Brewing tea removes lead from water

High surface area of the tea leaves means they can adsorb toxic metals released by the boiling water.

That comforting hot cup of tea—or refreshing glass of iced tea on a hot summer day—could help reduce the amount of toxic metals in drinking water, according to a new paper published in the journal ACS Food & Science Technology.

“We’re not suggesting that everyone starts using tea leaves as a water filter,” said co-author Vinayak Dravid, who studies sorbent materials at Northwestern University. “Our goal was to measure tea’s ability to adsorb heavy metals. By quantifying this effect, our work highlights the unrecognized potential for tea consumption to passively contribute to reduced heavy metal exposure in populations worldwide.”

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.)

A 2020 study suggested that tea leaves serve as a carrier of toxic metals from contaminated soil. Dravid et al. think this hypothesis is "misguided," suggesting instead that it's the high surface area of tea leaves and the fact that tea is prepared with boiling water—which is what releases flavor chemicals from the leaves into the water—that is responsible. The heavy metals in water partition onto the leaves while the tea steeps, resulting in lower heavy metal consumption by tea drinkers. This proposed mechanism might help explain why so many studies find health benefits to drinking tea.

Testing the teas

To test their hypothesis, the authors purchased Lipton and Infusions commercial tea bags, as well as a variety of loose-leaf teas and herbal alternatives: black tea, green tea, white peony tea, oolong tea, rooibos tea, and chamomile tea. The tea bags were of different types (cotton, cellulose, and nylon). They brewed the tea the same way daily tea drinkers do, steeping the tea for various time intervals (mere seconds to 24 hours) in water spiked with elevated known levels of lead, chromium, copper zinc, and cadmium. Tea leaves were removed after steeping by pouring the tea through a cellulose filter into a separate tube. The team then measured how much of the toxic metals remained in the water and how much the leaves had adsorbed.

It turns out that the type of tea bag matters. 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.

“Any tea that steeps for longer or has higher surface area will effectively remediate more heavy metals,” said co-author Benjamin Shindel, a former graduate student of Dravid who now works at the Department of Energy’s National Energy Technology Laboratory. “Some people brew their tea for a matter of seconds, and they are not going to get a lot of remediation. But brewing tea for longer periods or even overnight—like iced tea—will recover most of the metal or maybe even close to all of the metal in the water.”

“I’m not sure that there’s anything uniquely remarkable about tea leaves as a material,” said Shindel. “They have a high active surface area, which is a useful property for an adsorbent material and what makes tea leaves good at releasing flavor chemicals rapidly into your water. But what is special is that tea happens to be the most consumed beverage in the world. You could crush up all kinds of materials to get a similar metal-remediating effect, but that wouldn’t necessarily be practical. With tea, people don’t need to do anything extra. Just put the leaves in your water and steep them, and they naturally remove metals.”

It probably won't solve a major global water crisis, but it just might improve your health when it comes to illnesses correlated with heavy metal exposure, like heart disease and stroke.

ACS Food and Science Technology, 2025. DOI: 10.1021/acsfoodscitech.4c01030  (About DOIs).

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