Photo credit: arstechnica.com
Testing the Teas
A recent study utilized scanning electron microscopy to explore the structure of black tea leaves, magnified to 500 times. The research highlights that black tea, which undergoes wilting and complete oxidation, possesses a wrinkled surface. This unique texture potentially enhances its ability to adsorb various substances due to the increased surface area.
To investigate their theory, researchers sourced a selection of commercial tea bags from brands such as Lipton and Infusions, in addition to a variety of loose-leaf teas and herbal options. The selection included black tea, green tea, white peony tea, oolong tea, rooibos tea, and chamomile tea. The tea bags were made from several materials, including cotton, cellulose, and nylon. The brewing process mirrored the methods typical of daily tea consumers, involving steeping the teas for durations ranging from mere seconds to a full 24 hours in water that was deliberately spiked with elevated levels of lead, chromium, copper, zinc, and cadmium. After steeping, the tea leaves were filtered out, and the remaining water was analyzed for the concentration of toxic metals and how much was absorbed by the tea leaves.
Interestingly, the type of tea bag played a crucial role in the absorption of these contaminants. The findings indicated that cellulose tea bags were most effective in absorbing toxic metals from the water. In contrast, cotton and nylon bags showed minimal adsorption and the nylon variety even released microplastics. Additionally, the type of tea and the fineness of the grind also influenced the ability to absorb toxic metals, with finely ground black tea leaves proving the most effective. The wrinkled texture of processed leaves increases the surface area, and further grinding enhances this effect, creating more opportunities for binding with toxic metals.
However, the steeping duration emerged as the most critical factor in this study. The researchers discovered that an extended steeping time resulted in higher levels of toxic metal adsorption. Their experiments suggest that brewing tea for three to five minutes using a tea bag could remove approximately 15 percent of lead from drinking water, even in water containing concentrations as high as 10 parts per million.
Source
arstechnica.com