Several tea bag brands use polypropylene, a sealing plastic, to keep the tea bags from falling apart
Country Living reveal which tea bag brands do and don't have plastic in their tea bags. Luckily, there are a number of plastic-free tea bags.
Teabags: Is there plastic in yours?
Plastic-Free Tea Bags: Which Brands Have Removed Plastic?
Plastic in Tea Bags (and all the brands that do & don't contain it)
Is Your Tea Bag Made with Plastic? - Center for Environmental Health
Plastic Tea Bags - Does Your Choice of Tea Bag Contain Plastic?
Safer Tea Brands - Toxic & Plastic Free!
Which tea bags are free of plastic? - SCUBA News
Hey Tea Lover: If You're Drinking Tea From A Teabag, You Might Be
The Truth About Tea Bags: Should You Use Them or Not?