Availability Of Metals Research Articles

Eisenia fetida impact on cadmium availability and distribution in specific components of the earthworm drilosphere.

Although the potential of vermiremediation for restoring metal-contaminated soils is promising, the effects of earthworms on the availability of soil metals are still debatable. Most previous studies considered the soil as a "whole black box." Mobilization or immobilization of metals are affected by earthworm activities within drilosphere hotspots under different soil conditions, which has not been specifically studied. Therefore, an improved 2D terrarium was designed to study the impact of earthworm activities on cadmium (Cd) fate in the drilosphere hotspots (burrow wall soils, burrow casts, and surface casts) of different artificially spiked Cd treatments (CK: 0 mg kg-1; LM: 1 mg kg-1; and HM: 5 mg kg-1) with different organic amendments (2% and 10%). The results revealed that Cd increased earthworm activities with the highest cast production in HM and the highest burrow length in LM. Earthworms exhibited a stronger tendency to reduce total Cd concentration by 4.48-13.58% in casts of LM soils, while 3.37-5.22% in burrow walls under HM treatments. Overall, earthworms could increase the availability of Cd in casts under all conditions (55.46-121.01%). The organic amendments decreased the total Cd concentration and increased the availability of Cd in the disturbed soil. A higher amount of organic amendment significantly decreased total Cd concentration of the drilosphere by 1.16-5.83% in LM and HM treatments, while increasing DTPA-Cd concentrations in all components by 23.13-55.20 %, 14.63-35.11%, and 3.30-11.41% in CK, LM, and HM treatments, respectively, except for earthworm non-disturbed soil and no-earthworm soil in HM treatments. Redundancy analysis (RDA) revealed that the moisture, pH, and total carbon contents in soil are the main factors affecting Cd bioavailability. In this study, we decoded the "black box" of soil by making it relatively simple to better understand the effects and mechanisms of earthworm activities on soil metal availability and consequently provided comprehensive insights for using earthworms in soil vermiremediation.

Soil properties determine the impact of nZVI on Lactuca sativa L and its rhizosphere

Nanoscale zero-valent iron (nZVI) is a promising material tool for the remediation of metal(loid)-contaminated soils since it reduces metal(loid) availability and plant uptake, thereby enhancing the development of the plants. However, the effects of nZVI as nanoparticles on soil properties, plants, and the microbial rhizosphere in unpolluted soils are poorly understood. Here we tested the impact of nZVI at different doses (0.5 and 5% of commercial suspension) on soil properties, lettuce plants, and their microbial rhizosphere in two non-contaminated soils with distinct physico-chemical properties (alkaline versus acidic soil). To this end, a pot experiment was performed with lettuce plants in a growth chamber for a month. Both soils showed an increase in of pH and available Fe after nZVI application. However, these effects were more marked in the acidic soil. In this regard, the plants in this soil showed increased biomass and Fe content. TEM analysis revealed that although the roots and leaves of plants grown in the alkaline soil showed better cell integrity than those in acidic soil—an observation that was consistent with the visual appearance of the plants—the former were more affected by the nZVI treatment. Regarding the microbial rhizosphere, in general, nZVI enhanced enzyme activity regardless of the soil type. Microbial functional diversity showed a significant decline in response to nZVI in alkaline soil. In contrast, the 0.5% nZVI treatment had a positive effect on this parameter in acidic soil. Bacterial genetic diversity was less affected by the presence of nZVI than fungal diversity, which was higher in nZVI-treated acidic soils. In addition, alterations of bacterial and fungal communities were associated with available Fe in acidic soil. In conclusion, soil properties play a key role in determining the effects of nZVI on lettuce plants and their rhizosphere.

Towards a clean environment: To what extent can trees serve as phytoremediators for chemically polluted soils?

The study investigated the potential of five common tree species in West Africa to bioaccumulate heavy metals in their various plant components over the course of different growth phases and at varying contamination levels (control, double the permissible level and triple the permissible limit). Heavy metals in plant tissues were extracted and analyzed using standard wet chemistry procedures. The results showed metal concentrations in tree tissues to positively and significantly correlate with contamination level, growth stage, and plant component. Metal mobility and availability in the tree tissues were in descending order of Mn >Zn>Cu=Pb>Cd. We found heavy metals to be principally accumulated in the stem tissues following a metal exclusion theory, independent of tree species. Tree roots demonstrated a significant accumulation of heavy metals second only to the stem. The results revealed that heavy metal mobility and bioavailability in plant tissue was tree-specific, growth stage-dependent, and metal-specific; showing that trees have a preferential affinity to accumulate a specific metal or pollutant. The study established Shorea roxborghi to be a mono-accumulator of manganese while Tectona grandis and Terminalia ivorensis were multi-accumulators of metals such as Mn, Cu, Zn and Pb. The interactive effects of contamination levels and tree species showed Tectona grandis and Terminalia ivorensis grown in chemically polluted soils at triple the permissible level to have the highest heavy metal uptake with the highest phytoextraction potential. We conclude that all the tree species considered in this study could potentially be effective phytoremediators of chemically polluted soils through their ability in phytoextraction of metals such as lead, zinc, copper, and manganese as well as through phytostabilization of cadmium in contaminated soils.

The International Seabed Authority and the United Nations 2030 Agenda for sustainable development

Deep sea mining in the Area (seabed and subsoil beyond national jurisdiction) is regarded by some stakeholders as a threat to the achievement of Goal 14 of the United Nations, 2030 Agenda for sustainable development. However, the availability of metals and mineral resources will be crucial to comply with most Sustainable Development Goals. Despite the need to foster a circular economy and reduce waste to a minimum, it seems unlikely that the decarbonization of the economy could be achieved without primary mining. Future minerals supply, facing significant obstacles, can source from increased primary terrestrial and deep-seabed supply, or deep-seabed displacing terrestrial. This work develops principles and an integrated, holistic framework for deep-seabed mining to play a role in future demand through sustainable global sourcing and collective action on the global commons through the International Seabed Authority. Optimum global welfare requires balancing all the competing uses of the marine environment and their contributions to private and public benefits enjoyed by all Humanity, in both current and future generations, and weighted by equity concerns for a more progressive distribution as required by the United Nations Convention on the Law of the Sea.

A genetic selection for Mycobacterium smegmatis mutants tolerant to killing by sodium citrate defines a combined role for cation homeostasis and osmotic stress in cell death.

Mycobacteria can colonize environments where the availability of metal ions is limited. Biological or inorganic chelators play an important role in limiting metal availability, and we developed a model to examine Mycobacterium smegmatis survival in the presence of the chelator sodium citrate. We observed that instead of restricting M. smegmatis growth, concentrated sodium citrate killed M. smegmatis. RNAseq analysis during sodium citrate treatment revealed transcriptional signatures of metal starvation and hyperosmotic stress. Notably, metal starvation and hyperosmotic stress, individually, do not kill M. smegmatis under these conditions. A forward genetic transposon selection was conducted to examine why sodium citrate was lethal, and several sodium-citrate-tolerant mutants were isolated. Based on the identity of three tolerant mutants, mgtE, treZ, and fadD6, we propose a dual stress model of killing by sodium citrate, where sodium citrate chelate metals from the cell envelope and then osmotic stress in combination with a weakened cell envelope causes cell lysis. This sodium citrate tolerance screen identified mutants in several other genes with no known function, with most conserved in the pathogen M. tuberculosis. Therefore, this model will serve as a basis to define their functions, potentially in maintaining cell wall integrity, cation homeostasis, or osmotolerance. IMPORTANCE Bacteria require mechanisms to adapt to environments with differing metal availability. When Mycobacterium smegmatis is treated with high concentrations of the metal chelator sodium citrate, the bacteria are killed. To define the mechanisms underlying killing by sodium citrate, we conducted a genetic selection and observed tolerance to killing in mutants of the mgtE magnesium transporter. Further characterization studies support a model where killing by sodium citrate is driven by a weakened cell wall and osmotic stress, that in combination cause cell lysis.

Inorganic Thin-Film Solar Cells: Challenges at the Terawatt-Scale

Thin-film solar cells have been referred to as second-generation solar photovoltaics (PV) or next-generation solutions for the renewable energy industry. The layer of absorber materials used to produce thin-film cells can vary in thickness, from nanometers to a few micrometers. This is much thinner than conventional solar cells. This review focuses on inorganic thin films and, therefore, hybrid inorganic–organic perovskite, organic solar cells, etc., are excluded from the discussion. Two main families of thin-film solar cells, i.e., silicon-based thin films (amorphous (a-Si) and micromorph silicon (a-Si/c-Si), and non-silicon-based thin films (cadmium telluride (CdTe) and copper–indium–gallium diselenide (CIGS)), are being deployed on a commercial scale. These commercial technologies, until a few years ago, had lower efficiency values compared to first-generation solar PV. In this regard, the concept of driving enhanced performance is to employ low/high-work-function metal compounds to form asymmetric electron and hole heterocontacts. Moreover, there are many emerging thin-film solar cells conceived to overcome the issue of using non-abundant metals such as indium (In), gallium (Ga), and tellurium (Te), which are components of the two commercial thin-film technologies, and therefore to reduce the cost-effectiveness of mass production. Among these emerging technologies are kesterite CZTSSE, intensively investigated as an alternative to CIGS, and Sb2(S,Se)3. In this review, after a general overview of the current scenario of PV, the three main challenges of inorganic thin-film solar cells, i.e., the availability of (safe) metals, power conversion efficiency (PCE), and long-term stability, are discussed.

Effect of Different Phosphate Fertilizers on the Availability of some Heavy Metals in El-Gabal El Asfer Soil under Maize and Wheat Cropping System

Effect of Different Phosphate Fertilizers on the Availability of some Heavy Metals in El-Gabal El Asfer Soil under Maize and Wheat Cropping System

Occurrence and Health Risk Assessment of Heavy Metals in Lychee (Litchi chinensis Sonn., Sapindaceae) Fruit Samples

This study aimed to assess the occurrence of eight heavy metals in lychee (Litchi chinensis Sonn.) fruit samples collected from orchards of the Dehradun and Haridwar districts in Uttarakhand, India. Lychee fruit samples were collected from ten (10) sampling locations from May to June 2023 and analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). Results showed that lychee fruit samples showed varying levels of selected heavy metals, i.e., Cd (0.009–0.095 mg/kg), Cr (0.079–0.960 mg/kg), Cu (0.095–0.258 mg/kg), Fe (0.254–0.531 mg/kg), Pb (0.000–0.011 mg/kg), Mn (0.862–1.903 mg/kg), Ni (0.166–0.310 mg/kg), and Zn (0.076–0.149 mg/kg). It was observed that lychee fruit sampling sites near urban and industrial areas had higher concentrations of heavy metals as compared to those in rural and agricultural areas. In addition, principal component analysis (PCA) and clustered heatmap dendrogram results showed that several sites had significant similarities in terms of heavy metal availability. Overall, the levels of all heavy metals were below the safe limits as suggested by health risk studies. The selected indices such as daily intake of metals (DIM), health risk index (HRI), and target hazard quotient (THQ) did not exceed the standard limit which indicated consumption of lychee fruit was safe at all sampling sites. The results of this study emphasize the need to regularly monitor lychee heavy metal levels and implement sustainable agricultural and environmental practices to reduce contamination sources.

Evaluation of the Phytoremediation Potential of the Sinapis alba Plant Using Extractable Metal Concentrations.

Testing the feasibility of soil phytoremediation requires the development of models applicable on a large scale. Phytoremediation mechanisms include advanced rhizosphere biodegradation, phytoaccumulation, phytodegradation, and phytostabilization. The aim of this study was to evaluate the phytoremediation potential of the Sinapis alba. Identification of the factors influencing the extraction process of metals from contaminated soils in a laboratory system suitable for evaluating the phytoavailability of these metals in three solutions (M1-CaCl2, M2-DTPA, and M3-EDTA) included the following: distribution of metals in solution (Kd), soil properties and mobile fractions (SOC, CEC, pH), response surface methodology (RSM), and principal component analysis (PCA). The evaluation of the phytoremediation potential of the Sinapis alba plant was assessed using bioaccumulation coefficients (BACs). The accumulation of heavy metals in plants corresponds to the concentrations and soluble fractions of metals in the soil. Understanding the extractable metal fractions and the availability of metals in the soil is important for soil management. Extractable soluble fractions may be more advantageous in total metal content as a predictor of bioconcentrations of metals in plants. In this study, the amount of metal available in the most suitable extractors was used to predict the absorption of metals in the Sinapis alba plant. Multiple regression prediction models have been developed for estimating the amounts of As and Cd in plant organs. The performance of the predictive models generated based on the experimental data was evaluated by the adjusted coefficient of determination (aR2), model efficiency (RMSE), Durbin-Watson (DW) test, and Shapiro-Wilk (SW) test. The accumulation of the analyzed metals followed the pattern Root > Pods > Leaves > Seeds, stems > Flowers for As and Leaves > Root > Stem > Pods > Seeds > Flowers for Cd in soil contaminated with different metal concentrations. The obtained results showed a phytoremediation potential of the Sinapis alba plant.

Temporal modelling of the biofilm lifecycle (TMBL) establishes kinetic analysis of plate-based bacterial biofilm dynamics

Bacterial biofilms are critical to pathogenesis and infection. They are associated with rising rates of antimicrobial resistance. Biofilms are correlated with worse clinical outcomes, making them important to infectious diseases research. There is a gap in knowledge surrounding biofilm kinetics and dynamics which makes biofilm research difficult to translate from bench to bedside. To address this gap, this work employs a well-characterized crystal violet biomass accrual and planktonic cell density assay across a clinically relevant time course and expands statistical analysis to include kinetic information in a protocol termed the TMBL (Temporal Mapping of the Biofilm Lifecycle) assay. TMBL's statistical framework quantitatively compares biofilm communities across time, species, and media conditions in a 96-well format. Measurements from TMBL can reliably be condensed into response features that inform the time-dependent behavior of adherent biomass and planktonic cell populations. Staphylococcus aureus and Pseudomonas aeruginosa biofilms were grown in conditions of metal starvation in nutrient-variable media to demonstrate the rigor and translational potential of this strategy. Significant differences in single-species biofilm formation are seen in metal-deplete conditions as compared to their controls which is consistent with the consensus literature on nutritional immunity that metal availability drives transcriptomic and metabolomic changes in numerous pathogens. Taken together, these results suggest that kinetic analysis of biofilm by TMBL represents a statistically and biologically rigorous approach to studying the biofilm lifecycle as a time-dependent process. In addition to current methods to study the impact of microbe and environmental factors on the biofilm lifecycle, this kinetic assay can inform biological discovery in biofilm formation and maintenance.

Quantitative Distribution and Contamination Risk Assessment of Cu and Zn in Municipal Sewage Sludge

One of the methods of managing sewage sludge (SS) is its soil application. This possibility is promoted by the chemical composition rich in organic matter and nutrients. However, heavy metal contents in SS must meet respective permissible limits. Among the heavy metals in SS, Cu and Zn are found in the largest amount; thus, this study focuses on these elements. The main aim of the study is to investigate the quantitative distribution of metals in sequentially separated fractions of sewage sludge. Additionally, the potential risk of environmental contamination with heavy metals was assessed in the case of SS application for agricultural purposes. The relevant analyses were conducted on four different examples of municipal SS. Based on the total amounts as well as those determined in the SS fractions, the following indices were calculated: Igeo (geoaccumulation index), ICF, (individual contamination factor), and RAC (risk assessment code). The use of data from the sequential analysis as well as the calculated indices made it possible to assess the usefulness of SS in practice in terms of potential introduction of Cu and Zn into the environment with the sludge dose. It was found that total Cu (Cutot) and Zn (Zntot) did not exceed the permissible limits binding within respective Polish and international regulations. Regardless of the years of study and the analyzed SS, Cutot ranged from 260.9 to 393.5 mg·kg−1, and Zntot from 475.5 to 1153.1 mg·kg−1. The amounts of Cu and Zn were predominantly reducible (bound to iron and manganese hydroxides, Fr. II) and oxidizable complexes (bound to organic matter and sulfides, Fr. III). The average amounts of Cu in Fr. II ranged from 149.4 to 172.4 mg·kg−1, while those of Zn in Fr. II ranged from 370.9 to 754.6 mg·kg−1. Cu amounts in Fr. III were from 160.9 to 183 mg·kg−1 and Zn amounts in Fr. III were from 104.9 to 171.9 mg·kg−1. Total content of metals as well as TOC values strongly determined the quantitative level of both elements in the SS fractions. Generally, with the increase in the total amount of metals, their levels in the sludge fractions increased. In turn, the increase in TOC resulted in a decrease in the amounts of Cu and Zn in the sludge fractions. Calculated Igeo and ICF ratios showed high and very high SS contamination with Cu and Zn. Igeo values for Cu, regardless of the year of study and sludge sample, that ranged from 4.62 to 5.43 and for Zn from 3.41 to 4.86. At the same time, the ICF values for Cu ranged from 8.59–23.04, and for Zn 15.42–44.47. The RAC values indicated a low (Cu) and medium (Zn) risk of using SS in terms of the potential metal availability in the environment. The RAC values ranged from 1.46 to 4.40% for Cu and from 9.63 to 23.13% for Zn.

Influence of sulfide on diazotrophic growth of the methanogen Methanococcus maripaludis and its implications for the origin of nitrogenase

Methanogens inhabit euxinic (sulfide-rich) or ferruginous (iron-rich) environments that promote the precipitation of transition metals as metal sulfides, such as pyrite, reducing metal or sulfur availability. Such environments have been common throughout Earth’s history raising the question as to how anaerobes obtain(ed) these elements for the synthesis of enzyme cofactors. Here, we show a methanogen can synthesize molybdenum nitrogenase metallocofactors from pyrite as the source of iron and sulfur, enabling nitrogen fixation. Pyrite-grown, nitrogen-fixing cells grow faster and require 25-fold less molybdenum than cells grown under euxinic conditions. Growth yields are 3 to 8 times higher in cultures grown under ferruginous relative to euxinic conditions. Physiological, transcriptomic, and geochemical data indicate these observations are due to sulfide-promoted metal limitation, in particular molybdenum. These findings suggest that molybdenum nitrogenase may have originated in a ferruginous environment that titrated sulfide to form pyrite, facilitating the availability of sufficient iron, sulfur, and molybdenum for cofactor biosynthesis.

Identifying electric vehicles batteries technology trends: a prospective study based on patent mining

The purpose of this paper is to identify recent trends in battery technologies being produced for Electric Vehicles [EV] propulsion, including advantages regarding pollution reduction. We used the software Patent2Net to investigate, through patent granted mining, by the International Patent Office [IPO], showing the linkages between inventors, patent applicants, and technology platform trends. Results show an increase in patent granted for EV batteries in the last 10 years, meaning that the knowledge on batteries technology and innovation has been continuously improved. Japanese technologies assume incumbency in the field, showing innovation diversity while dealing in almost all EV battery technology platforms. In spite of outdated technologies, such as Lead-acid batteries, keep on fighting in specific niches, Lithium batteries appear as the prevailing technology, as shown in sixteen patents. Lithium EV battery technologies/innovation trends, however, seem not determinative, as concerns on the availability of Lithium and other related metals, central to these technologies, becomes paramount.

Effects of an assistive electric field on heavy metal passivation during manure composting

Composting is one of main technologies for treating and thus utilizing livestock manure and sludge. However, heavy metals are major concerns in compost utilization due to their potential environmental hazards and health risks. This study aimed to investigate the effects of electric field-assisted composting on the variations of heavy metals and the affecting factors. The results showed that electric field significantly reduced the contents of bioavailable heavy metals including Mn, Zn, Cu, Ni, and Cd, with their bioavailable concentrations decreasing by 61.7, 63.8, 64.9, 83.7, and 63.8 %, respectively. The heavy metals being transformed into stable states were increased, indicating that the electric field also passivated these heavy metals and reduced their biological toxicity and stabilized their forms. Spearman's correlation analysis revealed that the changes in substances, temperature, and organic matter were the dominant environmental factors affecting the forms of heavy metals. Microbial community analysis indicated an increase in the abundance of metal-resistant bacteria such as Pseudomonas and Bacillus during electric field-assisted composting, with their relative abundances being increased to 2.66 % and 15.63 % in the pile of electric field-assisted composting, respectively, compared to the values of 1.88 % and 4.36 % respectively in the conventional composting. The current study suggests that electric field-assisted composting can significantly reduce the availability of heavy metals in the compost, and thus mitigate the health risks associated with its application.

Effects of biosolid biochar on crop production and metal accumulation through a rice-wheat rotation system in fields

ABSTRACT Biosolid-borne heavy metals are the main concern in soils. Therefore, the effects of biosolid biochar application in soils were evaluated in our study through a rice-wheat rotation in fields. The results showed that after the application of biosolid biochar, soil organic matter (SOM), soil pH, and soil total heavy metal concentrations (Cd, Zn, Cu, and Pb) were significantly increased. But the CaCl2 extracted metals concentrations were decreased, and no significant differences in metal concentrations of soil deeper layers (20–100 cm) were found among different treatments. The Cd, Zn, Cu, and Pb concentrations in rice decreased by 13.2%, 37.0%, 9.92%, and 63.0%, respectively, and the concentrations of Cd, Zn, Cu, and Pb in wheat decreased by 20.85%, 19.7%, 48.6%, and 23.6%, respectively, compared with the control treatment. Biosolid biochar can decrease metal availability in soils and increase crop production in fields, thus is suggested to use in fields.

High-Efficiency Separator Capacity-Compensation Strategy Applied to Sodium-Ion Batteries.

Sodium-ion batteries (SIBs) are expected to replace partial reliance on lithium-ion batteries (LIBs) in the field of large-scale energy storage as well as low-speed electric vehicles due to the abundance, wide distribution, and easy availability of sodium metal. Unfortunately, a certain amount of sodium ions are irreversibly trapped in the solid electrolyte interface (SEI) layer during the initial charging process, causing the initial capacity loss (ICL) of the SIBs. A separator capacity-compensation strategy is proposed, where the capacity compensator on the separator oxidizes below the high cut-off voltage of the cathode to provide additional sodium ions. This strategy shows attractive advantages, including adaptability to current production processes, no impairment of cell long-cycle life, controlled pre-sodiation degree, and strategy universality. The separator capacity-compensation strategy is applied in the NaNi1/3 Fe1/3 Mn1/3 O2 (NMFO)||HC full cell and achieve a compensated capacity ratio of 18.2%. In the Na3 V2 (PO4 )3 (NVP)||HC full cell, the initial reversible specific capacity is increased from 61.0 mAh g-1 to 83.1 mAh g-1 . The separator capacity-compensation strategy is proven to be universal and provides a new perspective to enhance the energy density of SIBs.

Enrichment of Cd, Cr, Pb and Biological Detoxification Strategies in Sewage Irrigated Soils

Aim: Long-term use of sewage-sludge and improper management of agricultural lands can lead to an elevated heavy metal concentration in the soil resulting in barren soil. The present investigation was carried out to study the influence of different soil characteristics on the enrichment of Cd, Cr and Pb and their detoxification strategies in sewage irrigated soil profiles of Prayagraj region, India. Methodology: Di-acid mixture method used for soil analysis. The clean filtrate was used for the estimation of the heavy metals (Cd, Cr and Pb) by Atomic Absorption Spectrophotometer (AAS) (AAnalyst600, Perkin Elmer Inc., MA, USA). Isolation and identification of Cd, Cr and Pb Detoxifying microorganisms were isolated from the sewage-irrigated soils by nutrient agar medium. Results: It was observed that surface soils contained higher amount of DTPA- extractable heavy metals (Cd 3.00-3.20 mg kg-1,Cr 5.20-6.40 mg kg-1 and Pb 6.80-7.20 mg kg-1) and these amounts along with CEC (26.10 Cmol (p+) kg-1) and organic carbon (OC) Content (0.58%) decreased with the depth of soil profiles. Among the tested microorganisms, the highest accumulation of heavy metals in the sewage irrigated soils was observed in Citrobacter spp. to the extent of Cd 13.2%, Cr 36%, and Pb 42%. However, the lowest accumulation was observed in Escherichia coli to the extent of Cd 1.2%, Cr 8.4%, and Pb 10.2%. Conclusion: The horizons A of the studied soil profiles contain almost 12% more Cd, 9.11% more Cr, and 52% more Pb as compared to the contents of horizons B. Biological detoxification system metal uptake is largely influenced by the availability of metals. The highest accumulation of heavy metals was observed in the order of Pb > Cr > Cd by the selected microorganisms in the order of Citrobacter spp. >Bacillus spp. > Pseudomonas aerugia > Rhizopus arrhizus > Escherichia coli, resulting in the detoxification of the metals in the sewage irrigated soils. GRAPHICAL ABSTRACT

Control of nutrient metal availability during host-microbe interactions: beyond nutritional immunity.

The control of nutrient availability is an essential ecological function of the host organism in host-microbe systems. Although often overshadowed by macronutrients such as carbohydrates, micronutrient metals are known as key drivers of host-microbe interactions. The ways in which host organisms control nutrient metal availability are dictated by principles in bioinorganic chemistry. Here I ponder about the actions of metal-binding molecules from the host organism in controlling nutrient metal availability to the host microbiota. I hope that these musings will encourage new explorations into the fundamental roles of metals in the ecology of diverse host-microbe systems.

Revealing the Combined Effects of Microplastics, Zn, and Cd on Soil Properties and Metal Accumulation by Leafy Vegetables: A Preliminary Investigation by a Laboratory Experiment

A pot experiment was carried out to investigate the effects of polyethylene (PE), a broadly utilized polymer type, on soil properties and lettuce growth. Two Zn- and Cd-contaminated soil samples were obtained from urban and rural areas of Greece, respectively. PE fragments (<5 mm) were added at different concentrations (2.5%, 5% w/w). Lettuce seeds were then planted in the pots in a completely randomized experiment. Plant growth patterns and tissue metal accumulation were investigated. The presence of PE in soils resulted in a reduction in pH, significantly enhanced the organic matter content, and increased the cation-exchange capacity. The availability of both metals was also increased. Metal migration from soil to plant was determined using appropriate tools and indexes. A higher metal concentration was detected in lettuce roots compared with that in the edible leaves. The presence of PE MPs (2.5% w/w) increased the amount of available Zn more than that of Cd in highly contaminated soils. When PE MPs were added to agricultural soil, Zn concentrations increased in the plant leaves by 9.1% (2.5% w/w) and 21.1% (5% w/w). Considering that both metals and microplastics cannot be easily and quickly degraded, the fact that the less toxic metal is more available to plants is encouraging. Taking into account the physicochemical soil features, decision makers may be able to limit the risks to human health from the coexistence of heavy metals and microplastics in soils.

Material efficiency strategies across the industrial chain to secure indium availability for global carbon neutrality

A global energy transition toward carbon neutrality system requires increased critical metals, and the availability of critical byproduct metals raises concerns due to their dependence on host metals. To ensure the supply security of critical byproduct metals, material efficiency (ME) strategies are needed. Taking indium as an example, this paper explores the indium availability for global energy transition goals, and then illustrates the effects of ME strategies on securing indium availability throughout the whole industry chain. The system dynamics model serves to understand the joint production mechanism of zinc-indium and the nexus between energy transition and indium demand. Results show that the indium supply shortage for global energy transition could be intensified due to a less zinc-intensive economy. To address this challenge, focusing on indium demand reduction is more effective than emphasizing expanding indium supply for global sustainable development goals and material content reduction is the most promising strategy among the five ME strategies. Whereas, eliminating the concerns of indium availability thoroughly for facilitating a carbon neutrality transition requires coordinated ME strategies both from supply-side and demand-side. Moreover, the proposed analysis framework of ME strategies for securing indium availability for energy transition could also be applied for other byproduct metals.