Tea bags have been getting some bad press lately. Well, tea bags are always getting bad press for their contents but this time it is the bag itself causing the problem.
It seems that the tea bags that are described as “silken” are actually made with plastic. Some of these plastics are food-grade nylon or polyethylene terephthalate (PET) but they have a melting point of ~250 °C and are generally not considered harmful to health. However, an article appeared in the Atlantic a couple of weeks ago that said that the molecules of these plastics would start to break down at a lower temperature (~76 °C) which could allow the bags to leach out toxins. The example in the article was a Lipton Pyramid Tea Bag made of PET but there was no concrete evidence of toxicity and no measure of toxins.
Another type of plastic used in these silky tea bags is polylactic acid (PLA), a biodegradable plastic made from cornstarch (which can be genetically modified or not). This bioplastic is commonly used as the input material for 3-D printers and doesn’t seem to carry the same health concerns as PET. While technically PLA is biodegradable and may well break down into its constituent parts (carbon dioxide and water), it needs an industrial composting facility heated to 60 °C and the addition of digestive microbes. In a compost bin, or in a regular landfill, there is no evidence that it will break down there any faster than any other form of plastic (source).
The bad news didn’t stop there though. Apparently paper tea bags may have similar culpability. Many paper bags are treated with epichlorohydrin as a paper reinforcement to stop the tea bag tearing. Epichlorohydrin is also used to make insect fumigant and is considered to be a carcinogen and moderately toxic. The exposure limits set by WHO are 0.4 μg/litre. I’m assuming that moderate tea-drinking with these tea bags would leave you well below the exposure limits but I can’t find confirmation of that.