Insights into the effects of tea pruning litter biochar on major micronutrients (Cu, Mn, and Zn) pathway from soil to tea plant: An environmental armour

A critical review of biochar as an environmental functional material in soil ecosystems for migration and transformation mechanisms and ecological risk assessment

At present, biochar has a large application potential in soil amelioration, pollution remediation, carbon sequestration and emission reduction, and research on the effect of biochar on soil ecology and environment has made positive progress. However, under natural and anthropogenic perturbations, biochar may undergo a series of environmental behaviors such as migratory transformation, mineralization and decomposition, and synergistic transport, thus posing certain potential risks. This paper outlines the multi-interfacial migration pathway of biochar in "air-soil-plant-animal-water", and analyzes the migration process and mechanism at different interfaces during the preparation, transportation and application of biochar. The two stages of the biochar mineralization process (mineralization of easily degradable aliphatic carbon components in the early stage and mineralization of relatively stable aromatic carbon components in the later stage) were described, the self-influencing factors and external environmental factors of biochar mineralization were analyzed, and the mineral stabilization mechanism and positive/negative excitation effects of biochar into the soil were elucidated. The proximity between field natural and artificially simulated aging of biochar were analyzed, and the change of its properties showed a trend of biological aging > chemical aging > physical aging > natural aging, and in order to improve the simulation and prediction, the artificially simulated aging party needs to be changed from a qualitative method to a quantitative method. The technical advantages, application scope and potential drawbacks of different biochar modification methods were compared, and biological modification can create new materials with enhanced environmental application. The stability performance of modified biochar was compared, indicating that raw materials, pyrolysis temperature and modification method were the key factors affecting the stability of biochar. The potential risks to the soil environment from different pollutants carried by biochar were summarized, the levels of pollutants released from biochar in the soil environment were highlighted, and a comprehensive selection of ecological risk assessment methods was suggested in terms of evaluation requirements, data acquisition and operation difficulty. Dynamic tracing of migration decomposition behavior, long-term assessment of pollution remediation effects, and directional design of modified composite biochar materials were proposed as scientific issues worthy of focused attention. The results can provide a certain reference basis for the theoretical research and technological development of biochar.

The Level of Selected Metals in Made Tea and Tea Infusion from the Roadside Tea Plants and Health Risk Assessment

The effects of human activities are becoming clearer every year, with multiple reports of struggling and eroded ecosystems resulting in new threats of plant and animal extinctions throughout the world. It has been speculated that roadside tea-growing soils impact on metal dynamics from soil to tea plants and subsequently to tea infusion which may be threatened by increasingly unpredictable and dangerous surroundings. Furthermore, heavy metals released from vehicles on the national highway (NH) could be a source of metal contamination in roadside tea soils and tea plants. This study was articulated to realize the effect of NH on a buildup of selected metals (Cu, Cd, Fe, Mn, Ni, and Zn) in made tea along with repeated tea infusion. In general, metal concentration was found significantly higher in made tea prepared from the young shoots collected from the vicinity of NH. The results also showed that distance from the NH and infusion process significantly influenced to content of the analysed metal in tea infusions. The mean average daily intake (ADI) and hazard quotient (HQ) values of analysed tea samples were found in the orderMn˃Fe˃Zn˃Cu˃Ni˃Cd and Mn˃Cu˃Zn˃Fe˃Ni˃Cd, respectively. The HQ values of all analysed metals were found << 1, indicating that ingestion of tea infusion with analysed heavy metals should not cause a danger to human health. However, this study further demonstrates the consumption of tea infusion prepared from made tea around the vicinity of NH may contribute to a significantly higher quantity of metal intake in the human body. From the hierarchical cluster analysis, it has been observed that there are three homogenous groups of analysed heavy metals.

Environmental applications of lignin-based hydrogels for Cu remediation in water and soil: adsorption mechanisms and passivation effects

Heavy metal pollution, particularly the excessive release of copper (Cu), is an urgent environmental concern. In this study, sodium lignosulfonate/carboxymethyl sa-son seed gum (SL-Cg-g-PAA) designed for remediation of Cu-contaminated water and soil was successfully synthesized through a free radical polymerization method using lignin as a raw material. This hydrogel exhibits remarkable Cu adsorption capability when applied to water, with a maximum adsorption capacity reaching 172.41 mg/g. Important adsorption mechanisms include surface complexation and electrostatic attraction between Cu(Ⅱ) and oxygen-containing functional groups (-OH, -COOH), as well as cation exchange involving -COONa and -SO3Na. Furthermore, SL/Cg-g-PAA effectively mitigated the bioavailability of heavy metals within soil matrices, as evidenced by a notable 14.1% reduction in DTPA extracted state Cu (DTPA-Cu) content in the S4 treatment (0.7% SL/Cg-g-PAA) compared to the control group. Concurrently, the Cu content in both the leaves and roots of pakchoi exhibited substantial decreases of 55.19% and 36.49%, respectively. These effects can be attributed to the precipitation and complexation reactions facilitated by the hydrogel. In summary, this composite hydrogel is highly promising for effective remediation of heavy metal pollution in water and soil, with a particular capability for the immobilization of Cu(Ⅱ) and reduction of its adverse effects on ecosystems.

Pollution indices of selected metals in tea (Camellia sinensis L.) growing soils of the Upper Assam region divulge a non-trifling menace of National Highway

The study investigated the influence of a National Highway (NH) traversing tea estates (TEs) on heavy metal (HM) contamination in the top soils of Upper Assam, India. The dispersion and accumulation of six HMs, viz. cadmium (Cd), copper (Cu), iron (Fe), manganese (Mn), nickel (Ni), and zinc (Zn), within tea-growing soils were assessed using diverse indices: contamination factor (CF), degree of contamination (DC), enrichment factor (EF), geo-accumulation index (Igeo), modified degree of contamination (MDC), Nemerow pollution index (PINemerow), pollution load index (PLI), potential ecological risk factor (Eri), and potential ecological risk index (RI). The order of HM prevalence was Fe > Mn > Zn > Ni > Cu > Cd. Elevated Cd levels near the NH prompted immediate attention, while Cd and Zn showed moderate pollution in CF, EF, and RI. The remaining metals posed minimal individual risk (Eri< 40), resulting in an overall contamination range of "nil to shallow," signifying slight contamination from the studied metals. From MDC values for investigated metals, it was found to be "zero to very low degree of contamination" at all locations except the vicinity of NH. Soil pollution, as determined by PLI, indicated unpolluted soils in both districts, yet PINemerow values indicated slight pollution. The statistical analysis revealed that there is a significant decrease in most of the indices of HM as the distance from NH increases. The application of multivariate statistical techniques namely Principal Component Analysis and Cluster Analysis showed the presence of three distinct homogenous groups of distances based on different indices. This investigation underscores NH-associated anthropogenic effects on TE soil quality due to HM deposition, warranting proactive mitigation measures.

Field application of hydroxyapatite and humic acid for remediation of metal-contaminated alkaline soil

The quality of soil is essential for ensuring the safety and quality of agricultural products. However, soils contaminated with toxic metals pose a significant threat to agricultural production and human health. Therefore, remediation of contaminated soils is an urgent task, and humic acid (HA) with hydroxyapatite (HAP) materials was applied for this study in contaminated alkaline soils to remediate Cd, Pb, Cu, and Zn. Physiochemical properties, improved BCR sequential extraction, microbial community composition in soils with superoxide dismutase (SOD), peroxidase (POD), and chlorophyll content in plants were determined. Among the studied treatments, application of HAP-HA (2:1) (T7) had the most significant impact on reducing the active forms of toxic metals from soil such as Cd, Pb, Cu, and Zn decreased by 18.59%, 9.12%, 11.83%, and 3.33%, respectively, but HAP and HA had a minor impact on metal accumulation in Juncao. HAP (T2) had a beneficial impact on reducing the TCleaf/root of Cd, Cu, and Zn, whereas HAP-HA (T5) showed the best performance for reducing Cd and Cu in EFleaf/soil. HAP-HA (T5 and T7) showed higher biomass (57.3%) and chlorophyll (17.9%), whereas HAP (T4) showed better performance in POD (25.8%) than T0 in Juncao. The bacterial diversity in soil was increased after applying amendments of various treatments and enhancing metal remediation. The combined application of HAP and HA effectively reduced active toxic metals in alkaline soil. HAP-HA mixtures notably improved soil health, plant growth, and microbial diversity, advocating for their use in remediating contaminated soils.

The Distribution Characteristics and Potential Risk Assessment of Lead in the Soil of Tieguanyin Tea Plantations in Anxi County, China

Assessing the distribution and risks associated with the soil lead content in the Tieguanyin tea plantations of Anxi County is critical, given the county's significance as the primary Tieguanyin tea production area in Fujian Province. This study examined the distribution characteristics of soil lead in Anxi County's tea plantations according to the Kriging spatial interpolation of the parameters of the semivariance function of the exponential model. Moreover, the sources of lead content were analyzed, considering geological backgrounds and anthropogenic influences. Ecological risks and the issuance of early warnings were also assessed. The soil lead content in the rocks of the Tieguanyin tea plantations in Anxi County followed the order: andesite > dacite > rhyolite > granite. The soil lead content gradually decreased from the center toward the east and west, forming four distinct north-south parallel zones. High-lead-content areas were identified at the border of Jiandou, Bailai, and Hushang; in the central part of Lutian; and in the southern part of Huqiu. The high levels of soil lead in the tea plantations possibly originated from industrial and mining activities, automobile exhaust, and agricultural activities. The distribution of single-factor pollution indices and potential risk evaluation based on the Soil Environmental Quality Standard, Environmental Technical Conditions for Tea Production Area, and Environmental Technical Conditions for Organic Tea Production Area indicated that the soil in Tieguanyin tea plantations in Anxi County was clean and safe for tea cultivation.

Transcriptomic Analysis of the Effect of Pruning on Growth, Quality, and Yield of Wuyi Rock Tea

Pruning is an important agronomic measure in tea plantation management. In this study, we analyzed the effect of pruning on gene expression in tea leaves from a transcriptomics perspective and verified the results of a transcriptomic analysis in terms of changes in physiological indicators of tea leaves. The results showed that pruning enhanced the gene expression of nine metabolic pathways in tea leaves, including fatty acid synthesis and carbohydrate metabolism, nitrogen metabolism, protein processing in the endoplasmic reticulum, and plant hormone signal transduction, thereby promoting the growth of tea plants and increasing tea yield. However, pruning reduced the gene expression of nine metabolic pathways, including secondary metabolites biosynthesis, flavonoid biosynthesis, phenylpropanoid biosynthesis, and sesquiterpenoid and triterpenoid biosynthesis, and lowered the content of caffeine, flavonoids, and free amino acids in tea plant leaves. In conclusion, pruning could promote the growth of tea plants and increase the yield of tea, but it was not conducive to the accumulation of some quality indicators in tea leaves, especially caffeine, flavonoids, and free amino acids, which, in turn, reduced the quality of tea. This study provides an important theoretical reference for the management of agronomic measures in tea plantations.

Effects of pruning on tea tree growth, tea quality, and rhizosphere soil microbial community

Pruning is an important agronomic measure in tea plantation management. This study analyzed the effects of pruning on tea tree growth, tea quality, rhizosphere soil physicochemical indexes, microbial communities, and metabolic pathways. The results showed that pruning was beneficial for promoting tea tree growth and increasing tea yield, but not for the synthesis and accumulation of quality-related compounds in tea leaves. After pruning, organic matter, available phosphorus content and catalase, acid phosphatase, and sucrase activities in rhizosphere soil were significantly higher than those in unpruned tea trees, while total phosphorus, total potassium, and available nitrogen content were significantly lower than those in unpruned tea trees. The results of microbial community analysis of tea rhizosphere soil showed that the key changed characteristic microorganisms after pruning were Haliangium, Acidicaldus, Reyranella, Acidobacterium, Aquicella, and Granulicella, and the key changed characteristic microbial metabolic pathways were ko00072, ko00473, ko00750, ko01055, ko00521, and ko02040. Furthermore, the results found that pruning promoted Haliangium, Acidicaldus, and Reyranella abundances, ko00072, ko00473, and ko00750, respectively, microbial metabolic pathways in tea trees rhizosphere soil, and reduced Acidobacterium, Granulicella, and Aquicella abundance, ko01055, ko00521, and ko02040, respectively, microbial metabolic pathways, thereby increasing the activities of soil catalase, acid phosphatase, and sucrase, improving soil organic matter decomposition efficiency and available phosphorus content, and promoting tea yield, but not synthesis and accumulation of quality-related compounds in tea leaves. This study provides an important theoretical reference for the management of agronomic measures in tea plantations. IMPORTANCE Pruning is an important agronomic measure in tea cultivation and management. We found that pruning was beneficial to increase tea yield, but it would reduce tea quality, especially the content of polyphenols, theanine, flavonoids, and free amino acids in tea leaves was reduced. The reason for this phenomenon was that pruning promotes the enrichment of special functional microorganisms and the enhancement of special metabolic pathways in the soil, leading to changes in the nutrient cycle in the soil.

Bio-assembled MgO-coated tea waste biochar efficiently decontaminates phosphate from water and kitchen waste fermentation liquid

Crystal morphology of metal oxides in engineered metal-biochar composites governs the removal of phosphorus (P) from aqueous solutions. Up to our best knowledge, preparation of bio-assembled MgO-coated biochar and its application for the removal of P from solutions and kitchen waste fermentation liquids have not yet been studied. Therefore, in this study, a needle-like MgO particle coated tea waste biochar composite (MTC) was prepared through a novel biological assembly and template elimination process. The produced MTC was used as an adsorbent for removing P from a synthetic solution and real kitchen waste fermentation liquid. The maximum P sorption capacities of the MTC, deduced from the Langmuir model, were 58.80 mg g−1 from the solution at pH 7 and 192.8 mg g−1 from the fermentation liquid at pH 9. The increase of ionic strength (0–0.1 mol L−1 NaNO3) reduced P removal efficiency from 98.53% to 93.01% in the synthetic solution but had no significant impact on P removal from the fermentation liquid. Precipitation of MgHPO4 and Mg(H2PO4)2 (76.5%), ligand exchange (18.0%), and electrostatic attraction (5.5%) were the potential mechanisms for P sorption from the synthetic solution, while struvite formation (57.6%) and ligand exchange (42.2%) governed the sorption of P from the kitchen waste fermentation liquid. Compared to previously reported MgO-biochar composites, MTC had a lower P sorption capacity in phosphate solution but a higher P sorption capacity in fermentation liquid. Therefore, the studied MTC could be used as an effective candidate for the removal of P from aqueous environments, and especially from the fermentation liquids. In the future, it will be necessary to systematically compare the performance of metal-biochar composites with different metal oxide crystal morphology for P removal from different types of wastewater.

Graphical Abstract

Monitoring and evaluating the dietary risk of trace elements content in bottled and hand-shaken tea in Taiwan

Tea is the most frequently consumed beverage worldwide and is obtained from the leaves Camellia sinensis. The traditional way of tea consumption through brewing is gradually being replaced by the consumption of bottled and hand-shaken tea. Despite the different ways of tea consumption, trace elements accumulation and contamination of tea leaves have caused concerns. However, limited studies have reported trace element concentrations in different types of tea in bottled or hand-shaken tea and their health risks. This study aimed to determine the level of trace elements (V, Cr, Co, As, Cd, Pb, Mn, and Zn) in green tea, black tea, and Oolong tea in two varieties of products (bottled and hand-shaken tea). The health risks associated with tea consumption in various age subgroups among Taiwan's general population were also estimated. A Monte Carlo simulation was applied to estimate the distribution of daily trace elements intake through bottled and hand-shaken tea consumption. As to the non-carcinogenic risks, the Monte Carlo simulation showed that hand-shaken green tea had a higher percentage of hazard index (HI) >1 (1.08%~6.05%) among all age groups. As to carcinogenic risks, the Monte Carlo simulation showed that the risks of As exposure from bottled Oolong tea and hand-shaken black, green, and Oolong teas in the 90th percentile in >18 to ≤65 and >65-year-old groups were higher than 10^-6. The current study findings provided some information about trace elements of both bottled and hand-shaken tea and human health risks in the general population of Taiwan.

Rapid and Effective Lead Elimination Using Cow Manure Derived Biochar: Balance between Inherent Phosphorus Release and Pollutants Immobilization

Cow manure derived biochar (CMBC) can serve as a promising functional material, and CMBC can be regarded as an ecofriendly approach compared to conventional ones. CM bioadsorbent can be employed for heavy metal immobilization (such as for lead) as well as an amendment to increase soil fertility (e.g., phosphorus). Few studies have examined the surface interactions between pollutants and bioadsorbents when inherent nutrient release is present. In this work, CMBC was prepared and applied for Pb(II) removal, and the vital roles of released phosphorus from CMBC were comprehensively disclosed. Furthermore, CMBC could immobilize part of the Pb(II) in soil and promote plant growth. CM400 was an effective adsorbent whose calculated Q_e reached 691.34 mg·g^-1, and it rapidly adsorbed 98.36 mg·g^-1 of Pb(II) within 1 min. The adsorption mechanisms of Pb(II) by CMBC include ion exchange, physical adsorption, electrostatic attraction, chemical precipitation, surface complexation, and cation-π bond interaction. Based on the residual phosphorus content and adsorption effect, complexation rather than the chemical precipitation had a greater contribution toward adsorption. Besides, as the concentration of Pb(II) increased, the main adsorption mechanisms likely transformed from chemical precipitation to ion exchange and complexation. CMBC not only had a good effect on Pb(II) removal in the solution, but also immobilized the Pb(II) in soil to restrain plant uptake as well as promote plant growth. The main novelty of this work is providing more insights to the cow manure bio adsorbent on Pb immobilization and phosphorus release. This study is expected to serve as a basis and reference for analyzing the release effects of inherent nutrients and the interfacial behaviors with heavy metals when using CMBC and other nutrient-rich carbon-based fertilizers for pollution control.