Tea, a very popular beverage, may have an unsuspected effect on the quality of the water we drink. A recent study reveals that steeping tea could purify water by removing toxic heavy metals.
New study showing that steeping tea naturally removes lead and other toxic heavy metals from water.
Credit: Vinayak P. David Group/Northwestern University
Researchers at Northwestern University have discovered that tea leaves can adsorb heavy metals like lead and cadmium. This natural process allows these dangerous contaminants to be filtered from water. The metal ions attach to the surface of the tea leaves, where they remain trapped until the used tea bag is discarded.
The study, published in the journal
ACS Food Science & Technology, does not, however, suggest using tea leaves as a water filter. Nevertheless, it highlights tea's ability to reduce exposure to heavy metals worldwide. The researchers measured this adsorption capacity, thus underscoring a little-known benefit of tea consumption.
Tea leaves, with their large active surface, are particularly effective at adsorbing metals. This property, which also allows tea to quickly release its flavors into water, makes it a natural adsorbent material. The fact that tea is the most consumed beverage in the world adds to the importance of this discovery.
The research team explored how different types of tea, bags, and steeping methods affect the adsorption of heavy metals. They tested varieties such as black, green, oolong, and white tea, as well as herbal teas like chamomile and rooibos. The results show that cellulose bags are the most effective, unlike those made of cotton or nylon. The steeping time plays a crucial role in the adsorption of metal ions. The longer the tea steeps, the more contaminants it adsorbs.
Scanning electron microscope image of black tea leaves, magnified 300 times. Black tea, withered and fully oxidized, has a wrinkled surface, potentially increasing the available surface for adsorption.
Credit: Vinayak P. David Group/Northwestern University
The researchers estimate that preparing tea can remove about 15% of lead from drinking water, even at high concentrations. This adsorption capacity depends on several factors, including steeping time and the water-to-tea ratio. These results open new perspectives for public health research, particularly in regions where exposure to heavy metals is a problem.
How does tea adsorb heavy metals?
Adsorption is a process by which metal ions attach to the surface of a material. In the case of tea, the leaves offer a large active surface, allowing lead, cadmium, and other heavy metal ions to cling to them. This phenomenon is similar to how a magnet attracts metal particles.
The structure of tea leaves, especially after being processed into black tea, increases this active surface. The wrinkles and open pores of the leaves provide more binding sites for metal ions. Thus, the larger the surface, the greater the adsorption capacity.
This property is enhanced by grinding the leaves, which exposes even more surface area. However, the most important factor remains the steeping time. The longer the tea leaves remain in contact with water, the more heavy metals they can adsorb.
What are the advantages of cellulose bags?
Cellulose bags, made from wood pulp, are particularly effective at adsorbing heavy metals. Unlike cotton or nylon bags, cellulose bags offer a larger active surface.
This increased surface allows metal ions to attach more easily. Moreover, cellulose bags are biodegradable and do not release microplastics into the environment, unlike nylon bags.
The cellulose particles released by these bags are simply fibers that the human body can ingest. This makes cellulose bags a safer option for preparing tea, while also contributing to water purification.