Insight into complexation of Cd(II) and Cu(II) to fulvic acid based on feature recognition of PARAFAC combined with 2DCOS

Spatio-temporal dynamics variation of dissolved organic matter and water quality parameters in Giheung Reservoir: A vertical perspective

Water reservoirs in densely populated areas play a crucial role in water supply, irrigation, and flood regulation. This study investigated the spatiotemporal dynamics of dissolved organic matter (DOM) and its interactions with water quality parameters in Giheung Reservoir, South Korea. Monthly water samples were collected at three depths, measuring fifteen physicochemical properties alongside DOM characterization using Excitation-Emission Matrix Parallel Factor Analysis (EEM-PARAFAC), identifying four DOM components: C1 (microbial protein-like), C2 (humic-like), C3 (terrestrial humic-like), and C4 (tyrosine/tryptophan-like). Seasonal stratification influenced DOM distribution, with humic-like DOM (C2, C3) accumulating in deeper layers during summer, while protein-like DOM (C1, C4) dominated surface waters due to enhanced biological productivity, and mixing periods homogenizing DOM across depths. The dimictic thermal regime, with moderate summer stratification and full mixing in spring and autumn, governed these patterns. 2D correlation spectroscopy (2D-COS) identified sequential DOM variation across layers, with humic-like DOM increasing at depth during stratification. Fluorescence indices-Fluorescence Index (FI), Humification Index (HIX), and Biological Index (BIX)-were integrated into structural equation modeling (SEM), showing that temperature and dissolved oxygen strongly drive protein-like DOM, while nitrogen and phosphorus compounds shape DOM reactivity. These findings enhance understanding of DOM biogeochemical processes and provide valuable insights for reservoir management to maintain water quality.

Fulvic acid impact on constructed wetland-microbial electrolysis cell system performance: Metagenomic insights

This study explores the roles of fulvic acid (FA) in both a conventionally constructed wetland (CCW) and a newly constructed wetland-microbial electrolysis cell (ECW). The results showed that FA increased the average removal efficiency of chemical oxygen demand, total phosphorus, total nitrogen, and ammonia nitrogen in ECW by 8.6, 46.2, 33.0, and 27.9 %, respectively, compared to CCW, and reduced the global warming potential by > 60 %. FA promoted the proliferation of electroactive bacteria (e.g., Chlorobaculum and Candidatus Tenderia) and FA-degrading bacteria (e.g., Anaerolineaceae and Gammaproteobacteria) and reduced methanogens (e.g., Methanothrix) via type-changing. The study's findings suggest that FA influences pollutant removal and microbiome dynamics by altering dissolved oxygen levels and redox potential. In summary, FA and ECW enhanced the efficiency of constructed wetlands by facilitating electron transfer and consumption, and supporting microbial growth and metabolism.

Transforming contaminant ligands at water-solid interfaces via trivalent metal coordination

In environmental matrices, the migration and distribution of contaminants at water-solid interfaces play a crucial role in their capture or dissemination. Scientists working in environmental remediation and wastewater treatment are increasingly aware of metal-contaminant coordination; however, interfacial behaviors remain underexplored. Here, we show that trivalent metal ions (e.g. Al3+ and Fe3+) mediate the migration of pollutant ligands (e.g. tetracycline (TC) and ofloxacin) to the organic solid interface. In the absence of Al3+, humic acid (HA) colloids (50 mg/L) capture 26.1 % of the TC in water (initial concentration: 10 mg/L) via weak intermolecular interactions (binding energy: -5.71 kcal/mol). Adding Al3+ (2.5 mg/L) significantly enhances the binding of TC to an impressive 94.2 % via Al3+ mediated coordination (binding energy: -84.89 kcal/mol). The significant increase in binding energy results in superior interfacial immobilization. However, excess free Al3+ competes for TC binding via direct binary coordination, as confirmed based on the unique fluorescence of Al3+-TC complexes. Density functional theory calculations reveal the intricate process of HA-Al3+ binding via carboxyl and phenolic hydroxyl sites. The HA-Al3+ flocs then leverage the remaining coordination capacity of Al3+ to chelate with TC. As well as providing insights into the pivotal role of metal ion on the self-purification of natural water bodies, our findings on the interfacial behavior of metal-contaminant coordination will propel coagulation technology to the capture of microscale pollutants.

Novel Developments and Progress in Two-Dimensional Correlation Spectroscopy (2D-COS)

This first of the two-part series of the comprehensive survey review on the progress of the two-dimensional correlation spectroscopy (2D-COS) field during the period 2021-2022, covers books, reviews, tutorials, novel concepts and theories, and patent applications that appeared in the last two years, as well as some inappropriate use or citations of 2D-COS. The overall trend clearly shows that 2D-COS is continually growing and evolving with notable new developments. The technique is well recognized as a powerful analytical tool that provides deep insights into systems in many science fields.

Diverse Applications of Two-Dimensional Correlation Spectroscopy (2D-COS)

This second of the two-part series of a comprehensive survey review provides the diverse applications of two-dimensional correlation spectroscopy (2D-COS) covering different probes, perturbations, and systems in the last two years. Infrared spectroscopy has maintained its top popularity in 2D-COS over the past two years. Fluorescence spectroscopy is the second most frequently used analytical method, which has been heavily applied to the analysis of heavy metal binding, environmental, and solution systems. Various other analytical methods including laser-induced breakdown spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, capillary electrophoresis, seismologic, and so on, have also been reported. In the last two years, concentration, composition, and pH are the main effects of perturbation used in the 2D-COS fields, as well as temperature. Environmental science is especially heavily studied using 2D-COS. This comprehensive survey review shows that 2D-COS undergoes continuous evolution and growth, marked by novel developments and successful applications across diverse scientific fields.

Remediation of the microecological environment of heavy metal-contaminated soil with fulvic acid, improves the quality and yield of apple

The excessive application of chemical fertilizers and pesticides in apple orchards is responsible for high levels of manganese and copper in soil, and this poses a serious threat to soil health. We conducted a three-year field experiment to study the remediation effect and mechanism of fulvic acid on soil with excess manganese and copper. The exogenous application of fulvic acid significantly reduced the content of manganese and copper in soil and plants; increased the content of calcium; promoted the growth of apple plants; improved the fruit quality and yield of apple; increased the content of chlorophyll; increased the activity of superoxide dismutase, peroxidase, and catalase; and reduced the content of malondialdehyde. The number of soil culturable microorganisms, soil enzyme activity, soil microbial community diversity, and relative abundance of functional bacteria were increased, and the detoxification of the glutathione metabolism function was enhanced. The results of this study provide new insights that will aid the remediation of soil with excess manganese and copper using fulvic acid.

Abandoned disposable masks become hot substrates for plastisphere, whether in soil, atmosphere or water

A large number of surgical masks (SMs) to be discarded indiscriminately during the spread of COVID-19. The relationship between the changes of masks entering the environment and the succession of the microorganisms on them is not yet clear. The natural aging process of SMs in different environments (water, soil, and atmosphere) was simulated, the changes and succession of the microbial community on SMs with aging time were explored. The results showed that the SMs in water environment had the highest aging degree, followed by atmospheric environment, and SMs in soil had the lowest aging degree. The results of high-throughput sequencing demonstrated the load capacity of SMs for microorganisms, showed the important role of environment in determining microbial species on SMs. According to the relative abundance of microorganisms, it is found that compared with the water environment, the microbial community on SMs in water is dominated by rare species. While in soil, in addition to rare species, there are a lot of swinging strains on the SMs. Uncovering the ageing of SMs in the environment and its association with the colonization of microorganisms will help us understand the potential of microorganisms, especially pathogenic bacteria, to survive and migrate on SMs.

Biomass composite with exogenous organic acid addition supports the growth of sweet sorghum (Sorghum bicolor 'Dochna') by reducing salinity and increasing nutrient levels in coastal saline-alkaline soil

Introduction

In coastal saline lands, organic matter is scarce and saline stress is high. Exploring the promotion effect of intervention with organic acid from biological materials on soil improvement and thus forage output and determining the related mechanism are beneficial to the potential cultivation and resourceful, high-value utilization of coastal mudflats as back-up arable land.

Method

Three exogenous organic acids [humic acid (H), fulvic acid (F), and citric acid (C)] were combined with four kinds of biomass materials [cottonseed hull (CH), cow manure (CM), grass charcoal (GC), and pine needle (PN)] and applied to about 0.3% of medium-salt mudflat soil. The salinity and nutrient dynamics of the soil and the growth and physiological differences of sweet sorghum at the seedling, elongation, and heading stages were observed under different treatments to screen for efficient combinations and analyze the intrinsic causes and influencing mechanisms.

Results

The soil salinity, nutrient dynamics, and forage grass biological yield during sweet sorghum cultivation in saline soils differed significantly (p < 0.05) depending on the type of organic acid-biomass composite applied. Citric acid-pine needle composite substantially reduced the soil salinity and increased the soil nutrient content at the seedling stage and improved the root vigor and photosynthesis of sweet sorghum by increasing its stress tolerance, allowing plant morphological restructuring for a high biological yield. The improvement effect of fulvic acid-pine needle or fulvic acid-cow manure composite was manifested at the elongation and heading stages.

Discussion

Citric acid-pine needle composite promoted the growth of saline sweet sorghum seedlings, and the effect of fulvic acid-pine needle composite lasted until the middle and late stages.

Release of free-state ions from fulvic acid-heavy metal complexes via VUV/H2O2 photolysis: Photodegradation of fulvic acids and recovery of Cd2+ and Pb2+ stripping voltammetry currents

Fulvic acid (FA), a ubiquitous organic matter in the environment, can enhance the mobility and bioavailability of Cd²⁺ and Pb²⁺ through competitive complexation to form FA-heavy metal ions (FA-HMIs) complexes with excellent solubility. Because FA-HMIs are electrochemically inactive, square wave anodic stripping voltammetry (SWASV) cannot accurately detect the content of bioavailable Cd²⁺ and Pb²⁺ in soils and sediments. This study ostensibly aimed to efficiently recover SWASV signals of Cd²⁺ and Pb²⁺ in FA-HMIs by disrupting FA-HMIs complexes using the combined vacuum ultraviolet and H₂O₂ (VUV/H₂O₂) process. Essentially, this study explored the photodegradation behavior and photolysis by-products of FA and their effects on the conversion of FA-HMIs complexes to free-state Cd²⁺ and Pb²⁺ using multiple characterization techniques, as well as revealed the complexation mechanism of FA with Cd²⁺ and Pb²⁺. Results showed that reactive groups such as carboxyl and hydroxyl endowed FA with the ability to complex Cd²⁺ and Pb²⁺. After FA-HMIs underwent VUV/H₂O₂ photolysis for 9 min at 125 mg/L of H₂O₂, FA was decomposed into small molecular organics while removing its functional groups, which released the free-state Cd²⁺ and Pb²⁺ and recovered their SWSAV signals. However, prolonged photolytic mineralization of FA to inorganic anions formed precipitates with Cd²⁺ and Pb²⁺, thereby decreasing their SWSAV signals. Moreover, the VUV/H₂O₂ photolysis significantly improved the SWASV detection accuracy toward the Cd²⁺ and Pb²⁺ in real soil and sediment samples, verifying its practicality.

Insight into the Soil Dissolved Organic Matter Ligand-Phenanthrene-Binding Properties Based on Parallel Faction Analysis Combined with Two-Dimensional Correlation Spectroscopy

Dissolved organic matter (DOM) can strongly bind to organic contaminants and control phenanthrene in soil. Herein, four individual parallel factor analysis (PARAFAC) components were found in soil DOM. Component C1 was the humic-like component ligand T, and component C2 was a combination of humic fluorophore ligands M1 and M2. Furthermore, components C3 and C4 were characterized as terrestrial and ubiquitous humic substances. Then, the modified Stern-Volmer complexation model was used to reveal soil DOM component-phenanthrene-binding properties. The overall binding characteristics of a PARAFAC component could not express the phenanthrene-binding properties. Therefore, two-dimensional correlation spectroscopy was used to reveal DOM ligand-phenanthrene-binding properties. After binding with phenanthrene, DOM ligands T, M2, A2, and C1 were quenched but DOM ligands M1, A1, and C2 were excited. The ligands with higher humification presented higher phenanthrene-binding ability. With these promising results, the DOM ligand-phenanthrene-binding characteristics offered theoretical support for soil pollution control.

Effect of dissolved organic matter on the bioavailability and toxicity of cadmium in zebrafish larvae: Determination based on toxicokinetic-toxicodynamic processes

The presence of dissolved organic matter (DOM) strongly influences the bioavailability of metals in aquatic environments; however, the association between the binding activities and the concentrations of DOM compositions is not well documented, leading to uncertainties in metal toxicity assessment. We creatively quantify the mitigation and acceleration effects of DOM compositions on cadmium (Cd) bioaccumulation and toxicity in zebrafish larvae using abiotic ligand (ABLs) and biotic ligand (BLs) in a toxicokinetic-toxicodynamic (TK-TD) model. The BL-TK-TD model could accurately predict the protective effect of fulvic acid while overestimating the complexing capacity of citric acid. The model also could successfully simulate the protective effects of native DOM in most cases from 32 natural water bodies in China. The observed LC50 values of Cd showed a peak effect for the native DOM fraction comprising hydrophilic acidic contents (3.55 ± 0.44 mg L ^- 1) in natural water from 32 sites. The BL-TK-TD model provides practically useful information to identify the effect of different DOM compositions on metal bioavailability and toxicity in aquatic environments and guides future water management policies aimed at controlling aquatic heavy metal pollution.

Revealing the Inner Changes of Component Composition Derived from DOM PARAFAC Based on Two-Dimensional Correlation Spectroscopy

Plenty of humic acid components compositions are contained in dissolved organic matter (DOM) derived from composting. Fluorescence signals were employed to characterize the changes in DOM components in the component process. In the composting process, five individual DOM fluorescence parallel factor analysis (PARAFAC) components were identified. At the end of the composting, PARAFAC component C5, which represented high humification and complex structure compounds, was detected, but the simple structure DOM PARAFAC component C1 was absent. In this study, a technique combining EEM-PARAFAC with two-dimensional correlation spectroscopy (2DCOS) further supplied detailed information about the dynamics of DOM peaks in PARAFAC components. 2DCOS results showed that the variation of the peaks in PARAFAC components was different in the composting process. The formation of a complex DOM fluorescence substance was attributed to the residues from the simple fluorescence peak degradation. The evolution of the DOM fluorescence peaks in each PARAFAC component indicated that simple structure compounds helped the formation of the complex DOM fluorescence substance in the composting process. These results revealed that EEM/PARAFAC combined with 2DCOS could be used to track the evolution of DOM PARAFAC components during the composting process.