Microwaving a ready meal in its plastic tray can release thousands of microscopic plastic particles into the food within minutes even when the packaging is labelled “microwave-safe”, according to a new analysis.
The analysis, published by Greenpeace International on Tuesday, is based on peer-reviewed studies examining what happens when plastic food containers are heated.
It says that heat can trigger the release of both microplastics and nanoplastics, particles so small they are invisible to the naked eye. It also releases chemicals like bisphenols and phthalates used in plastic manufacturing which research links to hormone disruption, infertility and certain cancers.
One of the studies cited in the new report found that between 326,000 and 534,000 microplastic and nanoplastic particles leached into food simulants after just five minutes of microwaving, up to seven times more than particles released during oven heating under similar conditions.
The analysis also found that heating plastics like polypropylene and polystyrene increased the migration of additives into food or food simulants. These included plasticisers and antioxidants, substances added to plastics to improve flexibility and durability but not permanently bound to the material, making them more likely to migrate when exposed to heat.
“People think they’re making a harmless choice when they buy and heat a meal packaged in plastic,” said Graham Forbes, global plastics campaign lead from Greenpeace USA. “In reality, we are being exposed to a cocktail of microplastics and hazardous chemicals that should never be in or near our food.”
“Governments have let the petrochemicals and plastics industries turn our kitchens into testing labs. This report shows that corporate claims of ‘microwave-safe’ are no more than wishful thinking.”
In most regulatory systems, “microwave-safe” means a container will not visibly melt or break apart at certain temperatures. It does not necessarily assess the release of microscopic plastic particles or chemical additives into food.
The report says more than 4,200 hazardous chemicals are known to be used in or present in plastics, with most not specifically regulated in food packaging. Some like bisphenols, phthalates and PFAS – often referred to as “forever chemicals” – and metals like antimony are linked to cancer, infertility, hormone disruption, and metabolic disease.
It cites evidence that at least 1,396 food-contact plastic chemicals have been detected in human bodies, with research associating exposure to conditions such as neurodevelopmental disorders, cardiovascular disease, obesity and type 2 diabetes.
The analysis does not present new laboratory experiments by Greenpeace. Instead, it synthesises findings from published research showing that heating, storage, and wear can all increase particle release.
In one study referenced, worn or scratched plastic containers released nearly double the number of microplastic particles compared with new packaging.
Concerns about heating plastic containers aren’t new. Previous studies showed that microwaving plastic baby food containers and pouches could release almost 2 billion nanoplastics and 4 million microplastics per square centimetre of container surface.
The same study found that refrigeration and room-temperature storage for more than six months could release millions to billions of particles into food, and that 75 per cent of cultured embryonic kidney cells died after two days of exposure to microplastic and nanoplastic particles in laboratory conditions.
There’s also growing evidence that plastic packaging leaches off tiny invisible particles in water, even when not heated. A study in 2024 found a litre of bottled water contained an average of 240,000 plastic particles – 10 to 100 times more than previously estimated – most of them nanoparticles small enough to penetrate human cells and potentially enter the bloodstream and major organs.
Plastic-packaged ready meals are one of the fastest-growing segments of the global food system, worth nearly $190bn, the report noted. Global production reached 71 million tonnes in 2024, averaging 12.6kg per person. Plastic packaging accounts for around 36 per cent of all plastics produced, and global plastic production is projected to more than double by 2050.
Greenpeace argues that regulation hasn’t kept pace with emerging research on the release of microplastics from food packaging and that labels like “microwave safe” give consumers false reassurance.
“Are we being poisoned while trying to feed our families? The risk is clear, the stakes are high and the time to act is now. We cannot rely on misleading promises from corporations,” Mr Forbes said.
“Governments must act now by delivering a strong Global Plastics Treaty that protects human health and cuts plastic production at the source.”
Microplastics have been found everywhere from the deepest points in the ocean to inside our bodies from as early as birth.
Some nations have banned single-use plastics in order to reduce plastic waste that releases the particles in soil, water and air but enforcement remains challenging.
There have been ongoing conversations among countries, chaired by the UN, to create a legally binding global plastics treaty. However, despite years of talks, differences remain over putting a limit on new plastic production and assigning responsibility for the health risks, among other things.
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