reports investigation, is now in the midst of a PFAS phaseout that’s expected to take until 2025. “We have made significant progress to date on our PFAS goal,” and will provide more updates in a report this spring, Burger King told STAT in a statement.

Justin Boucher, operations manager at the Food Packaging Forum in Switzerland, said in a statement that even though the new study showed there’s definitely still PFAS in some food packaging, it “importantly also confirms the downward trend of PFAS in paper and board food packaging” as a result of such phaseout commitments. More than half (55%) of the materials tested in the study had low amounts of total fluorine.

Reassessing the safety of food additives 

There are two problems with the FDA’s current structure for regulating food additives, including food containers and wrappers, according to Maffini. First, very little data is required to prove that a substance is safe. Second, there’s no process for re-reviewing a substance if new safety data come to light.

Because of the 1958 Delaney Clause, which mandated that the FDA couldn’t approve food additives known to cause cancer, the agency is mostly interested in making sure that the food additives will not cause genetic mutations, according to Maffini. But the three simple lab tests used to glean this data don’t capture other potential health effects of additives, said Maffini.

“Hormones are incredibly exquisite in the way they work,” she said, and “there is no recommendation for screening, even in vitro tests, for endocrine disruption of any kind.”

An FDA spokesperson called Maffini’s statements inaccurate, saying that the agency “reviews all relevant safety information to ensure the chronic exposure to substances added to food is safe,” and that agency reviews data including “sub-chronic and chronic safety toxicity, genotoxicity and carcinogenicity, reproductive and developmental toxicity, and data on metabolism.” However, Maffini said that it’s clear that the agency’s guidelines for food contact substances differ from the standards for direct food additives, and that the process by which companies decide how much of their chemicals people are exposed to — and thus how much information they have to submit to the FDA — is opaque.

At the Environmental Protection Agency, many pollution standards have to be revisited every few years to make sure the regulations are up to date with the latest science. However, no such process is in place at the FDA. Various PFAS have been approved for food contact use since at least 1968, but research into these compounds has exploded since then, and the data on the compounds is very different now. “They were approved years, if not decades ago, and probably with little or no information,” said Maffini. “And now, we know more; the science advances, and those should be either revoked or evaluated and reassessed for safety and the conditions of use.”

The FDA said that its review process is designed to prioritize safety. “The FDA reviews new scientific information to better ensure that the authorized uses of PFAS in food contact substances continues to be safe,” the agency told STAT in a statement. “When the FDA identifies potential safety concerns, the agency ensures that these concerns are addressed or that these substances are no longer used in food contact applications.” The agency pointed to ongoing, voluntary industry phaseout of short-chain PFAS, expected to be completed by the end of the year, as an example of the process at work.

Congress had called for FDA Commissioner Robert Califf to present a plan for how to reassess the safety of food additives and generally recognized as safe (GRAS) substances, which also have shaky safety checks. The report was due in March, but an FDA spokesperson said it has not yet been sent to the Hill.

In the meantime, besides avoiding single-use items and using more glass or ceramic containers, there’s unfortunately not much people can do to protect themselves from PFAS in food containers, according to experts.

“You are in the hands of the company that is selling you the food,” said Venier. “There are some companies that have claimed to have moved away from PFAS, like the popcorn industry. But for the most part, there’s no way to know if the food packaging material that you are using contains PFAS or not.”