Good news for tea lovers: That daily brew might be purifying the water, too. A new study from Northwestern University researchers has demonstrated the remarkable ability of brewing tea to naturally adsorb heavy metals like lead and cadmium, effectively filtering dangerous contaminants from drinks. Heavy metal ions stick to the surface of the tea leaves, where they remain trapped until the used tea bag is disposed of.
The research, published on February 25, 2025, in ACS Food Science & Technology, focuses on how different types of tea, tea bags, and brewing methods affect the adsorption of heavy metals. 'We’re not saying everyone should start using tea leaves as water filters,' noted Vinayak Dravid, the study’s senior author. 'Our goal was to measure tea’s ability to adsorb heavy metals and quantify this effect, highlighting tea consumption's potential to reduce heavy metal exposure globally.'
First author Benjamin Shindel elaborated on this finding, explaining the significant role of tea’s high active surface area as key to its effectiveness. 'Tea's ability to adsorb contaminants is notable not only because it's widely consumed, but, unlike other materials, people need not do anything extra—just steep the leaves.'
To ascertain how various factors influenced this effect, the researchers tested 'true' teas such as black, green, oolong, and white, as well as herbal teas like chamomile and rooibos. They conducted controlled experiments using water solutions with known quantities of heavy metals such as lead, chromium, copper, zinc, and cadmium, and measured how much metal remained after steeping tea leaves for varying periods, ranging from seconds to 24 hours.
One interesting aspect of their findings was the nature of the tea bags themselves. The team determined cotton and nylon bags performed poorly, only adsorbing negligible amounts of contaminants. On the other hand, cellulose bags, which are biodegradable and made from wood pulp, excelled due to their high surface area. 'The key to successful sorbent material is high surface area,' Shindel explained.
When the researchers changed steeping times, the results highlighted the importance of duration—longer steeping time led to greater adsorption of metals. Their measurements indicated steeping tea for five minutes could remove as much as 15% of lead from water even at high concentrations, emphasizing the public health relevance of these findings. When steeped overnight, such as for iced tea, not only was the metal removal more effective, but it could approach close to total remediation.
Notably, this method of purification might carry substantial health benefits. If populations worldwide incorporated just one additional cup of tea daily, Shindel speculated, there could be declines in illnesses correlated with heavy metal exposure.
'Tea preparation removes significant amounts of lead from drinking water, and the effects should not be underestimated,' said Shindel. He indicated this study's results add valuable data for future research on public health and trace the correlations between tea consumption and lower incidence rates of heart disease and strokes among populations with high tea intake.
Overall, the findings of this Northwestern University study open pathways for how we regard everyday actions—like brewing tea—as contributors to health and well-being. So, the next time you pour yourself a cup, know you're doing more than just quenching your thirst.