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Microwaving a cooked meal in a plastic tray can release thousands of microscopic plastic particles into the food within minutes, even if the package says it’s “microwave safe,” according to a new analysis.
The analysis, published Tuesday by Greenpeace International, is based on a peer-reviewed study that looked at what happens when plastic food containers are heated.
It says heat can trigger the release of both microplastics and nanoplastics, and these particles are so small that they can’t be seen with the naked eye. It also releases chemicals used in plastic manufacturing such as bisphenols and phthalates, which have been studied in connection with hormonal disruption, infertility, and certain cancers.
One study cited in the new report found that between 326,000 and 534,000 microplastic and nanoplastic particles were leached into food analogs after just five minutes of microwave heating. This is up to seven times more particles than would be released during oven heating under similar conditions.
The analysis also found that heating plastics such as polypropylene and polystyrene increases the migration of additives into food or food analogues. These include plasticizers and antioxidants. These substances are added to plastics to improve flexibility and durability, but they do not permanently bond to the material and are more likely to migrate when exposed to heat.
“People think they are making a harmless choice when they buy and heat food packaged in plastic,” said Graham Forbes, Global Plastics Campaign Leader at Greenpeace USA. “The reality is that we are exposed to a mixture of microplastics and harmful chemicals that should never be in or near our food.”
“Governments have allowed the petrochemical and plastics industries to turn kitchens into laboratories. This report shows that companies’ claims of ‘microwave-safe’ are nothing more than wishful thinking.”
In most regulatory systems, “microwavable” means that the container will not visibly melt or break at a certain temperature. It does not necessarily assess the release of fine plastic particles or chemical additives into food.
According to the report, more than 4,200 hazardous chemicals are known to be used or present in plastics, most of which are not specifically regulated in food packaging. Often referred to as “forever chemicals,” substances such as bisphenols, phthalates, and PFAS, as well as metals such as antimony, have been linked to cancer, infertility, hormonal disorders, and metabolic diseases.
The report cites evidence that at least 1,396 food-contact plastic chemicals have been detected in humans, with studies linking exposure to conditions such as neurodevelopmental disorders, cardiovascular disease, obesity and type 2 diabetes.
The Karahan Kuyumkyular waste dump in Turkey’s Adana province is sighted during an investigation into plastic waste being dumped and incinerated in the country. (Greenpeace via PA Wire)
This analysis does not show any new laboratory experiments by Greenpeace. Instead, it synthesizes published research showing that heating, storage, and abrasion can increase particulate release.
One study found that worn or scratched plastic containers released nearly twice as many microplastic particles as new containers.
Concerns about heating plastic containers are not new. Previous research has shown that heating plastic baby food containers and pouches in the microwave can release approximately 2 billion nanoplastics and 4 million microplastics per square centimeter of the container’s surface.
The same study found that millions to billions of particles can be released into food when kept refrigerated and at room temperature for more than six months, and that two days of exposure to microplastic and nanoplastic particles in laboratory conditions killed 75 percent of cultured fetal kidney cells.
There is also growing evidence that small, invisible particles can leach into water from plastic packaging, even when not heated. A 2024 study found that every liter of bottled water contains an average of 240,000 plastic particles. This is 10 to 100 times higher than previous estimates, most of which are nanoparticles small enough to enter human cells and potentially enter the bloodstream and major organs.
Ready-to-eat food packaged in plastic is one of the fastest growing segments of the global food system, with a value of nearly $190 billion, the report said. Global production will reach 71 million tons in 2024, reaching an average of 12.6 kg per person. Plastic packaging accounts for approximately 36% of all plastic produced, and global plastic production is expected to more than double by 2050.
Greenpeace argues that regulations have not kept up with new research into the release of microplastics from food packaging, and claims such as ‘microwave safe’ are giving consumers a false sense of security.
“Are we being poisoned trying to feed our families? The risks are clear, the stakes are high, and the time to act is now. We cannot rely on misleading promises from companies,” Forbes said.
“Governments must act now by securing a strong Global Plastics Treaty that protects human health and reduces plastic production at the source.”
Microplastics are found everywhere from the time we are born, from the deepest parts of the ocean to our bodies.
Some countries have banned single-use plastics to reduce plastic waste that releases particles into the soil, water and air, but enforcement remains difficult.
Talks continue between countries, chaired by the United Nations, to create a legally binding global plastics treaty. But despite years of talks, disagreements remain over, among other things, limits on new plastic production and the allocation of responsibility for health risks.
