The surprising ways food packaging is exposing us to microplastics

At this point, most people know that microplastics are everywhere. Scientists have shown that tiny particles, amounting to the weight of a plastic spoon, can be found in our brains; hundreds of fragments of plastic are in each breath we take.

But the exact origins of those tiny pieces of plastic have been unclear. Are they coming from plastics discarded in landfills and decomposing over dozens of years? Or are they spilling out of the plastic water bottles and containers we seal our food in? The answer matters — for individuals hoping to avoid the particles and politicians who may want to restrict the microplastics we eat, drink and breathe.

Scientists are finding answers — but not always the ones that they expected. New research shows that microplastics are shedding from reusable plastic containers and food packaging, but the particles can also come from glass bottles with painted caps, as well as highly processed foods packaged in any material.

“We have not really understood all the factors that can lead to the release of micro and nanoplastics,” said Lisa Zimmerman, a plastics researcher and scientific communication officer at the Food Packaging Forum, a Swiss nonprofit.

In a study published last month, French researchers analyzed dozens of samples of water, tea, sodas, beer and wine in various containers — glass bottles, plastic bottles and metal cans. They expected to find the most microplastic particles in beverages housed in plastic.

Instead, the researchers found that — across all the beverages they tested — the highest number of particles were found in glass bottles. In glass containers, they found about 100 microplastic particles per liter of beverage, or five to 50 times more than in plastic bottles or cans.

“We were surprised,” said Alexandre Dehaut, research project manager at ANSES, France’s food safety agency, and one of the authors of the paper. “Glass is a material that’s inert and has been used for a long time by humans.”

Scientists were confused — until they realized all of the glass bottles they tested, except for wine bottles, had metal caps. Those caps were decorated with polyester paint and matched the color and material of the particles found in the plastic bottles. The prevalence of the particles decreased by more than half when the caps were blown and rinsed before bottling — suggesting that, at least in some cases, there may be fairly easy ways to reduce microplastic exposure.

“We managed to lower the content by 60%,” Dehaut said.

Another study, released last year, found that packaging might not matter as much as food processing. After analyzing multiple types of proteins — meats, seafood and plant-based meats — researchers at the Ocean Conservancy and the University of Toronto found that highly processed products contained significantly more tiny particles than minimally processed products. For example, a chicken nugget had 62 microplastic particles per serving; a chicken breast had just two.

For highly processed foods, “there are just more opportunities for contamination to be introduced,” said Britta Baechler, director of ocean plastics research for the Ocean Conservancy and one of the authors of that study. Processed foods pass through a complicated web of conveyor belts and machines — with many parts made of plastic — before being packaged and sent to the grocery store. The largest exposure to microplastics, then, may come before the consumer is in contact with the food.

That doesn’t mean that plastic containers are off the hook, however. A paper published Tuesday, from researchers at the Food Packaging Forum, integrated the findings from seven robust studies that showed the particles are shedding from certain types of containers, especially when handled in certain ways.

For example, plastic dishes made of melamine shed increasing amounts of particles when washed. Reusable plastic cups shed more particles when exposed to hot water. Plastic water bottles released more microplastics when their plastic caps were screwed and unscrewed multiple times.

Kimberly Wise White, vice president of regulatory and scientific affairs at the American Chemistry Council, a plastics trade group, said that the study provided a useful overview of microplastics research — but microplastics have not been proved to cause harm. “No adverse health effects have been conclusively linked to microplastic exposure,” she said.

Zimmerman, the lead author of the study published Tuesday, said the research confirms what scientists had been advising: Avoid storing food in plastic whenever possible and, in particular, avoid heating plastic containers. But, she added, the recent studies show microplastics can come from unexpected places — and more research is needed.

“Plastic is present everywhere,” she said. “We need to know what we can do.”