- cross-posted to:
- health
- [email protected]
- cross-posted to:
- health
- [email protected]
Most nutrition studies focus on things like polyphenols, caffeine, or other chemicals released during brewing, but such research overlooks a unique aspect of tea: unlike most food and drink, tea leaves are not directly consumed, and the brewing process allows tea leaves to adsorb chemicals as well as release them—most notably heavy metal toxins like lead, arsenic, or cadmium. (Adsorption is when a substance adheres to the surface of something; absorption is when a material takes in a substance.)
Well, maybe I’ll start drinking tea.
I remember this making its rounds on HN lately. People are skeptical because of other numerous studies stating other findings that were contrary to this.
Can anyone get the official paper? https://pubs.acs.org/doi/10.1021/acsfoodscitech.4c01030 is the only real resource I can find and its a paywall.
Here you go:
Thank you!!
yeah there you go. no pdf bc it’s watermarked and i’m a bit too paranoid for that. supplementary info is free to read
ABSTRACT: The study of adsorbent materials rarely extends beyond engineered systems. This research explores metal adsorption resulting from the preparation of tea, which is the most widely consumed beverage globally. Tea is brewed from the processed leaves of the Camellia sinensis plant, a material understudied, relative to its outsized economic and cultural importance. The features that make tea leaves ideal for their intended purpose also help them function as an efficient sorbent. In this Letter, the properties of tea leaves relevant to the adsorption of metal content in drinking water are measured and used to estimate, for the first time, the adsorptive performance under a variety of conditions of tea preparation, with an eye toward public health benefits. We find that the preparation of black tea under typical conditions results in the removal of a meaningful fraction of lead from drinking water and that this value is highly dependent on steeping time. KEYWORDS: tea, heavy metals, lead, adsorption, water remediation, global health
continuing…
These data, presented in Figure 1b, demonstrate that the stirred room-temperature and 85 °C samples were fairly similar, with both rapidly approaching equilibrium, whereas the unstirred room-temperature sample approached thermodynamic equilibrium much more slowly. This result shows how heat impacts the kinetic performance during tea preparation but also implies that it is unlikely that heat is in and of itself affecting the thermodynamic equilibrium, as the stirred sample had similar kinetic performance. This differs from findings on the adsorption of uranium to tea leaves, which anticipated that heat may allow for greater thermodynamic capacities,14 but agrees with other findings on the adsorption of zinc to tea waste.19 Several varieties of whole tea leaves�green, black, oolong, and white�as well as two varieties of herbal teas�chamomile and rooibos�were tested in batch adsorption trials to compare their adsorptive performance. These teas represent a diverse selection of the most consumed varieties of true teas and herbal tea substitutes from around the world. Starting from an initial Pb concentration of ∼1 ppm, the final concentration of the water is shown on a log scale in Figure 1c. While most tea varieties performed quite similarly, chamomile, which has the form factor of a flower (unlike the other tea leaves tested), was an outlier in performance, remediating the water more poorly. The Yunnan black whole tea leaves that were tested in the experiments from Figure 1a−c were ground finely and tested alongside the original, whole leaves. This grinding process, which likely exposed additional surface area for adsorption, improved the performance of the tea leaves with respect to metal adsorption (shown in Figure 1d). In addition, tea bags made from cotton, cellulose, and nylon materials were tested in a fashion similar to the experiments depicted in panels c and d of Figure 1. Nylon and cotton tea bags exhibited trivial amounts of adsorption, whereas cellulose tea bags (often sold as “wood pulp” tea bags) were highly effective in remediating the metal content in the water (shown in Figure 1e). This difference in adsorption performance underscores the importance of materials selection in tea bag design, especially when additionally considering the release of microplastics associated with nylon tea bags.5 These adsorption experiments were conducted at an adsorbent loading of 100 mg in 40 mL tubes of water, agitated on a shaker table. While the focus of most of the experiments in this Letter is Pb, Cr(VI), Cu, Zn, and Cd were additionally each tested in batch adsorption trials. Pb is the heaviest of these elements by atomic weight; thus, when equivalent amounts by mass of each of these elements are found in contaminated water samples, Pb has the lowest molar concentration. The performance of black tea leaves in remediating these five elements (shown in Figure 1f) precisely follows, as expected, the trend in increasing atomic weights: Cr(VI) < Cu < Zn < Cd < Pb. The effects of pH and the use of tap water rather than deionized water for experimentation were also explored. Hydrochloric acid and sodium hydroxide were used to modify the pH of water samples before adsorption trials using black tea leaves, and the measured pH of the samples is shown alongside the remaining fraction of Pb in solution in Figure 1g. One can see that adsorption remains relatively constant across a range of pH values from 4 to 10 that encompass the likely pH values of drinking water. In Figure 1h, the results of using tap water are shown as a proof of concept. These show an adsorptive capacity comparable to that of the deionized water samples with full Langmuir isotherms tested in the experiment underlying Figure 1a. To parse the processing methods and structural features that may have an impact on adsorption properties in tea leaves, scanning electron microscopy (SEM) was performed on the six tested tea varieties. Hierarchical imaging with increasing magnification is shown for three of the samples, alongside a simplified processing flowchart, in Figure 2. White tea, which is steamed and not baked or oxidized (unlike most teas), shows a relatively smooth and unwrinkled surface. Black tea, which is wilted and fully oxidized, exhibits a more wrinkled and tortuous surface, potentially increasing the available surface area for adsorption. Researchers have evaluated the surface areas of unmodified green and black tea leaves and found them to vary between 1 and 4 m2/g.19−22 The chamomile flower, which had an adsorption capacity much lower than that of either, is smoother than black tea at the highest magnification, although it contained some moieties with complex shapes, as shown in the highest-magnification image. However, the species of chamomile flowers is different from that of true teas, which are all derived from the C. sinensis plant, and thus may have very different surface properties and internal porosities. Images of all six tea varieties can be found in Figure S2. Energy dispersive spectroscopy (EDS) was performed in a scanning electron microscope on tea samples before and after the adsorption of Pb to confirm its presence on the surface. EDS elemental mapping showing an even distribution of metal content on the surface of tea leaves can be found in Figures S3 and S4. 3.2. Modeling the Effect of Tea Preparation on Drinking Water Remediation. To interpret the data from our experimentation in a manner that provides insight into the generalized adsorptive performance during tea preparation, we created a simple mathematical model in MATLAB to calculate the predicted performance of remediating drinking water through tea preparation. The data at thermodynamic equilibrium reflected in the derived Langmuir model parameters (fitting parameters and R2 values for the Langmuir fits, as well as R2 values for linear, Freundlich, and Dubinin- Radushevksy isotherm fits performed on the data, can be found in Tables S3 and S4) were combined with parameters from the kinetics experiments. After the data from our kinetics experiments were fit with both pseudo-first-order (PFO) and pseudo-second-order (PSO) adsorption kinetics (shown in Table 1), it was found that the PSO model fit better for the heated and agitated samples (fitting parameters and R2 values can be found in Figure S1 and Tables S1 and S2), indicating that the data were in a capacity-limited regime rather than a concentration-limited regime, as well as implying that the mechanism of adsorption is likely chemisorption rather than physisorption.23 In these kinetics models, qt represents the amount of adsorbate that has been adsorbed onto the adsorbent at any given time t while qe is the equilibrium adsorption capacity. Rate constants k1 and k2 are the pseudofirst-order and pseudo-second-order rate constants, respectively. Using the ratio of adsorbent (tea) to solution (water), our model takes a first estimate of the final concentration using the Langmuir asymptote and then refines this estimate by using the whole Langmuir equation to determine the location on the Langmuir curve for a given set of conditions, and thus the adsorption capacity at that concentration at thermodynamic equilibrium. The model then factors in the fraction of the way to equilibrium reached at a set value of time, representing the amount of time for which the tea is brewed or steeped. We used this model to output a variety of contour plots, showing the fraction of metal remediated (in this case, Pb) under a combination of tea preparation conditions. These are shown in Figure 3, and parameters can be found in Table S5. The left plot shows how, at most concentrations, the fraction of metal remediated varies primarily on the basis of how long the tea is prepared. Longer brewing times intuitively correlate with improved remediation. For example, for a standard ratio of 2 g of tea leaves per cup, steeping for 5 min is estimated from our experimental data to remediate 15% of Pb ions from contaminated water samples at Pb concentrations of <10 ppm (a very highly contaminated and toxic sample of drinking water). At even higher concentrations, the adsorption capacity of the tea starts to become a limiting factor with the tea leaves “running out of room” for metal ions on their surface. The right plot shows the fraction of Pb remediated, with initial conditions of 100 ppb Pb and 5 min of brewing time, as a function of the two PSO kinetics parameters. Parameter 1 (qe), on the x-axis, represents the adsorption capacity at equilibrium, analogous to the Langmuir asymptote but at a particular concentration relevant to the kinetics experiment, rather than as the concentration approaches the high limit. Parameter 2 (k2), on the y-axis, represents the kinetic rate constant, where higher values indicate faster kinetics. This plot shows the potential effects of factors like heat, agitation, or chemical/structural processing of the tea relevant to kinetic adsorption properties on the performance during tea preparation expressed as the fraction of Pb remediated. Higher heat during adsorption or tea leaves processed to improve porosity or surface area may drive up the values of the two parameters, leading to better performance at a set time. The experimentally determined values of the kinetic constants used in the left plot, for reference, were 8.4 and 0.0043 for qe and k2, respectively. The experimentation and modeling contained in this report may be relevant to understanding the potential benefits of tea preparation on a local or global scale.
and the last part
The experimentation and modeling contained in this report may be relevant to understanding the potential benefits of tea preparation on a local or global scale. The practical utility here is in recognizing and leveraging existing cultural practices for unintended benefits, especially in contexts where access to advanced water treatment is limited. While it can be very difficult to determine the individual benefits of tea consumption, these data suggest it is possible that across a large population, high levels of tea consumption may have the ability to lower metal intake by a statistically significant percentage that may be reflected in public health outcomes. We do not report on the ability of tea leaves to remediate other toxic substances, such as microorganisms or organic pollutants, but metal toxicity alone accounts for a substantial fraction of the world’s total health burden.24−28 This research raises awareness of a simple, accessible, and culturally embedded practice that may offer an unintended benefit in mitigating heavy metal exposure, particularly relevant in regions with coexisting lead contamination and high levels of tea consumption. A rudimentary estimate, working from the assumption that tea preparation removes 15% of metals while accounting for one-fifth of the average person’s liquid consumption over the day�as is possible in countries with high levels of tea consumption�would reduce lead intake from drinking water by 3% on a population level. This is an amount that could be meaningful enough to be reflected in mortality data for diseases with strong associations with metal toxicity.24,29 While not a complete solution to lead contamination, in the absence of dedicated water treatment infrastructure, this passive remediation offered by tea preparation provides a readily available and culturally integrated means of reducing lead exposure, potentially contributing to improved public health outcomes. The authors encourage future research in related fields to explore this potential and disentangle confounding variables to determine whether tea consumption has a measurable effect on metal toxicity in real-world populations. Finally, this Letter begins to explore the processing−structure−property−performance relationships in tea leaves, bringing the paradigm of materials science to an unlikely adsorbent system. The authors hope that others use this methodology to explore additional interesting phenomena in “consumed materials” like tea leaves, bioinspired membranes, and filtration media that mimic the properties of tea and repurposed materials derived from spent tea leaves.
As always a single study means nothing. You have to wait for the meta study that collects all the other studies and determines the general trend