Microplastics

Suppose you're designing a clinical trial to determine whether people from Inner Mongolia are better or worse swimmers than those from Outer Mongolia. 
Tiny plastic particles, categorized by their size as microplastics, <5mm or nanoplastics, 1-100nm are everywhere.
A recent study reported in the New England Journal Of Medicine (NEJM) has drawn the attention of the community of physicians and scientists researching and treating