Temperatures greater than 40 degrees Celsius (104 degrees Fahrenheit) can degrade plastics, even food-grade plastics. A research team at McGill University in Canada wanted to know how much plastic is shed from tea bags in hot water. It turns out, a lot. A single plastic teabag, steeped for 5 minutes, releases billions of microplastics into your cup. Not kidding. They found 11.6 billion microplastics and 3.1 billion nanoplastics in a single cup.
If you want to avoid that, switch to loose-leaf tea. If you prefer tea bags, make sure your brand uses paper. Check carefully, because some paper bags are also reinforced with plastic.