I think that's mostly BPA and phthalates, and microplastics are often listed along with those, but I'm unsure if it was actually tested or if we notices people had a lot of microplastics and just assumed that was a likely source.
I remember at least one study that pointed to 250k nanoplastics in a liter of bottled water [0]. Possibly these types of particles weren't studied. There are certainly many different toxicants to be looking out for; overwhelming to the point of being pointless.
[0]: https://www.nih.gov/news-events/nih-research-matters/plastic...
Also the negligible levels of plastic detected in plastic water bottles is surprising. I was under the impression, based on other reports, that water in plastic bottles is something we should avoid.