In a study published in June in Environmental Science & Technology, Hussain and his colleagues reported that, when microwaved, these containers released millions of bits of plastic, called microplastics, and even tinier nanoplastics.
[…]
Once they’ve snuck past the body’s defense systems, “the chemicals used in plastics hack hormones,” says Leonardo Trasand, a professor at the NYU Grossman School of Medicine and the director of the Center for the Investigation of Environmental Hazards. Hormones are signaling molecules underlying basically everything the body does, so these chemicals, called endocrine disruptors, have the potential to mess with everything from metabolismto sexual development and fertility.
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Judith Enck, a former EPA regional administrator and the president of Beyond Plastics, a policy and advocacy group against plastic pollution, stopped microwaving plastic 30 years ago. She thinks that you should, too: “My goodness, especially if you have kids or if you’re pregnant, do not put plastic in the microwave.”
“It’s a pain in the neck,” she acknowledges, but “even this one study should be a wake-up call—not just to new parents but to the FDA. They need to be far more proactive.” Transand agrees: “The FDA is glacially behind.”
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“I don’t believe that there are microwave-safe plastics.” Trasand and Enck agree that while independent studies should continue testing how much plastic is being released from food packaging, there is already enough evidence to show that “microwave-safe plastic” isn’t really safe. “I think the FDA needs to tell companies that they can no longer say any plastic is microwavable,” says Enck.
The problem here is that in order to change a microwave to UV, you need to add energy to it. Generally, diffraction and distortion of light waves don't change what part of the spectrum they're on - that's why water doesn't change the color of light passing through it. The wavelength changes, but critically, the frequency doesn't, and frequency is really what defines the energy of a given photon, which in turn defines the part of the spectrum it's on. So if the microwave is turning into UV somehow, that means it has to be stealing energy from the container or food, which would make the food colder.
I'd expect the only UV rays that would be emitted within a properly functioning microwave would be from the appliance light bulb inside of it if it's still an incandescent design or from the food/container itself if it gets sufficiently hot. I'm not sure of any mechanism in the magnetron that would make UV in any substantial amounts.