We feel a bit guilty biting into a hamburger, pizza or hotdog. They comfort the taste buds but not the body, with all the fat, salt, cholesterol and various additives. There is another issue: fast-food packaging. The hamburger is wrapped in some form of paper, fries come in a cardboard container and pizza is delivered in a box. Since all these items are greasy and moist, ordinary paper won’t do. That’s why various chemicals are used to provide moisture and grease resistance.
Ideally, the packaging material should be both hydrophobic and lipophobic to repel both water and fat. Chemically, this is quite challenging. One class of chemicals: polyfluoroalkyl substances (PFASs), is up to the task but unfortunately is also mired in controversy.
These molecules are composed of a chain of carbon atoms to which fluorine atoms are attached. It is the fluorines on the periphery of the molecule that are responsible for repelling water and fat. But the presence of the carbon-fluorine bonds, which are very strong, also makes these molecules extremely resistant to degradation, with the result that they have been detected globally in water, soil, sediment, wildlife and — alarmingly — in human blood. Why the concern? Because some PFASs have been linked with thyroid disease, low birth weight, decreased sperm quality, higher cholesterol as well as kidney and testicular cancer. It is important, however, to understand what “linked with” means.
Animals treated with polyfluorinated compounds can indeed exhibit the conditions mentioned but the doses are much higher than human exposure. Furthermore, exposure of animals to a single substance is a questionable model for extrapolating effects in people who are exposed to thousands of compounds — natural and synthetic — on a daily basis. There are numerous interactions possible that can mitigate the effects seen with individual compounds. As far as people go, there have been associations with disease when blood levels of PFASs are high, which can happen with occupational exposure. However, associations can never prove that there is a cause-and-effect relationship. For example, people may have high blood levels of these chemicals because they eat a lot of packaged fast foods, so it may be their diet that causes the problem.
Also, the specific molecular structure of PFASs is important. It is PFAS molecules with a chain of eight carbons that have been linked to health problems. One of the most famous is perfluorooctanoic acid (PFOA), a compound that was widely used before being phased out in the preparation of Teflon coatings. Only tiny traces remained in the final product but during production some PFOA was released into the environment. DuPont and its spinoff company, Chemours, recently settled thousands of lawsuits reaching $670 million from nearby residents claiming that PFOA poisoned the water and caused disease.
In North America, Europe and Japan these long-chain fluorinated compounds have been phased out. But because they resist biodegradation, they are still widely present in the environment. Furthermore, they are still produced in China and Russia. In food packaging, they have been replaced by shorter-chain fluorinated compounds that leave the body much more quickly and are less bioaccumulative. Still, these too show up in the environment. And not everyone is convinced that they are less toxic than their longer-chain counterparts. A recent study found that 46 percent of food-contact paper and 20 percent of food-contact cardboard contains fluorinated compounds. To what extent isn’t clear. The study did not investigate to what extent any of these fluorinated compounds migrate into food, or whether they end up in the body of consumers.
Detecting the presence of a substance does not automatically mean that it presents a risk. It is always a question of dose. Still, the search continues for alternatives. There are some, such as silicones and various hydrocarbons, but they are not as functional and have also raised toxicity concerns. Obviously one way to cut down on exposure to chemicals used in packaging is to rely less on fast foods. And that pays nutritional dividends as well.
Joe Schwarcz is the director of McGill University’s Office for Science and Society. Read his blog at www.mcgill.ca/oss.