Synthetic fibres in clothing (like that cotton-poly blend shirt you're most likely wearing) and motor vehicle tyres are some of the bigger sources. These both also release particles directly into the atmosphere allowing them to get absolutely everywhere, unlike plastic in landfills that probably has a harder time escaping into the wider environment.
Can you give me some citations? I know that microwaving plastic containers is about the worst thing you can do with regards to microplastics, because it releases tons of them right into your food:
https://www.wired.com/story/for-the-love-of-god-stop-microwa...
This is a hot area of research but that means it’s a hotbed of flawed and sensationalist research. Dunking embryonic cells in a bath of ridiculous concentrations of nanoplastic chemicals and watching them die is cute and a tired, stupid trick. If you put any of your cells in your favorite drinking water they’re going to lyse. It doesn’t prove shit.
For tyre particulate : https://spiral.imperial.ac.uk/bitstream/10044/1/101707/9/Tyr...