Hybrid and enhanced electrokinetic system for soil remediation from heavy metals and organic matter.

The electrokinetic (EK) process has been proposed for soil decontamination from heavy metals and organic matter. The advantages of the EK process include the low operating energy, suitability for fine-grained soil decontamination, and no need for excavation. During the last three decades, enhanced and hybrid EK systems were developed and tested for improving the efficiency of contaminants removal from soils. Chemically enhanced-EK processes exhibited excellent efficiency in removing contaminants by controlling the soil pH or the chemical reaction of contaminants. EK hybrid systems were tested to overcome environmental hurdles or technical drawbacks of decontamination technologies. Hybridization of the EK process with phytoremediation, bioremediation, or reactive filter media (RFM) improved the remediation process performance by capturing contaminants or facilitating biological agents' movement in the soil. Also, EK process coupling with solar energy was proposed to treat off-grid contaminated soils or reduce the EK energy requirements. This study reviews recent advancements in the enhancement and hybrid EK systems for soil remediation and the type of contaminants targeted by the process. The study also covered the impact of operating parameters, imperfect pollution separation, and differences in the physicochemical characteristics and microstructure of soil/sediment on the EK performance. Finally, a comparison between various remediation processes was presented to highlight the pros and cons of these technologies.

Enhanced bioremediation of soils contaminated with nicosulfuron using the bacterial complex A12.

AIMS: To construct an efficient bacterial complex to degrade nicosulfuron and clarify its degradative characteristics, promote the growth of maize (Zea mays), and provide a theoretical foundation for the efficient remediation of soil contaminated with nicosulfuron. METHODS AND RESULTS: Biocompatibility was determined by the filter paper sheet method by mixing Serratia marcescens A1 and Bacillus cereus A2 in a 1:1 ratio, yielding A12. The optimum culture conditions for the bacterial composite were obtained based on a three-factor, three-level analysis using response surface methodology, with 29.25 g L-1 for maltodextrin, 10.04 g L-1 for yeast extract, 19.93 g L-1 for NaCl, which resulted in 92.42% degradation at 4 d. The degradation characteristics of A12 were clarified as follows: temperature 30°C, pH 7, initial concentration of nicosulfuron 20 mg L-1, and 4% inoculum. The ability to promote growth was determined by measuring the ratio of the lysosphere diameter (D) to the colony diameter (d), and the ability of the complex A12 to promote growth was higher than that of the two single strains. CONCLUSION: Nicosulfuron degradation in sterilized and unsterilized soils reached 85.4% and 91.2% within 28 d, respectively. The ability of the strains to colonize the soil was determined by extraction of total soil DNA, primer design, and gel electrophoresis. The bioremediation effect of A12 was confirmed by the maximum recovery of fresh weight (124.35%) of nicosulfuron-sensitive crop plants and the significant recovery of soil enzyme activities, as measured by the physiological indices in the sensitive plants.

Biochar-mediated bioremediation: a sustainable strategy to increase Avena sativa L. tolerance to crude oil soil contamination.

The present work investigated the effects of different doses of biochar (2.5%, 5%, 10%), a by-product of the pyrolysis of woody biomass, on the growth of oat plants (Avena sativa L., cv "Danko") grown under different crude oil concentrations (0.5%, 1%, 2%, 3%, 6%) added to the soil, evaluating both biometric (i.e. fresh weight) and biochemical (i.e., content of malondialdehyde and proline, and total antioxidant power) parameters. The findings indicate that biochar positively influences the fresh weight of oat plants across all concentrations of crude oil investigated. On the other hand, regarding oxidative stress, measured by malondialdehyde and proline content, biochar led to a significant reduction, with statistical significance observed at biochar concentrations > 2.5% and crude oil levels > 2% (malondialdehyde: ranging from -25% to -38%; proline ranging from -33% to -52%). Soil amendment with biochar increased the total antioxidant power, particularly at biochar concentrations > 2.5% and crude oil levels > 2% (ranging from + 20% to + 98%). These results suggest that biochar has a great potential in mitigating the negative effects of crude oil contamination on plant growth and oxidative stress levels, thereby highlighting its value as a conditioner in contaminated soils.

Biochar from Co-Pyrolyzed Municipal Sewage Sludge (MSS): Part 2: Biochar Characterization and Application in the Remediation of Heavy Metal-Contaminated Soils.

The disposal of municipal sewage sludge (MSS) from wastewater treatment plants poses a major environmental challenge due to the presence of inorganic and organic pollutants. Co-pyrolysis, in which MSS is thermally decomposed in combination with biomass feedstocks, has proven to be a promising method to immobilize inorganic pollutants, reduce the content of organic pollutants, reduce the toxicity of biochar and improve biochar's physical and chemical properties. This part of the review systematically examines the effects of various co-substrates on the physical and chemical properties of MSS biochar. This review also addresses the effects of the pyrolysis conditions (temperature and mixing ratio) on the content and stability of the emerging pollutants in biochar. Finally, this review summarizes the results of recent studies to provide an overview of the current status of the application of MSS biochar from pyrolysis and co-pyrolysis for the remediation of HM-contaminated soils. This includes consideration of the soil and heavy metal types, experimental conditions, and the efficiency of HM immobilization. This review provides a comprehensive analysis of the potential of MSS biochar for environmental sustainability and offers insights into future research directions for optimizing biochar applications in soil remediation.

Use of phytoextraction with Noccaea caerulescens to limit the transfer of cadmium and zinc to subsequent rocket crops.

Soil trace metal (TM) contamination is a worldwide issue and threatens food production and security. Remediation of cadmium (Cd) and zinc (Zn) contaminated soils by phytoextraction with the Zn/Cd hyperaccumulator Noccaea caerulescens is widely studied but few studies have investigated the efficiency of this technique to reduce Cd and Zn soil-to-crop transfers to subsequent vegetable crops. The vegetable biomonitor rocket Diplotaxis tenuifolia was grown in pots on 13 moderately contaminated soils that had previously been cropped with N. caerulescens. Using mixed-effects models, we show the drivers of rocket biomass, Cd and Zn concentrations. Our models show, for our study soils, the benefit of previous N. caerulescens uptake of Cd and Zn in decreasing Cd and Zn concentrations in a subsequent rocket crop. We also show a slight positive impact of N. caerulescens biomass (and therefore uptake) on rocket growth. Our data show that exchangeable soil concentrations are major drivers of Cd and Zn rocket concentrations. Other soil variables negatively driving rocket Cd and Zn concentrations are NO3- content, organic matter content, cation exchange capacity, and soil manganese which stimulate rocket biomass and/or influence TM bioavailability. Rocket D. tenuifolia seems to be a good biomonitor for contaminated soils as it is tolerant to relatively high TM soil concentrations. We demonstrate that 40 % of rockets grown on soils below 2 mg total Cd kg-1 dry soil have foliar Cd concentrations above the European maximum allowed level confirming the need to review soil legal thresholds to protect consumers' health. In conclusion, our study suggests promising use of N. caerulescens phytoextraction for bioavailable contaminant stripping which is all the more interesting given the increasing demand for urban growing spaces.

Investigation of the effects of biochar amendment on soil under freeze‒thaw cycles and the underlying mechanism.

Biochar (BC) is widely utilized as a soil amendment; however, for widely distributed seasonally frozen soils, the effect of BC on soil and the optimal utilization of BC during the freeze‒thaw process are still unclear. In this study, the effects of freeze‒thaw aged biochar (FT-BC) and BC on soil properties and wheat cultivation were systematically investigated, and the underlying interaction mechanism between BC and soil was explored. The results show that FT-BC dramatically reduces the adverse effects of freeze‒thaw cycles on soil, enhances wheat growth, and increases dry matter yield by 17.5 %, which is mainly attributed to the ability of FT-BC to maintain soil structure, reduce water loss rates to below 0.20 g/h, and decrease nitrogen leaching by more than 20 % during freeze‒thaw cycles. Additionally, fresh BC had a greater effect on the fixation of cadmium than FT-BC in the soil, reducing its accumulation in wheat by 22.5 %. Multiple characterizations revealed that the freeze‒thaw process increased the porosity and specific surface area of FT-BC, providing more sites for water and nitrogen adsorption, whereas the dissolved organic matter released from fresh BC had a better ability to trap cadmium. These findings provide insights into the interactions between BC and soil components during the freeze‒thaw process and suggest the optimized utilization of fresh BC and FT-BC for different soil repair purposes.

Design and construction of magnetic nanomaterials and their remediation mechanisms for heavy metal contaminated soil.

Soil heavy metal pollution poses huge threat to ecosystem and human health. In-situ chemical remediation aims to immobilize free heavy metals in soil through adding passivators, thereby greatly reducing the mobility and bioavailability of heavy metals. Magnetic nanomaterials (MaN) have strong adsorption and immobilization capabilities for heavy metals due to their significant surface effects, small size effects and interfacial effects. Compared with traditional remediation materials, MaN can be recovered and reused using external magnetic fields. These advantages give MaN broad application prospects in the field of soil remediation. This work provides a comprehensive review of the application of MaN in heavy metal contaminated soil, including the design and application effect of various types of MaN, the influence of MaN on soil properties, environmental toxicity, and microbial composition, the in-situ remediation mechanism of MaN on heavy metal contaminated soil. On the other hand, there are potential risks associated with the remediation of heavy metal contaminated soil using MaN, including their impact on the soil ecosystem and biosafety concerns, requiring further research. Finally, this review proposes the future prospects for the application of MaN in the remediation of heavy metal polluted soil.

Effective and green in-situ remediation strategies based on TEMPO-nanocellulose/lignin/MIL-100(Fe) hydrogel nanocomposite adsorbent for lead and copper in agricultural soils.

Hydrogel adsorbents are promising tools for reducing heavy metals' bioavailability in contaminated soil. However, their practical feasibility remains limited by the low stability, inefficient removal efficiency, and potential secondary pollution. Optimizing the adsorption operation and the functional properties of hydrogel adsorbents could eliminate this method's drawbacks. Herein, three innovative in-situ remediation strategies for Pb/Cu-contaminated soil were adopted based on the concept of novel TEMPO-cellulose (TO-NFCs)/lignin/acrylamide@MIL-100(Fe) nanocomposite hydrogel adsorbent (NCLMH). Characteristic analyses revealed ideal Pb/Cu adsorption mechanisms by swelling, complexation, electrical attraction, and ion exchange via carboxyl/hydroxyl/carbonyl groups and unsaturated Fe(III) sites on ANCMH besides FeOOH formation. The highest maximum theoretical adsorption capacities of Pb(II) and Cu(II) on ANCMH were 416.39 and 133.98 mg/g, under pH 6.5, governed by pseudo-second-order/Freundlich models. Greenhouse pot experiments with contaminated soils amended with two-depth layers of 0.5% NCLMHs (SA@NCLMH) displayed a decline in Pb and Cu bioavailability up to 85.9% and 74.5% within 45 d. Soil column studies simulating continuous water soil flushing coupled with NCLMH layers, instead of conventional extractant fluids, and connected to NCLMH-sand column as purification unit (CF@NCLMH) achieved higher removal rates for Pb, and Cu of 89.5% and 77.2% within 24 h. Alternatively, conducting multiple-pulse soil flushing mode (MF@NCLMH) gained the highest Pb and Cu removal of 96.5% and 85.4%, as the water flushing-stop flux events allowed adequate water movement/residence period, promoting Pb/Cu desorption-adsorption from soil to NCLMH. Also, the NCLMH-sand column conducting and easy separation of the stable/reusable NCLMHs prevented the potential secondary pollution. Interestingly, the three remediated soils reached the corresponding regulation of the permissible limits for Pb and Cu residential scenarios in medium-to-heavily agricultural polluted soils, alleviating the Pb/Cu bioaccumulation and phytotoxicity symptoms in cultivated wheat, especially after MF@NCLMH treatment. This study introduces promising alternative remediation strategies with high sustainability and feasibility in acidic-to-neutral heavy metal-contaminated agricultural soil.

Impacts of farmland decontamination on 137Cs transfers in rivers after Fukushima nuclear accident: Evidence from a retrospective sediment core study.

Following the Fukushima Daiichi Nuclear Power Plant disaster in March 2011, the Japanese government initiated an unprecedented decontamination programme to remediate 137Cs-contaminated soils and allow population return. This programme involved the removal of topsoil under farmland and residential land, and its replacement with "fresh soil" composed of granitic saprolite. However, decontamination was limited to these two land uses, without remediating forests, which cover 70 % of the surface area in the affected region. In this unprecedented context, the specific impact of this unique decontamination programme on 137Cs transfers in river systems remains to be quantified at the catchment scale. In this study, based on the analysis of a sediment core collected in June 2021 in the Mano Dam reservoir draining a decontaminated catchment, the effects of soil decontamination on particle-bound 137Cs dynamics and sediment source contributions in response to a succession of extreme precipitation events were retrospectively assessed. The sequence of sediment layer deposition and its chronology were reconstructed through the analysis of several diagnostic properties (organic matter, elemental geochemistry, visible colourimetry, granulometry) and contextual information. During abandonment (2011-2016), cropland contribution decreased (31 %). Concurrently, 137Cs activity and deposition flux decreased (19 and 29%year-1, respectively). Following decontamination (2017), sediment transfer increased (270 %) in response to increased contributions from decontaminated cropland and "fresh soil" (625 % and 180 % respectively). Meanwhile, forest contributions remained stable. In contrast, 137Cs activity dropped (65 %), although 137Cs deposition flux remained constant. Forests acted as a stable source of 137Cs. Accordingly, 137Cs deposition flux after decontamination (2016-2021) was similar to that observed during the 5-years period of land abandonment (2011-2016), as a result of the regrowth of spontaneous vegetation over farmland, protecting soil against erosion. Future research should further investigate the impact of longer land abandonment that prevailed in some regions decontaminated lately on the 137Cs fluxes in the rivers.

Mechanistic Implications of the Varying Susceptibility of PAHs to Pyro-Catalytic Treatment as a Function of Their Ionization Potential and Hydrophobicity.

Transition metal catalysts in soil constituents (e.g., clays) can significantly decrease the pyrolytic treatment temperature and energy requirements for efficient removal of polycyclic aromatic hydrocarbons (PAHs) and, thus, lead to more sustainable remediation of contaminated soils. However, the catalytic mechanism and its rate-limiting steps are not fully understood. Here, we show that PAHs with lower ionization potential (IP) are more easily removed by pyro-catalytic treatment when deposited onto Fe-enriched bentonite (1.8% wt. ion-exchanged content). We used four PAHs with decreasing IP: naphthalene > pyrene > benz(a)anthracene > benzo(g,h,i)perylene. Density functional theory (DFT) calculations showed that lower IP results in stronger PAH adsorption to Fe(III) sites and easier transfer of π-bond electrons from the aromatic ring to Fe(III) at the onset of pyrolysis. We postulate that the formation of aromatic radicals via this direct electron transfer (DET) mechanism is the initiation step of a cascade of aromatic polymerization reactions that eventually convert PAHs to a non-toxic and fertility-preserving char, as we demonstrated earlier. However, IP is inversely correlated with PAH hydrophobicity (log Kow), which may limit access to the Fe(III) catalytic sites (and thus DET) if it increases PAH sorption to soil OM. Thus, ensuring adequate contact between sorbed PAHs and the catalytic reaction centers represents an engineering challenge to achieve faster remediation with a lower carbon footprint via pyro-catalytic treatment.

Shifts in Microbial Community Structure and Co-occurrence Network along a Wide Soil Salinity Gradient.

The response of microbiomes to salinity has been clarified in different geographic scales or ecosystems. However, how soil microbial community structure and interaction respond to salinity across wide salinity range and climatic region is still unclearly resolved. To address this issue, we examined the microbial community's composition in saline soils from two climatic regions (coastal wetland and arid desert). Our research confirms that soil salinity had a negative effect on soil nutrient content. Salinity decreased the relative abundance of bacteria, but increased archaea abundance, leading to the shifts from bacteria dominant community to archaea dominant community. Low-water medium-salinity soil (LWMS) had the most complex archaeal community network, whereas for bacteria, the most complex bacterial community network was observed in low-water high-salinity soils (LWHS). Key microbial taxa differed in three salinity gradients. Salinity, soil water content, pH, total nitrogen (TN), and soil organic carbon (SOC) were the main driving factors for the composition of archaeal and bacterial community. Salinity directly affected archaeal community, but indirectly influenced bacteria community through SOC; pH affected archaeal community indirectly through TN, but directly affected bacterial community. Our study suggests that soil salinity dramatically influences diversity, composition, and interactions within the microbial community.

Stabilization of lead (Pb)- and arsenic (As)-contaminated soil using pen shells (Atrina pectinata).

Pen shells (PS), a type of shellfish, are abundantly consumed, and their inedible shell residues are often discarded near the coast without consideration of reutilization. This study sought to investigate the use of natural pen shells (NPS) and calcined pen shells (CPS) to stabilize Pb and As-contaminated soil. During the investigation, NPS and CPS were applied to the contaminated soil in amounts ranging from 1 to 10 wt% and cured for 28 days. After the curing process, the mineral phase was examined through X-ray powder diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) analysis. The XRD and SEM-EDX results revealed the presence of riversideite and ettringite, which contribute to Pb and As stabilization in the CPS-treated soil. The leachability of Pb and As in the treated soil was further examined with three types of chemical extraction methods. Extraction results using 0.1 M HCl displayed a notable pH fluctuation in the extractant due to the residual amendments (NPS and CPS). The fluctuation resulted in a strong correlation of leached Pb and As with the pH of the extractant, which might hinder an accurate assessment of stabilization. In order to minimize the effect of pH, an EDTA-NH4OAc extraction was employed, suggesting its potential as a suitable assessment method. EDTA-NH4OAc extraction showed a higher effectiveness of CPS than NPS at 10 wt% of input amounts. In the SBET extraction, that uses a strongly acidic solution, a higher As leachability was observed by increasing the addition of CPS, which implied a CPS-related chemical fixation mechanism. The comparison of various extraction methods showed a higher CPS effectiveness as compared to NPS. However, it was recommended that CPS-treated soil required caution in strongly acidic conditions, especially for arsenic. This study explores the applicability of PS, which has not been investigated as an amendment for Pb and As-contaminated soil previously. Furthermore, this study revealed that utilization of various extraction methods is beneficial for gaining a comprehensive understanding of the role of CaCO3-based amendment in Pb and As-contaminated soil.

Planting halophytes increases the rhizosphere ecosystem multifunctionality via reducing soil salinity.

Soil salinization poses a significant global challenge, exerting adverse effects on both agriculture and ecosystems. Planting halophytes has the potential ability to improve saline-alkali land and enhance ecosystem multifunctionality (EMF). However, it remains unclear which halophytes are effective in improving saline-alkali land and what impact they have on the rhizosphere microbial communities and EMF. In this study, we evaluated the Na+ absorption capability of five halophytes (Grubovia dasyphylla, Halogeton glomeratus, Suaeda salsa, Bassia scoparia, and Reaumuria songarica) and assessed their rhizosphere microbial communities and EMF. The results showed that S. salsa possessed the highest shoot (3.13 mmol g-1) and root (0.92 mmol g-1) Na+ content, and its soil Na+ absorption, along with B. scoparia, was significantly higher than that of other plants. The soil pH, salinity, and Na+ content of the halophyte rhizospheres decreased by 6.21%, 23.49%, and 64.29%, respectively, when compared to the bulk soil. Extracellular enzymes in the halophyte rhizosphere soil, including α-glucosidase, ß-glucosidase, ß-1,4-N-acetyl-glucosaminidase, neutral phosphatase, and alkaline phosphatase, increased by 70.1%, 78.4%, 38.5%, 79.1%, and 64.9%, respectively. Furthermore, the halophyte rhizosphere exhibited higher network complexity of bacteria and fungi and EMF than bulk soil. The relative abundance of the dominant phyla Proteobacteria, Firmicutes, and Ascomycota in the halophyte rhizosphere soil increased by 9.4%, 8.3%, and 22.25%, respectively, and showed higher microbial network complexity compared to the bulk soil. Additionally, keystone taxa, including Muricauda, Nocardioides, and Pontibacter, were identified with notable effects on EMF. This study confirmed that euhalophytes are the best choice for saline-alkali land restoration. These findings provided a theoretical basis for the sustainable use of saline-alkali cultivated land.

Impact of biochar produced at different pyrolysis conditions on heavy metal contaminated soil.

This study aimed to assess the effectiveness of urban derived biochars such as Sugarcane bagasse (SB), Brinjal Stem (BS), and Citrus Peel (CP) produced at two different pyrolysis conditions (450 and 600 °C for 60 min) for soil heavy metal bioremediation potential. An ex-situ study was conducted to remediate single heavy metal-contaminated SoilRite with lead (Pb), copper (Cu), chromium (Cr) and cadmium (Cd), with biochars applied at different rates. Heavy metal status in soilrite was evaluated using various extraction methods (water-soluble, exchangeable, TCLP (Toxicity Characteristic Leaching Procedure), and PBET (Physiologically Based Extraction Tests)) to determine the biochar treatments' efficacy. The findings show that SB biochar at 450-60 are more effective in immobilizing heavy metals in water-soluble (Cd-100% Pb and Cu-70%), exchangeable (Pb:91%, Cd and Cu by 70-80%) and PBET-extracted forms (Cd-91%, Pb-80%, and Cu-75%), whereas biochar derived from BS (84%) and CP (90%) at 600-60 are more effective in immobilizing TCLP-extracted form of Pb and Cu. Urban derived biochars significantly reduced the toxicity of Pb, Cu, and Cd in various extractable forms and can stabilize and convert them into less accessible forms except for Cr. These extraction methods aid in evaluating environmental risks and influencing remediation strategies for soil heavy metal pollution. Urban biochar, as a cost-effective and eco-friendly solution, significantly solves this issue, facilitating sustainable waste management.

Microbial electrochemical Cr(VI) reduction in a soil continuous flow system.

Microbial electrochemical technologies represent innovative approaches to contaminated soil and groundwater remediation and provide a flexible framework for removing organic and inorganic contaminants by integrating electrochemical and biological techniques. To simulate in situ microbial electrochemical treatment of groundwater plumes, this study investigates Cr(VI) reduction within a bioelectrochemical continuous flow (BECF) system equipped with soil-buried electrodes, comparing it to abiotic and open-circuit controls. Continuous-flow systems were tested with two chromium-contaminated solutions (20-50 mg Cr(VI)/L). Additional nutrients, buffers, or organic substrates were introduced during the tests in the systems. With an initial Cr(VI) concentration of 20 mg/L, 1.00 mg Cr(VI)/(L day) bioelectrochemical removal rate in the BECF system was observed, corresponding to 99.5% removal within nine days. At the end of the test with 50 mg Cr(VI)/L (156 days), the residual Cr(VI) dissolved concentration was two orders of magnitude lower than that in the open circuit control, achieving 99.9% bioelectrochemical removal in the BECF. Bacteria belonging to the orders Solirubrobacteriales, Gaiellales, Bacillales, Gemmatimonadales, and Propionibacteriales characterized the bacterial communities identified in soil samples; differently, Burkholderiales, Mycobacteriales, Cytophagales, Rhizobiales, and Caulobacterales characterized the planktonic bacterial communities. The complexity of the microbial community structure suggests the involvement of different microorganisms and strategies in the bioelectrochemical removal of chromium. In the absence of organic carbon, microbial electrochemical removal of hexavalent chromium was found to be the most efficient way to remove Cr(VI), and it may represent an innovative and sustainable approach for soil and groundwater remediation. Integr Environ Assess Manag 2024;00:1-17. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Compost amendment in urban gardens: elemental and isotopic analysis of soils and vegetable tissues.

Urban horticulture poses a sustainable form of food production, fosters community engagement and mitigates the impacts of climate change on cities. Yet, it can also be tied to health challenges related to soil contamination. This work builds on a previous study conducted on eleven urban gardens in the city of Vienna, Austria. Following the findings of elevated Pb levels in some soil and plant samples within that project, the present study investigates the elemental composition of soil and plants from two affected gardens 1 year after compost amendment. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of skin, pulp and seeds of tomato fruits revealed minor variations in elemental composition which are unlikely to have an impact on food safety. In turn, a tendency of contaminant accumulation in root tips and leaves of radishes was found. Washing of lettuce led to a significant reduction in the contents of potentially toxic elements such as Be, Al, V, Ni, Ga and Tl, underscoring the significance of washing garden products before consumption. Furthermore, compost amendments led to promising results, with reduced Zn, Cd and Pb levels in radish bulbs. Pb isotope ratios in soil and spinach leaf samples taken in the previous study were assessed by multi-collector (MC-) ICP-MS to trace Pb uptake from soils into food. A direct linkage between the Pb isotopic signatures in soil and those in spinach leaves was observed, underscoring their effectiveness as tracers of Pb sources in the environment.

Environmental remediation of emerging contaminants using subcritical water: A review.

The continuous rise of emerging contaminants (ECs) in the environment has been a growing concern due to their potentially harmful effects on humans, animals, plants, and aquatic life, even at low concentrations. ECs include human and veterinary pharmaceuticals, hormones, personal care products, pesticides, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organic dyes, heavy metals (HMs), and others. The world's growing population contributes to the release of many kinds of chemicals into the environment, which is estimated to be more than 200 billion metric tons annually and results in over 9 million deaths. The removal of these contaminants using conventional physical, chemical, and biological treatments has proven to be ineffective, highlighting the need for simple, effective, inexpesive, practical, and eco-friendly alternatives. Thus, this article discusses the utilization of subcritical water oxidation (SBWO) and subcritical water extraction (SBWE) techniques to remove ECS from the environment. Subcritical water (water below the critical temperature of 374.15 °C and critical pressure of 22.1 Mpa) has emerged as one of the most promising methods for remediation of ECs from the environment due to its non-toxic properties, simplicity and efficiency of application. Furthermore, the impact of temperature, pressure, treatment time, and utilization of chelating agents, organic modifiers, and oxidizing agents in the static and dynamic modes was investigated to establish the best conditions for high ECs removal efficiencies.

Performance and mechanistic study of biochar and magnesium-enhanced phytoremediation in cadmium-contaminated soil by alfalfa.

Recently, phytoremediation has been regarded as a green and environment friendly technique to treat metals contaminated soils. Thus, in this study, pot experiments were designed to investigate the combine effects of biochar and magnesium (MPs) to purify cadmium (Cd)-contaminated soils by Medicago sativa L. (alfalfa). The results showed that the combined use of biochar and Mg significantly increased the accumulation of Cd and promoted the transport of Cd from root to shoot in alfalfa, simultaneously. Importantly, the combined use of biochar and Mg could increase the accumulation of Cd in shoot and whole plant (shoot + root) of alfalfa up-to 59.1% and 23.1%, respectively. Moreover, the enhancement mechanism can be analyzed from several aspects. Firstly, the photosynthesis was enhanced, which was beneficial to plant growth. The product of photosynthesis provided energy for uptake and transport of Cd. Meanwhile, its transport in phloem could promote the transport of Cd. Secondly, the enhancement of antioxidant capacity of alfalfa effectively protected the membrane structure of alfalfa, which indicated that Cd could enter alfalfa from the channel on the cell membrane. Lastly, the chemical form of Cd and microbial community structure in soil were changed. Overall, these changes reduced the Cd toxicity in soil, enhanced the resistance capability of alfalfa, increased the Cd uptake by alfalfa and promoted the growth of alfalfa. Thus, the obtained results suggested that the combined use of biochar and Mg is an effective approach to enhance phytoremediation performance for purifying Cd-contaminated soils.

A META analysis on the efficacy of functional materials for soil chromium remediation.

Metallic chromium pollution in soil is widespread, which aroused intensive research in recent decades. In mainstream research, most studies use materials with a reducing ability to adsorb and reduce hexavalent chromium. However, comprehensive analyses and systematic verifications of these different materials are scarce. Therefore, this study conducted a meta-analysis of relevant papers published from 2013 to October 2024 to compare and analyze the performance and usage conditions of some common materials, such as iron-based materials, mineral inorganic materials, organic materials, and layered double hydroxide materials. We synthesized 31 papers for 186 pairwise comparisons and selected the Standardized Mean Difference (SMD) as the appropriate effect size for mean-to-mean comparisons. Fe-based materials had the most stable performance based on its numerous data support, while organic materials had the worst performance. The difference in performance between inorganic mineral materials was the greatest, which was closely related to the selection of components. The difference in the effectiveness of inorganic materials was the greatest, which was closely related to the selection of components and there was room for further improvement. Through further analysis of the impact of environmental factors on material performance, it can be concluded that the effect of the material was better under alkaline, non-sandy, low organic matter, and high CEC soil conditions.

Miscanthus sp. root exudate alters rhizosphere microbial community to drive soil aggregation for heavy metal immobilization.

The heavy metals (HMs) spatial distribution in soil is intricately shaped by aggregation processes involving chemical reactions and biological activities, which modulate HMs toxicity, migration, and accumulation. Pioneer plants play a central role in preventing HMs at source, yet the precise mechanisms underlying their involvement in soil aggregation remain unclear. This study investigates HMs distribution within rhizosphere and bulk soil aggregates of Miscanthus sp. grown in tailings to elucidate the impact of root exudates (REs) and rhizosphere microbes. The results indicate that Miscanthus sp. enhance soil stability, increasing the proportion of macroaggregates by 4.06 %-9.78 %. HMs tend to concentrate in coarse-aggregates, particularly within rhizosphere environments, while diminishing in fine-aggregates. Under HMs stress, lipids and lipid-like molecules are the most abundant REs produced by Miscanthus sp., accounting for under up to 26.74 %. These REs form complex with HMs, promoting microaggregates formation. Charged components such as sugars and amino acids further contribute to soil aggregation. REs also regulates rhizosphere bacteria and fungi, with Acidobacteriota, Chloroflexi were the dominant bacterial phyla, while Ascomycota and Basidiomycota dominate the fungal community. The synergistic effect of REs and microorganisms impact soil organic matter and nutrient content, facilitating HMs nanoparticle heteroaggregation and macroaggregates formation. Consequently, soil structure and REs shape the distribution of HMs in soil aggregation. Pioneer plants mediate REs interaction with rhizosphere microbes, promoting the distribution of HMs into macroaggregates, leading to immobilization. This study sheds light on the role of pioneer plants in regulating soil HMs, offering valuable insights for soil remediation strategies.