Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences

The potential degradability of persistent organic pollutants (POPs) in soil: a perspective from soil aggregates

Aggregates are the fundamental units of soil structure. Clarifying the distribution characteristics of soil organic carbon (SOC), microbial properties (e.g. microbial abundance/diversity, soil enzyme composition/activity) and persistent organic pollutants (POPs) in soil aggregates, along with influencing factors such as aggregate size, specific surface area (SSA), and nutrient content, is crucial for grasping POPs degradation mechanisms in soil. This study reviewed existing literature and identified that SOC mainly accumulated in 0.25-2 mm aggregates, then >2 mm, 0.053-0.25 mm, and <0.053 mm ones. Meta-analysis revealed that microbial abundance and diversity were significantly lower in >2 mm aggregates (p < 0.05), with no difference in the other three. Soil enzyme activities did not show significant variations across different aggregates. Soil nutrients exerted the most pronounced influence on microbial communities within the 0.25-2 mm aggregates whereas the enzyme activities were prominent within the <0.053 mm and >2 mm aggregates, with a generally positive effect. PAHs are mainly distributed in <0.053 mm fractions. For different types of POPs, their distribution in the soil is closely related to their own species characteristics, while their content in aggregates shows a significant positive correlation with SOC and SSA. The heterogeneity in SOC, microbial properties, and POPs distribution increased POPs degradation complexity. Our study provides a basis for understanding POPs environmental behavior and insights for soil remediation. Future research should focus on the interaction mechanisms among nutrients, pollutants, and microbial properties at the aggregate scale to lay the foundation for soil remediation strategies.

Assessing the phytotoxicity of emerging pollutants on vegetable crops grown with sewage effluent

The use of sewage effluent in agriculture introduces a variety of emerging contaminants-including nanomaterials, surfactants, cosmetic products, endocrine-disrupting chemicals (EDCs), flame retardants (FRs), antibiotic resistance genes (ARGs), personal care products (PCCPs), antibiotics, pesticides, and micro(nano)plastics (MNPs)-into agroecosystems, posing significant risks to crop safety and human health. This review assesses the phytotoxicity of these pollutants on vegetable crops, emphasizing their detrimental effects on plant physiology, nutritional quality, and long-term soil health. We explore multifaceted mechanisms driving contaminant uptake and bioaccumulation, such as direct cellular translocation, endocytosis, rhizosphere interactions, molecular mimicry of transporters etc. To address these challenges, we have also proposed integrated remediation strategies and cross-cutting techniques, including bioaugmentation with tailored microbial consortia, advanced oxidation processes, phytoremediation CRISPR-engineered microbes for targeted degradation etc. By synthesizing physiological, molecular, and ecological insights, this work provides a roadmap for mitigating contamination risks, enhancing food safety, and promoting sustainable agricultural practices in sewage-impacted systems.

Assembling Hexahedral Supramolecular Nano-Aggregates on Rice Wax Layer Matrices to Promote the Leaf Deposition and Bioavailability of Bactericides for Plant Protections

Naturally hydrophobic wax layer microstructures in plants seriously hinder the leaf adhesion and deposition of pesticide droplets, thereby causing low pesticide bioavailability and inevitable environmental pollution. Inspired by the supramolecular self-assembly strategy, two anisotropic supramolecular building units (BiTA18@β-CD and BiTA18@γ-CD) are invented based on the host-guest complexation between a benzimidazole-modified bactericidal molecule (BiTA18) and β-/γ-cyclodextrin (β-CD/γ-CD), which self-assemble into nano-sized hexagonal cuboids on the rice microcrystalline matrix. This consequence markedly enhances the retention of bactericidal ingredients on target plants. More intriguingly, these oligosaccharide-coated supramolecular materials, with superior biocompatibility, can break through the bacterial biofilm barrier, limit bacterial motility and extracellular enzyme secretion, and induce electrolyte leakage and ROS accumulation in bacteria, ultimately annihilating the stubborn pathogenic bacterium. Combining these excellent advantages, the optimal supramolecular material (BiTA18@β-CD) displays broad-spectrum and efficient control efficacies of 54.4% and 71.7% against rice bacterial blight and citrus bacterial canker, respectively, surpassing those of kasugamycin (34.3%/34.1%), thiodiazole-copper-20%SC (39.9%/42.7%), and BiTA18 (42.7%/46.9%) at 200 µg mL-1. Besides, the current supramolecular systems are safe for non-target organisms like earthworms and zebrafishes. This study provides a key inspiration for the construction of supramolecular building units assembled on rice microcrystalline substrates to improve the utilization of pesticides.

Ultrastable Agrochemical Emulsions Designed by Electrostatic Entanglement of Cellulose Nanocrystals and Partially Cation-Substituted Hyaluronate

Global reliance on synthetic surfactants has led to significant environmental challenges, with current management and policy efforts proving to be largely ineffective. Sustainable and environment-friendly surfactants offer a promising solution for mitigating these impacts. This study introduces an emulsifier composed of cellulose nanocrystals (CNCs) and partially cation-substituted hyaluronate (CHA), both of which are derived from abundant and cost-effective natural polysaccharides. The synergistic interplay of electrostatic interactions and controlled molecular entanglement between these macromolecules significantly enhances the stability and ripening resistance of the water-in-oil emulsion. This optimized formulation demonstrates remarkable longevity, maintaining emulsion integrity for over 365 days while exhibiting exceptional salt tolerance and pH stability across various environmental conditions. Additionally, this entangled polysaccharide-based Pickering emulsion demonstrates strong adhesion to leaf surfaces, resisting the effects of strong winds and the water-repellent properties of the lotus leaves. These characteristics associated with microbial compatibility suggest that emulsifiers based on CNCs and CHA provide safer and more sustainable alternatives to conventional surfactants, especially pertinent to the agrochemical sector.

Microfluidic Study on Green Remediation of Nonaqueous Phase Liquid (NAPL) Contamination in Heterogeneous Groundwater Systems Using Dihydrolevoclucosenone (Cyrene)

One of the primary challenges in conventional remediation of nonaqueous phase liquid (NAPL) contamination in groundwater is the heterogeneous nature of the groundwater system. Conventional remediation agents are often carried away by groundwater flow in high-permeability layers, making it difficult to access NAPL contaminants in low-permeability layers and are prone to generate secondary contamination. This study explores the use of dihydrolevoclucosenone (Cyrene), a bioderived green solvent, as an alternative to traditional remediating agents for NAPL remediation. Through microfluidic experiments and accompanying numerical modeling, we demonstrate that Cyrene enhances the dissolution and mobilization of NAPL contaminants, particularly in low-permeability zones, achieving residual NAPL reductions of up to 80% compared with water and Tween 80 solutions. These findings underscore Cyrene's dual environmental benefits as an eco-friendly solvent for both treating solid waste (e.g., stalks) and for NAPL remediation, paving the way for sustainable and green solutions in environmental management.

Potential bacterial resources for bioremediation of organochlorine pesticides and flame retardants recognized from forest soil across China

Microbe-mediated remediation becomes a desire method for removal of persistent organic pollutants (POPs) due to its eco-friendly and sustainable nature. The improvement of practical feasibility requires constructing comprehensive species pool, while it is still limited by the rapid recognition of potential bacterial resources from environment. Here, based on the relative abundances of bacterial OTUs and pollutant concentrations, we established indexes to assess their tolerance to organochlorine pesticides (OCPs) and flame retardants (FRs) that are atmospheric transported and naturally accumulated in forest soil via forest filter effect. By exploring the tolerance pattern from tropical to temperate forests across China, we demonstrated that diversity, community composition, and relative abundances of POP-tolerant bacteria were significantly related to POPs' distribution and concentration. By recognizing over a hundred of genera composed of POP-tolerant species, we found that OCP-tolerant taxa were wide-distributed, while bacterial communities were more responsive to the contamination level of FRs and FR-tolerant taxa were accumulated along the increase of FRs pollution. Our indexes successfully recognized well-known POPs-degrading genera, including Rhodococcus, Bacillus, Arthrobacter, Stenotrophomonas, and Pseudomonas, as well as a series of versatile taxa affiliated with families Ktedonobacteraceae, Acetobacteraceae, Solirubrobacteraceae, and Nocardiaceae, which were extremely rare and likely ignored in laboratory-scale experiments. Together, our findings provide valuable clues to expand the library of POPs-degrading candidates that is helpful in screening bacterial resources for bioremediation.

Smart β-cyclodextrin-dominated helical supramolecular dendritic assemblies improve the foliar affinity and biofilm disruption for treating alarming bacterial diseases

Recent outbreaks of alarming bacterial diseases have significantly impacted global agricultural productivity. Conventional bactericides exhibit certain limitations in efficiently impeding biofilm formation and annihilating biofilm-dispersed pathogens, and often expose to high off-target movement during foliar spraying. Here, we produce an innovative helical dendrimer-like supramolecular material (PhA28@β-CD) assembled by a bioactive small-molecule 2-chlorophenylisopropanolamine (PhA28) and β-cyclodextrin (β-CD) through host-guest recognition principle. In this system, the advisable optimization by a macrocyclic oligosaccharide-β-CD significantly enhances the water-solubility, biocompatibility, and bioavailability of PhA28. At a low-dose of 6.8 μg/mL, PhA28@β-CD discloses an outstanding biofilm disruption rate of 82.4 %, notably exceeding that of PhA28 (60.6 %), which thereby reduces the biofilm-associated virulence. Meanwhile, the self-assembled PhA28@β-CD possesses superior wetting and dispersing properties on hydrophobic leaves, leading to effective foliar deposition and prolong retention of active components. In vivo studies reveal that PhA28@β-CD exhibits superior curative (66.0 %) and protective (72.6 %) activities against citrus canker at 200 μg/mL, markedly surpassing those of the existing bactericide thiodiazole‑copper (46.8 % and 52.2 %) and single PhA28. This material also has broad-spectrum control efficiency (53.0 % ~ 59.5 %) against rice bacterial blight. This research lays the groundwork for developing carbohydrate-optimized multifunctional dendrimer-like assemblies aimed at disrupting biofilms and improving sustained bioavailability to combat bacterial diseases.

Experimental investigation on heat and moisture transfer of propylene glycol-mixed steam in porous media

Propylene glycol (PG)-mixed steam enhanced extraction is a promising remediation technique for removing semi-volatile organic compounds (SVOCs) from the unsaturated zone. However, the mechanisms of heat and moisture transfer during PG-mixed steam injection remain unclear. In this study, a 2D experimental system was developed to enable non-invasive monitoring of the spatio-temporal distribution of temperature and degree of saturation during steam injection into porous media. Experiments were conducted to observe the migration of PG-mixed steam in horizontal and vertical planes across three varying particle sizes, while pure superheated steam injection experiments serving as a comparison. Temperature field results show that the addition of PG decreases the zone of influence during steam migration, while significantly enhancing the emergence of the superheated steam zone. The influence of particle size on the area variance of the saturated steam zone is greater than that of the superheated steam zone. The downward migration of the superheated steam front due to density different between PG vapor and air is impeded with decreasing permeability. Furthermore, saturation field results reveal that the condensed liquid within the superheated zone is a PG solution. The downward migration of condensates with high PG concentration might increase the potential risk of beneath groundwater pollution, highlighting the significance of understanding PG migration during PG-mixed steam injection.

Remediation of a diesel contaminated soil by means of anionic and non-ionic surfactants: Effect on soil phosphorus availability and Vicia Faba L. growth

In the present study, the effectiveness of two surfactants (Polysorbate 80 - Tween 80 and Sodium Dodecyl Benzensulphonate - SDBS) was investigated for the remediation of a hydrocarbon-contaminated soil. Moreover, it was elucidated the impact of surfactants on soil phosphorus (P) availability and phytotoxic effect on the growth of Vicia Faba L. An experimental laboratory-scale apparatus (bench and pilot scale) was set up for the simulation of a soil flushing intervention. Different surfactant concentrations and flushing flow rates were investigated. Hydrocarbon extraction efficiency was evaluated after treatment and phytotoxicity tests were performed by means of germination index (GI). The treated soil with the pilot scale apparatus was then used for Vicia Faba (faba beans) cultivation in pots. The growth of Vicia Faba plants was monitored and, at the end of the growth period, the plants were uprooted and subjected to biometric and chemical analyses. Results highlighted that the use of surfactants significantly increased the efficiency of hydrocarbons extraction compared to flushing test with water (19.6 %, 53.9 %, and 65.6 % for water, 0.1 % by weight of Tween 80 and SDBS, respectively, at pilot scale). Referring to Vicia Faba L., the plants grown in the blank control and in the soil treated with Tween 80 reached the same average height thus suggesting that this surfactant does not inhibit plant growth. In contrast, the lowest plant growth occurred in the soils treated with SDBS; this suggests a negative impact on plant growth. Due to the reduced plant growth, total P uptake was the lowest in plants grown in SDBS-treated soils, although such soils experienced a 20 % increase of soil available P. This increase could be ascribed to P supplied by the surfactant or high P availability as a consequence of soil pH decrease.

A comprehensive review of soil remediation contaminated by persistent organic pollutants using electrokinetic: Challenging enhancement techniques

The hydrophobic, hard-to-naturally-decompose compounds, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and pesticides, are categorized as persistent organic pollutants (POPs). POPs are toxic/hazardous and present serious risks to human health. Electrokinetic (EK) remediation is highly flexible and cost-effective, suitable for both in-situ and ex-situ applications. It effectively targets a wide range of contaminants, including metals and organic compounds, especially in low-permeability and low-hydraulic conductivity soils, where traditional methods are less effective. This technology is easy to install and can be combined with other strategies for enhanced remediation in complex soil environments. This paper underscores EK remediation as a promising method for addressing soil pollution caused by these organic pollutants, especially in low-permeability soil. The present review starts with the classification, toxicity effects, and source of POPs in the environment. Theoretical aspects and fundamentals of EK, including transport mechanisms and principles, are also reviewed. The theoretical underpinnings of effective factors are comprehensively explored, such as surface charge, zeta potential, pHpzc, and numerical modeling of transport fluxes. Moreover, a comprehensive examination is undertaken regarding the operation and design considerations of the EK process, encompassing factors like pH, electrode arrangement, electrolyte, and voltage. Subsequently, it is highlighted that EK has the potential to come in synergistically in contact with other remediation technologies to augment the POPs' degradation. Various enhancement techniques are also explored, including solvent extraction, chemical oxidation, bioremediation, and permeable reactive barriers to combine with EK. Each method is examined in terms of its advantages, limitations, recent developments, and ongoing research. Finally, the potential and challenges associated with enhanced EK methods combined with other techniques for the removal of POPs were reviewed.

Environmental problems of emerging toxic metals and treatment technology and methods

The increasing industrial use of toxic metals essential for modern electronics and renewable energy presents significant environmental and health challenges. This review was needed to address the environmental risks posed by toxic metals, particularly those accumulating in soil and sediment ecosystems. The objective is to examine the sources of toxic metal pollution, their ecological impacts, and the effectiveness of existing treatment technologies. By comprehensively reviewing the recent literature, we analyzed the physiological and molecular responses of plants to toxic metals, focusing on their toxicity mechanisms. Key parameters measured include toxic metal concentration, soil and sediment health, microbial diversity, and plant stress responses. Our findings highlight that toxic metals, such as lithium, nickel, and indium, fueled by industrial activities, including mining and electronic waste disposal, significantly disrupt ecosystems. These metals bioaccumulate, harming soil microbial communities and aquatic life. For instance, in soil ecosystems, cadmium and lead inhibit microbial functions, while in aquatic systems, resuspension of sediment-bound metals leads to persistent contamination. Data show that phytoremediation and microbial techniques are effective in reducing toxic metal concentrations up to 30-40%. In conclusion, long-term monitoring and sustainable remediation strategies are essential to mitigate these environmental impacts. Future efforts should focus on enhancing the efficiency of bioremediation techniques and integrating these methods into global toxic metal management practices.

Influence of decades-long irrigation with secondary treated wastewater on soil microbial diversity, resistome dynamics, and antibiotrophy development

In arid and semi-arid regions, the use of treated wastewater (TWW) for irrigation is gaining ground to alleviate pressure on natural water sources. Despite said treatment, the existing methods fail to eliminate potentially dangerous contaminants. As such, this study assessed the impact of long-term TWW irrigation (5 and 25 years) on soil physicochemical properties and bacterial resistance to heavy metals (Pb, Cu, Cd) and antibiotics (tetracycline and amoxicillin). The results revealed heightened salinity and conductivity and reduced pH in irrigated soils. TWW induces harmful effects by reducing microbial density and size, leading to the disappearance of sensitive populations. Conversely, resilient populations, which mainly utilize antibiotics as a carbon source, have adapted. Metagenomic 16S amplicon sequencing analysis demonstrated a shift, notably reducing Actinobacteria, Bacteroidetes, and Firmicutes while increasing Acidobacteriota and Patescibacteria in treated soils. Operational Taxonomic Units affiliated with either Halomonadacea, or Saccharimonadacea and Vicinamibacteracea, were defined as indicators of the absence or presence of TWW contamination, respectively. We conclude that TWW irrigation significantly increases bacterial resistance to heavy metals, whereas the impact of antibiotics is nuanced, with antibiotrophy leveraging lower concentrations in treated soils.

Transformation of sedimentary dissolved organic matter in electrokinetic remediation catalogued by FT-ICR mass spectrometry

In electrokinetic remediation (EKR), the sedimentary dissolved organic matter (DOM) could impede remediation by scavenging reactive species and generating unintended byproducts. Yet its transformation and mechanisms remained largely unknown. This study conducted molecular-level characterization of the water-extractable DOM (WEOM) in EKR using negative-ion electrospray ionization coupled to 21 tesla Fourier transform ion cyclotron resonance mass spectrometry (21 T FT-ICR MS). The results suggested that ∼55 % of the ∼7,000 WEOM compounds identified were reactive, and EKR lowered their diversity, molecular weight distribution, and double-bond equivalent (DBE) through a combination of electrochemical and microbial redox reactions. Heteroatom-containing WEOM (CHON and CHOS) were abundant (∼ 35% of the total WEOM), with CHOS generally being more reactive than CHON. Low electric potential (1 V/cm) promoted the growth of dealkylation and desulfurization bacteria, and led to anodic CO2 mineralization, anodic cleavage of -SO and -SO3, and cathodic cleavage of -SH2; high electric potential (2 V/cm) only enriched desulfurization bacteria, and differently, led to anodic oxygenation and cathodic hydrogenation of unsaturated and phenolic compounds, in addition to cathodic cleavage of -SH2. The long-term impact of these changes on soil quality and nitrogen-sulfur-carbon flux may be need to studied to identify unknown risks and new applications of EKR.

Modern perspectives of heavy metals alleviation from oil contaminated soil: A review

Heavy metal poisoning of soil from oil spills causes serious environmental problems worldwide. Various causes and effects of heavy metal pollution in the soil environment are discussed in this article. In addition, this study explores new approaches to cleaning up soil that has been contaminated with heavy metals as a result of oil spills. Furthermore, it provides a thorough analysis of recent developments in remediation methods, such as novel nano-based approaches, chemical amendments, bioremediation, and phytoremediation. The objective of this review is to provide a comprehensive overview of the removal of heavy metals from oil-contaminated soils. This review emphasizes on the integration of various approaches and the development of hybrid approaches that combine various remediation techniques in a synergistic way to improve sustainability and efficacy. The study places a strong emphasis on each remediation strategy that can be applied in the real-world circumstances while critically evaluating its effectiveness, drawbacks, and environmental repercussions. Additionally, it discusses the processes that reduce heavy metal toxicity and improve soil health, taking into account elements like interactions between plants and microbes, bioavailability, and pollutant uptake pathways. Furthermore, the current study suggests that more research and development is needed in this area, particularly to overcome current barriers, improve our understanding of underlying mechanisms, and investigate cutting-edge ideas that have the potential to completely transform the heavy metal clean up industry.

Organic and heavy metal pollutants in dredged sediment of Oran Harbor, Algeria

Harbors on all coasts regularly silt up, receiving sedimentary inputs that progressively reduce the water depths available for navigation. Consequently, they are routinely dredged to guarantee the depths necessary for navigation. Sediments act as a reservoir for anthropogenic contaminants such as heavy metals and persistent organic pollutants (POPs) that enter the aquatic system associated with particles or in solution. The objective of this study is to assess the state of pollution by POPs and heavy metals such as copper and zinc, used in large quantities in antifouling paints, in the sediments of the port of Oran. These were characterized by different methods: size, XRD, calcination, FTIR, NMR, GC-MS, and AAS, in order to determine their main characteristics and heavy metals and POPs content. The particle size is determined by laser particle size distribution. Thus, sediments from Oran port are composed of means and end sands, silt, and clay. The XRD analysis shows that the sediments consist mainly of silicates and calcite. The organic matter was determined by ignition loss at 450 and 550 °C; it is about 7%. Analysis by FTIR, 1H and 13C NMR, and GC-MS of POPs excerpts shows that the sediments are highly polluted by aliphatic and aromatic hydrocarbons (3372 mg/kg). Finally, metals were determined by AAS method. The results show significant pollution of Zn (313.5 mg/kg) and moderate pollution by Cu (75.6 mg/kg).

Polycyclic aromatic hydrocarbon: underpinning the contribution of specialist microbial species to contaminant mitigation in the soil

The persistence of PAHs poses a significant challenge for conventional remediation approaches, necessitating the exploration of alternative, sustainable strategies for their mitigation. This review underscores the vital role of specialized microbial species (nitrogen-fixing, phosphate-solubilizing, and biosurfactant-producing bacteria) in tackling the environmental impact of polycyclic aromatic hydrocarbons (PAHs). These resistant compounds demand innovative remediation strategies. The study explores microbial metabolic capabilities for converting complex PAHs into less harmful byproducts, ensuring sustainable mitigation. Synthesizing literature from 2016 to 2023, it covers PAH characteristics, sources, and associated risks. Degradation mechanisms by bacteria and fungi, key species, and enzymatic processes are examined. Nitrogen-fixing and phosphate-solubilizing bacteria contributions in symbiotic relationships with plants are highlighted. Biosurfactant-producing bacteria enhance PAH solubility, expanding microbial accessibility for degradation. Cutting-edge trends in omics technologies, synthetic biology, genetic engineering, and nano-remediation offer promising avenues. Recommendations emphasize genetic regulation, field-scale studies, sustainability assessments, interdisciplinary collaboration, and knowledge dissemination. These insights pave the way for innovative, sustainable PAH-contaminated environment restoration.

A novel subsurface slopes hazardous mapping with engineering geologic and geophysical characterizations

Engineering geological characterizations, and geophysical mapping of subsurface structures to monitor some susceptible infrastructural facilities to hazardous slopes for effectiveness, safety to lives and properties, in addition to policy management for sustainable development. Novel integrated engineering geology, geoelectrical resistivity (ER), and borehole data analysis, to characterize subsurface for slope instability, determining critical zones prone to hazardous slopes in Peninsular Malaysian (PM), east coast areas was focused on. Engineering Laboratory soil investigations using disturbed and undisturbed samples collected to obtain firsthand information on the subsurface soils, and rocks physical properties, integrated with ER data to obtain subsurface geoelectric profiles. Regions delineated as loose and marked as water saturated residual soils prone to slopes corresponds to ER values < 100 Ω-m. ER values between 100 ≥ 500 Ω-m, were delineated as residual soils zones devoid of water contents. Subsurface geoelectric profiles related to hard materials were delineated as weathered and fractured bedrock zones corresponding to ER values between 500 ≥ 2000 Ω-m. Granitic bedrock units delineated as subsurface lithological zones with ER values > 4000 Ω-m. Slope Mass Ratings (SMR), was carried out to construct suitability, and slope assessment system (SAS) model ratings map for the four classes obtained.

Innovative remediation strategies for persistent organic pollutants in soil and water: A comprehensive review

Persistent organic pollutants (POPs) provide a serious threat to human health and the environment in soil and water ecosystems. This thorough analysis explores creative remediation techniques meant to address POP pollution. Persistent organic pollutants are harmful substances that may withstand natural degradation processes and remain in the environment for long periods of time. Examples of these pollutants include dioxins, insecticides, and polychlorinated biphenyls (PCBs). Because of their extensive existence, cutting-edge and environmentally friendly eradication strategies must be investigated. The most recent advancements in POP clean-up technology for soil and water are evaluated critically in this article. It encompasses a wide range of techniques, such as nanotechnology, phytoremediation, enhanced oxidation processes, and bioremediation. The effectiveness, cost-effectiveness, and environmental sustainability of each method are assessed. Case studies from different parts of the world show the difficulties and effective uses of these novel techniques. The study also addresses new developments in POP regulation and monitoring, highlighting the need of all-encompassing approaches that include risk assessment and management. In order to combat POP pollution, the integration of diverse remediation strategies, hybrid approaches, and the function of natural attenuation are also examined. Researchers, legislators, and environmental professionals tackling the urgent problem of persistent organic pollutants (POPs) in soil and water should benefit greatly from this study, which offers a complete overview of the many approaches available for remediating POPs in soil and water.

Effect of cations on monochlorobenzene adsorption onto bentonite at the coexistence of Tween 80

The effect of several prevalent cations (including Na+, K+, Mg2+, Ca2+, Al3+, and Fe3+) on the adsorption of monochlorobenzene (MCB) onto bentonite was investigated at the coexistence of nonionic surfactant Tween 80 (T80) in surfactant-enhanced remediation (SER). They are all favorable for MCB and T80 adsorption, especially Mg2+ and Ca2+. Adsorption of MCB is strongly depended on T80 micelles. When its concentration exceeds the solubility, MCB is easier to bind with T80 micelles and be adsorbed by bentonite. Acidic environment can facilitate MCB and T80 adsorption, but the effect of cations on the adsorption is most significant under alkaline conditions. Adsorption capacity of MCB increases first followed by a slight decrease with increasing cations concentrations. The maximum adsorption rate of MCB determined is about 68.4% in a solution containing Mg2+ in the isothermal adsorption of MCB, while it is only 6.8% in a cation-free solution. Various characterizations showed that cations mainly changed the repulsion between bentonite particles and T80 micelles and the agglomeration and structure of bentonite, thus affecting the adsorption of MCB and T80 micelles. Our research demonstrated the nonnegligible promotion of MCB adsorption on bentonite by cations and acidic environment, which will adversely affect SER efficiency.

Adsorption behavior and the potential risk of As(V) in soils: exploring the effects of representative surfactants

Arsenic contamination in soils poses a critical global challenge, yet the influence of surfactants on arsenic adsorption behavior is often underestimated. This study aims to investigate the effects of three representative surfactants, namely cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS), and polyethylene glycol anhydrous sugar alcohol monooleate (Tween 80), on arsenic adsorption behavior in soils. The adsorption isotherm shifts from a single Temkin model without surfactants to both the Langmuir and Temkin models in the presence of surfactants, indicating the simultaneous occurrence of monolayer and multilayer adsorption for arsenic in soils. Moreover, the surfactants can inhibit the adsorption and hasten the attainment of adsorption equilibrium. SDS displayed the most inhibitory effect on arsenic adsorption, followed by Tween 80 and CTAB, due to the competitive adsorption, electrostatic interaction, and hydrophobic interaction. Variations in zeta potential with different surfactants further elucidate this inhibitory phenomenon. Through orthogonal experiment analyses, pH emerges as a primary factor influencing arsenic adsorption in soils, with surfactant concentration and type identified as secondary factors. Temperature notably affects CTAB, with the adsorption inhibition rate plummeting to a mere 0.88% at 50 °C. Sequential extraction analysis revealed that surfactants enhanced the bioavailability of arsenic. The FTIR, XRD, SEM, and CA analyses further support the mechanism underlying the effect of surfactants on arsenic adsorption in soil. These analyses indicate that surfactants modify the composition and abundance of functional groups, hinder the formation of arsenic-containing substances, and improve soil compactness, smoothness, and hydrophilicity. This study provides valuable insights into the effect of surfactants in arsenic-contaminated soils, which is often ignored in previous work.

The uptake and degradation of polychlorinated biphenyls in constructed wetlands planted with Myriophyllum aquaticum

The unregulated dismantling and improper disposal of electronic waste lead to severe soil contamination by polychlorinated biphenyls (PCBs). Constructed wetlands (CWs) play an important role in PCBs removal as a result of the co-existence of anaerobic and aerobic conditions. However, the effects and mechanisms of different PCBs concentrations in soils on plant uptake and PCBs degradation within CWs are unclear. We evaluated the uptake and degradation of PCBs at different concentrations by Myriophyllum aquaticum (Vell.) Verdc. Planting significantly increased PCBs removal by 8.70% (p < 0.05) in soils with 1500 and 2500 μg/kg PCBs, whereas no significant effect was observed at 500 and 1000 μg/kg. PCBs levels did not significantly affect plant growth and PCBs accumulation. The contribution of plant uptake to PCBs removal was only 0.10-0.12%, indicating that microbial degradation was the dominant pathway for PCBs removal after planting with M. aquaticum. In the treatments with PCBs ≥ 1500 μg/kg, M. aquaticum increased the microbial population, altered the microbial community structure and enriched PCB-degrading bacteria. Functional prediction revealed that microbes in M. aquaticum rhizosphere secreted more peroxidase and glycosyltransferase than non-plant control, which were likely involved in PCBs metabolism.

Efficient removal of heavy metals in water utilizing facile cross-link conjugated linoleic acid micelles

Micellar-enhanced ultrafiltration (MEUF) technology is an effective method to treat low-concentration heavy metal wastewater. However, the leakage of surfactants in the ultrafiltration (UF) process will inevitably cause secondary pollution. In this study, a biosurfactant of conjugated linoleic acid (CLA) with conjugated double bonds was selected to bind its micelles by simple thermal crosslinking to obtain morphologically stable stearic acid (SA) nanoparticles. The pure SA nanoparticles were obtained by repeated dialysis. The stability of the SA nanoparticles was verified by comparing the particle size distribution and solubility of the materials before and after crosslinking at different pH levels. The effectiveness of SA nanoparticle-enhanced UF in removing heavy metals was verified by exploring the adsorption performance of SA nanoparticles. The dialysis device was used to simplify the UF device, wherein SA nanoparticles were assessed as adsorbents for the elimination of Cu2+, Pb2+, and Cd2+ ions from aqueous solutions under diverse process parameters, including pH, contact time, metal ion concentration, and coexisting ions. The findings indicate that the SA nanoparticles have no evidence of secondary contamination in UF and exhibit compatibility with a broad pH range and coexisting ions. The maximum adsorption capacities for Cu2+, Pb2+, and Cd2+ were determined to be 152.77, 403.56, and 271.46 mg/g, respectively.

Advancements in biosurfactant production using agro-industrial waste for industrial and environmental applications

The adverse effects of waste generation on the environment and public health have raised global concerns. The utilization of waste as a raw material to develop products with enhanced value has opened up novel prospects for promoting environmental sustainability. Biosurfactants obtained from agro-industrial waste are noteworthy due to their sustainability and environmental friendliness. Microorganisms have been employed to generate biosurfactants as secondary metabolites by making use of waste streams. The utilization of garbage as a substrate significantly reduces the expenses associated with the process. Furthermore, apart from reducing waste and offering alternatives to artificial surfactants, they are extensively employed in bioremediation, food processing, agriculture, and various other industrial pursuits. Bioremediation of heavy metals and other metallic pollutants mitigated through the use of bacteria that produce biosurfactants which has been the more recent research area with the aim of improving its quality and environmental safety. Moreover, the production of biosurfactants utilizing agricultural waste as a raw material aligns with the principles of waste minimization, environmental sustainability, and the circular economy. This review primarily focuses on the production process and various types of biosurfactants obtained from waste biomass and feedstocks. The subsequent discourse entails the production of biosurfactants derived from various waste streams, specifically agro-industrial waste.

Research progress on remediation of organochlorine pesticide contamination in soil

Deteriorated soil pollution has grown into a worldwide environmental concern over the years. Organochlorine pesticide (OCP) residues, featured with ubiquity, persistence and refractoriness, are one of the main pollution sources, causing soil degradation, fertility decline and nutritional imbalance, and severely impacting soil ecology. Furthermore, residual OCPs in soil may enter the human body along with food chain accumulation and pose a serious health threat. To date, many remediation technologies including physicochemical and biological ways for organochlorine pollution have been developed at home and abroad, but none of them is a panacea suitable for all occasions. Rational selection and scientific decision-making are grounded in in-depth knowledge of various restoration techniques. However, soil pollution treatment often encounters the interference of multiple factors (climate, soil properties, cost, restoration efficiency, etc.) in complex environments, and there is still a lack of systematic summary and comparative analysis of different soil OCP removal methods. Thus, to better guide the remediation of contaminated soil, this review summarized the most commonly used strategies for OCP removal, evaluated their merits and limitations and discussed the application scenarios of different methods. It will facilitate the development of efficient, inexpensive and environmentally friendly soil remediation strategies for sustainable agricultural and ecological development.

Ni/Co/Carbon nitride derived from ZIF-67 (MOF) nanocomposite: Enhanced light-driven photocatalytic degradation of methylparaben, mechanism & toxicity

A nickel oxide/cobalt/carbon nitride (Ni/Co/CN) nanocomposite synthesized via co-precipitation was used for the degradation of methylparaben (MEP). Various analytical techniques were used to ascertain the structural, optical, and electrochemical characteristics of the synthesized nanocomposite. The unique nature of the compound without any free particles over the CN was established. Photocatalytic degradation studies demonstrated the superiority of 3-Ni/Co/CN over bare NiO, Co/CN, 1-Ni/Co/CN, and 5-Ni/Co/CN. Near complete MEP degradation (100%) was achieved after 120 min of incubation with MEP 75 mg L-1 in acidic medium pH (3) for an initial concentration of 3-Ni/Co/CN (10 mg/100 mL). HPLC-MS/MS analysis was used to elucidate the degradation pathway, and the catalyst was found stable for four subsequent cycles. Hence, our nanocatalyst effectively degraded MEP. Furthermore, microbial, aquatic, and animal studies demonstrated the environmental efficiency of the synthesized nanomaterials.

Source, transport, and toxicity of emerging contaminants in aquatic environments: A review on recent studies

Emerging contaminants (ECs) are gaining global attention owing to their widespread presence and adverse effects on human health. ECs comprise numerous composite types and pose a potential threat to the growth and functional traits of species and ecosystems. Although the occurrence and fate of ECs has been extensively studied, little is known about their long-term biological effects. This review attempts to gain insights into the unhindered connections and overlaps in aquatic ecosystems. Microplastics (MPs), one of the most representative ECs, are carriers of other pollutants because of their strong adsorption capacity. They form a complex of pollutants that can be transmitted to aquatic organisms and humans through the extended food chain, increasing the concentration of pollutants by tens of thousands of times. Adsorption, interaction and transport effects of emerging contaminants in the aquatic environment are also discussed. Furthermore, the current state of knowledge on the ecotoxicity of single- and two-pollutant models is presented. Herein, we discuss how aquatic organisms within complex food networks may be particularly vulnerable to harm from ECs in the presence of perturbations. This review provides an advanced understanding of the interactions and potential toxic effects of ECs on aquatic organisms.

Efficient remediation of soils contaminated with petroleum hydrocarbons using sustainable plant-derived surfactants

Surfactant-enhanced multiphase extraction is recognized as an effective method to remove petroleum related contaminants from soil. Owing to the high biodegradability and low biotoxicity, plant-derived surfactants are considered as promising alternatives to synthetic surfactants. In this study, two plant surfactants were respectively extracted from Sapindus mukorossi (PS-1) and Fructus Gleditsiae sinensis (PS-2). Component analysis and chemical structure characterization indicated that triterpenoid saponins were the main components of both plant surfactants. The removal efficiency of tetradecane by PS-1 and PS-2 was 75.6% and 62.2%, respectively, which was comparable with that by Tween-80. The results were validated by column leaching experiments. The abundant hydroxyl, aldehyde and epoxy groups in the plant surfactants made them readily self-assemble to form micelles via hydrogen bonding and van der Waals interactions, which promoted the solubilization of tetradecane in the liquid phase, particularly at appropriate ionic strength and temperature. Due to the reduced electrostatic attraction by the acidic and ionizable functional groups in the plant surfactants, their sorption capacities (0.15 and 0.24 g1-n Ln·kg-1 for PS-1 and PS-2, respectively) onto the soil were much lower than that of Tween-80, making them much easier to be extracted from contaminated soil. This study would deepen our understanding to improve the performances of plant surfactants in petroleum hydrocarbons-contaminated soil remediation.

Non-negligibly negative role of e-waste-derived pyrogenic carbon in the soil washing of copper and polybrominated diphenyl ethers

The open incineration of electrical and electronic waste (e-waste) results in the accumulation of pyrogenic carbon in the soil. However, the effect of the e-waste-derived pyrogenic carbon (E-PyC) on the performance of soil washing at e-waste incineration sites remains unclear. In this study, the effectiveness of a citrate-surfactant mixed solution in removing copper (Cu) and decabromodiphenyl ether (BDE209) at two e-waste incineration sites was evaluated. The removal efficiencies of Cu (24.6-51.3%) and BDE209 (13.0-27.9%) were low in both soils and were not significantly improved by ultrasonic. Soil organic matter analysis, hydrogen peroxide and thermal pretreatment experiments, and microscale soil particle characterization demonstrated that the poor removal of soil Cu and BDE209 was due to steric effects of E-PyC on the release of the solid fraction of pollutants and the competitive sorption of the labile fraction of pollutants by E-PyC. Weathering of soil Cu weakened the influence of E-PyC but strengthened the negative impact of natural organic matter (NOM) on soil Cu removal by promoting complexation between NOM and Cu2+ ions. This study demonstrates that the negative effect of E-PyC on Cu and BDE209 removal by soil washing is non-negligible, which has implications for decontaminating e-waste incineration sites by soil washing.

Soil acidification and salinity: the importance of biochar application to agricultural soils

Soil acidity is a serious problem in agricultural lands as it directly affects the soil, crop production, and human health. Soil acidification in agricultural lands occurs due to the release of protons (H+) from the transforming reactions of various carbon, nitrogen, and sulfur-containing compounds. The use of biochar (BC) has emerged as an excellent tool to manage soil acidity owing to its alkaline nature and its appreciable ability to improve the soil's physical, chemical, and biological properties. The application of BC to acidic soils improves soil pH, soil organic matter (SOM), cation exchange capacity (CEC), nutrient uptake, microbial activity and diversity, and enzyme activities which mitigate the adverse impacts of acidity on plants. Further, BC application also reduce the concentration of H+ and Al3+ ions and other toxic metals which mitigate the soil acidity and supports plant growth. Similarly, soil salinity (SS) is also a serious concern across the globe and it has a direct impact on global production and food security. Due to its appreciable liming potential BC is also an important amendment to mitigate the adverse impacts of SS. The addition of BC to saline soils improves nutrient homeostasis, nutrient uptake, SOM, CEC, soil microbial activity, enzymatic activity, and water uptake and reduces the accumulation of toxic ions sodium (Na+ and chloride (Cl-). All these BC-mediated changes support plant growth by improving antioxidant activity, photosynthesis efficiency, stomata working, and decrease oxidative damage in plants. Thus, in the present review, we discussed the various mechanisms through which BC improves the soil properties and microbial and enzymatic activities to counter acidity and salinity problems. The present review will increase the existing knowledge about the role of BC to mitigate soil acidity and salinity problems. This will also provide new suggestions to readers on how this knowledge can be used to ameliorate acidic and saline soils.

Influence of grain size, organic carbon and organic matter residue content on the sorption of per- and polyfluoroalkyl substances in aqueous film forming foam contaminated soils - Implications for remediation using soil washing

A soil that was historically contaminated with Aqueous Film Forming Foam (AFFF) was dry sieved into size fractions representative of those produced during soil washing. Batch sorption tests were then conducted to investigate the effect of soil parameters on in situ per- and polyfluoroalkyl substances (PFAS) sorption of these different size fractions: < 0.063 mm, 0.063 to 0.5 mm, 0.5 to 2 mm, 2 to 4 mm, 4 to 8 mm, and soil organic matter residues (SOMR). PFOS (513 ng/g), 6:2 FTS (132 ng/g) and PFHxS (58 ng/g) were the most dominant PFAS in the AFFF contaminated soil. Non-spiked, in situ K_d values for 19 PFAS ranged from 0.2 to 138 L/Kg (log K_d -0.8 to 2.14) for the bulk soil and were dependant on the head group and perfluorinated chain length (spanning C₄ to C₁₃). The K_d values increased with decreasing grain size and increasing organic carbon content (OC), which were correlated to each other. For example, the PFOS K_d value for silt and clay (< 0.063 mm, 17.1 L/Kg, log K_d 1.23) were approximately 30 times higher compared to the gravel fraction (4 to 8 mm, 0.6 L/Kg, log K_d -0.25). The highest PFOS K_d value (116.6 L/Kg, log K_d 2.07) was found for the SOMR fraction, which had the highest OC content. K_oc values for PFOS ranged from 6.9 L/Kg (log K_oc 0.84) for the gravel fraction to 1906 L/Kg (log K_oc 3.28) for the silt and clay, indicating that the mineral composition of the different size fractions also influenced sorption. The results here emphasize the need to separate coarse-grained fractions and fine-grained fractions, and in particular the SOMR, to optimize the soil washing process. Higher K_d values for the smaller size fractions indicate that coarser soils are better suited for soil washing.

Research progress of bio-slurry remediation technology for organic contaminated soil

Bio-slurry remediation technology, as a controllable bioremediation method, has the significant advantage of high remediation efficiency and can effectively solve the problems of high energy consumption and secondary pollution of traditional organic pollution site remediation technology. To further promote the application of this technology in the remediation of organically polluted soil, this paper summarizes the importance and advantages of bio-slurry remediation technology compared with traditional soil remediation technologies (physical, chemical, and biological). It introduces the technical infrastructure and its technological processes. Then, various factors that may affect its remediation performance are discussed. By analyzing the applications of this technology to the remediation of typical organic pollutant-(polycyclic aromatic hydrocarbons(PAHs), polychlorinated biphenyls(PCBs), total petroleum hydrocarbons(TPH), and pesticide) contaminated sites, the following key features of this remediation technology are summarised: (1) the technology has a wide range of applications and can be used in a versatile way in the remediation projects of various types of organic-contaminated soil sites such as in clay, sand, and high organic matter content soil; (2) the technology is highly controllable. Adjusting environmental parameters and operational conditions, such as nutrients, organic carbon sources (bio-stimulation), inoculants (bio-augmentation), water-to-soil ratio, etc., can control the remediation process, thus improving the restoration performance. To sum up, this bio-slurry remediation technology is an efficient, controllable and green soil remediation technology that has broad application prospects.

Review of the application of surfactants in microemulsion systems for remediation of petroleum contaminated soil and sediments

Microemulsions are important for soil and sediment remediation technology. The characteristics of the surfactants that make up these microemulsions include low sorption into soil or sediments, low surface and interfacial tension, the ability to penetrate tiny pores, and good solubilization of contaminants. This review revealed that microemulsions formulated with nonionic and anionic surfactants have higher recovery efficiencies for hydrophobic contaminants than cationic ones, as evidenced by the surveyed studies reporting effective remediation of soils and sediments using on microemulsions. These microemulsified systems have been found to remove petroleum and its derivatives from soil or sediments at percentages ranging from 40 to 100%. As such, this review can aid with the choice of surfactants used in microemulsions for remediation, such as those with plant-based components, which are promising solutions for the remediation of contaminated soils due to their contaminant extraction efficiency and biodegradability.

Soil acidification and the liming potential of biochar

Soil acidification in managed ecosystems such as agricultural lands principally results from the increased releasing of protons (H⁺) from the transformation reactions of carbon (C), nitrogen (N) and sulphur (S) containing compounds. The incorporation of liming materials can neutralize the protons released, hence reducing soil acidity and its adverse impacts to the soil environment, food security, and human health. Biochar derived from organic residues is becoming a source of carbon input to soil and provides multifunctional values. Biochar can be alkaline in nature, with the level of alkalinity dependent upon the feedstock and processing conditions. This review covers the fundamental aspects of soil acidification and of the use of biochar to address constraints related to acidic soil. Biochar is increasingly considered as an effective soil amendment for reducing soil acidity owing to its liming potential, thereby enhancing soil fertility and productivity in acid soils. The ameliorant effect on acid soils is mainly because of the dissolution of carbonates, (hydro)-oxides of the ash fraction of biochar and potential use by microorganisms.