Transport Of Pb Research Articles

Recruitment of beneficial microbes and differential metabolites promoted Pb transport in Salix integra Thunb. after inoculation with Bacillus megaterium B6

Recruitment of beneficial microbes and differential metabolites promoted Pb transport in Salix integra Thunb. after inoculation with Bacillus megaterium B6

Root exudate–assisted phytoremediation of copper and lead contamination using Rumex acetosa L. and Rumex K-1

Heavy metal pollutants can be effectively removed from soil through phytoremediation using root exudates. Herein, experiments were conducted to assess the phytoremediation capabilities of Rumex acetosa L. and Rumex K-1 root exudates for copper (Cu) and lead (Pb) contamination. Results indicated that these root exudates effectively adsorbed Cu and Pb. Furthermore, the optimal adsorption conditions of Cu by the root exudates of both plants were as follows: light duration of 36 h, light intensity of 8000 Lx, temperature of 25 °C and CO(NH2)2 concentration of 0 %. Moreover, the optimal adsorption conditions of Pb by Rumex acetosa L. and Rumex K-1 root exudates were light duration of 48 h and 24 h, respectively, light intensity of 8000 Lx, temperature of 25 °C and CO(NH2)2 concentration of 0 %. In addition, the root exudates from both plants enhanced the enrichment and transport of Cu and Pb. Moreover, the root was found to be the main accumulation site of Pb, while the stems and leaves were the main accumulation sites of Cu. With the application of root exudates, plant growth increased, with growth indices in Rumex acetosa L. and Rumex K-1 groups treated with exudates being 1.08–1.81-fold and 1.06–1.9-fold higher, respectively, compared with the untreated ones; physiological indexes showed 1.14–2.62-fold and 1.14–2.71-fold improvements, respectively. Remediation efficiency indexes showed 1.05–1.62-fold and 1.10–1.89-fold improvements, respectively. Rumex acetosa L. and Rumex K-1 exhibited promising potential for the phytoremediation of Cu and Pb, with root exudates playing a critical role in metal adsorption and stabilisation, suggesting their potential for enhancing remediation capabilities. This study sheds light on the mechanisms of root exudate–assisted phytoremediation and provides insights into alleviating heavy metal pollution.

Photoaged tire wear particles hinder the transport of Pb(II) in urban soils under acid rain: Experimental and numerical investigations

Rapid urbanization brought lots of serious environmental contamination, including the accumulation of heavy metals, acid rain, and the emission of tire wear particles (TWPs), with detrimental effects for terrestrial ecosystems. Nevertheless, how naturally aged TWPs affect the mobilization of heavy metals in soils under acid rain is still unclear. Here, we investigate the adsorption and transport mechanisms of Pb(II) co-existing with acid rainwater in soil-TWP mixtures via batch experiments, column experiments and modeling. Results showed that photoaged TWP significantly prolonged the Pb(II) adsorption equilibrium time (1 to 16 h) and enhanced the Pb(II) adsorption capacity of soils. Soil column profiles confirmed that TWP effectively boosted the initial accumulation of lead in the topsoil and thus impeded the downward transport of lead. The retardation factor (R) estimated by the linear two-site sorption model (TSM) fitting the Pb(II) breakthrough curves gradually increased from 1.098 to 16.38 in soils with TWP (0–10 %). Comparative results of linear or nonlinear TSM suggested nonlinear sorption replacing linear sorption as the main Pb(II) sorption mechanism under 1 % and 10 % TWP. This research provides significant insights into the implications of TWP on the Pb(II) retention behaviors and highlights the severer potential remobilization risks of Pb(II) in urban soils under different acid rain environments.

Pb Pollution Stress in Alnus cremastogyne Monitored by Antioxidant Enzymes

Lead (Pb) is a common toxic heavy metal element that can be absorbed by plant roots and enter the food chain, damaging human health. Alnus cremastogyne has a wide native range, is fast growing, has a wide range of timber uses, and has rhizomatous roots that can improve planted soils. In this study, we evaluated whether Alnus cremastogyne has the potential to remediate Pb-contaminated soils through a 6-month pot experiment in soils with different Pb concentrations (0, 50, 100, 200, and 400 mg/kg). Our results indicate that Alnus cremastogyne plant height, basal diameter, and organ biomass decreased, H2O2 and MDA content increased, and the activities of antioxidant enzymes and osmotic regulators increased and then decreased with increasing lead concentrations. The Pb bioconcentration factor of Alnus cremastogyne was less than 1 at all Pb concentrations, and Pb accumulated mainly in the root system. This indicates that Alnus cremastogyne is not a Pb-enriched plant and does not have outstanding Pb transport capacity. The growth of Alnus cremastogyne was not significantly affected at low Pb concentrations, and its plant height, basal diameter, and biomass were significantly suppressed under high Pb stress. Therefore, Alnus cremastogyne is not a suitable species for the remediation of lead-contaminated soils but can be used as a silvicultural species in environments with low lead levels.

Synergistic effects of microplastic stability and adsorption rate on co-transport of microplastics and Pb under surfactant

The emergence of microplastics (MPs) and their coexistence with heavy metal contaminants pose potential risks to the safety of the subsurface environment and public health. Therefore, it is crucial to explore the co-transport of MPs (polypropylene (PP), polyethylene (PE), polystyrene (PS), polymethyl methacrylate (PMMA) and polytetrafluoroethylene (PTFE)) with the heavy metal Pb(II) under the surfactant (sodium dodecyl benzene sulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB)). In this study, column experiments were performed to investigate the co-transport of MPs and Pb(II) under surfactants. The co-transport mechanism of MPs with Pb(II) under surfactant was revealed by MPs stability and batch adsorption experiments. Experimental results showed that the presence of Pb(II) did not influence the mobility of MPs under CTAB and SDBS; however, MPs can affect the mobility of Pb(II). Specifically, under CTAB, the MPs increased the recovery rate of Pb(II) from 86% to 87.55%–97.55%. However, under SDBS, the high mobility of PS, PE, and PP inhibited the transport of Pb(II), and the recoveries of Pb(II) decreased from 79% to 57.53%–70.96%. The low mobility of PTFE and PMMA slightly promoted the transport of Pb(II). This could be attributed to two reasons. One aspect is the adsorption rate of Pb(II) by MPs, which plays a pivotal role in influencing the transport tendency of Pb(II) with MPs. Another aspect is the MPs stability, as greater stability enhances their dispersity and accelerates the adsorption rate of Pb(II), thereby facilitating the co-transport of Pb(II) with MPs. This study could provide valuable insights for assessing the transport and environmental impact of MPs and heavy metals in the presence of surfactants.

Recovery of biochar particles laden with lead in saturated porous media by DC electric field

The co-transport behavior of environmental pollutants with biochar particles has aroused great interests from researchers due to the concerns about pollutant diffusion and environmental exposure after biochar is applied to soil. In this work, the recovery and co-transport behavior of biochar micron-/nano-particles (BCMP and BCNP) and lead (Pb2+) in saturated porous media were investigated under different ionic strength conditions (IS = 1, 5 and 10 mM) under a direct current electric field. The results showed that the electric field could significantly enhance the mobility of Pb adsorbed biochar particles, particularly BCNP. The recovery of Pb laden biochar particles was improved by 1.8 folds, reaching 78.8% at maximum under favorable condition at +0.5 V cm−1. According to the CDE (Convection-Dispersion-Equation) model and DLVO (Derjaguin-Landau-Verwey-Overbeek) theory analysis, the electric field facilitated the transport of Pb carried biochar mainly by increasing the negative charges on biochar surface and improving the repulsive force between biochar and porous media. High IS was favorable for biochar transport under the electric field, but inhibited desorbing Pb2+ from biochar (18% by maximum at IS = 10 mM). By switching the electric field power, a two-stage strategy was established to maximize the recovery of both biochar particles and Pb, where BCNP and Pb recovery were higher than electric field free case by 90% and 35%, respectively. The findings of this study can help build a biochar recovery approach to prevent potential risks from biochar application in heavy metal contaminated soil remediation.

SYNTHESIS AND CHARACTERIZATION OF LOW-COST PLASTICIZED POLYMERIC MEMBRANES FOR SEPARATION OF BIVALENT CATIONS

Recently, polymer inclusion membranes (PIMs) have surfaced as a viable solution for selective transport and metallic ions separation. The efficiency of such membranes is subject to a number of factors, including the preparation method and relevant physico-chemical characteristics. In this paper, an improvement of a novel category of PIMs for performing ions separation is reported. The membranes were prepared using a mixture of two polymers: cellulose triacetate (CTA) and poly(methyl methacrylate) (PMMA), three different carriers, Aliquat 336 (basic), di-(2-ethylhexyl) phosphoric acid (D2EHPA) (acid) and tributyl phosphate (TBP) (neutral) and plasticized by dioctyle phthalate (DOP). All synthesized membranes were characterized using Fourier Transform Infrared (FTIR) spectroscopy, Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). A study of the transport of Co(II), Cu(II), Ni(II) and Pb(II) species using the synthesized membranes was conducted. Our results indicate that facilitated transport through PIMs is an effective way of solving the permanent problem of membrane stability.

Screening of Maize Varieties with High Biomass and Low Accumulation of Pb and Cd around Lead and Zinc Smelting Enterprises: Field Experiment

In the long-term production process of lead and zinc smelting enterprises, atmospheric subsidence leads to the accumulation of heavy metals in surrounding farmland, which poses a serious threat to the growth of crops and food safety. Given the knowledge that heavy metal pollution in cultivated land does not support treatment and restoration, determining how to ensure the quality and safety of agricultural products is the main problem facing the agricultural industry at present. Previous studies have mainly focused on the low accumulation of heavy metals in maize varieties, while the removal of heavy metals from soil through high biomass has been studied less. In order to identify the maize varieties that demonstrate high removal and low accumulation of heavy metals, 29 maize varieties were planted in soil contaminated with lead (Pb) and cadmium (Cd), and the growth status of the maize varieties and the absorption and transport of Pb and Cd by different tissues were studied. The results showed that heavy metals had the least effect on the growth of the Longhuangbai3, Jinqiuyu 35, Jinyi 418, and Qiuqing 88 varieties, and the content of Pb and Cd in maize varieties was in the order leaf > stem > root > grain. It was found that soil remediation and safe production can be taken into account in the results of the Qiuqing 88 (Pb, Cd), Fengdeng 2025 (Cd), and Yayu 719 (Pb, Cd) varieties. Moreover, the Xinzhongyu 801 (Cd) and Longdan 1701 (Pb) varieties demonstrated high metal accumulation in the edible part, which poses a potential risk to human health; thus, they are not recommended for local cultivation.

Combined transcriptomics and metabolomics to analyse the response of Cuminum cyminum L. under Pb stress

Lead (Pb) can disrupt plant gene expression, modify metabolite contents, and influence the growth of plants. Cuminum cyminum L. is highly adaptable to adversity, but molecular mechanism by which it responds to Pb stress is unknown. For this study, transcriptomic and metabolomic sequencing was performed on root tissues of C. cyminum under Pb stress. Our results showed that high Pb stress increased the activity of peroxidase (POD), the contents of malondialdehyde (MDA) and proline by 80.03 %, 174.46 % and 71.24 %, respectively. Meanwhile, Pb stress decreased the activities of superoxide dismutase (SOD) and catalase (CAT) as well as contents of soluble sugars and GSH, which thus affected the growth of C. cyminum. In addition, Pb stress influenced the accumulation and transport of Pb in C. cyminum. Metabolomic results showed that Pb stress affected eight metabolic pathways involving 108 differentially expressed metabolites, primarily amino acids, organic acids, and carbohydrates. The differentially expressed genes identified through transcriptome analysis were mainly involved the oxidation reductase activity, transmembrane transport, phytohormone signaling, and MAPK signaling pathway. The results of this study will help to understand the molecular mechanisms of C. cyminum response to Pb stress, and provide a basis for screening seeds with strong resistance to heavy metals.

Short-Term Observations of Rainfall Chemistry Composition in Bellsund (SW Spitsbergen, Svalbard)

Global warming results in increasingly widespread wildfires, mostly in Siberia, but also in North America and Europe, which are responsible for the uncontrollable emission of pollutants, also to the High Arctic region. This study examines 11 samples of rainfall collected in August in a coastal area of southern Bellsund (Svalbard, Norway). It covers detailed analysis of major ions (i.e., Cl−, NO3−, and SO42−) and elements (i.e., Cu, Fe, Mn, Pb, and Zn) to Hybrid Single-Particle Langrarian Integrated Trajectory( HYSPLIT) backward air mass trajectories. The research of wildfires, volcanic activities, and dust storms in the Northern Hemisphere has permitted the assessment of their relations to the fluctuations and origins of elements. We distinguished at least 2 days (27 and 28 August) with evident influence of volcanic activity in the Aleutian and Kuril–Kamchatka trenches. Volcanic activity was also observed in the case of the Siberian wildfires, as confirmed by air mass trajectories. Based on the presence of non-sea K (nsK), non-sea sulphates (nss), and Ca (the soil factor of burned areas), the continuous influence of wildfires on rainfall chemistry was also found. Moreover, dust storms in Eurasia were mainly responsible for the transport of Zn, Pb, and Cd to Svalbard. Global warming may lead to the increased deposition of mixed-origin pollutants in the summer season in the Arctic.

Adsorption of Pb(II) by UV-aged microplastics and cotransport in homogeneous and heterogeneous porous media

To investigate the adsorption effects of aged microplastics (MPs) on Pb(II) and their co-transport properties in homogeneous (quartz sand) and heterogeneous (quartz sand with apple branches biochar) porous media, we explored the co-transport of UV-irradiated aged MPs and coexisting Pb(II) along with their interaction mechanisms. The UV aging process increased the binding sites and electronegativity of the aged MPs' surface, enhancing its adsorption capacity for Pb(II). Aged MPs significantly improved Pb(II) transport through homogeneous media, while Pb(II) hindered the transport of aged MPs by reducing electrostatic repulsion between these particles and the quartz sand. When biochar, with its loose and porous structure, was used as a porous medium, it effectively inhibited the transport capacity of both contaminants. In addition, since the aged MPs cannot penetrate the column, a portion of Pb(II) adsorbed by the aged MPs will be co-deposited with the aged MPs, hindering Pb(II) transport to a greater extent. The transport experiments were simulated and interpreted using two-point kinetic modeling and the DLVO theory. The study results elucidate disparities in the capacity of MPs and aged MPs to transport Pb(II), underscoring the potential of biochar application as an effective strategy to impede the dispersion of composite environmental pollutants.

Electron transport and thermoelectric properties in (Pb,Ho)-modified Ca0.5Sr0.5MnO3−δ manganites with perovskite-type structure

Doped calcium manganite perovskites CaMnO3−δ which constitute some of the most promising materials for all-oxide thermoelectric generators for conversion of heat to electricity operating in air over a wide temperature range have been modified by Sr–Pb–Ho co-doping. The Ca0.5Sr0.45−xPb0.05HoxMnO3−δ samples (x = 0.05, 0.10, 0.15 and 0.20) synthesized by the citrate-nitrate method of precursor preparation are shown to have an orthorhombic crystal structure (space group Pbnm) at room temperature. The relationship between temperature, concentration of donor ions, Jahn-Teller distortions and energy parameters of carrier formation and mobility that affect the thermoelectric properties of electron-doped manganites has been studied. The temperature-activated nature of the electrical conductivity (σ) was revealed to be consistent with the adiabatic mechanism of small-radius polaron transport. The increase in the absolute values of the Seebeck coefficient (S) with rising temperature and the decrease in σ above 500 K are attributed to the decrease in the concentration of Mn3+ ions due to their disproportionation into Mn2+ and Mn4+ ions. The equilibrium constants of the disproportionation reaction, carrier concentration and mobility have been derived from the temperature dependencies of S(T) and σ(T) in the conditions when δ ≈ 0. The best values of power factor (S2σ) and dimensionless thermoelectric figure-of-merit (ZT = S2σT/κ) have been found at the substitution level x = 0.15.

Interaction and Transport Characteristics of Lead and Cadmium in Different Soil-wheat Systems

In this study, four groups of lead(Pb) and cadmium(Cd) combined treatments with different concentration ratios were set up in Hailun black soil, Xianning brown-red soil, and Changwu Heilu soil, and wheat(Zhengmai 9023) was planted for a five-month pot experiment to analyze the Pb-Cd interaction behavior on heavy metal bioaccumulation in wheat under three soil-wheat systems. The low pH brown-red soil had the highest water-soluble Cd and Pb contents with significant Pb-Cd interactions in the soil, whereas the black soil with high organic matter and Heilu soil with high calcium carbonate content exhibited lower Cd and Pb activities. Among the three soils, wheat height and dry weight showed the poorest growth performance in the Heilu soil, but the wheat height increased by 2.68-8.49 cm compared with that in the control under the Pb-Cd combined treatment, whereas Pb-Cd interaction had the least effect on wheat height and dry weight in black soil and inhibited the growth of wheat in the brown-red soil. In the transport process of Cd or Pb in wheat, Pb-Cd interaction showed quite different effects in the three soil-wheat systems. Under the 125 mg·kg-1 and 250 mg·kg-1 Pb treatments, the Pb content in wheat grain planted in brown-red soil significantly increased by 73.2% and 19.1% with the addition of Cd, respectively, and therefore there was a synergistic effect between Pb and Cd. Under the 0.3 mg·kg-1 and 0.6 mg·kg-1 Cd treatments, the Cd content in wheat grains planted in black soil decreased by 51% and 33% with the addition of Pb, respectively; therefore, there was an antagonist effect between Pb and Cd. In the Heilu soil, a synergistic effect of Cd on Pb transport in wheat leaves was only observed under high Pb treatment. Therefore, pH and organic matter content were the key factors that determined the interaction behavior of Pb and Cd. The wheat food security risk of Pb and Cd combined pollution was higher than that of single metal pollution in acidic brown-red soil and lower in high organic matter black soil, whereas the interaction of Pb and Cd had little impact on the wheat food security risk of alkaline Heilu soil.

Global patterns and drivers of lead concentration in inland waters

Water bodies are important carriers for lead (Pb) biogeochemical cycling, which is a key pathway of Pb transport. Although existing studies on Pb loading in inland waters have developed rapidly, a quantitative assessment of the distribution patterns and drivers of Pb concentration in inland waters at the global scale remains unclear. Here, by analyzing 1790 observations collected from 386 independent publications, we assessed the spatial distribution and drivers of Pb concentration in inland waters worldwide. We found that (1) globally, the median of Pb concentration in inland waters was 5.81 μg L−1; (2) among different inland water types, Pb concentration was higher in rivers, and the highest Pb concentration was in industrial land in terms of land use type; (3) Pb concentration in inland waters were positively driven by potential evapotranspiration, elevation and road density; and (4) Pb concentration showed a negative relationship with absolute latitude, decreasing from tropic to boreal regions. Overall, our global assessment of the patterns and drivers of Pb concentration in inland waters contributed to a better understanding of the natural and anthropogenic attributions of Pb in the inland hydrological cycling.

Multiphysics Modeling for Solid Oxide Electrolyzer Cell with Heterogenous Synthetic Microstructure

Solid oxide fuel cell (SOFC) and electrolyzer cell (SOEC) are the main focus for researchers in recent times to diminish greenhouse gas emissions and meet cleaner energy demand, as these devices have highest energy conversion rates and efficiencies [1]. The major hinderance in commercializing SOEC is due to its faster cell degradation under higher current density, compared against its SOFC counterpart. The delamination of oxygen electrode (OE) from the electrolyte (EL) is one of the major causes for the cell degradation [2].We employed a multi-physics numerical model to understand the electrochemical performance of a SOEC half-cell more precisely at a microscale. In this study, widely used mixed ionic and electronic conductor (MIEC) La1-xSrxCo1-yFeyO3-d (LSCF) and Gadolinium-doped Ceria (GDC) composite is used as the oxygen electrode and, pure ionic conductor 8 mol% Y2O3 doped ZrO2 (YSZ) is used as the electrolyte. A GDC buffer layer is tucked in between to prevent undesirable side reactions between OE and EL during long term polarization operation. Until now, a homogenous OE structure has commonly been used with effective physicochemical properties to predict the performance of SOFC/SOEC [3,4]. Only a few researchers have worked on heterogenous microstructure model [5] and simulated the electrochemical performance of the cell.Synthetic microstructure of LSCF-GDC porous electrode as shown in Figure 1 are constructed with an opensource software Dream 3D with particle size ranging from 0.45um - 1.5um. We developed in-house Matlab code for labelling domains, interfaces (2PB and 3PB) and digitally removing the unconnected phases to reduce numerical instabilities while solving the mathematical model in COMSOL Multiphysics 6.0. Mesh in these domains is constructed using Iso2Mesh toolbox [6] and translated as mphtxt file which is later imported into COMSOL. This practice reduces the computational time and memory.We employed Nernst-Planck theory for solving the transport of species like vacancy, hole and electron within LSCF inside OE. Multi-step charge transfer at two phase boundary (2PB) and triple phase boundary (3PB) interfaces for oxygen evolution reaction are formulated by Butler-Volmer expressions [4]. A physics-based impedance model under DC bias is developed to separate the electrochemical contributions from 2PB and 3PB transport pathways. The voltage-current curve during long-term polarization test is coupled with the model for validation and approximation of process parameters. Furthermore, we will simulate the crack propagation at OE-buffer layer interface in various directions and orientations to understand the failure mechanism on the synthetically constructed microstructure.

Proteomic profiles and leaf antioxidative metabolism in cacao juvenile plants subjected to Pb and Pb+Fe doses and to soil flooding

Under natural conditions, plants can be affected by several types of abiotic stresses, such as flooding and the accumulation of toxic metals in the soil. Pb is a non-essential metallic element for plants and is highly toxic for living beings. Fe, as an essential micronutrient, is involved in fundamental plant processes, such as photosynthesis. The main objective of this work was to evaluate the proteomic profiles and the activity of key enzymes of leaf antioxidant metabolism in juvenile plants of the CCN 51 cacao genotype, grown in flooding soil and subjected to a dose of Pb and to different equimolar doses of Pb+Fe. Doses of Pb and Pb+Fe did not interfere with the predawn leaf water potential (ΨWL) of plants, but soil flooding was a key factor for the decline of ΨWL. There was a differential accumulation of Pb and Fe in the roots and leaves, both in flooded soil and non-flooded. Most of Fe and Pb uptake by the root system predominantly accumulated in the roots and only a small fraction was translocated to the shoot, regardless of the water content in the soil. Flooding and the variation of Pb+Fe doses in the soil did not change the transport of Pb to the plant shoot since there were no major alterations in the levels of Pb in the leaves. Leaf enzymatic antioxidant metabolism was altered, mainly by flooding, in relation to Pb or Pb+Fe doses applied in soil. The time of exposure of plants to stressor factors was important for the changes in the activity of key enzymes of the leaf antioxidant metabolism. Soil flooding, with doses of 2 mmol Pb kg−1 soil + 0.5 mmol Fe kg−1 soil, at 6 and 24 h after treatment application, had a greater influence on ΨWL, antioxidant enzymatic metabolism and leaf proteome, and affected proteins related to photosynthesis, DNA, antioxidative system and carbohydrate metabolism, whose abundance was overexpressed or repressed compared to the control.

Co-transport behavior and Trojan-horse effect of colloidal microplastics with different functional groups and heavy metals in porous media

The emerging global problems of microplastics pollution and their co-occurrence with other pollutants have presented major new challenges for environmental health and protection. This study used column experiments to investigate the co-transport behavior and Trojan-horse effect of colloidal microplastics (non-functional polystyrene microspheres (MS), carboxyl-modified polystyrene microspheres (CMS) and sulfonate-modified polystyrene microspheres (SMS)) and lead (Pb) in porous media. Results showed that a Trojan-horse effect occurred during the co-transport of colloidal microplastics and Pb. In the process of co-transport, colloidal microplastics and Pb mutually inhibited each other’s transport at an ionic strength of 1 mM, which may be due to Pb absorption by microplastics, resulting in the destabilization of agglomerates and a reduction in the electronegativity of microplastics. At an ionic strength of 100 mM, colloidal microplastics and Pb promoted each other’s transport, potentially due to their competition for adsorption in porous media. The functional groups present on colloidal microplastics inhibited the transport of Pb at low ionic strengths, while at high ionic strengths Pb transport was promoted. Furthermore, deposition experiments verified that quartz crystal microbalance with dissipation (QCM-D) monitoring could effectively account for and predict the transport and deposition behavior of microplastics in the presence or absence of Pb.

Isotopes illustrate vertical transport of anthropogenic Pb by reversible scavenging within Pacific Ocean particle veils

Reversible scavenging, the oceanographic process by which dissolved metals exchange onto and off sinking particles and are thereby transported to deeper depths, has been well established for the metal thorium for decades. Reversible scavenging both deepens the elemental distribution of adsorptive elements and shortens their oceanic residence times in the ocean compared to nonadsorptive metals, and scavenging ultimately removes elements from the ocean via sedimentation. Thus, it is important to understand which metals undergo reversible scavenging and under what conditions. Recently, reversible scavenging has been invoked in global biogeochemical models of a range of metals including lead, iron, copper, and zinc to fit modeled data to observations of oceanic dissolved metal distributions. Nonetheless, the effects of reversible scavenging remain difficult to visualize in ocean sections of dissolved metals and to distinguish from other processes such as biological regeneration. Here, we show that particle-rich "veils" descending from high-productivity zones in the equatorial and North Pacific provide idealized illustrations of reversible scavenging of dissolved lead (Pb). A meridional section of dissolved Pb isotope ratios across the central Pacific shows that where particle concentrations are sufficiently high, such as within particle veils, vertical transport of anthropogenic surface-dissolved Pb isotope ratios toward the deep ocean is manifested as columnar isotope anomalies. Modeling of this effect shows that reversible scavenging within particle-rich waters allows anthropogenic Pb isotope ratios from the surface to penetrate ancient deep waters on timescales sufficiently rapid to overcome horizontal mixing of deep water Pb isotope ratios along abyssal isopycnals.

Endocytosis-Mediated Transport of Pb in Rat Blood Cells.

Blood is an important reservoir for Pb storage in living organisms, and the storage of Pb in blood cells inhibits its discharge from blood. However, the mechanism and molecular targets of Pb entry and exit from blood cells have not been elucidated, which is the major barrier to reducing blood Pb levels in normal human beings. In this study, we explored the effect of Pb-binding proteins on blood Pb levels in rats at environmentally relevant concentrations (0.32 μg/g) by identifying the functions of Pb-binding proteins and validating them with inhibitors. The results showed that Pb-binding proteins in blood cells were mainly related to phagocytosis, while in plasma, they were mainly involved in the regulation of endopeptidase activity. Meanwhile, at the normal population Pb levels, endocytosis inhibitors, endopeptidase activity inhibitors, and coadministration of both can reduce the level of Pb in MEL (mouse erythroleukemia cells) cells by up to 50, 40, and 50%, respectively, while in rat blood, the reduction can reach up to 26, 13, and 32%, respectively. Collectively, these findings reveal that endocytosis increases blood Pb levels and provides a possible molecular target for Pb excretion at ambient concentrations.

Electrokinetic-Assisted Phytoremediation of Pb-Contaminated Soil: Influences of Periodic Polarity Reversal Direct Current Field

The effect of electric stimulation on the phytoremediation of Pb-contaminated soil by tall fescue and wheat seedlings was investigated by monitoring the time-dependent changes in soil properties and Pb accumulation in plants with or without a direct current (DC) exchange field. The results showed that plants could strengthen electrical conductivity (EC) and current in the soil environment. The periodic exchange electrode helped maintain a stable soil pH. Electric stimulation enhanced phytoremediation efficiency, and the enhancement effect increased with plant growth. Compared with the treatments without a DC exchange electric field, the Pb content in plots with tall fescue and wheat seedlings under DC exchange electric field increased 107–250.6% and 32.7–84.4%, respectively, after 30 d of planting. DC exchange electric field significantly increased the Pb enrichment coefficient of tall fescue and wheat seedlings. The upward transport of Pb from wheat seedling roots to shoots was greatly promoted by electric stimulation for 18 d. However, Pb transport in both plants was restrained after 18 d of electric stimulation. Additionally, DC exchange electric stimulation can improve the phytoremediation of heavy-metal-contaminated soil. More attention should be paid to the selection and testing of promising hyperaccumulators for electrokinetic-assisted phytoremediation of Pb-contaminated soil.