Tea plant is capable of hyper-accumulating fluoride (F) in leaves, suggesting drinking tea may cause excessive F intake in our body and threaten the health. This study investigated the changes in the structure, composition, and F content in the leaf cell wall of the tea (Camellia sinensis) under different F conditions to demonstrate the role of cell wall in F enrichment in tea plants. The cell wall was shown as the main part for F accumulation (67%–92%), with most of F distributed in the pectin fraction (56%–71%). With increasing F concentration, a significant increase (p < 0.05) was observed in the F content of cell wall and its components, the level of cell wall metal ions (i.e. Cu, Mg, Zn, Al, Ca, Ba, Mn), as well as the content of total cell wall materials, cellulose, and pectin. Meanwhile, the level of Cu, Mg, Zn, pectin, and cellulose was significantly positively correlated with the F content in the leaf cell wall. F addition was shown to increase the fluorescence intensity of LM19 and 2F4 antibody-labeled low-methylesterified homogalacturonans (HGs), while decrease LM20-labeled high-methylesterified HGs, coupled with an increase in the activity and gene expression of pectin methyl esterases (PMEs) in tea leaves. All these results suggest that F addition can increase pectin content and demethylesterification, leading to increased absorption of metal cations and chelation of F in the cell wall through the action of metal ions.

Tea plants (Camellia sinensis (L.) O. Kuntze) can hyperaccumulate fluoride (F). The accumulation of F in tea leaves may induce serious health problems in tea consumers. It has been reported that selenium (Se) could reduce the accumulation of heavy metals in plants. Thus, the aim of this study was to investigate whether exogenous Se could reduce F accumulation in tea plant. The results showed that Se treatment could decrease F content in tea leaves, increase F accumulation in roots, decrease the proportion of water-soluble F in tea leaves and increase the Se content. Low F levels promoted the accumulation of Se in tea plants. Se treatment could modulate F-induced oxidative injury by decreasing malondialdehyde level and increasing the activities of superoxide dismutase, peroxidase and catalase. Moreover, Se inhibited F-induced increase in leaf iron, calcium, aluminum, leaf and root magnesium and lead contents. These results showed that Se application could decrease F content and increase Se content in tea leaves, which may be served as a novel strategy for production of healthy tea.

Though the interaction between humic acid (HA) and heavy metals has been widely reported, the effects of HA on the toxicity of heavy metals to plants are still in debate. In this study, the regulation mechanisms of HA on Pb stress in tea plant (Camellia sinensis L.) was investigated through hydroponic experiments, and the experimental results were explained by using transmission electron microscope (TEM), scanning transmission X-ray microscopes (STXM) and isobaric tags for relative and absolute quantitation (iTRAQ) differential proteomics. Significant alleviation of Pb stress was found with HA coexistence. TEM results showed that HA greatly mitigated the damage of cells caused by Pb stress. Compared with sole Pb treatment, the addition of HA increased the contents of pectin and pectic acid in the cell wall by 10.5% and 30.5%, while arabinose (Ara) and galactose (Gal) decreased by 20.5% and 15.9%, respectively, which were beneficial for increasing Pb adsorption capacity of the cell wall and promoting cell elongation. Moreover, iTRAQ differential proteomics analysis proved that HA strengthened the antioxidant system, promoted the synthesis of cell wall, and stabilized protein and sulfur-containing substance metabolism in molecular level. Notably, the concentration of calcium (Ca) in the cell wall of HA coexistence treatment was 47.4% higher than Pb treatment. STXM results also indicated that the distribution of Ca in the cell wall was restored with the presence of HA. This might promote the formation of the egg-box model, thus alleviating Pb stress in cells. Our results reveal the regulation mechanisms of HA on Pb detoxification in plants and provide useful information for improving the safety of agricultural products.

Traditional tea (Camellia sinensis) and herbal tea are being consumed across the world. However, long term consumption of tea can increase the chances of fluorosis owing to the presence of fluoride (F) in teas. Therefore, it is imperative to assess the health risk associated with tea consumption. The main objectives of this study were to: 1) estimate total F in 47 popular teas, including traditional and herbal teas and F concentrations in 1% (w/v) infusion of 5 min, and 2) assess the exposure risks of F from tea consumption in children and adults. The data showed that total F was the least in herbal teas (33–102 mg/kg) and their infusions (0.06–0.69 mg/L) compared to traditional teas (296–1112 mg/kg) and their infusions (1.47–6.9 mg/L). During tea infusion, 6–96% and 18–99% of the F was released into the water from herbal and traditional teas, respectively. Ten samples of traditional teas, including five green teas had chronic daily intake (CDI) values of F > 0.05 mg/d/kg bw, the stipulated permissible limits of F intake from all sources. Although the F from teas posed no immediate health hazards with hazard quotient <1, some tea samples could potentially contribute >4 mg F/d, thereby adding to the overall F burden. Therefore, together with F from food and water sources, daily F consumptions from teas might increase its health risks to humans. So, caution should be excised when drinking teas containing high F.

Environmentally friendly products are the need of the hour, particularly in this pandemic situation because synthetic products need such toxic chemicals for their formulation and finishing which are carcinogenic for the globe. The current study is the utilization of waste black tea leaf (BT)–based tannin brown natural colorant for silk dyeing using microwave treatment. Dye (tannin) has been isolated in various media before and after microwave treatment up to 6 min and applied at various conditions. It has been found that 30 mL of aqueous extract of 3.0 pH obtained from 6.0 g of powder containing 3.0 g/100 mL of salt as an exhausting agent after microwave treatment for 5 min, when employed at 55 °C for 45 min, has given good color yield onto silk. Iron (3%) and acacia extract (2%) as pre-chemical and bio mordant, iron (2%) and pomegranate extract (2%) as post chemical and bio-mordant, and Al (3 %) and pomegranate extract (3%) as meta chemical and bio-mordant have given new shades with good to excellent fastness ratings. It is inferred that waste black tea leaves (BTs) in an aqueous medium have an excellent potential to serve as a source of natural tannin brown dye for the coloration of surface-modified silk fabrics under the influence of cost, energy, and time-effective microwave treatment. Additionally, the utilization of a low amount of sustainable chemical and bio-mordants has valorized the dyeing of silk by developing soothing and sustainable shades with good fastness properties.

As the global climate changes, elevated atmospheric temperature and nitrogen (N) deposition co-occur in natural ecosystems, which affects rhizosphere soil nutrient by altering allocation of roots and its availability to soil microorganism. Elevated temperature in combination with N deposition is expected to affect soil available N and its relation to microbial properties, but this issue has not been extensively examined. Here, we investigated soil available N and its relation to microbial properties in rhizosphere of Camellia sinensis L. seedlings exposed to elevated temperature using a passive warming device in combination with N-added soil. Elevated temperature did not significantly affect soil pH, total organic carbon (TOC), total nitrogen (TN), the ratio of carbon and nitrogen (C:N ratio), total phosphorus (TP), available N ((N in ammonium (NH₄⁺-N) and N in nitrate (NO₃–-N)) (NH₄⁺-N + NO₃–-N)/TN, α-glucosidase (αG), β-glucosidase (βG), cellobiohydrolase (CBH), N-acetyl-glucosaminidase (NAG), and phenol oxidase (PPO) activities, while significantly stimulated root total length of tea seedlings (3.9%), root dry biomass (10.2%), soil microbial biomass carbon (MBC) (7.4%), microbial biomass nitrogen (MBN) (8.6%), and acid phosphatase (ACP) (8.8%). While N addition significantly (p < 0.05) stimulated root dry biomass of tea seedlings (14.1%), root total length (6.2%), root average diameter (6.7%), soil TN, available N, (NH₄⁺-N + NO₃–-N)/TN, and MBN under elevated temperature. Soil aG, βG, CBH, and ACP activity increase significantly (p < 0.05) under elevated temperature + N relative to elevated temperature alone. Generally, N addition led to increased available nitrogen and microbial properties in rhizosphere soil of tea seedlings exposed to elevated temperature by stimulating root properties, soil nitrogen, microbial biomass N, and enzyme activity. Redundancy analysis and Pearson correlation analysis suggested that N addition lead to higher correlation between soil available N and microbial properties exposed to elevated temperature. Our results indicated nitrogen addition exerts a stronger effect than elevated temperature on soil fertility and microbiological cycle in the rhizosphere of Camellia sinensis L. seedlings. The conclusion helps us understand the response mechanism of soil rhizosphere microenvironment to N deposition under global warming scenarios.

Fluoride is highly present in the environment, especially in water and its derivatives. Excessive fluoride contribution to diet poses a health risk. Tea leaves accumulate fluoride and the consumption of tea (Camellia sinensis) could pose a risk to human by the excessive fluoride intake. Ninety tea samples were analyzed by potentiometry using a selective fluoride ion electrode. Mixed tea samples (2.82 ± 1.11 mg/L) and black tea samples (2.28 ± 0.79 mg/L) recorded the highest fluoride levels. The contribution of drinking water is important for increasing fluoride levels in teas. The daily consumption of two cups (250 mL per cup) of mixed and black teas prepared with La Laguna tap water does pose a health risk for children (4–8 years old) because of the high contribution percentages (74.4% and 63.6%, respectively) of the Tolerable Upper Intake Level set in 2.5 mg/day by the EFSA (European Food Safety Authority). A minor consumption in children (4–8 years old) and adults during pregnancy is advisable.

Environmental benefits of biochar require a simple and effective method for preparation of functional N-doped biochar. In this study, urea/ZnCl₂ was developed to prepare N-doped biochar via in situ hydrothermal carbonization (HTC) of Camellia sinensis waste at 120–280 °C for 2 h under 1.0–9.8 MPa. Physicochemical and structural properties of the N-doped biochar were investigated by Raman spectra, elemental analysis, BET surface area, SEM, TEM, XRD, and XPS. The results showed that the N content in biochar could reach up to 7.79% at 280 °C. Surface chemistry suggested that pyridinic N, pyrollic N, and graphitic N were the major N species on the biochar. Moreover, the N-doped biochar was successfully employed to remove metal ions Cu²⁺, Pb²⁺, Zn²⁺, and Cr⁶⁺. Adsorption data fit closely to the pseudo-second-order kinetic equation and the Langmuir adsorption isotherm model for all metal ions.

A hydroponic experiment was performed to investigate the Cd absorption and subcellular distribution in tea plant, Camellia sinensis. Increased Cd accumulation potential was observed in the tea plant in a Cd-enriched environment, but most of the Cd was absorbed by the roots of C. sinensis. The Cd in all the root fractions was mostly distributed in the soluble fraction, followed by the cell wall fraction. By contrast, the Cd was least distributed in the organelle fraction. The adsorption of Cd onto the C. sinensis roots was described well by the Langmuir isotherm model than the Freundlich isotherm. Most of the Cd (38.6 to 59.4%) was integrated with pectates and proteins in the roots and leaves. Fourier transform infrared spectroscopy (FTIR) analysis showed that small molecular organic substances, such as amino acids, organic acids, and carbohydrates with N–H, C=O, C–N, and O–H functional groups in the roots, bonded with Cd(II). The Cd accumulation in the C. sinensis leaves occurred in the cell wall and organelle fractions. C. sinensis has great capability to transport Cd, thereby indicating pollution risk. The metal homeostasis of Fe, Mn, Ca, and Mg in C. sinensis was affected when the Cd concentration was 1.0–15.0 mg/L.