Among other things, tea has already been shown to reduce depression, reduce the risk of diabetes, and possibly even extend its drinkers' lifespans. New research now indicates that tea also removes toxic heavy metals from the water in which it's being brewed.
The study was conducted at Northwestern University in Illinois, by a team led by Prof. Vinayak Dravid and PhD student Benjamin Shindel.
To start things off, the scientists added specific quantities of lead, chromium, copper, zinc and cadmium to samples of clean water, then heated that water to just below the boiling point. Next, they added different types of tea leaves – both loose and commercially bagged – to those samples, then allowed them to steep for anywhere from a few seconds up to 24 hours.
Once the brewing period was over, the scientists analyzed the water samples to see how the heavy metal levels had changed (if at all). True teas such as black, green, oolong and white were tested, along with herbal varieties like chamomile and rooibos. Different bag materials were also used, including cotton, nylon and cellulose.
It was ultimately found that on average, the brewing of a "typical" cup of tea – consisting of a mug of water and a bag of tea steeped for three to five minutes – removed approximately 15% of heavy metal concentrations from the water. This was even the case for very toxic lead concentrations as high as 10 parts per million. What's more, longer brewing times removed even more of the metals, although most people aren't likely to brew their tea for much more than several minutes.
The main factor at work in the process is the high active surface area of the dried, wrinkled, porous tea leaves, which the waterborne metal ions stick to. Those adsorbed ions remain trapped in the leaves, and end up being thrown out along with them. And because there's no actual chemical reaction taking place, the performance proved to be similar for all of the different types of tea.
The cotton and nylon tea bags had little effect one way or the other, but such was definitely not the case with the natural-source biodegradable cellulose bags. As is the case with the tea leaves themselves, the cellulose fibers boast a large active surface area, allowing the bags to adsorb a significant quantity of heavy metal ions.
All of that being said, no one is suggesting that tea could be used to remediate metal-tainted water on a large scale. Drinking it in place of other liquids, however, may certainly be a healthy practice.
"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," says Shindel. "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."
A paper on the research was recently published in the journal ACS Food Science & Technology.
Source: Northwestern University
