From a presentation last year by a researcher that works on the toxicity of nanoplastics at The German Federal Institute for Risk Assessment, I recall that they so far haven't found evidence of the toxicity of nano- and microplastics even if you would assume high exposure scenarios (e.g. having a diet consisting of only plastic-laden oysters), but that further research needs to be undertaken.

Their website on the topic (in German[0]) states the same thing: No evidence that they pose any health risk to humans, but further research is necessary for any conclusive statements.

[0]: https://www.bfr.bund.de/de/mikroplastik__fakten__forschung_u...