Brewing tea is not only a health treat, it may also make your drinking water cleaner. New research has revealed an unexpected benefit: Tea can absorb heavy metals like lead and cadmium during the brewing process, effectively filtering harmful substances out of the water. In short, brewing tea and purifying water at the same time is really amazing.
"We found that brewing tea can significantly reduce the amount of metals in drinking water. The longer the tea leaves are steeped, the greater the removal effect," said Benjamin Shindel, the study's first author. He is a doctoral candidate in materials science and engineering at Northwestern University in Evanston, Illinois. In experiments, researchers found that just a few minutes of brewing can improve water quality, and if the tea leaves are steeped overnight, the effect is even more amazing.
In the United States, tap water is generally strictly regulated and safe to drink. But old lead pipes and fittings sometimes mix heavy metals, such as lead, into the water. Although this situation is uncommon, it is worrying. Brewed tea leaves may be a simple and natural solution to reduce potential exposure risks.
However, tea leaves themselves may also contain metals, complicating matters. “The idea of using tea leaves as a tool to absorb metals from water is very interesting and not something that has been considered before,” said Ana Navas-Acien, PhD, chair of the Department of Environmental Health Sciences at Columbia University’s School of Public Health in New York City, who was not involved in the study.
The researchers tried a variety of teas, including black tea, green tea, oolong tea, white tea, chamomile tea and rooibos tea, and compared loose tea leaves with commercial tea bags. They prepared aqueous solutions containing known amounts of lead, chromium, copper, zinc and cadmium, heated them to near boiling point, then added tea leaves and steeped them for anywhere from a few seconds to 24 hours. They then measured the amount of metals that remained in the water and calculated how much the brewing process had removed.
The results were interesting. The material of the tea bag affected the effect: cotton and nylon bags were poor absorbers, while cellulose bags performed well. Researchers believe that cellulose, a natural material derived from wood pulp, has a large surface area and many binding points, so it is naturally better at "grabbing" metal ions. Tea bags commonly found in supermarkets are made of a variety of materials, including plant fibers such as cellulose and hemp, plastics such as nylon, and even biodegradable plastics.
Finely ground tea, especially black tea, has a slightly stronger adsorption capacity, perhaps because of the larger surface area. Shindel also speculates that decaffeinated tea should have a similar effect. As for brewing time, it is undoubtedly the key factor. The longer it is brewed, the more metals are removed. "Some people only brew tea for a few seconds, which has almost no purification effect. But if you brew it for a longer time, even overnight like making iced tea, you can remove most or even almost all of the metals," he explained.
Tea soup is rich in natural organic matter such as tea polyphenols, which can react with heavy metals to form precipitation after binding, thereby reducing the toxic effects of heavy metals on the human body. Tea polyphenols are special compounds containing multiple hydroxyl polyphenol chemical structures. The special chemical structure makes them highly reducible and chelating, so they can form stable complexes with heavy metals or generate precipitation, change the metal form, etc., so as to achieve the purpose of reducing the heavy metal content in the aqueous solution. Other substances may be able to do this, but the convenience of tea is unmatched. You don't need to do anything extra, just soak the tea leaves in water and you can naturally remove the metals.
Because lead, arsenic, cadmium and mercury are highly toxic, special attention should be paid to the situation of these four heavy metals in food, especially long-term (chronic) intake, because they can accumulate in the human body and damage organs, especially vulnerable groups such as fetuses and young children. Although these metals can cause acute poisoning, this situation is mostly caused by non-dietary routes. Each of these four metals will form different compounds with other elements, and the properties of these compounds and the toxic effects on the human body after ingestion are different.
Lead is colorless and tasteless in water and can only be found through testing. The EPA says there is no such thing as a "safe amount of lead exposure." Especially for pregnant women, infants, and young children, lead may affect brain development; for adults, it may cause kidney problems, high blood pressure, and cognitive impairment. Cadmium is not much better. Drinking it may cause vomiting and diarrhea, and inhaling it may damage the kidneys, brittle bones, and even cause cancer.
What does this mean for ordinary tea lovers? Studies estimate that brewing a tea bag in a cup of water (3-5 minutes) can remove about 15% of lead. If tea accounts for one-fifth of your daily drinks, it may reduce lead intake by about 3%. This doesn't sound like much, but Shindel thinks it's still an interesting finding: "We are not suggesting that everyone change their tea drinking habits, nor do we need to make bitter tea to remove metals. I just think that for people who drink tea regularly, this may invisibly reduce metal intake slightly.
