From the article:
To come to this conclusion, the team tested tea bags made from nylon-6, polypropylene, and cellulose, all typical packaging for teas. They found that when brewing tea, "polypropylene releases approximately 1.2 billion particles per milliliter, with an average size of 136.7 nanometres; cellulose releases about 135 million particles per milliliter, with an average size of 244 nanometres; while nylon-6 releases 8.18 million particles per milliliter, with an average size of 138.4 nanometres."
Literally what he did in the next paragraph: