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.