Tea leaves pull heavy metals from water, significantly lowering the amount of lead and other dangerous compounds that people may be unknowingly drinking, a new study found. About five billion cups of tea are consumed each day around the world. “You can see the implications,” said Vinayak Dravid, a materials scientist at Northwestern. “How often do we touch billions of people?” In many countries, the water used to steep tea is contaminated with lead from aging pipes. Lead is especially dangerous to children.
Recent research has highlighted potential applications for used tea leaves, from biofuels to gluten-free cookies. Dr. Dravid and his team tested how different types of tea – black, white, oolong, green, rooibos, herbal, loose leaf, and plain old Lipton – behaved in water with varying amounts of lead.
The tea was then allowed to steep for variable periods of time. Afterward, the scientists measured how much lead remained in the water. Compounds called catechins in tea leaves act like ‘little Velcro’ hooks to which lead molecules latch. Dr. Francl said that the ‘ridges and valleys’ of the tea leaves provided the necessary surface area for that interaction.
While those properties have been known for some time, Dr. Dravid and his colleagues were the first to look at the lead-detoxifying powers of a single cup of tea. They found that black tea leaves became wrinkled after roasting and were thus best equipped to absorb heavy metals.
Green tea and black tea had fairly equivalent amounts of metal absorbed. White tea, on the other hand, undergoes a much more gentle preparation. Its leaves remain smooth, offering less surface area from which to draw heavy metals from water. Herbal tea enthusiasts may be disappointed to learn that chamomile tea does a poor job of heavy-metal filtering, too, probably because it is made with chamomile flowers, not tea leaves.
The researchers found that steeping a cup of black tea for five minutes could remove 15 percent of lead from the water, which is helpful, but there is ‘no safe level’ of lead exposure, according to the E.P.A. With lead and other contaminants, any decrease is meaningful to some extent, especially if you have a lack of resources or infrastructure that would already remediate some of these problem materials.
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