Single Cd Research Articles

Toxic Effects of Several Common Heavy Metals in Soils on Terrestrial Invertebrates

In this paper, the ecotoxicology research method combines field investigation and indoor simulation experiment. Sampling and analysis of heavy metal pollution of solid soil samples from lead-acid battery factory, identified Pb, Cd and Cr as the pollution research objects, discussed the biological reaction mechanism of Eiseniafetida under the stress of heavy metals Pb, Cd and Cr, and obtained the results. The results of the lethal and sublethal effects of Pb, Cd and Cr on Pb, Cd and Cr and the effect of biomarkers. The main research results are as follows: In the acute toxicity test of Aisheng worm, the theoretical half-lethal concentrations (LC50) of single Pb, Cd, and Cr exposure for 14 days were 2620.93, 362.83, and 229.44 mg/kg, respectively, and their toxicity was Cr>Cd>Pb .

Single Atom-Engineered NIR-II Gold Clusters with Ultrahigh Brightness and Stability for Acute Kidney Injury.

Near-infrared-II (NIR-II) imaging has shown great potential for monitoring the pathological progression and deep tissue imaging but is limited to present unmet NIR-II agent. Present fluorophores show a promising prospect for NIR-II imaging, but brightness and photostability are still highly challenging during real-time monitoring. In this work, atom-engineered NIR-II Au24 Cd1 clusters with ultrahigh brightness, stability, and photostability are developed via single atomic Cd doping. Single atom Cd substitutions contribute to Cd 4d state in HOMO and redistribution of energy level near the gap, exhibiting 56-fold fluorescence enhancement of Au24 Cd1 clusters. Meanwhile, single atomic Cd reinforces CdAu bond energy, formation energy, and stabilized cluster structure, leading to persistent stability for up to 1month without decay, as well as excellent photostability of 1h without photobleaching, much longer than clinically approved indocyanine green (<5min). In vivo imaging shows gold clusters can monitor acute kidney injury (AKI) even after 72h of injury, enabling evaluating progression at a very long window. Meanwhile, the bioactive gold clusters can alleviate AKI-induced oxidative stress damage and acute neuroinflammation. Single atom-engineered gold clusters exhibit molecular tracking and diagnostic prospect in kidney-related diseases.

Effects of cadmium on mercury accumulation and transformation by Arundo donax L.

High biomass energy plants are a promising alternative to hyperaccumulators for the remediation of heavy metals (HMs). Arundo donax L. (A. donax) is a rapidly growing rhizomatous grass with high biomass production. However, the feasibility of using A. donax for the phytoremediation of combined mercury (Hg) and cadmium (Cd) pollution under neutral conditions is unclear. In this study, a hydroponic experiment was performed to investigate the impact of Hg-Cd stress on the growth and physiological properties of A. donax and HMs accumulation and transformation. Either single Hg or Cd stress slightly enhanced stem height, fresh biomass, and chlorophyll content, whereas combined Hg-Cd stress reduced these parameters. Furthermore, combined Hg-Cd stress increased the leaf content of malondialdehyde in A. donax, indicating that the combined pollution aggravated oxidative stress in A. donax. Hg volatilization was observed during the 10-day experiment, implying that a portion of the Hg2+ was transformed into Hg0 by A. donax. The bioaccumulation factor (BAF) values of A. donax were far greater than 1 for both Hg and Cd, whereas the translocation factor (TF) values were less than 1, indicating that phytovolatilization and phytostabilization rather than phytoextraction contributed to the remediation of Hg and Cd by A. donax. The solution pH decreased at the beginning of the experiment, suggesting that acidic root exudates of A. donax facilitated the accumulation and transformation of Hg under neutral conditions. Overall, the effects of Cd on Hg accumulation and transformation by A. donax followed the rule of "low promotion and high inhibition." This study demonstrates that A. donax is a potential candidate for the phytoremediation of combined Hg-Cd pollution under neutral conditions.

The interaction effects of biodegradable microplastics and Cd on Folsomia candida soil collembolan.

In real-field soil conditions, multiple chemicals exposure may be the real scenario for soil biota. The co-occurrence of microplastics (MPs) and cadmium (Cd) is common in soils, which may pose a potential risk to soil ecosystems. Degradable microplastics are producing more MPs, and the potential effects on soil ecosystems are unknown. Therefore, a standard soil animal collembolan Folsomia candida was used to evaluate the single and interaction effects of biodegradable MPs (PLA) and Cd. The results showed that single and co-biodegradable PLA and Cd all had negative influences on the survival, reproduction, and growth of F. candida, and the effects intensified with PLA concentrations. The survival rate, reproduction rate, adult body length, and juvenile body length decreased by 20.0%, 24.2%, 22.9%, and 32.2% at MPs-100 treatment. But combined PLA and Cd alleviated the toxicity of single Cd on F. candida at lower PLA concentrations. The number of juveniles increased by 29.3%, the survival rate increased by 7.52%, the adult body length increased by 11.7%, and the juvenile body length increased by 19.0% at MPs-1 + Cd than single Cd treatment. Biochemical assays on antioxidant enzymes had the same results. Antioxidant enzymes CAT and POD were more sensitive than SOD. CAT and POD activities were induced quickly at shorter exposure periods, and MP treatment thus may be promising biomarkers on soil collembolan for soil MP exposure. PLA is degraded with time in soils; therefore, the long-term effects of co-MPs and Cd in soils are suggested to be further studied.

Single‐Atom Cadmium‐N4 Sites for Rechargeable Li–CO2 Batteries with High Capacity and Ultra‐Long Lifetime

AbstractThe rechargeable Li–CO2 battery shows great potential in civil, military, and aerospace fields due to its high theoretical energy density and CO2 capture capability. To facilitate the practical application of Li–CO2 battery, the design of efficient, low‐cost, and robust non‐noble metal cathodes to boost CO2 reduction/evolution kinetics is highly desirable yet remains a challenge. Herein, single‐atom cadmium is reported with a Cd‐N4 coordination structure enable rapid kinetics of both the discharge and recharge process when employed as a cathode catalyst, and thus facilitates exceptional rate performance in a Li–CO2 battery, even up to 10 A g−1, and remains stable at a high current density (100 A g−1). An unprecedented discharge capacity of 160045 mAh g−1 is attained at 500 mA g−1. Excellent cycling stability is maintained for 1685 and 669 cycles at 1 A g−1 and capacities of 0.5 and 1 Ah g−1, respectively. Density functional theory calculations reveal low energy barriers for both Li2CO3 formation and decomposition reactions during the respective discharge and recharge process, evidencing the high catalytic activity of single Cd sites. This study provides a simple and effective avenue for developing highly active and stable single‐atom non‐precious metal cathode catalysts for advanced Li–CO2 batteries.

The single and combined effects of sulfamethazine and cadmium on soil nitrification and ammonia-oxidizing microorganisms.

The coexistence of antibiotics and heavy metals in soil has attracted increasing attention due to their negative effects on microorganisms. However, how antibiotics and heavy metals affect functional microorganisms related to nitrogen cycle remains unclear. The goals of this work were to explore the individual and combined effects of sulfamethazine (SMT) and cadmium (Cd), selected as target pollutants in soil, on potential nitrification rates (PNR) and ammonia oxidizers (ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB)) structure and diversity by 56-day cultivation experiment. Results showed that PNR in Cd- or SMT-treated soil decreased at the beginning of the experiment and then increased over time. PNR was significantly correlated with AOA and AOB-amoA relative abundance (P < 0.01). SMT addition (10 and 100mgkg-1) significantly improved AOA activity by 13.93% and 17.93%, respectively, and had no effect on AOB at day 1. Conversely, Cd at 10mgkg-1 significantly inhibited AOA and AOB by 34.34% and 37.39%, respectively. Moreover, the relative abundance of AOA and AOB in combined SMT and Cd addition clearly higher relative to single Cd at 1day. The single and combined Cd and SMT increased and reduced the community richness of AOA and AOB, respectively, but reduced the diversity of both after 56days. Cd and SMT treatments significantly changed the relative abundance of AOA phylum levels and AOB genus levels in the soil. It was mainly manifested in reducing the relative abundance of AOA Thaumarchaeota, and increasing the relative abundance of AOB Nitrosospira. Besides, AOB Nitrosospira was more tolerant to the compound addition of both than single application.

Influencing Factors of Bidens pilosa L. Hyperaccumulating Cadmium Explored by the Real-Time Uptake of Cd2+ Influx around Root Apexes under Different Exogenous Nutrient Ion Levels.

Though Bidens pilosa L. has been confirmed to be a potential Cd hyperaccumulator, the accumulation mechanism is not yet clear. The dynamic and real-time uptake of Cd2+ influx by B. pilosa root apexes was determined using non-invasive micro-test technology (NMT), which partly explored the influencing factors of the Cd hyperaccumulation mechanism under the conditions of different exogenous nutrient ions. The results indicated that Cd2+ influxes at 300 μm around the root tips decreased under Cd treatments with 16 mM Ca2+, 8 mM Mg2+, 0.5 mM Fe2+, 8 mM SO42- or 18 mM K+ compared to single Cd treatments. The Cd treatments with a high concentration of nutrient ions showed an antagonistic effect on Cd2+ uptake. However, Cd treatments with 1 mM Ca2+, 0.5 mM Mg2+, 0.5 mM SO42- or 2 mM K+ had no effect on the Cd2+ influxes as compared with single Cd treatments. It is worth noting that the Cd treatment with 0.05 mM Fe2+ markedly increased Cd2+ influxes. The addition of 0.05 mM Fe2+ exhibited a synergistic effect on Cd uptake, which could be low concentration Fe2+ rarely involved in blocking Cd2+ influx and often forming an oxide membrane on the root surface to help the Cd uptake by B. pilosa. The results also showed that Cd treatments with high concentration of nutrient ions significantly increased the concentrations of chlorophyll and carotenoid in leaves and the root vigor of B. pilosa relative to single Cd treatments. Our research provides novel perspectives with respect to Cd uptake dynamic characteristics by B. pilosa roots under different exogenous nutrient ion levels, and shows that the addition of 0.05 mM Fe2+ could promote the phytoremediation efficiency for B. pilosa.

Ecological risk assessment and early warning of heavy metal cumulation in the soils near the Luanchuan molybdenum polymetallic mine concentration area, Henan Province, central China

The Luanchuan molybdenum polymetallic mine concentration area is rich in mineral resources and has a long history of mining. The environmental impact of long-term mining activities cannot be ignored. It is of great significance to study the ecological risk and the accumulation trends of heavy metals in the soil of mining areas for scientific prevention and control of heavy metal pollution. Taking the Taowanbeigou River Basin in the mine concentration area as the research object, the ecological pollution risk and cumulative effect of heavy metals in the soil of the basin were studied by using the comprehensive pollution index method, potential ecological risk assessment method and geoaccumulation index method. On this basis, the cumulative exceeding years of specific heavy metals were predicted by using the early warning model. The comprehensive potential ecological risk of heavy metals in the soil near the Luanchuan mine concentration area is moderate, and the single element Cd is the main ecological risk factor, with a contribution rate of 53.6%. The overall cumulative degrees of Cu and Pb in the soil are “none-moderate”, Zn and Cd are moderate, Mo has reached an extremely strong cumulative level, Hg, As and Cr risks are not obvious, and the overall cumulative risks order is Mo>Cd>Zn>Cu>Pb>Hg. According to the current accumulation rate and taking the risk screening values for soil contamination of agricultural land as the reference standard, the locations over standard rates of Cu, Zn and Cd will exceed 78% in 90 years, and the over standard rate of Pb will reach approximately 57% in 200 years. The cumulative exceeding standard periods of As, Cr and Hg are generally long, which basically indicates that these elements do not pose a significant potential threat to the ecological environment. Mining activities will accelerate the accumulation of heavy metals in soil. With the continuous development of mining activities, the potential pollution risk of heavy metals in the soil of mining areas will also increase.©2023 China Geology Editorial Office.

Effects of Heavy Metal Pollution in Soil of Coal Gangue Area on Germination and Seedlings of Typical Remediation Plants

The problem of soil heavy metal pollution caused by coal gangue accumulation areas is becoming more and more serious. In situ plant remediation technology has become one of the most promising methods to solve heavy metal soil pollution due to its advantages of the green economy. In this experiment, the characteristics of heavy metal pollution in the shallow soil (vertical depth 0~20 cm) 300 m outside the square circle of a typical coal gangue accumulation area in the Fengfeng Mining Area of Hebei Province, China were used as the prototype. Alfalfa and ryegrass were selected as the test plants. Pot experiments were carried out at different heavy metal concentrations (Cu:14/64/100 mg/kg, Pb:15/38/170 mg/kg, Cd:1/4/8 mg/kg) levels to study and reveal the effects of single and compound soil heavy metal pollution on seed germination and seedling growth characteristics of alfalfa and ryegrass. The results showed that: (1) Under the condition of single Cd pollution, the germination index of alfalfa seeds and the germination potential of ryegrass seeds show a trend of “low concentration promotion and high concentration inhibition”. Under the condition of single Pb and Cu pollution in soil, the germination indices show obvious inhibition and damage effect; that is, with an increase in concentration, the germination rate, germination potential, germination potential, and vigor index show a decreasing trend. When Pb is 170 mg/kg or Cu is 100 mg/kg or Cd is 8 mg/kg, the inhibitory effect on seed germination and seedling growth of the two plants is the most harmful. (2) Due to the different concentrations of heavy metal combined pollution, there are synergistic or antagonistic effects between Cu, Pb and Cd in soil on alfalfa and ryegrass. That is to say, under low concentrations of heavy metal pollution, the inhibitory effect of combined stress is greater than that of single stress, and under high concentration of heavy metal pollution, the inhibitory effect of combined stress is less than that of single stress. (3) Whether in the single pollution or combined pollution of soil, ryegrass is always more tolerant than alfalfa, indicating that ryegrass has more potential for remediation.

The presence of microplastics (MPs) reduces the toxicity of cadmium (Cd) to Cirrhinus mrigala larva

Cumulative studies have shown that microplastics (MPs) and cadmium (Cd) co-exist widely, but their combined toxic effects on aquatic organisms are still not well understood. In this study, Cirrhinus mrigala larvae were exposed to single and binary combinations for 7 days, and the growth performance, survival, intestinal contaminant migration, intestinal histopathology, enzyme activity, and expression of antioxidant-related and detoxification-related genes were measured. The results showed that PS-MPs, Cd, and their combined exposure cause intestinal tissue damage, which in turn affects the growth and survival of C. mrigala larvae, and combined exposure of PS-MPs and Cd reduces stagnant growth and death caused by single Cd exposure. Under both single and binary exposure, PS-MPs can accumulate in the intestine of C. mrigala larvae, but Cd-induced damage to intestinal tissues can increase the accumulation of PS-MPs in the intestine of C. mrigala larvae. PS-MPs, Cd and their combined exposure can cause abnormalities in enzyme activity and expression of antioxidant genes and detoxification genes. The results of continuous 7-day dynamic monitoring showed that the relative expression of cat in the Cd exposure group was significantly higher than that of the control group on days 1, 2 and 4; the relative expression of gpx was significantly higher than that of the control group on days 3, 4 and 7; the relative expression of mnsod was significantly higher than that of the control group on days 1, 3 and 7; and the relative expression of cusod was significantly higher than that of the control group on days 4, 6 and 7. These results indicated that the presence of MPs acted as an antagonist, reducing the toxicity of Cd to aquatic organisms. Overall, this study contributes to further understanding of the inter-regulatory relationship between MPs and Cd and the combined toxic effects on aquatic organisms.

Effects of cadmium and lead co-exposure on glucocorticoid levels in rural residents of northwest China

Cadmium (Cd) and lead (Pb) are important environmental endocrine disruptors that are associated with adverse health problems. However, the effects of co-exposure to Cd and Pb on glucocorticoids (GCs) in the body at environmental levels are limited. A total of 468 subjects from the Dongdagou-Xinglong cohort (DDG-XL) were included in this study. We measured the serum levels of two representative endogenous GCs [cortisol (CRL) and cortisone (CRN)], and whole blood levels of Cd and Pb. Multiple linear regression models were constructed to explore the associations of single or combined Cd and Pb exposure with serum CRL and CRN levels. The interactive effects of Cd and Pb on GCs were further assessed using mediation analysis and moderation analysis. Single-heavy metal exposure analysis with adjustment for potential confounders showed that the serum CRL level decreased when the blood Cd or Pb concentration gradually increased (P trend <0.01). Additionally, subjects with high Cd or Pb exposure (Q4) had significantly reduced serum CRN levels compared to those with low Cd or Pb exposure (Q1) (P < 0.05). In Cd and Pb co-exposure analysis, significant negative dose-response relationships were observed between co-exposure to Cd and Pb and serum CRL and CRN levels. Furthermore, mediation analysis showed that Cd completely mediated the relationship between Pb and GCs, and moderation analysis suggested that Pb might weaken the negative relationship between Cd and GCs. These findings suggest that single or combined exposure to Cd and Pb interferes with the homeostasis of serum CRL and CRN levels. Furthermore, we innovatively propose that Cd and Pb may have interactive effects on GCs levels, and Pb can antagonize the negative relationship between Cd and GCs, which may provide clues for further studies on endocrine and metabolic disorders related to these heavy metals.

Optimal Icosahedral Copper-Based Bimetallic Clusters for the Selective Electrocatalytic CO2 Conversion to One Carbon Products.

Electrochemical CO2 reduction reactions can lead to high value-added chemical and materials production while helping decrease anthropogenic CO2 emissions. Copper metal clusters can reduce CO2 to more than thirty different hydrocarbons and oxygenates yet they lack the required selectivity. We present a computational characterization of the role of nano-structuring and alloying in Cu-based catalysts on the activity and selectivity of CO2 reduction to generate the following one-carbon products: carbon monoxide (CO), formic acid (HCOOH), formaldehyde (H2C=O), methanol (CH3OH) and methane (CH4). The structures and energetics were determined for the adsorption, activation, and conversion of CO2 on monometallic and bimetallic (decorated and core@shell) 55-atom Cu-based clusters. The dopant metals considered were Ag, Cd, Pd, Pt, and Zn, located at different coordination sites. The relative binding strength of the intermediates were used to identify the optimal catalyst for the selective CO2 conversion to one-carbon products. It was discovered that single atom Cd or Zn doping is optimal for the conversion of CO2 to CO. The core@shell models with Ag, Pd and Pt provided higher selectivity for formic acid and formaldehyde. The Cu-Pt and Cu-Pd showed lowest overpotential for methane formation.

Assessment soil cadmium and copper toxicity on barley growth and the influencing soil properties in subtropical agricultural soils

Evaluation joint cadmium (Cd) and copper (Cu) phytotoxicity in wide range of subtropical agricultural soils is highly vital for phytoremediation of soils contaminated with Cd and Cu. In this study, barley root elongation assays were performed in 30 representative soils in response to single and combined Cd and Cu inhibition. The single Cd caused nearly 50% inhibition of barley root elongation, and Cu induced more than 50% inhibition in most soils. Mixed Cd + Cu caused significant inhibition on barley growth with average relative root elongation values of 20.0% and 30.4% in soil with a pH < 7 and pH > 7, respectively. An antagonistic interaction was evaluated in combined Cd + Cu toxicity, which was strong in soils containing low soluble Cu and Cd contents. Soil pH was the controlling factor in predicting single and mixed Cd and Cu phytotoxicity, which could explain 44% and 46% variation of single Cd and Cu toxicity, respectively. Soil organic carbon and effective cation exchange capacity were another important factor positively influencing metal toxicity, which further improved empirical prediction models accuracy, with determined coefficient (r2) values of 0.44–0.84. These results provide a theoretical basis for soils Cd and Cu pollution control.

Kalihiacyloxyamides A-H, α-acyloxy amide substituted kalihinane diterpenes isolated from the sponge Acanthella cavernosa collected in the South China Sea

Eight unreported α-acyloxy amide substituted kalihinane diterpenes, named kalihiacyloxyamides A-H were isolated from the South China Sea sponge Acanthella cavernosa. The planar structures and absolute configurations were elucidated by detailed 1D and 2D NMR experiments along with HRESIMS analysis, single crystal X-ray diffraction and CD spectroscopic analysis. Two compounds showed significant cytotoxicity against K562 cell line with IC50 values of 6.4 and 6.3 μM, while two other compounds displayed moderate cytotoxicity against MDA-MB-231 with IC50 values of 7.3 and 7.9 μM.

Chiral Dy(III) Fluorescent Single-Molecule Magnet Based on an Achiral Flexible Ligand

A novel multi-channel barcode module was developed by using chiral co-crystals which contain field-induced SMM behavior and different emission bands. The chiral co-crystals [Zn(H2L)Dy(DBM)2]4(ClO4)4⋅9CH3OH⋅H2O (1a) and [Zn(H2L)Dy(DBM)2]4(ClO4)4⋅8CH3OH⋅0.5H2O (1b) (H4L = 2,2′-[1,2-ethanediylbis[(hydroxyethylimino)methylene]]bis[6-methoxy-4-methyl-phenol], HDBM = dibenzoylmethane) were obtained through one-pot reaction of ZnII and DyIII with the achiral ligands H4L and HDBM. X-ray single crystal diffraction and CD spectroscopy confirmed that they are enantiomers crystallized in P43 (1a) and P41 (1b), both consisting of two ∆-[Zn(H2L)Dy(DBM)2]+ cations, two Λ-[Zn(H2L)Dy(DBM)2]+ cations and four (ClO4)− anions. The presence of DyIII ions endow them with the property of field-induced slow magnetic relaxation. The relatively low energy barrier of 35.0(9) K for complex 1 may be due to the poor axiality of the ligand field caused by the long Dy-Ophenoxy bond lengths and the small Ophenoxy-Dy-Ophenoxy bond angles. Moreover, when the organic ligands H4L (λex = 350 nm) and DyIII (λex = 420 nm) are excited, different emission spectra are observed.

Microvalves for Applications in Centrifugal Microfluidics.

Centrifugal microfluidic platforms (CDs) have opened new possibilities for inexpensive point-of-care (POC) diagnostics. They are now widely used in applications requiring polymerase chain reaction steps, blood plasma separation, serial dilutions, and many other diagnostic processes. CD microfluidic devices allow a variety of complex processes to transfer onto the small disc platform that previously were carried out by individual expensive laboratory equipment requiring trained personnel. The portability, ease of operation, integration, and robustness of the CD fluidic platforms requires simple, reliable, and scalable designs to control the flow of fluids. Valves play a vital role in opening/closing of microfluidic channels to enable a precise control of the flow of fluids on a centrifugal platform. Valving systems are also critical in isolating chambers from the rest of a fluidic network at required times, in effectively directing the reagents to the target location, in serial dilutions, and in integration of multiple other processes on a single CD. In this paper, we review the various available fluidic valving systems, discuss their working principles, and evaluate their compatibility with CD fluidic platforms. We categorize the presented valving systems into either "active", "passive", or "hybrid"-based on their actuation mechanism that can be mechanical, thermal, hydrophobic/hydrophilic, solubility-based, phase-change, and others. Important topics such as their actuation mechanism, governing physics, variability of performance, necessary disc spin rate for valve actuation, valve response time, and other parameters are discussed. The applicability of some types of valves for specialized functions such as reagent storage, flow control, and other applications is summarized.

Magnetic ion relaxation time distribution within a quantum well

Time-resolved optically detected magnetic resonance (ODMR) is a valuable technique to study the local deformation of the crystal lattice around magnetic ion as well as the ion spin relaxation time. Here we utilize selective Mn-doping to additionally enhance the inherent locality of the ODMR technique. We present the time-resolved ODMR studies of single {(Cd,Mg)Te/(Cd,Mn)Te} quantum wells (QWs) with manganese ions located at different positions along the growth axis -- in the center or on the sides of the quantum well. We observe that spin-lattice relaxation of Mn$^{2+}$ significantly depends on the ion-carrier wavefunction overlap at low-magnetic fields. Interestingly, the effect is clearly observed in spite of very low carrier density, which suggests the potential for control of the Mn$^{2+}$ ion relaxation rate by means of the electric field in future experiments.

Pfaffia glomerata is a hyperaccumulator candidate: Cd and Zn tolerance, absorption, transfer, and distribution

Pfaffia glomerata is a candidate for phytoremediation due to its high biomass and high bioaccumulation efficiency of multiple heavy metals. It is essential to further evaluate its tolerance, absorption, transfer, and distribution to multiple heavy metals. In the current study, we evaluated the tolerance, absorption, transfer, and distribution of P. glomerata in a Cd/Pb/Cu/Zn combined-contaminated environment by two hydroponic experiments. The results demonstrated that P. glomerata was not affected by Cd/Pb/Cu/Zn exposure, except for the 50 μM Cd/Pb/Cu/Zn treatment, which significantly decreased the stem biomass. In a single Cd, Pb, Cu, and Zn exposure, the root of P. glomerata absorbed Cd/Pb/Cu/Zn in the order of Cd > Zn > Pb > Cu. Almost all Pb and Cu accumulated in the plant roots and were hardly transferred to the aboveground parts. Therefore, the order of total Cd/Pb/Cu/Zn extraction of a single plant in multiple Cd/Pb/Cu/Zn exposures at the same concentration was Cd > Zn > Pb > Cu. The bioconcentration factor (BCF) of Cd and Zn in roots, stems, and leaves increased with the concentration of Cd and Zn in the solution, and was > 1. In contrast with Cd and Zn, the BCFs of Cu and Pb in the stems and leaves were < 1. The element distribution of Pb, Cu, Zn, and Mn in the stem of P. glomerata was dispersed, indicating that the stem of P. glomerata does not have a detoxification mechanism for distributing metals to the area of low biological activity. The total amount of tartaric acid, critic acid, and DOC secreted by P. glomerata roots decreased with the increase in Cd/Pb/Cu/Zn exposure. However, further investigation is needed to unravel the interaction between the LMWOAs secreted by the root of P. glomerata and heavy metals.

Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida)

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H2O2) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn2+, Pb2+, and Cd2+ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

Enhanced cadmium phytoremediation capacity of poplar is associated with increased biomass and Cd accumulation under nitrogen deposition conditions

Nitrogen (N) deposition plays a significant role in soil cadmium (Cd) phytoremediation, and poplar has been considered for the remediation of contaminated soil because of its enormous biomass and strong Cd resistance. To reveal the underlying physiological and root phenotypic mechanisms of N deposition affecting Cd phytoextraction in poplar, we assessed root phenotypic characteristics, Cd absorption and translocation, chlorophyll fluorescence performance, and antioxidant enzyme activities of a clone of Populus deltoides × P. nigra through combined greenhouse Cd and N experiments. Our results showed that Cd significantly changed the root phenotype by reducing root length, tip number, and diameter. Cd also caused the peroxidation of lipids, damaged the photosystem II (PSII) reaction centre, and reduced photosynthetic capacity, resulting in a decrease in biomass accumulation in poplar. The N60 (60 kg N·ha−1·yr−1) and N90 (90 kg N·ha−1·yr−1) treatments promoted the net photosynthetic rate of poplar by increasing the activity of antioxidant enzymes and proline content and repairing the PSII reaction centre, thus increasing the biomass accumulation of poplar exposed to Cd stress. Simultaneously, the N60 and N90 treatments might have increased Cd uptake from the soil by upregulating total root length, root tips, and fine root length. Cd mainly accumulated in roots and stems but not in leaves. The N30 (30 kg N·ha−1·yr−1) treatment had no obvious effects on these parameters compared with the single Cd treatment. Consequently, our study suggested that adequate N can improve biomass and Cd accumulation to enhance the phytoremediation capacity of poplar for Cd, which might be related to the improvement of leaf physiological defence and the change in root phenotypic characteristics.