Some 2 billion people drink tea on a daily basis worldwide, and numerous studies have suggested various health benefits from regular tea consumption. Most nutrition studies focus on things like polyphenols, caffeine, or other chemicals released during brewing, but such research overlooks a unique aspect of tea: unlike most food and drink, tea leaves are not directly consumed, and the brewing process allows tea leaves to adsorb chemicals as well as release them—most notably heavy metal toxins like lead, arsenic, or cadmium. (Adsorption is when a substance adheres to the surface of something; absorption is when a material takes in a substance.). //

The team found that cellulose tea bags work the best at adsorbing toxic metals from the water while cotton and nylon tea bags barely adsorbed any contaminants at all—and nylon bags also release contaminating microplastics to boot. Tea type and the grind level also played a part in adsorbing toxic metals, with finely ground black tea leaves performing the best on that score. This is because when those leaves are processed, they get wrinkled, which opens the pores, thereby adding more surface area. Grinding the tea further increases that surface area, with even more capacity for binding toxic metals.

But the most significant factor was steeping time: the longer the steeping time, the more toxic metals were adsorbed. Based on their experiments, the authors estimate that brewing tea—using a tea bag that steeps for three to five minutes in a mug—can remove about 15 percent of lead from drinking water, even water with concentrations as high as 10 parts per million.