I'm shocked too ;)

If you've ever handled kilos of materials like these orthophthalates, you realize they are not very volatile materials. At all. IOW, they really don't like to evaporate. They are like syrups, intended not to go away by themselves or dissipate much through time. That's their job as "plasticizers" in the plastic compounding process, to just slightly soften the resulting product as they are premixed in small amounts with the raw polymer pellets along with pigments and other additives before molding.

I can't access the whole paper, but for me the next step would be to consider the possibility whether the phthalates are possibly leaching from the human subjects themselves into the wristbands by more direct means than could be accomplished by airborne delivery.

I'm no graduate student but I did pioneer a laboratory technique or two for analyzing them[0] when others had still made no progress decades ago. Not exactly easy compared to some other toxic industrial chemicals, then and now. Plus for trace analysis it requires its own kind of meticulousness.

[0] Pthalates, not wristbands so far, which would be a whole 'nother can of worms.