Tea has been shown to reduce depression, reduce the risk of diabetes, and may even extend the life of those who drink it. New research shows that tea leaves can also remove toxic heavy metals from tea water. The research was conducted by a team led by Professor Vinayak Dravid and doctoral student Benjamin Hindel at Northwestern University in Illinois.


First, the scientists added specific amounts of lead, chromium, copper, zinc and cadmium to a sample of clean water and then heated the water to just below the boiling point. Next, they added different types of tea leaves (both loose and commercially available in bags) to the samples and allowed them to steep for anywhere from a few seconds to 24 hours.

After brewing, scientists analyzed the water samples to see how, if at all, the heavy metal levels had changed. Real teas such as black, green, oolong and white tea were tested, along with herbal varieties such as chamomile and rooibos. Different bag materials are also used, including cotton, nylon, and cellulose.


Study tested many different teas Vinayak P. David Group/Northwestern University

It was ultimately found that, on average, brewing a "typical" cup of tea - consisting of a cup of water and a tea bag steeped for three to five minutes - removed approximately 15% of the heavy metal concentration in the water. The same is true for toxic lead concentrations as high as 10 parts per million. Additionally, while most people don't brew tea for more than a few minutes, longer brewing times can remove even more metals.

The main factor at play in this process is that dry, wrinkled, porous tea leaves have a high active surface area, and metal ions in the water adhere to the tea leaves. These adsorbed ions are trapped in the tea leaves and are eventually thrown out with the tea leaves. Since no actual chemical reaction occurs, all different types of tea behave similarly.


Scanning electron microscope image of dried black tea leaves showing their surface area

Cotton and nylon tea bags have little effect on adsorbing heavy metals, but the adsorption effect of naturally derived biodegradable cellulose bags is definitely not ideal. As is the case with the tea itself, cellulose fibers have a large active surface area, allowing the bags to absorb large amounts of heavy metal ions.

To summarize, no one is suggesting using tea for large-scale remediation of metal-contaminated water. However, drinking tea instead of other liquids is definitely a healthy approach.

"Across the entire population, if people drank an extra cup of tea a day, perhaps over time we would see a reduction in diseases that are closely related to exposure to heavy metals," Schindel said. "Alternatively, it could help explain why people who drink more tea may have lower rates of heart disease and stroke than people who drink less tea."

A paper on the research was recently published in the journal ACS Good Science&.