A group of New York City high school students did a study of the DNA composition of tea. What they found was actually pretty disturbing. More than a third of the herbal teas they tested contained material other than what was listed on the label. For anyone with allergies to certain plants this could be a real problem. If a tea (whether it is an herbal teasan or a true tea) is mechanically cut I think some impurity is inevitable. But I also think behooves the tea company to test their products before sending it to market. Hopefully studies like this will lead to more stringent guidelines. Click on the title of this post for a link to the Scientific American article about this story and check out the video below.
You can read the results of their study here.