Scientists have found that heavy metal particles adhere to the surface of tea leaves.
Tea lovers may have another reason to savor their favorite brew: new research from Northwestern University suggests that brewing tea can help remove harmful heavy metals like lead and cadmium, potentially acting as a natural water filter.
“Contamination from lead, as well as other metals, in drinking water is a serious challenge around the world. Lead toxicity across all sources is estimated to directly contribute around one percent of the total global health burden of disease,” Benjamin Shindel, the study’s first author, told The Epoch Times.
Tea May Passively Reduce Heavy Metal Exposure
In the study, published Tuesday in the journal ACS Food Science & Technology, scientists discovered that heavy metal particles stick to the surface of tea leaves, remaining trapped there until the used tea bag is discarded. The tea leaves and tea bags absorb the heavy metals in hot water.
Vinayak Dravid, a professor of materials science and engineering, and the study’s senior author, pointed out that tea leaves have a high active surface area, which is a useful property for an absorbent material.
The researchers found that the type of bag used is crucial. While cotton and nylon bags absorbed minimal heavy metals, cellulose bags performed significantly better. The cotton and nylon bags removed practically no heavy metals from water, Shindel said, and pointed out that nylon was “problematic” because it releases microplastics.
The majority of tea bags currently used for teas on the market are made from natural materials, like cellulose, he continued. “These may release micro-particles of cellulose,” which, he explained, is a fiber which our bodies can handle.
High-end pyramid tea bags, recognized for their transparent, mesh-like appearance, are typically made from nylon.
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These cellulose-based tea bags are frequently marketed as “biodegradable” or “plant-based.” For loose tea enthusiasts, cotton tea bags offer a reusable alternative that can be filled with loose tea leaves multiple times.
Steeping Time Makes a Difference
According to the study findings, steeping time also played a vital role in the effectiveness of tea in removing metals. Dravid and team hypothesized that longer steeping times allow more heavy metals to be absorbed, noting that this could range from minutes to several hours to maximize tea’s cleansing potential.
“We found that a variety of tea preparation methods will passively cause the removal of a meaningful fraction of lead from drinking water,” Shindel said. “The performance is most closely tied to steeping time: the longer the time tea is steeped, intuitively the more metal content it can remove.”
They estimated that a typical cup of tea can remove about 15 percent of lead from drinking water, even from levels as high as 10 parts per million, which is considered toxic.
But with lower concentrations of lead, tea leaves should remove a similar fraction of the metal content in the water, Shindel said.
Researchers Tested All Types of Tea
To conduct the study, Dravid and team examined different types of tea, tea bags, and brewing methods to see how these factors influence the absorption of heavy metals. They tested “true” teas such as black, green, oolong, and white, in addition to herbal options that included chamomile and rooibos—also known as “red bush tea” or “African red tea.”
They created water solutions containing known amounts of lead and other metals, and then heated these solutions just below boiling before adding the tea.
While most tea varieties showed similar results, chamomile, which comes as a flower rather than leaves, performed significantly worse in water remediation.
‘Unrecognized Potential’
In a statement, Dravid emphasized that “we’re not suggesting that everyone starts using tea leaves as a water filter.”
He added that in this study, the 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,” Dravid added.
“Our study underscores the need for simple, drop-in and easy-to-use approaches to complex problems like water quality,” Dravid told The Epoch Times. “As for me,” he added, “it reinforces the notion that, while we try to clean our environment as a whole, it may be feasible to clean water ‘one glass at a time.’”
Expert Advises Caution Regarding Findings
“This data is interesting because it elucidates a potential mechanism for some of the health benefits associated with tea consumption,” Dr. Ryan Marino, medical toxicologist, emergency physician, and addiction medicine specialist at Case Western Reserve University School of Medicine, told The Epoch Times.
Marino noted while we know that brewed tea contains multiple compounds that exert effects on humans and their health, our knowledge of these compounds has not explained all associated health benefits, and so the study’s findings offer another avenue to explore in future scientific research.
‘Unclear’ if Brewing Is Enough to Improve Health
Marino emphasized that although this data suggests brewing tea can remove trace amounts from the water, it is unclear if this would remove an amount sufficient to have any health effects, “which is a question for future research as well.”
Marino added that tea brewing would be expected to be a subjective, “somewhat unreliable,” and limited means of adsorbing metals. Since people use different water, containers, brewing times, and methods, the amount absorbed can vary significantly.
“So the best method for avoiding exposure to such metals remains through primary prevention by regulation of industry, waste products, and water, air, and food,” he said. “Which are tasks that the US EPA and US FDA currently do.”
Lastly, Marino said it’s important to note that plants, like tea leaves, will also usually contain some amount of heavy metals themselves because of the soil and water that they are grown in, in addition to additional contaminants from their production, “which could further limit this potential benefit and requires further study.”
The new study challenges conventional wisdom that discourages extended tea brewing times. While it’s commonly believed that tea plants absorb heavy metals from soil, the researchers emphasize that additional studies are necessary to fully verify these findings.
Rachel Ann T. Melegrito contributed to this report.
