No, they-are-not-actually-contamination. Some studies might have inaccurate numbers due to contamination. That's all.

Important to correct for, but doesn't invalidate the whole microplastics concern.

This is both good and bad. Good ASR can often understand low quality / garbled speech that I could not figure out, but it also "over corrects" sometimes and replaces correct but low prior words with incorrect but much more common ones.

With OCR the risk is you get another xerox[1] incident where all your data looks plausible but is incorrect. Hope you kept the originals!

(This is why for my personal doc scans, I use OCR only for full text search, but retain the original raw scans forever)

[1] https://www.dkriesel.com/en/blog/2013/0802_xerox-workcentres...