From the article:
> They found that on average, the gloves imparted about 2,000 false positives per millimeter squared area.
I dunno, that seems like a lot of false positives. Doesn’t that strongly imply that overestimation would be a pretty likely outcome here? Sounds like a completely sterile 1mm^2 area would raise a ton of false positives because of just the gloves.
Then the tested result is Actual Sample Result - Negative Sample Result.
So you'd expect a microplastic sample to have 2,000 plus N per mm^2, and N is the result of your test.