Food testing reveals how diet can add to exposure to ‘forever chemicals’

Per- and polyfluoroalkyl substances (PFAS)—a vast family of chemicals used largely for their nonstick, water-repellent and grease-resistant properties—are called “forever chemicals” because of their remarkable resistance to degradation. They are now ubiquitous in our environment.

Several years ago, a research team led by Sébastien Sauvé, a professor in the Department of Chemistry at Université de Montréal and holder of the Canada Research Chair in Citizen Science of Emerging Contaminants, showed that Quebec’s drinking water is contaminated by PFAS.

Now, Sauvé and his colleagues have published a new study showing that another path of exposure warrants closer attention: food.

The findings are published in the Journal of Food Composition and Analysis.

The team analyzed foods sold in Quebec grocery stores for 76 different PFAS compounds. They found PFAS in many food categories, sometimes at concentrations high enough to contribute to daily exposure as much as drinking water does. In fact, estimated PFAS intake from some samples of fish, seafood and meat was considerably higher than from water.

Highest in animal-based products

The highest PFAS concentrations were found in foods rich in animal protein. On average, PFAS levels were approximately 1.9 nanograms per gram (ng/g) in fish, 1.3 ng/g in seafood and 1.2 ng/g in meat. Dairy and plant-based products generally had lower concentrations, ranging from 0 to 0.75 ng/g.

But concentration doesn’t necessarily equal exposure. To estimate what actually enters the body, the team factored in the quantities of food typically consumed. By this measure, grains emerge as an important source of exposure.

While grains are not among the most contaminated foods, they are consumed in large quantities—in the form of bread, pasta and other grain products. As a result, even relatively low PFAS concentrations can contribute significantly to total exposure.

“This distinction is important,” Sauvé commented. “To estimate our exposure to a contaminant, we must consider both its concentration in the food and the amount of the food that we consume. Since we eat such large quantities of grain products, the effect of the contamination is amplified.”

Vegetarian and vegan diets: Less PFAS?

At first glance, the results might seem to favor a vegetarian or vegan diet. The research team modeled PFAS exposure for various diets, ranging from omnivorous to diets with little or no meat. The estimated total PFAS intake was lower for people who consume fewer animal products.

However, the chart below tells a more nuanced story, Sauvé said.

Animal proteins account for a substantial share of exposure among omnivores. Fish and seafood, in particular, contain both the highest concentrations and greatest variety of PFAS detected in the study.

However, grains contribute significantly to exposure in all diets, largely because they are consumed in such large quantities. So switching to a plant-based diet will reduce some exposure but won’t eliminate PFAS entirely.

It’s about bioaccumulation

Furthermore, not all PFAS are created equal. PFAS is an umbrella term for a vast family of chemicals. Among the 76 tested for in the study, it was mainly long-chain PFAS that turned up in food. Long-chain PFAS generally stay in the body longer, while short-chain PFAS are eliminated more quickly.

Fish and seafood are good examples of this pattern. Certain long-chain PFAS, including PFOS and PFOA, can bioaccumulate in organisms and then move up the food chain: a small aquatic creature accumulates them, a fish eats that creature, a larger fish eats that fish, and so on. At each stage, concentrations can increase, as is the case with heavy metals such as mercury.

Land animals are also likely to accumulate the PFAS present in their diet, but they are generally lower on the food chain, since most are herbivores.

Plants do not readily absorb long-chain PFAS, which tend to stay tightly bound to soil particles. But other PFAS, particularly smaller molecules, can be more mobile and are more easily taken up by plants.

“We therefore find some PFAS in grains and other plant-based foods, even though the measured concentrations are generally lower,” Sauvé said.

“This highlights an important fact: not all PFAS follow the same pathway in the environment. Their size, chemical structure and physicochemical properties influence their mobility, accumulation and ability to move from one environmental compartment to another.”

What should consumers do?

For now, it’s difficult to draw up a simple list of foods to avoid, Sauvé said. The study is preliminary and covers only 100 samples across numerous food categories.

“That isn’t enough to conclude, for example, that one species of fish is consistently more contaminated than another,” Sauvé cautioned. “What the results do show is that there is significant variation between samples.”

Sauvé and his team are now analyzing more than 500 samples to determine more precisely which foods have the highest concentrations and, eventually, what factors account for those concentrations.

The message for consumers, therefore, is not to banish fish, meat or grains from their diets but simply to recognize that water isn’t the only source of exposure to PFAS.

Sauvé believes the next step should be increased monitoring of PFAS in food. “There are already standards and targets for drinking water,” he noted. “We’re far from that point with food, but it makes no sense to put food in a different category from drinking water.”

The UdeM study is more a wake-up call than a dietary guide. It shows that food can be a significant source of PFAS exposure and that much work remains to be done to measure this contamination, understand its origins and determine which foods are most problematic.

Who’s behind this story?

Swati Mestri

Swati Mestri holds a bachelor’s degree in Electronics Engineering and has worked as a content editor since 2019. She has experience editing research documents across technology, health care, and materials science, and has a particular interest in technology and space.

Full profile →

Andrew Zinin

Master’s in physics with research experience. Long-time science news enthusiast. Plays key role in Science X’s editorial success.

Full profile →