Plenty of science shows just how great having a daily cup of tea can be for you, including everything from preventing cardiovascular diseases to being antidiabetic and even anti-aging. Now, a new study from researchers at Northwestern University shows that brewing tea may also naturally absorb heavy metals, helping filter them out of your water.
In February, the researchers published their work in the journal ACS Food Science & Technology, showcasing how tea could be used as a natural filtration system to improve water quality. To come to this conclusion, it gathered different types of tea — including black, green, oolong, white, chamomile, and rooibos — as well as loose-leaf and bagged tea to see how brewing each affected the water. They created water solutions with "known amounts of lead and other metals (chromium, copper, zinc, and cadmium)," and heated the solutions to just below boiling. Finally, they added the leaves and allowed them to steep for various time intervals between seconds and a full 24 hours.
After the steeping sessions, the researchers measured the metal content in the water. They found that tea in cotton and nylon bags absorbed the least contaminants, while cellulose bags—often made of biodegradable wood pulp—" worked incredibly well. " These bags have a high surface area, which means more surface area for heavy metals to stick to.
“The cotton and nylon bags remove practically no heavy metals from water,” Benjamin Shindel, the study’s first author, shared in a release. “Nylon tea bags are already problematic because they release microplastics, but the majority of tea bags used today are made from natural materials, such as cellulose. These may release micro-particles of cellulose, but that’s just fiber which our body can handle.”
Black tea leaves, the researchers added, also performed the best, especially finely ground tea leaves. That's because they "wrinkle and their pores open,” Shindel added. “Those wrinkles and pores add more surface area. Grinding up the leaves also increases surface area, providing even more capacity for binding.”
And as you may expect, the longer the tea was left to seep, the better the outcome. “Any tea that steeps for longer or has higher surface area will effectively remediate more heavy metals,” Shindel stated. “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."
After all that work, the researchers found that tea preparation can remove about 15% of lead from drinking water. This finding applies only to a “typical” cup of tea, or one mug of water and one bag of tea, which is brewed for three to five minutes. Changing the parameters remediates different levels of lead.
Of course, the researchers don't expect you to start using tea to filter all your water. Rather, they hope this work will enhance our understanding of contaminants and how we can improve water quality in the future.
"For this study, our goal was to measure tea’s ability to absorb 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," Vinayak P. Dravid, the study’s senior author, added. "Across a population, if people drink an extra cup of tea per day, maybe over time we’d see declines in illnesses that are closely correlated with exposure to heavy metals. Or it could help explain why populations that drink more tea may have lower incidence rates of heart disease and stroke than populations that have lower tea consumption.”
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