Roxarsone binding to soil-derived dissolved organic matter: Insights from multi-spectroscopic techniques

Molecular insights into linkages among free-floating macrophyte-derived organic matter, the fate of antibiotic residues, and antibiotic resistance genes

Macrophyte rhizospheric dissolved organic matter (ROM) served as widespread abiotic components in aquatic ecosystems, and its effects on antibiotic residues and antibiotic resistance genes (ARGs) could not be ignored. However, specific influencing mechanisms for ROM on the fate of antibiotic residues and expression of ARGs still remained unclear. Herein, laboratory hydroponic experiments for water lettuce (Pistia stratiotes) were carried out to explore mutual interactions among ROM, sulfamethoxazole (SMX), bacterial community, and ARGs expression. Results showed ROM directly affect SMX concentrations through the binding process, while CO and N-H groups were main binding sites for ROM. Dynamic changes of ROM molecular composition diversified the DOM pool due to microbe-mediated oxidoreduction, with enrichment of heteroatoms (N, S, P) and decreased aromaticity. Microbial community analysis showed SMX pressure significantly stimulated the succession of bacterial structure in both bulk water and rhizospheric biofilms. Furthermore, network analysis further confirmed ROM bio-labile compositions as energy sources and electron shuttles directly influenced microbial structure, thereby facilitating proliferation of antibiotic resistant bacteria (Methylotenera, Sphingobium, Az spirillum) and ARGs (sul1, sul2, intl1). This investigation will provide scientific supports for the control of antibiotic residues and corresponding ARGs in aquatic ecosystems.

Activation of iron oxide minerals in an aquifer by humic acid to promote adsorption of organic molecules

In aquifers, the sequestration and transformation of organic carbon are closely associated with soil iron oxides and can facilitate the release of iron ions from iron oxide minerals. There is a strong interaction between dissolved organic matter (DOM) and iron oxide minerals in aquifers, but the extent to which iron is activated by DOM exposure to active iron minerals in natural aquifers, the microscopic distribution of minerals on the surface, and the mechanisms involved in DOM molecular transformation are currently unclear. This study investigated the nonbiological reduction transformation and coupled adsorption of iron oxide minerals in aquifers containing DOM from both macro- and micro perspectives. The results of macroscopic dynamics experiments indicate that DOM can mediate soluble iron release during the reduction of iron oxide minerals, that pH strongly affects DOM removal, and that DOM is more efficiently degraded at low rather than high pH values, suggesting that a low pH is conducive to DOM adsorption and oxidation. Spherical aberration-corrected scanning transmission electron microscopy (SACTS) indicates that the reacted mineral surfaces are covered with large amounts of carbon and that dynamic agglomeration of iron, carbon, and oxygen occurs. At the nanoscale, three forms of DOM are found in the mineral surface agglomerates (on the surfaces, inside the surface agglomerates, and in the polymer pores). The microscopic organic carbon and iron mineral reaction patterns can form through oxidation reactions and selective adsorption effects. Fourier transform ion cyclotron resonance mass spectra indicate that both synergistic and antagonistic reactions occur between DOM and the minerals, that the release of iron is accompanied by DOM decomposition and humification, that large oxygen- and carbon-containing molecules are broken down into smaller oxygen- and carbon-containing compounds and that more molecules are produced through oxidation under acidic rather than alkaline conditions. These molecules provide adsorption sites for sediment, meaning that more iron can be released. Microscopic evidence for the release of iron was acquired. These results improve the understanding of the geochemical processes affecting iron in groundwater, the nonbiological transformation mechanisms that occur at the interfaces between natural iron minerals and organic matter, groundwater pollution control, and the environmental behavior of pollutants.

Physiological effects of maize stressed by HPPD inhibitor herbicides via multi-spectral technology and two-dimensional correlation spectrum technology

Understanding the physiological effects of herbicides on crops is crucial for crop production and environmental management. The effects of 4-hydroxyphenylpyruvate dioxygenase inhibitor (HPPDi) herbicides at different concentrations on chlorophyll content in maize leaves, fresh weight of roots, stems and leaves, and fluorescence substances and functional groups in root exudates (REs) were studied by UV-Vis absorption spectroscopy, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR) and two-dimensional correlation analysis (2D-COS). The results showed that 5 mg/L and 10 mg/L HPPDi herbicides inhibited the synthesis of chlorophyll in maize leaves. The weight of roots, stems and leaves of maize after application was lighter than that of the control group. HPPDi herbicides affected the early growth of maize seedlings, and the effect was most obvious at high concentration. Synchronous fluorescence spectrum and three-dimensional (3D) fluorescence spectrum revealed that the fluorescence intensity of protein, fulvic acid and humic acid in maize REs changed prominently. With the increase of HPPDi herbicides concentration, the fluorescence intensity decreased gradually. Through FTIR and 2D-COS, functional groups such as C-H, CO, Cl, NO3-, C-O and O-H were found to participate in the interaction between HPPDi herbicides and maize REs as binding sites. C-O, C-Cl and C-C have the strongest binding ability, while CC and CO of aromatic rings, quinones or ketones first take part in the binding between HPPDi herbicides and maize REs. The results can provide a theoretical basis for evaluating the safety of HPPDi herbicides on maize and a method for discovering the effects of pesticides on environmental media and plant physiological effects.

Deciphering DOM-metal binding using EEM-PARAFAC: Mechanisms, challenges, and perspectives

Dissolved organic matter (DOM) is a pivotal component of the biogeochemical cycles and can combine with metal ions through chelation or complexation. Understanding this process is crucial for tracing metal solubility, mobility, and bioavailability. Fluorescence excitation emission matrix (EEM) and parallel factor analysis (PARAFAC) has emerged as a popular tool in deciphering DOM-metal interactions. In this review, we primarily discuss the advantages of EEM-PARAFAC compared with other algorithms and its main limitations in studying DOM-metal binding, including restrictions in spectral considerations, mathematical assumptions, and experimental procedures, as well as how to overcome these constraints and shortcomings. We summarize the principles of EEM to uncover DOM-metal association, including why fluorescence gets quenched and some potential mechanisms that affect the accuracy of fluorescence quenching. Lastly, we review some significant and innovative research, including the application of 2D-COS in DOM-metal binding analysis, hoping to provide a fresh perspective for possible future hotspots of study. We argue the expansion of EEM applications to a broader range of areas related to natural organic matter. This extension would facilitate our exploration of the mobility and fate of metals in the environment.

Characteristics of microplastic-derived dissolved organic matter and its binding with pharmaceuticals unveiled by fluorescence spectroscopy and two-dimensional correlation spectroscopy

Microplastics were an extensively detected pollutant in the environment, but microplastic-derived dissolved organic matter (MP-DOM) has received less attention, much less its impact on the binding behavior of pollutants (e.g., pharmaceuticals). In this study, DOM derived from two typical MPs, i.e., polyethylene terephthalate (PET) and polystyrene (PS) was generated by UV irradiation (a widely used way for MPs' aging treatment) and characterized by multiple spectroscopic techniques and methods. Chloramphenicol (CAP) and carbamazepine (CBZ) were selected to investigate the binding mechanism between MP-DOM and pharmaceuticals. After UV irradiation, the concentration of the dissolved organic carbon, colored DOM, and carboxyl/carbonyl groups of MP-DOM increased. Moreover, the humic-like substance released preceding and more under UV irradiation. Furthermore, the protein-like substances on PET-DOM and the humic-like substances on PS-DOM were positively correlated to the binding capacity to the pharmaceuticals, respectively. 2D-COS results revealed that the fluorescent materials having more oxygen-containing functional groups for MP-DOM preferentially interacted with the pharmaceuticals. Overall, the higher fluorescence quenching was related to the protein-like substance, CBZ, and PET-DOM as compared to the humic-like substance, CAP, and PS-DOM. It was verified by the relatively high binding ability (logKM) for them (the protein-like substance: 5.15; CBZ: 4.61; PET: 4.48). This study first proved the environmental reactivity of MP-DOM to the pharmaceuticals highlighting the significance of the spectral properties for the binding behavior of MP-DOM with pharmaceuticals and the competitive sorption role of MP-DOM to the pollutants in the natural environment.

The presence of copper ions alters tetracycline removal pathway in aerobic granular sludge: Performance and mechanism

This study investigated the removal characteristics of tetracycline (TC) in the presence of copper ions (Cu2+) in aerobic granular sludge by analyzing the TC removal pathway, composition and functional group changes of extracellular polymeric substances (EPS), and microbial community structure. The TC removal pathway changed from cell biosorption to EPS biosorption, and the microbial degradation rate of TC was reduced by 21.37% in the presence of Cu2+. Cu2+ and TC induced enrichment of denitrifying bacteria and EPS-producing bacteria by regulating the expression of signaling molecules and amino acid synthesis genes to increase the content of EPS and -NH2 groups in EPS. Although Cu2+ reduced the content of acidic hydroxyl functional groups (AHFG) in EPS, an increase in TC concentration stimulated the secretion of more AHFG and -NH2 groups in EPS. The long-term presence of TC presence of the relative abundances of Thauera, Flavobacterium and Rhodobacter and improved the removal efficiency.

Inhibitory effect of polyethylene microplastics on roxarsone degradation in soils

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox(V)), an extensively used organoarsenical feed additive, enters soils through the application of Rox(V)-containing manure and further degrades to highly toxic arsenicals. Microplastics, as emerging contaminants, are also frequently detected in soils. However, the effects of microplastics on soil Rox(V) degradation are unknown. A microcosm experiment was conducted to investigate soil Rox(V) degradation responses to polyethylene (PE) microplastics and the underlying mechanisms. PE microplastics inhibited soil Rox(V) degradation, with the main products being 3-amino-4-hydroxyphenylarsonic acid [3-AHPAA(V)], N-acetyl-4-hydroxy-m-arsanilic acid [N-AHPAA(V)], arsenate [As(V)], and arsenite [As(III)]. This inhibition was likely driven by the decline in soil pH by PE microplastic addition, which may directly enhance Rox(V) sorption in soils. The decreased soil pH further suppressed the nfnB gene related to nitroreduction of Rox(V) to 3-AHPAA(V) and nhoA gene associated with acetylation of 3-AHPAA(V) to N-AHPAA(V), accompanied by a decrease in the relative abundance of possible Rox(V)-degrading bacteria (e.g., Pseudomonadales), although the diversity, composition, network complexity, and assembly of soil bacterial communities were largely influenced by Rox(V) rather than PE microplastics. Our study emphasizes microplastic-induced inhibition of Rox(V) degradation in soils and the need to consider the role of microplastics in better risk assessment and remediation of Rox(V)-contaminated soils.

The role of organic and inorganic substituents of roxarsone determines its binding behavior and mechanisms onto nano-ferrihydrite colloidal particles

The retention and fate of Roxarsone (ROX) onto typical reactive soil minerals were crucial for evaluating its potential environmental risk. However, the behavior and molecular-level reaction mechanism of ROX and its substituents with iron (hydr)oxides remains unclear. Herein, the binding behavior of ROX on ferrihydrite (Fh) was investigated through batch experiments and in-situ ATR-FTIR techniques. Our results demonstrated that Fh is an effective geo-sorbent for the retention of ROX. The pseudo-second-order kinetic and the Langmuir model successfully described the sorption process. The driving force for the binding of ROX on Fh was ascribed to the chemical adsorption, and the rate-limiting step is simultaneously dominated by intraparticle and film diffusion. Isotherms results revealed that the sorption of ROX onto Fh appeared in uniformly distributed monolayer adsorption sites. The two-dimensional correlation spectroscopy and XPS results implied that the nitro, hydroxyl, and arsenate moiety of ROX molecules have participated in binding ROX onto Fh, signifying that the predominated mechanisms were attributed to the hydrogen bonding and surface complexation. Our results can help to better understand the ROX-mineral interactions at the molecular level and lay the foundation for exploring the degradation, transformation, and remediation technologies of ROX and structural analog pollutants in the environment.

Insights into the influence of Fe(III) on the interaction between roxarsone and humic acid using multi-spectroscopic techniques

The influence of Fe(III) on the interaction between roxarsone (ROX) and humic acid (HA) was investigated by multi-spectroscopic techniques. The fluorescence quenching experiment indicated that the fluorescence intensity of HA-ROX was quenched by Fe(III) through a static quenching process. Synchronous fluorescence spectra provided further information concerning the competitive combination between ROX and Fe(III) for HA. The results of the dialysis equilibrium experiment confirmed the existence of Fe(III) (0.05-0.1 mmol/L) promotes the combination of HA and ROX. Binding mechanisms were further characterized by FTIR spectroscopy, and the carboxyl functional group is involved in the binding process of HA/Fe/ROX. In addition, acidic and neutral conditions are more conducive to the combination of ROX and HA/Fe than alkaline conditions. The above discussion is of great significance in understanding the environmental fate of ROX under the coexistence of Fe(III) and HA.

Insights into organic matter evolution during food waste stabilization induced by 14-hour high-temperature fermentation

Large amounts of secondary pollutants are released during traditional composting, and rapid fermentation is desirable for the stabilization of food wastes. Food wastes were mixed with rice husk, placed in a bioreactor, and stirred continuously to achieve high-temperature fermentation for 14 h. The transformations of the mixtures were analyzed using elemental and spectral analysis combined with kinetic equations and two-dimensional correlation spectroscopy. The carbohydrates, proteins, and aliphatic compounds of food waste were degraded after 4 h of fermentation. Transformations of dissolved organic and sulfur- and nitrogen-containing substances followed first-order kinetic equations with reaction rate constants of 0.142 h^-1, 0.098 h^-1, and 0.016 h^-1, respectively. Organic matter conversion was in the following order: aliphatic → protein → carbohydrate and followed the order, acrylamide C → O-alkyl C → anomeric C at the molecular level. The fermentation process was characterized by the increase in protein- and fulvic-like compounds. Fulvic acid substances gradually accumulated during the late fermentation period. Thus, dissolved organic matter components were gradually transformed into humic substances with increasing fermentation time. The sequence of transformation during the fermentation process was, tyrosine-like → tryptophan-like → fulvic-like substances. Humification mainly occurred in the mature stage of composting; therefore, it was verified that the food waste was stabilized by a 14-h fermentation.

Insight into different adsorption behaviors of two fluoroquinolone antibiotics by sediment aggregation fractions

Sediment, consisting of different aggregation fractions, is a hotspot site for transport and transformation of various pollutants including antibiotics. However, the fate of different antibiotics in aquatic sediments mediated by sediment aggregation fraction adsorption and the mechanism behinds are still unclear. In this study, we investigated the adsorption behavior of two fluoroquinolone antibiotics (ciprofloxacin and ofloxacin) on four aggregation fractions separated from the sediment of Taihu Lake, a typical lake contaminated by antibiotics in China. The results showed that the adsorption of ciprofloxacin and ofloxacin fitted the Freundlich model, irrespective of sediment aggregation size. The adsorption of ciprofloxacin and ofloxacin was depended on the size of sediment aggregation fractions, and the macroaggregation (> 200 μm) exhibited the strongest capacity, followed by large microaggregation (63-200 μm), medium microaggregation (20-63 μm), and small and primary microaggregation (< 20 μm). This fraction size-dependent effects of sediment aggregations on antibiotic adsorption might be closely related to the differences in their specific surface areas, organic matter contents, and surface functional groups. The adsorption of ciprofloxacin and ofloxacin by sediment aggregation fractions was characterized by a combination of chemical and physical adsorptions, with the former being the dominant process. Compared with ofloxacin, ciprofloxacin could be more rapidly and easily absorbed by four sediment aggregation fractions, and more readily complexed with carboxyl groups on macroaggregation surface. The adsorption of two antibiotics by extracellular polymeric substance showed that tryptophan and tyrosine protein-like, humic-like substance on the surface of sediment could bind to both antibiotics through a complexation reaction. The π-π electron donor-acceptor interaction and hydrogen bonds were responsible for the antibiotic adsorption by sediment aggregation.

Effects of dissolved organic matter derived from chicken manure on the biotransformation of roxarsone in soil

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, ROX), widely used as a livestock feed additive, is excreted untransformed in large concentrations. Accumulation of this manure in the open environment increases dissolved organic matter (DOM) and ROX in soil within the aeration zone. And microbial action plays a dominant role in the transformation of ROX. However, the specific effect of DOM on the biotransformation of ROX is not known. In this paper, we investigated the transformation rate, metabolite content, and microbial community response of ROX in soils with different DOM concentrations (71.61, 100, 200, 500, and 800 mg L-1). The transformation of ROX was consistent with first-order transformation kinetics. DOM promoted the transformation of ROX, and with high DOM (DOM ≥200 mg L-1), ROX was transformed almost completely within two days. In this case, DOM provided nutrients to microorganisms and promoted their growth, accelerating the transformation of ROX. Also, the solubility of ROX was enhanced by DOM to increase its bioavailability. The microbial diversity was negatively correlated with DOM concentration and ROX transformation time; during the transformation of ROX, Bacillus, Arthrobacter, Enterococcus, Acinetobacter, and Pseudomonas became dominant in the soil with anomalously high levels of DOM. This study demonstrates the transformation process of ROX under actual environmental conditions where organic matter coexists with ROX, and this understanding is important for the prevention and control of arsenic pollution in soil within the aeration zone with anomalously high levels of DOM.

Structure, mechanism, and toxicity in antibiotics metal complexation: Recent advances and perspectives

Antibiotic-metal complexes (AMCs) formed by antibiotics and metal ions have attracted considerable attentions in recent years. Although different removal methods for AMCs have been reported in the literature, very few investigations have focused on the mechanisms and toxic effects of antibiotic-metal coordination. This review briefly describes the structural characteristics of various commonly used antibiotics and the coordination mechanisms with metal ions. Considering the complexity of the real environment, various environmental factors affecting AMC formation are highlighted. The effects of AMCs on microbial community structure and the role of metal ions in influencing resistant genes from the molecular perspective are of interest within this work. The toxicities and mechanisms of AMCs on different species of biota are also discussed. These findings underline the need for more targeted detection and analysis methods and more suitable toxicity markers to verify the combination of antibiotics with metal ions and reveal environmental toxicities in future. This review presents an innovative idea that antibiotics combined with metal ions will change the toxicity and environmental behavior of antibiotics.

The binding effect and photooxidation on oxytetracycline with algal extracellular polymeric substances and natural organic matter

Surface water contains a large amount of dissolved organic matter (DOM). Interactions between DOM and micropollutants have a significant impact on micropollutant degradation. In this study, algal extracellular polymeric substances (EPS) and natural organic matter (NOM) were selected as two DOM sources and oxytetracycline (OTC) as a representative micropollutant. EPS was mainly composed of tryptophan and protein-like organics, while NOM was mainly composed of fulvic acid-like, humic acid-like, and hydrophobic acid components. In addition, OTC degradation significantly decreased when bound with EPS and the C=O and C-H bonds of CH₂ or CH₃ groups may be involved in binding EPS and OTC, respectively, while -COOH may be involved in the binding of NOM and OTC. Furthermore, triplet intermediates were found to play a major role in OTC photodegradation in both EPS and NOM, with the contribution calculated as 49.96% and 44.61%, respectively. Steady-state concentrations of ³EPS* in EPS and ³NOM* in NOM were 3.59 × 10^-14 mol L^-1 and 5.54 × 10^-15 mol L^-1, respectively. These results provide new insights into the degradation of antibiotic-containing wastewater in the natural environment or engineering applications.

Impact of different manure-derived dissolved organic matters on the fate of arsenic-antibiotic in co-contaminated paddy soils

Manure application increases the transfer risk of antibiotic resistance to farmland. Especially, its impact remains unclear when it occurs in arsenic (As)-contaminated paddy soils, which is considered as a global environmental problem. In this work, we investigated the fate of antibiotic resistance genes (ARGs) in As-antibiotic co-contaminated paddy soils under the application of manure from different sources (pig manure, cow dung, and chicken manure). Differences in the aliphatic carbon and electron-donating capacities of these dissolved organic matters (DOM) regulated the transformation of iron and As by both biotic and abiotic processes. The regulation by pig manure was stronger than that by cow dung and chicken manure. DOM regulation increased the abundance of As-related functional genes (arsC, arrA, aioA, and arsM) in the soil and accelerated the transformation of As speciation, the highest proportion of As(III) being 45%-61%. Meanwhile, the continuous selection pressure provided by the highly toxic As(III) increased the risk of ARGs and mobile genetic elements (MGEs) via horizontal gene transfer. As-resistant bacteria, including Bacillus, Geobacter, and Desulfitobacterium, were finally considered as potential host bacteria for ARGs and MGEs. In summary, this study clarified the synergistic mechanism of As-antibiotic on the fate of ARGs in co-contaminated paddy soils, and provided practical guidance for the proper application of organic fertilizers.

Environmental Behavior and Remediation Methods of Roxarsone

Roxarsone (ROX) is used extensively in the broiler chicken industry, and most is excreted in poultry litter. ROX degradation produces inorganic arsenic, which causes arsenic contamination of soil and aquatic environment. Furthermore, elevated arsenic concentrations are found in livers of chickens fed ROX. Microorganisms, light, and ions are the main factors that promote ROX degradation in the environment. The adsorption of ROX on different substances and its influencing factors have also been studied extensively. Additionally, the remediation method, combining adsorption and degradation, can effectively restore ROX contamination. Based on this, the review reports the ecological hazards, discussed the transformation and adsorption of ROX in environmental systems, documents the biological response to ROX, and summarizes the remediation methods of ROX contamination. Most previous studies of ROX have been focused on identifying the mechanisms involved under theoretical conditions, but more attention should be paid to the behavior of ROX under real environmental conditions, including the fate and transport of ROX in the real environment. ROX remediation methods at real contaminated sites should also be assessed and verified. The summary of previous studies on the environmental behavior and remediation methods of ROX is helpful for further research in the future.

Comparison of the binding interactions of 4-hydroxyphenylpyruvate dioxygenase inhibitor herbicides with humic acid: Insights from multispectroscopic techniques, DFT and 2D-COS-FTIR

4-Hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor is one of the important herbicides to solve the problem of weed control. With the widespread and continued use of HPPD inhibitor (HPPDi) herbicides, it may inevitably put pressure on the environment. Humic acid (HA) can effectively interact with pesticides through sorption or covalent bond formation and promote the degradation of pesticides, which can reduce the risk of pesticides in the environment. In the present study, the interactions of four HPPDi herbicides (sulcotrione, tembotrione, topramezone and mesotrione) with HA were reported and comparative assessment of the binding using multispectral technology, density functional theory (DFT) calculation and two-dimensional correlation spectroscopy (2D-COS). Time-resolved measurements and the Stern-Volmer constant at different temperature verified that HPPDi can bind with HA through the static quenching mechanism. From the thermodynamic parameters, the interaction force between HA and sulcotrione, tembotrione, topramezone and mesotrione was provided by electrostatic force. DFT, binding constant and three-dimensional (3D) fluorescence peak variation all indicated that the order of the binding ability of the four HPPDi and HA was mesotrione > tembotrione > sulcotrione > topramezone. According to dynamic light scattering (DLS), pH 7 is most conducive to the formation of HA-HPPDi complexes. Fourier transform infrared spectroscopy (FTIR) and 2D-COS showed that HA combined with HPPDi through aromatic C-H, CO and C-X, and the first binding group to HA was almost all CO. Sulcotrione, tembotrione, topramezone and mesotrione quench the endogenous fluorescence of HA by a static quenching mechanism and bind to HA through electrostatic interaction to form a complex. These results provide important insights into the combination of environmental pollutants with HA.

Sorption of Pb(II) onto biochar is enhanced through co-sorption of dissolved organic matter

Biochar plays an important role in controlling migration of pollutants in soils. However, little information is available on the interactions between soil-derived dissolved organic matter (DOM), biochar and soluble metal species. The aim of this work was to present the adsorption process of soil DOM by biochar (corn straw biochar produced at 700 °C) and to determine whether co-sorption of DOM would change the affinity for Pb(II). The adsorption rates of biochar and biochar + DOM for Pb(II) were best fitted with a pseudo-second order kinetic model, and the equilibrium adsorption isotherm data agreed well with both the Langmuir and Freundlich models. Adsorption of DOM to biochar reached equilibrium after 15 h with an uptake of 52% of the supplied DOM. We used fluorescence excitation-emission matrices (EEMs) with parallel factor (PARAFAC) analysis to demonstrate that protein-like, fulvic acid-like and humic acid-like substances were the primary constituents of the DOM, which were quenched over time in the presence of biochar. Synchronous fluorescence spectra indicated that the protein-like structures were the predominant fluorescence substances in DOM. Two-dimensional correlation spectroscopy (2D-COS) showed the binding of DOM to biochar resulted in the quenching of fluorescence in the order: protein-like substances > humic-like substances (280 > 355 nm). Data supports the notion that DOM can increase the adsorption capacity of biochar for metal-ions.

Increase of Fluorescence of Humic-Like Substances in Interaction with Cd(II): a Photoinduced Charge Transfer Approach

Described is the enhancement of fluorescence intensity due to the interaction of a humic-like substance (HLS 1%) extracted from process water (PW) and Cd(II) ions in aqueous solution. Using Canonical Polyadic/Parallel Factor Analysis (CP/PARAFAC), two main components were seen that contributed to fluorescence, the first one increased it and the second one kept it constant in both static and dynamic fluorescence studies. Two-dimensional FTIR analysis indicated that the interaction of HLS 1% and Cd(II) ions occurred in the following order of affinity with the groups: C-O bonds in polysaccharides > C-O bonds in carboxylic acid. The results obtained suggest that the increase in fluorescence intensity and lifetime suggest a photoinduced charge transfer (PCT) between Cd(II) ions and carboxylic acid groups present in HLS 1%.

Phenylarsonics in concentrated animal feeding operations: Fate, associated risk, and treatment approaches

Phenylarsonics are present as additives in animal feed in some countries. As only a small fraction of these additives is metabolized in animals, they mostly end up in the environment. A comprehensive investigation of the fate of these additives is crucial for evaluating their risks. This review aims to provide a clear understanding of the transformation mechanism of phenylarsonics in vivo and in vitro and to evaluate their fate and associated risks. Degradation of phenylarsonics releases toxic As species (mainly as inorganic arsenic (iAs)). Trivalent phenylarsonics are the metabolites or biotic degradation intermediates of phenylarsonics. The cleavage of As groups from trivalent phenylarsonics catalyzed by C-As lyase or other unknown pathways generates arsenite (As(III)). As(III) can be further oxidized to arsenate (As(V)) and methylated to methyl-arsenic species. The half-lives associated with abiotic degradation of phenylarsonics ranged from a few minutes to tens of hours, while those associated with biotic degradation ranged from several days to hundreds of days. Abiotic degradation resulted in a higher yield of iAs than biotic degradation. The use of phenylarsonics led to elevated total As and iAs levels in animal products and environmental matrices, resulting in As exposure risk to humans. The oxidation of phenylarsonics to As(V) facilitated the sorptive removal of As, which provides a general approach for treating these compounds. This review provides solid evidence that the use of phenylarsonics has adverse effects on both human health and environmental safety, and therefore, supports their withdrawal from the global market.

New insights into the interaction between dissolved organic matter and different types of antibiotics, oxytetracycline and sulfadiazine: Multi-spectroscopic methods and density functional theory calculations

Dissolved organic matter (DOM) is composed of numerous fluorescent components. It is an indispensable parameter to affect the environmental fate of antibiotics in various ways. To assess the migration of antibiotics in environment compartments, it is crucial to understand the binding mechanism between DOM and antibiotics. How a particular component in DOM interacts with coexistence antibiotics is not still fully understood. Therefore, in the present study, interactions of two antibiotics oxytetracycline (OTC) and sulfadiazine (SD) with humic acid (HA) and L-tryptophan (L-Trp) which were representative DOM components, were investigated by multispectral techniques and density functional theory (DFT) calculations. The fluorescence quenching mechanism was static quenching. In the binding process, the quenching ability of OTC was stronger than that of SD in HA, which was the same as in L-Trp. DFT calculations were applied to confirm a stronger interaction between OTC and HA or L-Trp than SD. Meanwhile, analyzing the binding sequence by two-dimensional correlation spectroscopy (2D-COS), a humic-like substance bound antibiotics was earlier than a protein-like substance. In HA system, the combination of two antibiotics had a synergistic effect on HA quenching. In L-Trp system, the quenching relationship between the two antibiotics and L-Trp was antagonistic. The FTIR spectra showed that hydroxyl and amide were involved in the binding process of individual DOM components with OTC and SD. The work will help to further understand the behavior of coexistence antibiotics in the environment.

The binding characteristics of sediment-derived dissolved organic matter with ceftazidime: a microstructural and spectroscopic correlation study

This research focused on the characterization of sediment-derived dissolved organic matter (SDOM) extracted from sediment of Yellow River and the binding behaviors of ceftazidime (CAZ) with the presence of SDOM. The morphology, surface composition and structure of SDOM and the complexation between SDOM and CAZ in terms of component features, binding capacity and sequence were studied by multiple approaches. Results showed that SDOM was in situ autochthonous-dominated with a low weight-average molecular weight and aromaticity (the value of S_R was 2.523). The multiple morphological characteristics, high surface oxygen contents (53.49%) and more aliphatic (H/C = 1.91) of SDOM were further confirmed. Studies on SDOM-CAZ interaction suggested that the functional groups and chemical compositions of SDOM were susceptible to CAZ. In more detail, the aromatic protons and aliphatic protons of CAZ impacted significantly, and the binding between CAZ and SDOM might relate to noncovalent. The protein-like fractions were considered to be the primary participant with 49% fractions lost and the aromatics and amides as mainly active site interaction with CAZ. These findings have significant implications on the environmental fate of cephalosporin antibiotics and that of sediment-derived DOM.

Interaction of heavy metals and biocide/herbicide from stormwater runoff of buildings with dissolved organic matter

Stormwater runoff from roofs and façades can be contaminated by heavy metals and biocides/herbicides. High efficiency on-site treatment methods are now urgently needed to safeguard the ecosystem. The basis for developing such treatment facilities is an in-depth understanding of their interactions with dissolved organic matter (DOM), as this affects their migration in the environment. Hence, the interactions between copper (Cu), zinc (Zn), benzyl-dimethyl-tetradecylammonium chloride dihydrate (BAC), mecoprop-P (MCPP) and DOM at pH 5 to 9 were investigated separately in this study. The evaluation of the interaction processes was achieved by applying excitation emission matrix and parallel factor analysis (EEM-PARAFAC) to titration samples; obtained data were fitted by two different models. Mechanisms involved in BAC/MCPP-DOM interactions were revealed by Fourier-transform infrared spectroscopy (FTIR) and two-dimensional correlation spectrum (2D-COS) analysis. Results showed that the applied DOM was composed of the two different fluorescent components C1 and C2. More interaction with C1 than with C2 was observed for both Cu/Zn and BAC/MCPP. Increasing the pH enhanced the interactions between Cu/Zn and DOM. At pH 5 with a maximum quencher addition, the remaining fluorescence of CuC1 and ZnC1 were 15.7% and 87.1%, respectively. Corresponding data at pH 9 decreased to 3% and 69.5%. Contrarily, interactions between BAC/MCPP and DOM were impaired by high pH conditions. The increase of pH from 5 to 9 with maximum BAC and MCPP added raised the remaining fluorescence of BAC-C1 and MCPP-C1 by 15.9% and 21.3% separately. The fitting outcomes from the Ryan-Weber equation (Cu/Zn titration) and the Stern-Volmer equation (BAC/MCPP titration) corresponded well with the titration studies. FTIR coupled with 2D-COS analysis revealed that mechanisms involved in BAC/MCPP titration include hydrogen bonding, π-π interaction, and electrostatic effect. The order of mechanisms taking effect during the interaction with DOM is affected by the molecular structure of BAC and MCPP.

Transport of Veterinary Antibiotics in Farmland Soil: Effects of Dissolved Organic Matter

The application of manure as a fertiliser to farmland is regarded as a major source of veterinary antibiotic (VA) contamination in the environment. The frequent detection of such emerging contaminants and their potential adverse impacts on the ecosystem and human health have provoked increasing concern for VA transport and fate. Extrinsic dissolved organic matter (DOM) may be introduced into farmland soil along with Vas, and thus exert significant effects on the transport of VAs via hydrological processes upon rainfall. The leaching of VAs can be either enhanced or reduced by DOM, depending on the nature, mobility, and interactions of VAs with DOM of different origins. From the aspect of the diversity and reactivity of DOM, the state-of-the-art knowledge of DOM−VA interactions and their resulting effects on the sorption−desorption and leaching of VAs in farmland soil was reviewed. Spectroscopic techniques for examining the extent of binding and reactive components of DOM with VAs are summarized and their usefulness is highlighted. Models for simulating VA transport under the effects of DOM were also reviewed. It is suggested that distinct impacts of DOM of various organic fertiliser/amendment origins should be considered for predicting the transport of VAs in farmland soil.

Effect of colloidal fluorescence properties on the complexation of chloramphenicol and carbamazepine to the natural aquatic colloids

The complexation mechanism between pharmaceuticals and natural colloids is still uncertain due to the complexity, heterogeneity, and polydispersity of colloids. Therefore, this study investigated the effect of fluorescence properties on the complexation of chloramphenicol (CAP) and carbamazepine (CBZ) to the colloids from Poyang Lake Basin based on the multiple spectroscopic techniques and methods. Three-dimensional excitation-emission matrix fluorescence spectroscopy-parallel factor analysis results illustrated that two humic-like components and two protein-like components of colloids from the rivers and lakes were identified, with the much higher fluorescence intensity of the protein-like substance observed in lake samples. The protein-like substance decreased dramatically with the addition of CAP and CBZ, suggesting its higher binding capacity towards these drugs, especially for CBZ. In addition, the fluorescence quenching titration was proceeded to explore the binding mechanism between the colloids and the pharmaceuticals. Results of synchronous fluorescence spectra and two-dimensional correlation spectroscopy demonstrated that the fluorescence quenching effect occurred preferentially between the protein-like substances and the pharmaceuticals, with the stronger complexation for CBZ. Ryan-Weber model fitting results showed that the stability constant ranged from 4.02 to 5.04 with the higher binding capacity observed for the tryptophan-like substance. Combined, the fluorescence components in aquatic colloids could be significantly impacted the complexation of the pharmaceuticals. This study provides deep insights into the fate and pollution protection of pharmaceuticals.

New insights into the interactions between humic acid and three neonicotinoid pesticides, with multiple spectroscopy technologies, two-dimensional correlation spectroscopy analysis and density functional theory

The widespread use of neonicotinoid pesticides in agricultural production has caused pressure on the environment. In the present work, the interactions between humic acid (HA) and three neonicotinoid insecticides, dinotefuran, clothianidin and nitenpyram, were investigated by using multiple spectroscopy techniques combined with two-dimensional correlation spectroscopy analysis and density functional theory (DFT). Dinotefuran, clothianidin and nitenpyram could quench the endogenous fluorescence of HA through a static quenching process dominated by hydrogen bonds and van der Waals forces. According to the revised Stern-Volmer equation and DFT calculation, the binding abilities of the three pesticides with HA were ranked as dinotefuran < clothianidin < nitenpyram. The results of dynamic light scattering showed that neutral conditions were more conducive to the combination of HA and dinotefuran, clothianidin and nitenpyram. Through Fourier transform infrared spectroscopy (FTIR) combined with two-dimensional correlation analysis (2D-COS), the functional group with the strongest binding ability in the HA-dinotefuran, HA-clothianidin and HA-nitenpyram system was CH, CO and CO, respectively. The work will help to further understand the behavior of neonicotinoid pesticides in the environment.

Probing the roles of pH and ionic strength on electrostatic binding of tetracycline by dissolved organic matters: Reevaluation of modified fitting model

The binding performance of dissolved organic matters (DOM) plays a critical role in the migration, diffusion and removal of various residual pollutants in the natural water environment. In the current study, four typical DOMs (including bovine serum proteins BSA (proteins), sodium alginate SAA (polysaccharides), humic acid HA and fulvic acid FA (humus)) are selected to investigate the binding roles in zwitterionic tetracycline (TET) antibiotic under various ionic strength (IS = 0.001-0.1 M) and pH (5.0-9.0). The dialysis equilibration technique was employed to determine the binding concentrations of TET, and the influence of IS and pH on binding performance was evaluated via UV-vis spectroscopy, total organic carbon (TOC), and Excitation-Emission-Matrix spectra (EEM), zeta potentials and molecule size distribution analysis. Our results suggested that carboxyl and phenolic hydroxyl were identified as the main contributors to TET binding based on the fourier transform infrared spectroscopy (FTIR) analysis, and the binding capability of four DOMs followed as HA > FA » BSA > SAA. The biggest binding concentrations of TET by 10 mg C/L HA, FA, BSA and SAA were 0.863 μM, 0.487 μM, 0.084 μM and 0.086 μM, respectively. The higher binding capability of HA and FA is mainly attributed to their richer functional groups, lower zeta potential (HA/FA = -15.92/-13.54 mV) and the bigger molecular size (HA/FA = 24668/27750 nm). IS significantly inhibits the binding interaction by compressing the molecular structure and the surface electric double layer, while pH had a weak effect. By combining the Donnan model and the multiple linear regression analysis, a modified Karickhoff model was established to effectively predict the binding performance of DOM under different IS (0.001-0.1 M) and pH (5.0-9.0) conditions, and the R² of linear fitting between experiment-measured logK_DOC and model-calculated logK_OC were 0.94 for HA and 0.91 for FA. This finding provides a theoretical basis for characterizing and predicting the binding performance of various DOMs to residual micropollutants in the natural water environment.

Bisphenol A adsorption behavior on soil and biochar: impact of dissolved organic matter

Dissolved organic matter (DOM) released from soil (SDOM) and biochar (BDOM) plays an important role in the fate of pollutants for the application of biochar in soil remediation. However, little attention has been paid to the impact of DOM on the adsorption of soil and/or biochar-bisphenol A (BPA) system. Hence, batch sorption experiments combined with quenching titration experiments were processed to reveal these behaviors and complexation mechanisms based on red soil and corn straw biochar. Moreover, multiple spectral technologies and methods were also introduced including ultraviolet-visible, three-dimensional excitation-emission matrix, synchronous fluorescence spectrum, two-dimensional correlation spectroscopy (2D-COS), and parallel factor analysis. Isothermal adsorption results showed that the non-linearity and the adsorption capacity both increased after the addition of biochar, indicating that biochar could improve the surface adsorption capacity of the sorption system. Besides, the sorption capacity of BPA decreased for soil while increased for biochar after removal of the water-extractable DOM. 2D-COS analysis showed that the protein-like components preferentially occurred for both SDOM and BDOM under BPA surrounding. In addition, C2 (humic-like), C4 (tyrosine-like), and C5 (tryptophan-like) in the two DOMs were all involved in the quenching reaction with BPA, with C4 and C5 having higher quenching degree than C2, suggesting that protein-like substances had stronger affinity quenching effect with BPA. This study highlighted the significance of fluorescence property for DOM, which can extend the knowledge of the fate of pollutants in the application of biochar.

The application of two-dimensional correlation spectroscopy for the binding properties of heavy metals onto digestate-derived DOM from anaerobic digestion of chicken manure

Anaerobic digestate has been widely used for agricultural activities as an organic fertilizer product. Dissolved organic matter (DOM) derived from anaerobic digestate plays a key role in the speciation, bioavailability and ultimate fate of metals that is related to agriculture and food safety as well as the soil environment. Hence, the binding properties of Cu, Pb and Zn with digestate DOM are investigated using two-dimensional correlation spectroscopy (2D-COS) in combination with ultraviolet absorption, synchronous fluorescence spectra (SFS) and Fourier transform infrared (FTIR) spectroscopy. The 2D absorption COS shows that the DOM at 200 nm is most susceptive with the addition of Pb, followed by Zn and Cu. The log-transformed absorption spectra can also obtain more valuable signals than that from conventional absorption spectra. The 2D-SFS-COS indicates that protein-like peak is more sensitive to the variation of the concentration of metal ions, and fulvic-like substances can preferentially interact with the three heavy metals (HMs). The 2D-FTIR-COS reveals that Cu(II) and Zn(II) ions can be bonded preferentially to the N-H of secondary amide (II), and phenolic OH groups shows a favorable binding with Pb(II). Humic-like peaks with Cu(II) and Zn(II) obtains relatively higher log K_M values than fulvic- and protein-like substances. However, the proportion of initial fluorescence (f) for DOM-Cu(II) and DOM-Zn(II) decreased with an increase in wavelength. Protein-like materials have more fluorescent substances that can combine with Cu(II) and Zn(II). This study provides a guide for understanding the geochemical behavior of metal ions in agricultural soils when anaerobic digestate is applied as an organic fertilizer product.

Effects of digestate DOM on chemical behavior of soil heavy metals in an abandoned copper mining areas

The influence of digestate dissolved organic matter (DOM) on chemical behavior of soil heavy metals (HMs) in an abandoned copper mining areas was explored by fluorescence quenching titration and heavy metal extracting experiment. Five fluorescent components were obtained from digestate DOM by PARAFAC model combined with the EEM data. The stability constant (log K_M) values were in the range of 4.95-5.53, 5.05-5.29, 5.21-6.00, and 4.12-4.75 for DOM-Cr(III), DOM-Cu(II), DOM-Fe(III) and DOM-Pb(II) complexes, respectively. Alcohols, ethers and esters in digestate DOM were preferentially combined with Fe(III), Cu(II) and Zn(II). However, phenolic hydroxyl groups were more likely to combine with Cr(III) and Pb(II). The speciation distribution of HMs indicated that mining resulted in a higher concentration of Cu(II) in the grassland soil (GS) than those in the agricultural soil (AS) and forest land soil (FS). Fe-Mn oxides and organic forms of Pb(II) increased dramatically due to mining. Digestate DOM extraction can increase the content of Cr(III), Fe(III) and Pb(II), and decrease the content of Cu(II) and Zn(II) in the AS, GS, and FS. However, the contents of HMs in the mining soil (MS) and slag soil (SS) decreased due to the application of digestate DOM, except for Cu(II) in the SS.

Fractions Transformation and Dissipation Mechanism of Dechlorane Plus in the Rhizosphere of the Soil-Plant System

The fractions transformation and dissipation mechanism of Dechlorane Plus (DP) in the rhizosphere of soil-plant system were investigated and characterized by a 150-day experiment using a rhizobox system. The depuration, accumulation, and translocation of DP in rice plants were observed. The contributions of plant uptake, microbial degradation, and bound-residue formation to DP dissipation under the rhizosphere effect were modeled and quantified. The gradients of DP concentrations correlated well with microbial biomass in the rhizosphere (R² = 0.898). The rhizosphere facilitated the bioavailability of DP (excitation) and modified the bound-residue formation of DP (aging). DP concentrations in roots were positively correlated with the labile fraction of DP in soil (R² = 0.852-0.961). There were spatiotemporal variations in the DP fractions. Dissolved and soil organic carbon were important influences on fraction transformation. Contributions to total DP dissipation were in the following ranges: microbial degradation (8.33-54.14%), bound-residue formation (3.64-16.43%), and plant uptake (0.54-3.85%). With all of these processes operating, the half-life of DP in the rhizosphere was 105 days. The stereoselectivity of DP isomers in both rice and DP fractions in soil were observed, suggesting a link between stereoselective bioaccumulation of DP in terrestrial organisms and dissipation pathways in soil.

Mechanistic insights into the enhanced removal of roxsarsone and its metabolites by a sludge-based, biochar supported zerovalent iron nanocomposite: Adsorption and redox transformation

Roxarsone is a phenyl-substituted arsonic acid comprising both arsenate and benzene rings. Few adsorbents are designed for the effective capture of both the organic and inorganic moieties of ROX molecules. Herein, nano zerovalent iron (nZVI) particles were incorporated on the surface of sludge-based biochar (SBC) to fabricate a dual-affinity sorbent that attracts both the arsenate and benzene rings of ROX. The incorporation of nZVI particles significantly increased the binding affinity and sorption capacity for ROX molecules compared to pristine SBC and pure nZVI. The enhanced elimination of ROX molecules was ascribed to synergetic adsorption and degradation reactions, through π-π* electron donor/acceptor interactions, H-bonding, and As-O-Fe coordination. Among these, the predominate adsorption force was As-O-Fe coordination. During the sorption process, some ROX molecules were decomposed into inorganic arsenic and organic metabolites by the reactive oxygen species (ROS) generated during the early stages of the reaction. The degradation pathways of ROX were proposed according to the oxidation intermediates. This work provides a theoretical and experimental basis for the design of adsorbents according to the structure of the target pollutant.

The composition difference of macrophyte litter-derived dissolved organic matter by photodegradation and biodegradation: Role of reactive oxygen species on refractory component

The overgrowth of macrophytes has become serious due to increasing eutrophication in shallow lakes. The primary degradation processes of macrophytes litter, including photodegradation and biodegradation, induce considerable patchiness in the concentration and bioavailability of dissolved organic matter (DOM). In this study we investigated the composition evolution of DOM derived from emergent aquatic plant litter, Phragmites australis, in microbial degradation, photodegradation, and the combination of bio- and photo-degradation. Results revealed that the effects of photo- and biodegradation on the composition difference of macrophyte litter-derived DOM during short- and long-term degradation phase were different. Although large changes in DOM were observed after five days of incubation, the abundance and chemical composition were similar in the three treatments. However, more concentration of DOM was produced by combined photo- and biodegradation at the long-term degradation phase, and the composition of DOM showed less lignin-like formulae, as well as less condensed aromatic and aromatic compounds when compared to sole treatments. More reactive oxygen species (ROS) were found under the combined treatments, thus the contents of refractory components (condensed aromatic- and aromatic compound groups) were reduced. This study provide deeper insight into the fate of DOM and relevant biogeochemical processes in eutrophic lakes.

Study on the long-term effects of DOM on the adsorption of BPS by biochar

Bisphenol S (BPS), regarded as a valid alternative to Bisphenol A (BPA), has been found to induce acute toxicity, genotoxicity. In this paper, BPS pollution was repaired by corn straw biochar, and the effect of dissolved organic matter (DOM) on the remediation mechanism was investigated. Different DOMs were obtained by decomposing corn straw in red soil, yellow soil and brown soil. The DOMs were characterized by Elemental analysis, Fourier infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (Uv-vis) spectroscopy, Three-dimensional excitation-emission matrix (3D-EEM). Different kinds of DOMs were added into the biochar adsorption system to determine the optimal pH, optimal dosage, equilibrium adsorption capacity, adsorption kinetics, adsorption isotherms, thermodynamic characteristics, and explore the influence mechanism of DOM on the adsorption of BPS by biochar. The results of the adsorption experiments showed that DOM would suppress the BPS adsorption capacity on biochar. In addition, the DOM, produced by decomposition of corn straw with brown soil, had the strongest inhibitory effect on adsorption, and red soil was the soil with the lowest inhibitory effect on organic pollution removal by biochar.

Interactions between Imidacloprid and Thiamethoxam and Dissolved Organic Matter Characterized by Two-Dimensional Correlation Spectroscopy Analysis, Molecular Modeling, and Density Functional Theory Calculations

The heavy application of neonicotinoid insecticides in agricultural production has burdened the environment. In the present study, interactions of two neonicotinoid insecticides imidacloprid and thiamethoxam with dissolved organic matter (DOM) were investigated by spectroscopic techniques, molecular modeling, and density functional theory (DFT) calculations. The static mechanism of imidacloprid and thiamethoxam quenching the endogenous fluorescence of DOM was assessed through time-resolved analyses. During the binding process, a protein-like substance binds imidacloprid and thiamethoxam later than a humic-like substance, as analyzed by two-dimensional correlation spectroscopy, but more strongly than the humic-like substance, as suggested by molecular modeling and DFT calculations. The conformational changes of DOM are attributed to imidacloprid and thiamethoxam, as assessed with three-dimensional spectra. Fourier transform infrared spectroscopy indicated that DOM binds imidacloprid and thiamethoxam by hydroxyl, aliphatic C-H, amide I, and carboxyl to form stable DOM-imidacloprid and DOM-thiamethoxam complexes. Understanding the changes in the structural conformation of humic-like and protein-like substances with imidacloprid and thiamethoxam helps further understand the fate of the neonicotinoids in the environment.

Desorption kinetics of tetracyclines in soils assessed by diffusive gradients in thin films

Tetracyclines (TCs) are frequently detected in agricultural soils worldwide, causing a potential threat to crops and human health. In this study, diffusive gradients in thin films technique (DGT) was used to measure the distribution and exchange rates of three TCs (tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC)) between the solid phase and solution in five farmland soils. The relationship between the accumulated masses with time suggested that TCs consumption in soil solution by DGT would induce the supply from the soil solid phase. The distribution coefficient for the labile antibiotics (K_dl), response time (T_c) and desorption/adsorption rates (k_b and k_f) between dissolved and sorbed TCs were derived from the dynamic model of DIFS (DGT induced fluxes in soils). The K_dl showed similar sizes of labile solid phase pools for TC and OTC while larger pool sizes were observed for CTC in the soils. Although the concentrations of CTC were lowest in soil solution, the potential hazard caused by continuous release from soil particles could not be ignored. The long response time (>30 min in most cases) suggested that the resupply of TCs from soil solids was limited by their desorption rates (1.26-121 × 10^-6 s^-1). The soils in finer texture, with higher clay and silt contents (<50 μm) showed a greater potential for TCs release.

Autochthonous dissolved organic matter potentially fuels methane ebullition from experimental lakes

Shallow lakes are hotspots for carbon processing and important natural sources of methane (CH₄) emission. Ebullitive CH₄ flux may constitute the overwhelming majority of total CH₄ flux, but the episodic nature of ebullition events makes determining both quantity and the controlling factors challenging. Here we used the world's longest running shallow-lake mesocosm facility, where the experimental treatments are low and high nutrients crossed with three temperatures, to investigate the quantity and drivers of CH₄ ebullition. The mean CH₄ ebullition flux in the high nutrient treatment (41.5 ± 52.3 mg CH₄-C m^-2 d^-1) mesocosms was significantly larger than in the low nutrient treatment (3.6 ± 5.4 mg CH₄-C m^-2 d^-1) mesocosms, varying with temperature scenarios. Over eight weeks from June to August covered here warming resulted in a weak, but insignificant enhancement of CH₄ ebullition. We found significant positive relationships between ebullition and chlorophyll-a, dissolved organic carbon (DOC), biodegradable DOC, δ²H, δ¹⁸O and δ¹³C-DOC, autochthonous dissolved organic matter (DOM) fluorescent components, and a fraction of lipids, proteins, and lignins revealed using ultrahigh-resolution mass spectrometry, and a negative relationship between ebullitive CH₄ flux and the percentage volume inhabited of macrophytes. A 24 h laboratory bio-incubation experiment performed at room temperature (20 ± 2 °C) in the dark further revealed a rapid depletion of algal-DOM concurrent with a massive increased CH₄ production, whereas soil-derived DOM had a limited effect on CH₄ production. We conclude that eutrophication likely induced the loss of macrophytes and increase in algal biomass, and the resultant accumulation algal derived bio-labile DOM potentially drives enhanced outgassing of ebullitive CH₄ from the shallow-lake mesocosms.

Effects of bok choy on the dissipation of dibutyl phthalate (DBP) in mollisol and its possible mechanisms of biochemistry and microorganisms

Phytoremediation is an ecologically sustainable method for remediating contaminated soils, however, research on phytoremediation and its mechanisms are still rarely reported. The highest dibutyl phthalate (DBP) dissipation rate was 91% in 0-3mm bok choy rhizosphere via a 45-day rhizo-box experiment, and bok choy could regulate soil nutrients by increasing soil ammonia nitrogen (AN) and available phosphorus (AP). The biochemistry mechanism of interaction between dissolved organic matter (DOM) and DBP was also elucidated by various spectroscopy techniques. It was found that the alkyl ester in DBP produced the fastest response during the binding process, and the aromatic, hydroxyl and phenolic groups of the DOM humic-like substances preceded amide in DOM protein-like substance. It was found that DBP pollution reduced the Chao1 richness and Shannon index of bacteria in black soil via a pot experiment and high-throughput sequencing, which disturbed the metabolic activities and functional diversity of microorganisms in Mollisol. The microbial abundance increased in bok choy amendments, which has a specific microbial community structure and a high abundance of Actinobacteria and Acidobacteria. We concluded that some enriched genera were responsible for DBP dissipation, Alsobacter, Lacibacter, Myceligenerans, Schrenkiella parvula and Undibacterium. The findings of this study revealed that the possible biochemistry and microbial mechanisms of phytoremediation promoting the DBP dissipation in rhizosphere Mollisol and provided more useful information for phytoremediation of organic pollutants.

Investigating the binding properties between antimony(V) and dissolved organic matter (DOM) under different pH conditions during the soil sorption process using fluorescence and FTIR spectroscopy

Antimony (Sb) is listed as a priority pollutant by European Union and U.S. Environmental Protection Agency. However, reports on its environmental behavior, particularly the sorption process in soil are still limited. In this paper, Sb(V) was selected as the sorbate and the black soil as the sorbent. The initial sorption rate (k₂q_e,cal²) was calculated to be 0.1254 mg g^-1∙min^-1 and the maximum sorption amount (q_m) 57.33 mg g^-1. Once the dissolved organic matter (DOM) was removed from the soil, the values of k₂q_e,cal² and q_m went down to 0.1066 mg g^-1∙min^-1 and 19.01 mg g^-1, respectively. These results suggested that the existence of DOM significantly influenced the mass transfer rate and sorption amount of Sb(V) in soil. In order to find out the reason why DOM exerted such an influence, the binding interaction mechanism between Sb(V) and DOM was investigated under different pH values. The protein-like and humic-like substances as well as the functional groups of CO, phenol hydroxyl, C-O, C-H, C-X and sulfur/phosphorus contributed to the formation of DOM-Sb(V)-complexes under pH of 7.0, in which the humic-like substance and the functional groups containing oxygen showed higher binding affinity for Sb(V) than protein-like substance and other functional groups, respectively. The protein-like substance and some functional groups disappeared under pH of 4.0 and 10.0. Alkaline condition resulted in a bigger impact on reducing the number of functional groups than acid condition. It can be concluded that the strongest binding interaction occurred at pH of 7.0 then followed by 4.0 and 10.0. This paper might be helpful to further studying the environmental behavior of Sb(V) in soil.

Study on removal of pyrene by Agropyron cristatum L. in pyrene-Ni co-contaminated soil

Heavy metals and polycyclic aromatic hydrocarbons (PAHs) co-contamination in the soil is widespread. Phytoremediation is often used to remediate co-contaminated soil, but few studies focused on the effects of nickel on the dissipation and uptake of pyrene in phytoremediation. The dissipation of pyrene, the uptake, and distribution of pyrene in Agropyron cristatum L. (A. cristatum) were investigated in this study in the presence of nickel. The pyrene removal rate in single pyrene-contaminated soil with A. cristatum cultivation (48.97%) was the highest, which was higher than that of the co-contamination (47.88%). This was due to the high soil microbial activity and high dissolved organic matter (DOM) contents. In single pyrene-contaminated soil, pyrene was mainly accumulated in the soluble fraction in shoots and on the cell wall in roots of A. cristatuma. Besides, nickel could promote the adsorption of pyrene on the cell wall. Pyrene in A. cristatum could be transported through the apoplast and symplast, and the pyrene contents in the symplast were 2-3 times that of the apoplast. The uptake of pyrene by A. cristatum included both active absorption and passive transportation. Active absorption involved H⁺ transport and energy conversion processes, and passive transport was associated with water protein channels.

Insight into the binding properties of carbamazepine onto dissolved organic matter using spectroscopic techniques during grassy swale treatment

Carbamazepine (CBZ) is a worldwide anti-epileptic drug, whose fate and migration can be greatly influenced by contact with dissolved organic matter (DOM). The properties of DOM in road runoff can be greatly changed by grassy swale (GS) treatment, which influences the complexation of CBZ with DOM. Spectroscopic techniques were employed to explore the different binding properties between CBZ and DOM, and to understand the migration and biogeochemistry of CBZ. The two-dimensional correlation spectroscopy (2D-COS)demonstrated that effluent DOM displayed more binding sites for CBZ than influent DOM, and the binding sequencing of CBZ with DOM fluorophores can be greatly influenced by GS treatment. The results also suggest that protein-like materials exhibit higher log K_M values than other fluorescent components, indicating that fluorescent protein-like materials play a crucial role in the biogeochemical behavior of CBZ. Meanwhile, the log K_M values showed a remarkable increase after GS treatment. GS treatment can also remove most fluorescent DOM, reducing the risk of CBZ in the water environment.

Characterizing Properties and Environmental Behaviors of Dissolved Organic Matter Using Two-Dimensional Correlation Spectroscopic Analysis

Dissolved organic matter (DOM) exists ubiquitously in environments and plays critical roles in pollutant mitigation, transformation, and organic geochemical cycling. Understanding its properties and environmental behaviors is critically important to develop water treatment processes and environmental remediation strategies. Generalized two-dimensional correlation spectroscopy (2DCOS), which has numerous advantages, including enhancing spectral resolution and discerning specific order of structural change under an external perturbation, could be used as a powerful tool to interpret a wide range of spectroscopic signatures relating to DOM. A suite of spectroscopic signatures, such as UV-vis, fluorescence, infrared, and Raman spectra that can be analyzed by 2DCOS, is able to provide additional structural information hiding behind the conventional one-dimensional spectra. In this article, the most recent advances in 2DCOS applications for analyzing DOM-related environmental processes are reviewed, and the state-of-the-art novel spectroscopic techniques in 2DCOS are highlighted. Furthermore, the main limitations and requirements of current approaches for exploring DOM-related environmental processes and how these limitations and drawbacks can be addressed are explored. Finally, suggestions and new approaches are proposed to significantly advance the development of 2DCOS in analyzing the properties and behaviors of DOM in natural and engineered environments.

Noncovalent interactions between fluoroquinolone antibiotics with dissolved organic matter: A 1H NMR binding site study and multi-spectroscopic methods

Fluoroquinolone antibiotics (FQs) are considered to be emerging environmental contaminants that have been detected extensively in aquatic environment. It is of quite importance to explore FQs interacting with dissolved organic matter (DOM). The interactions of FQs with DOM were examined by nuclear magnetic resonance (NMR) spectroscopy, fluorescence quenching, UV-vis, Fourier transform infrared (FT-IR) spectroscopic techniques. The bindings of FQs to DOM had one single binding site and their quenching mechanisms were static, which were evaluated by the Stern-Volmer and Site-binding equations. Addition of DOM could result in micro-environmental changes of fluorophores groups in FQs. The location adjacent oxygen right of Ofloxacin (OFL) and the aromatic ring (the adjacency replaced by two nitrogen-containing groups) of Ciprofloxacin (CIP), Enrofloxacin (ENR), Norfloxacin (NOR) might be highly affected by DOM molecule. The negative enthalpy change (ΔH⁰), negative entropy change (ΔS⁰) and the positive Gibbs' energy change (ΔG⁰) figured out that the binding processes were exothermic but not thermodynamic favorable, the formation of HA-FQs complexes would be powered chiefly by the ΔS⁰. H-bonding, electrostatic effect, van der Waals force were the acting force in the binding reactions and the π-π stacking effect was the major binding force under alkaline conditions. Moreover, the protonated, deprotonated, or partially protonated state of FQs were found to have different binding capacity to DOM, and the binding reactions for FQs-HA system were suppressed as the ionic strength increased. Meanwhile, alterations of FQs conformation in the presence of DOM were evaluated by FT-IR and UV-vis spectra.

Adsorption behaviors of phenanthrene and bisphenol A in purple paddy soils amended with straw-derived DOM in the West Sichuan Plain of China

The objectives of this study were to investigate the adsorption and transfer behaviors of phenanthrene (PHE) and bisphenol A (BPA) in purple paddy soils amended with dissolved organic matter (DOM) derived from rice and canola straw in the West Sichuan Plain of China. In the pristine soil, PHE was preferentially adsorbed on both pristine clayey (L) and sandy (T) paddy soils than BPA, indicating that the retention/adsorption by soils is closely dependent on the chemical properties of organic pollutants (OPs). The noticeably higher adsorption of PHE and BPA on smaller size fraction of the soils (L2 and T2) were observed, possibly due to their higher surface areas and higher content in organic matters with higher aromaticity and hydrophobicity in this soil fraction. The DOMs derived from rice (RDOM) and canola (CDOM) straws possessed remarkable differences in E₂/E₃ and SUV₂₅₄ measurements, which reflected that their chemical composition might be different. When CDOM was introduced in the studied soil T1, adsorption of BPA was doubled, but the augment in adsorption was much less impressive with RDOM, showing the nature of derived DOM played an important role. The study also demonstrated that in the fine fraction of clayey soil (L2), the retention of a same OP (PHE) was remarkably dropped when CDOM or RDOM was introduced, whereas in a sandy soil of the same size fraction (T2), the phenomenon was the opposite, suggesting a potential risk that, in certain types of soil, the introduction of straw derived DOMs may enhance the mobility of some OPs. The humification time of straw seems not to affect the adsorptions of OPs in most studied systems. Adsorption kinetics of PHE and BPA in the adsorption systems with derived DOMs were well fitted to the two-step first-order model with r_adj² values of 0.994-0.998. Results of this study will provide further comprehensive fundamental data for risk assessment and control of organic pollutants (OPs) in farmland ecosystems.

Competitive sorption of lead and methylene blue onto black soil and their interaction with dissolved organic matter using two-dimensional correlation analyses

This study investigated the competitive sorption of black soil to adsorb Pb(II) and methylene blue (MB) from multi-contaminated soils. According to the experimental data, the process of adsorption can be clearly explained by pseudo-second-order kinetic equation. Both single and binary systems of the adsorption isotherms had a good fit with Langmuir models. The maximal adsorption abilities of Pb(II) and MB acquired from binary systems sorption were attenuated compared to those from the single system (Pb(II): 77.70 > 65.96 mg g^-1; MB: 242.31 > 222.36 mg g^-1). Pb(II) and MB can inhibit each other's sorption ability. A combination of three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence spectra as well as two-dimensional correlation spectroscopy (2D-COS) were employed to determine the binding of dissolved organic matter (DOM) for Pb(II) and MB during soil sorption process. As a result, 3D-EEM implicated that the two main composes of DOM were humic acid-like substances and the fluorescence of DOM specimens were gradually diminished with increasing concentrations of Pb(II) and MB. According to synchronous fluorescence spectra, static quenching of Pb(II) and MB mainly led to fluorescence quenching. Specifically, fluorescence-2D-COS implicated that Pb(II) and MB bound to fluorescence in the following sequence: the earlier occurrence of the humic-like fraction compared to that of protein-like fraction. FTIR-2D-COS results concluded that the structural change sequence of DOM by Pb(II) binding followed the order: 1700＞863＞1332＞1529＞1200＞1086 cm^-1 and the sequence of the MB binding affinities followed the order: 1520＞1399＞1345＞1152＞1602＞993＞881 cm^-1. These findings would be beneficial to understand the mechanism of adsorb multi-component systems and have the potential to contribute significance to the interaction mechanism of multi-component with soil DOM at the molecular level.

How do root exudates of bok choy promote dibutyl phthalate adsorption on mollisol?

This study investigates the interaction between the bok choy root exudates and dibutyl phthalate (DBP) onto mollisol during the adsorption. The result elucidated that the adsorption reached equilibrium within 12 h, the adsorption capacity of rhizosphere mollisol containing root exudates and ordinary mollisol were 243.46 mg kg^-1 and 281.95 mg kg^-1, separately. The adsorption kinetics and isotherm model followed the pseudo-second order and the Frendlish model, respectively, which hinted that the adsorption process was multi-layer heterogeneous chemisorption. We characterized the root exudates and analyzed its effects on soil physical and chemical properties and structure. The result revealed that the root exudates contained hydrocarbons, sulfur compounds and acids. Root exudates made the dissolved organic matter (DOM) dissolution from soil and the increase of organic matter, which might be one of the reasons that root exudates promote DBP adsorption on mollisol. We selected three-dimensional excitation-emission matrix (3D-EEM), synchronous fluorescence and Fourier transform infrared spectroscopy (FTIR) to analyze the interactions between root exudates and DBP, DOM and DBP, respectively. Fluorescence spectrum revealed that the main component of root exudates was protein, for DOM was humic acid, the fluorescence of root exudates and DOM gradually disappeared with the increase of DBP concentration. FTIR revealed that -COO in root exudates and -CH₂ in DOM respectively reacted with DBP. The results of this study are of great importance to reveal that the root exudates are significant in the environmental behavior of DBP adsorption on mollisol, and also provide more useful information for phytoremediation of organic pollutants in the mollisol.

Aromatic organoarsenic compounds (AOCs) occurrence and remediation methods

Many researchers at home and abroad have made a body of researches and have gained great achievements on the environmental occurrence, fate, and toxicity of inorganic arsenic. But there is less research on the use of aromatic organoarsenic compounds (AOCs), which are common feed additives for livestock in the poultry industry. In this review, we outline the current state of knowledge acquired on the occurrence and remediation of AOCs, respectively. We also identify knowledge gaps and research needs, including the elucidation of the environmental fate of AOCs, metabolic pathway, the impact of metabolic modification on toxicity, and advanced analytical or repaired methods that allows for monitoring, identification or removal of the degradation products.

Interactions between tetrahydroisoindoline-1,3-dione derivatives and human serum albumin via multiple spectroscopy techniques

Some tetrahydroisoindoline-1,3-dione derivatives (TDDs) possess potent herbicidal activity. To assess possible impacts of TDDs on humans, the interactions between TDDs and human serum albumin (HSA) were evaluated with steady-state and time-resolved fluorescence spectroscopy, synchronous fluorescence spectroscopy, Fourier transform-infrared spectroscopy, and circular dichroism spectroscopy. The thermodynamic data obtained at temperatures of 298, 307, and 316 K indicate that TDDs spontaneously bind to HSA and thus form a TDD-HSA complex. The conformation and secondary structure of HSA are changed, and the intrinsic fluorescence of HSA is statically quenched by TDDs. Moreover, the TDD-HSA complex is formed primarily through electrostatic interactions and has only one binding site on HSA. A competitive ligand-binding assay revealed that site II (subdomain IIIA) displays the greatest affinity for TDDs. In addition, an acute toxicity bioassay showed no zebrafish mortality upon exposure to 4000 μg L^-1 of TDDs. This work is helpful for understanding interactions between TDDs and HSA.