[rafaelferreira]

The summary says "detergent residue from professional dishwashers demonstrated the remnant of a significant amount of cytotoxic and epithelial barrier–damaging rinse aid remaining on washed and ready-to-use dishware", which might address the question about concentrations in regular use.

[sergioisidoro]

For me the word remnant confuses me.

I interpreted it as "leftovers of a significant amount" not a "significant amount of leftovers", meaning that it was used in high quantities, but only remnants (in non significant amounts) were found.

[Zandikar]

You shouldn't assume remnant means "non significant", just "fewer"/"less than" what you started with. If only 5% of the substance remains (aka, the remnants) is still enough to cause problems, those are remnants by definition, but could still be significant amounts in terms of their (chance of) effects/impact.

Side note, those numbers are entirely arbitrary to illustrate the point, not meant to be indicative in anyway of how much is actually left in the processes above.