I don't know what the most common sources of microplastic particles are, but the messaging needs to be such that people know we aren't getting rid of all plastics, just the stupid ones that are most responsible for potentially harming us. I think straws were banned because there was a video of a plastic straw stuck in sea turtle's nose, not because they're one of the top sources.
[1]: https://mashable.com/feature/carbon-footprint-pr-campaign-sh...