Investigating binding characteristics of cadmium and copper to DOM derived from compost and rice straw using EEM-PARAFAC combined with two-dimensional FTIR correlation analyses

A new insight into the straw decomposition associated with minerals: Promoting straw humification and Cd immobilization

Organic matter (OM) derived from the decomposition of crop residues plays a key role as a sorbent for cadmium (Cd) immobilization. Few studies have explored the straw decomposition processes with the presence of minerals, and the effect of newly generated organo-mineral complexes on heavy metal adsorption. In this study, we investigated the variations in structure and composition during the rice straw decomposition with or without minerals (goethite and kaolinite), as well as the adsorption behavior and mechanisms by which straw decomposition affects Cd immobilization. The degree of humification of extracted straw organic matter was assessed using excitation-emission matrix (EEM) fluorescence and Ultraviolet-visible spectroscopy (UV-vis), while employing FTIR spectroscopy and XPS to characterize the adsorption mechanisms. The spectra analysis revealed the enrichment of highly aromatic and hydrophobic components, indicating that the degree of straw decomposition and humification were further intensified during incubation. Additionally, the existence of goethite (SG) accelerated the humification of OM. Sorption experiments revealed that the straw humification increased Cd adsorption capacity. Notably, SG exhibited significantly higher adsorption performance compared to the organic matter without minerals (RS) and the existence of kaolinite (SK). Further analysis using FT-IR spectroscopy and XPS verified that the primary mechanisms involved in Cd immobilization were complexion with -OH and -COOH, as well as the formation of Cd-π binds with aromatic C=C on the surface of solid OMs. These findings will facilitate understanding the interactions of the rice straw decomposing with soil minerals and its remediation effect on Cd-contaminated farmland.

Riverine seasonal rainfall event tracing of organic pollution sources using fluorescence fingerprint difference spectrum

Elucidating the dynamics of dissolved organic matter (DOM) transport and transformation under seasonal rainfall events is essential for the conservation of riverine ecosystems, for mitigating the effects of climate change, and for crafting informed water management strategies. Therefore, this study aimed to investigate the evolutionary characteristics of organic pollution sources during consecutive rainfall events in early spring and to quantify their relative contributions to the process of surface water pollution. The results showed seasonal rainfall induces water quality exceedances in rivers due to the combined impacts of terrestrial inputs and endogenous releases. Humic acid (HA) (region V) and fulvic acid (FA) (region III) emerged as the predominant organic matter in the water column, with their fluorescence intensity altering as rainwater flushed the riverbed. Sources of pollution include agricultural and urban domestic sources (AS + DS) (72.29 %), industrial and urban domestic and microbial sources (IS + DS + MS) (37.71 %), and agricultural and industrial sources (AS + IS) (63.32 %), indicating that agricultural surface pollution discharges contribute significantly. The gas-chromatography-mass spectrometry (GC-MS) further confirmed that exogenous inputs were predominantly comprised of particulate pollutants. This study underscores the efficacy of fluorescence difference spectrometry in delineating the migration and transformation of river pollution sources during seasonal rainfall and facilitating the implementation of targeted management strategies for river ecosystems.

Joint utilization of Chinese milk vetch and lime materials mitigates soil cadmium risk and improves soil health in a double-cropping rice system

Cadmium (Cd) in paddy soil poses significant risks to humans due to its strong biological migration and toxicity. Chinese milk vetch (MV) is commonly used as green manure in the paddy fields of southern China and its potential to decrease the availability of Cd has been identified. Nevertheless, the effects of MV combined with lime materials (lime, L; limestone, LS) on Cd availability, soil properties, enzyme activity and comprehensive benefits are still not fully understood in double-cropping rice system. A field study was conducted to investigate these changes. The results indicated that all treatments notably decreased soil available Cd (Avail-Cd) by 19.3-44.3% and 14.9-43.1% during early and late rice, compared with CK. Moreover, the Cd fractions transformed to more stable forms. Compared to CK, all treatments reduced brown rice Cd content by 34.6-64.2% and 12.7-52.5% during the two periods. Furthermore, the translocation factors root to shoot, as well as shoot to brown rice, decreased. The combination led to improvements in soil properties, soil enzyme activity. Meantime, Cd in iron-manganese plaque (IMP) decreased by 31.9-51.1% and 29.0-42.7% respectively during two periods in amendments treatments. Soil pH and DOC were more important factors for Cd bioavailability than other properties. Additionally, rice Cd uptake was positively correlated with Cd in IMP. Enzyme activity exhibited a negative correlation with soil active Cd. Partial Least Squares Path Model (PLS-PM) indicated that the mitigation of Cd pollution helped to improve soil enzyme activity. Grey correlation analysis (GRA) indicated that MVLS showed the best comprehensive benefits in soil-plant system. Overall, the combination of MV and lime materials could reduce Cd availability, enhance soil properties and enzyme activity. And this could be strengthened by the combination. These findings will provide valuable insights for Cd-contaminated soil remediation.

Effect of Mn2+ on RO membrane organic fouling: Insights into the complexation and interfacial interaction

RO process is commonly used to treat and reuse manganese-containing industrial wastewater. Nevertheless, even after undergoing multi-stage treatment, the secondary biochemical effluent still exhibits a high concentration of Mn2+ coupled with organics entering the RO system, leading to membrane fouling. In this work, we systematically analyze the RO membrane organic fouling processes and mechanisms, considering the coexistence of Mn2+ with humic acid (HA), sodium alginate (SA), bovine serum albumin (BSA) and their mixtures (HBS). The impact of Mn2+ on membrane fouling was HBS > SA > HA > BSA, controlling polysaccharide pollutant concentrations should be a priority for mitigating membrane fouling. In the presence of Mn2+ with HA, SA, or HBS, membrane fouling is primarily attributed to the complexation of organics and Mn2+ and the facilitation of interfacial interaction energy. RO membrane BSA fouling was not directly affected by Mn2+, the addition of Mn2+ induced a salting-out effect, leading to the deposition of BSA in a single molecular on the membrane. Simultaneously, adhesion energy hinders the deposition of BSA on the membrane, resulting in milder membrane fouling. This study provided the theoretical basis and suggestions for RO membrane organic fouling control in the presence of Mn2+.

Effects of polypropylene films and leached dissolved organic matters on bacterial community structure in mangrove sediments

Over the past decades, the accumulation of plastics in mangrove ecosystems has emerged as a significant environmental concern, primarily due to anthropogenic activities. Polypropylene (PP) films, one of the plastic types with the highest detection rate, tend to undergo intricate aging processes in mangrove ecosystems, leading to the release of dissolved organic matter (DOM) that may further influence the local bacterial communities. Yet, the specific effects of new and weathered (aged) plastic films and the associated leached DOM on bacterial consortia in mangrove sediments remain poorly understood. In this study, an incubation experiment was conducted to elucidate the immediate effects and mechanisms of the new and relatively short-term (45 or 90 days) aged PP films, as well as their leached DOM (PDOM), on characteristics of DOM and the bacterial community structure in mangrove sediments under different tidal conditions. Surface morphology and functional group analyses showed that both new and aged PP films exhibited comparable degradation profiles under different tidal conditions over the incubation period. As compared to the new PP film treatments, the introduction of the short-term aged PP films significantly affected the content of humic-like compounds in sediments, and such effects were partially ascribed to the release of PDOM during the incubation. Although the addition of PP films and PDOM showed minor effects on the overall diversity and composition of bacterial communities in the sediments, the abundance of some dominant phyla exhibited a growth or reduction tendency, possibly changing their ecological functions. This study was an effective attempt to investigate the relationship among plastic surface characteristics, sedimentary physicochemical properties, and bacterial communities in mangrove sediments. It revealed the ecological ramifications of new and short-term plastic pollution and its leachates in mangrove seedtimes, enhancing our understating of their potential impacts on the health of mangrove ecosystems.

Fabricating whole pine needles biomass with phenylhydrazine-4-sulphonic acid for effective removal of cationic dyes and heavy metal ions from wastewater

We applied a holistic, sustainable, and green approach to develop an effective multipurpose adsorbent from whole pine needles (PNs), a forest waste lignocellulosic biomass. The PNs were oxidized and modified with phenylhydrazine-4-sulphonic acid (ɸHSO3H) to OPN-ɸHSO3H. The latter was characterized and tested as an adsorbent for cationic dyes, malachite green (MG), methylene blue (MB), crystal violet (CV), and metal ions (Hg2⁺ and Pb2⁺). The adsorption followed different kinetic models: Elovich for MG and MB, pseudo-second-order for CV, and pseudo-first-order for Hg2⁺ and Pb2⁺. Langmuir isotherm indicated maximum adsorption capacities of 303.4 ± 8.91 mgg-1 (MG), 331.4 ± 17.50 mgg-1 (MB), 376.6 ± 22.47 mgg-1 (CV), 210.8 ± 28.86 mgg-1 (Hg2⁺), and 172.9 ± 20.93 mgg-1 (Pb2⁺) within 30 min. Maximum removal efficiencies were 99.0% (MG), 98.0% (MB), 96.04% (CV), 95.5% (Hg2⁺), and 89.8% (Pb2⁺). The adsorbent demonstrated significant regeneration and reusability over ten cycles, proving highly efficient for both cationic dyes and metal ions, with wide potential for practical applications where more than one adsorbate is present.

Reduction of the exchangeable cadmium content in soil by appropriately increasing the maturity degree of organic fertilizers

To enhance the remediation effect of heavy metal pollution, organic fertilizers with different maturity levels were added to cadmium-contaminated soil. The remediation effect was determined by evaluating the form transformation and bioavailability of cadmium in heavy metal-contaminated soil. -Results showed that when the maturity was 50%, although the soil humus (HS) content increased, it didn't contribute to reducing the bioavailability of soil Cd. Appropriately increasing the maturity (GI ≥ 80%), the HS increased by 113.95%∼157.96%, and reduced significantly the bioavailability of soil Cd, among the exchangeable Cd decreased by 16.04%∼33.51% (P < 0.01). The structural equation modeling (SEM) revealed that HS content is a critical factor influencing the transformation of Cd forms and the reduction of exchangeable Cd accumulation; the HS and residual Cd content were positively correlated with the maturity (P < 0.01), while exchangeable Cd content was negatively correlated with maturity (P < 0.01), and the correlation increased with increasing maturity. In summary, appropriately increasing the maturity (GI ≥ 80%) can increase significantly HS, promote the transformation of exchangeable Cd into residual Cd, and ultimately enhance the effectiveness of organic fertilizers in the remediation of soil Cd pollution. These results provide a new insight into the remediation of Cd-contaminated soil through organic fertilizer as soil amendment in Cd-contaminated soil.

The promotion of the polycyclic aromatic hydrocarbons degradation mechanism by humic acid as electron mediator in a sediment microbial electrochemical system

To enhance the removal efficiencies of polycyclic aromatic hydrocarbons (PAHs) in sediments and to elucidate the mechanisms by which microbial electrochemical action aids in the degradation of PAHs, humic acid was used as an electron mediator in the microbial electrochemical system in this study. The results revealed that the addition of humic acids led to increases in the removal efficiencies of naphthalene, phenanthrene, and pyrene by 45.91%, 97.83%, and 85.56%, respectively, in areas remote from the anode, when compared to the control group. The investigation into the microbial community structure and functional attributes showed that the presence of humic acid did not significantly modify the microbial community composition or its functional expression at the anode. However, an examination of humic acid transformations demonstrated that humic acid extended the electron transfer range in sediment via the redox reactions of quinone and semiquinone groups, thereby facilitating the PAHs degradation within the sediment.

Impacts of mixed ferrous sulfate-biochar additives on humification and bacterial community during electric field-assisted aerobic composting

This study assessed the impact of nine mixed ferrous sulfates and biochars on electric field-assisted aerobic composting (EAC), focusing on the spectroscopy of dissolved organic matter (DOM) and microbial communities. Adding 1.05% ferrous sulfate and 5.25% biochar to EAC increased the specific ultraviolet absorbances at 254 and 280 nm by 142.3% and 133.9% on day 35, respectively. This ratio accelerated the early response of carboxyl groups (-COOH) and lignin (CꘌC), enhancing the relative abundance of Thermobifida (4.0%) and Thermopolyspora (4.3%). The condition contributed to humus precursor formation on day 5, increasing the maximum fluorescence intensity of the humus-like component by 74.2% compared to the control on day 35. This study is the first to develop a combined and efficient organic and inorganic additive by multiple-variable experimentation for DOM humification. Consequently, it optimizes EAC for solid waste recycling.

Seasonal studies of aquatic humic substances from Amazon rivers: characterization and interaction with Cu (II), Fe (II), and Al (III) using EEM-PARAFAC and 2D FTIR correlation analyses

Aquatic humic substances (AHS) are defined as an important components of organic matter, being composed as small molecules in a supramolecular structure and can interact with metallic ions, thereby altering the bioavailability of these species. To better understand this behavior, AHS were extracted and characterized from Negro River, located near Manaus city and Carú River, that is situated in Itacoatiara city, an area experiencing increasing anthropogenic actions; both were characterized as blackwater rivers. The AHS were characterized by 13C nuclear magnetic ressonance and thermochemolysis GC-MS to obtain structural characteristics. Interaction studies with Cu (II), Al (III), and Fe (III) were investigated using fluorescence spectroscopy applied to parallel factor analysis (PARAFAC) and two-dimensional correlation spectroscopy with Fourier transform infrared spectroscopy (2D-COS FTIR). The AHS from dry season had more aromatic fractions not derived from lignin and had higher content of alkyls moities from microbial sources and vegetal tissues of autochthonous origin, while AHS isolated in the rainy season showed more metals in its molecular architecture, lignin units, and polysacharide structures. The study showed that AHS composition from rainy season were able to interact with Al (III), Fe (III), and Cu (II). Two fluorescent components were identified as responsible for interaction: C1 (blue-shifted) and C2 (red-shifted). C1 showed higher complexation capacities but with lower complexation stability constants (KML ranged from 0.3 to 7.9 × 105) than C2 (KML ranged from 3.1 to 10.0 × 105). 2D-COS FTIR showed that the COO- and C-O in phenolic were the most important functional groups for interaction with studied metallic ions.

Role of low-proportion, hydrophobic dissolved organic matter components in inhibiting methylmercury uptake by phytoplankton

Uptake of methylmercury (MeHg), a potent neurotoxin, by phytoplankton is a major concern due to its role as the primary pathway for MeHg entry into aquatic food webs, thereby posing a significant risk to human health. While it is widely believed that the MeHg uptake by plankton is negatively correlated with the concentrations of dissolved organic matter (DOM) in the water, ongoing debates continue regarding the specific components of DOM that exerts the dominant influence on this process. In this study, we employed a widely-used resin fractionation approach to separate and classify DOM derived from algae (AOM) and natural rivers (NOM) into distinct components: strongly hydrophobic, weakly hydrophobic, and hydrophilic fractions. We conduct a comparative analysis of different DOM components using a combination of spectroscopy and mass spectrometry techniques, aiming to identify their impact on MeHg uptake by Microcystis elabens, a prevalent alga in freshwater environments. We found that the hydrophobic components had exhibited more pronounced spectral characteristics associated with the protein structures while protein-like compounds between hydrophobic and hydrophilic components displayed significant variations in both distributions and the values of m/z (mass-to-charge ratio) of the molecules. Regardless of DOM sources, the low-proportion hydrophobic components usually dominated inhibition of MeHg uptake by Microcystis elabens. Results inferred from the correlation analysis suggest that the uptake of MeHg by the phytoplankton was most strongly and negatively correlated with the presence of protein-like components. Our findings underscore the importance of considering the diverse impacts of different DOM fractions on inhibition of phytoplankton MeHg uptake. This information should be considered in future assessments and modeling endeavors aimed at understanding and predicting risks associated with aquatic Hg contamination.

Adsorption of humic acid from different organic solid waste compost to phenanthrene, is fluorescence excitation or quenching?

Humic acid (HA) from different organic solid waste (OSW) compost has been shown good adsorption properties for phenanthrene. However, the raw material of HA can affect its structure, resulting in differences in adsorption capacity. Therefore, this study focused on the adsorption characteristics of phenanthrene by HA from different OSW compost. In this work, chicken manure (CM), rice straw (RS) and lawn waste (LW) were selected as sources of composted HA. The adsorption mechanism of HA from different OSW compost were revealed through analytical techniques including three-dimensional fluorescence spectroscopy (EEM), two-dimensional correlation spectroscopy (2DCOS), and Fourier-transform infrared spectroscopy (FTIR). The results suggested that HA from LW compost had a better adsorption affinity for phenanthrene because of its more complex fluorescent component, where C1 as a simple component determined the adsorption process specifically. Furthermore, after HA from LW compost adsorbed phenanthrene, the increase in aromatic -COOH and -NH was the main reason for fluorescence quenching. These results indicated that HA from LW compost had better adsorption effect for phenanthrene. The results of this study were expected to provide a selection scheme for the control of phenanthrene pollution and environmental remediation.

Effect of pyrolysis temperature on the binding characteristics of DOM derived from livestock manure biochar with Cu(II)

Biochar-derived dissolved organic matter (BDOM) has the potential to influence the environmental application of biochar and the behavior of heavy metals. In this study, the binding properties of BDOM derived from livestock manure biochar at different pyrolysis temperatures with Cu(II) were investigated based on a multi-analytical approach. The results showed that the DOC concentration, aromatics, and humification degree of BDOM were higher in the process of low pyrolysis of biochar. The pyrolysis temperature changed the composition of BDOM functional groups, which affected the binding mechanism of BDOM-Cu(II). Briefly, humic-like and protein-like substances dominated BDOM-Cu(II) binding at low and high pyrolysis temperatures, respectively. The higher binding capacity for Cu(II) was exhibited by BDOM derived from the lower pyrolysis temperature, due to the carboxyl as the main binding site in humic acid had high content and binding ability at low-temperature. The amide in proteins only participated in the BDOM-Cu(II) binding at high pyrolysis temperature, and polysaccharides also played an important role in the binding process. Moreover, the biochar underwent the secondary reaction at certain high temperatures, which led to condensation reaction of the aromatic structure and the conversion of large molecules into small molecules, affecting the BDOM-Cu(II) binding sites.

Depth-dependent variations of physicochemical properties of sedimentary dissolved organic matter and the influence on the elimination of typical pharmaceuticals

Sedimentary dissolved organic matter (DOM) could exert a significant influence on the transformation of trace organic contaminants. However, the variations of sedimentary DOM properties with depth and their impact on trace organic contaminants biodegradation remain unclear. In this study, the qualitative changes in DOM properties with depth were assessed using spectral techniques. Specifically, within the sediment range of 0-30 cm, humic acid and fulvic acid fractions exhibited higher degrees of humification and aromatization at 10-20 cm, while hydrophilic fractions showed higher degrees of humification and aromatization at 20-30 cm. Furthermore, electrochemical methods were employed to quantitatively assess the electron transfer capacity of sedimentary DOM at different depths, which displayed consistent variation trend with humification and aromatization degree. The high degree of humification and aromatization, along with strong electron-accepting capability of DOM, significantly enhanced the biodegradation rates of tetracycline and ritonavir. To gain deeper insights into the influence of molecular composition of DOM on its properties, two-dimensional gas chromatography-quadrupole mass spectrometry analysis revealed that quinones and phenolic hydroxyl compounds govern the redox reactivity of DOM. Simulated experiment of DOM-mediated biodegradation of typical pharmaceuticals confirmed the role of quinones and phenolic hydroxyl groups in the redox reactivity of DOM.

New insights into the effect of pyrolysis temperature on the spectroscopy properties of dissolved organic matter in manure-based biochar

Dissolved organic matter (DOM) derived from biochar takes a crucial role in transport and bioavailability toward contaminants; hence, it is undeniable that a thorough analysis of its properties is important. So far, the effect of pyrolysis temperature on the functional groups, components, and evolutionary sequence of manure-based biochar DOM has not been adequately investigated. Here, DOM was released from two typical livestock manures (cow and pig) at five pyrolysis temperatures (300 ~ 700°C), and it was explored in depth with the aid of moving window 2D correlation spectroscopy (MW-2D-COS) and heterogeneous 2D correlation spectroscopy (hetero-2D-COS). The results demonstrated that the concentration, aromaticity, and hydrophobicity of DOM were greater at high temperatures, and more DOM was liberated from cow manure-based biochar at identical temperature. Protein-like compounds dominated at high temperatures. The pyrolysis temperatures of final configuration transformation points of the fulvic acid-like component and the aromatic ring C=C in DOM were 400°C and 500°C, respectively. Moreover, Fourier transform infrared spectroscopy combined with two-dimensional correlation analysis indicated that the functional group evolution of DOM depends on the pyrolysis temperature and feedstock type. The study provides a new perspective on manure management and environmental applications of biochar.

Biochar improved the solubility of triclocarban in aqueous environment: Insight into the role of biochar-derived dissolved organic carbon

Biochar as an effective adsorbent can be used for the removal of triclocarban from wastewater. Biochar-derived dissolved organic carbon (BC-DOC) is an important carbonaceous component of biochar, nonetheless, its role in the interaction between biochar and triclocarban remains little known. Hence, in this study, sixteen biochars derived from pine sawdust and corn straw with different physico-chemical properties were produced in nitrogen-flow and air-limited atmospheres at 300-750 °C, and investigated the effect of BC-DOC on the interaction between biochar and triclocarban. Biochar of 600∼750 °C with low polarity, high aromaticity, and high porosity presented an adsorption effect on triclocarban owing to less BC-DOC release as well as the strong π-π, hydrophobic, and pore filling interactions between biochar and triclocarban. In contrast and intriguingly, biochar of 300∼450 °C with low aromaticity and high polarity exhibited a significant solubilization effect rather than adsorption effect on triclocarban in aqueous solution. The maximum solubilization content of triclocarban in biochar-added solution reached approximately 3 times its solubility in biochar-free solution. This is mainly because the solubilization effect of BC-DOC surpassed the adsorption effect of biochar though the BC-DOC only accounted for 0.01-1.5 % of bulk biochar mass. Furthermore, the high solubilization content of triclocarban induced by biochar was dependent on the properties of BC-DOC as well as the increasing BC-DOC content. BC-DOC with higher aromaticity, larger molecular size, higher polarity, and more humic-like matters had a greater promoting effect on the water-solubility of triclocarban. This study highlights that biochar may promote the solubility of some organic pollutants (e.g., triclocarban) in aqueous environment and enhance their potential risk.

Spectroscopic insights into the binding characteristics of heavy metals to dissolved organic matter in landfill leachate

Landfill leachate is produced in the process of sanitary landfilling, which contains significant amounts of dissolved organic matter (DOM) and heavy metal contaminants. Insights into the interactions between heavy metals and DOM in landfill leachate are beneficial for the understanding of heavy metal fates and optimization of landfill leachate treatment. In this work, the coherent structural changes of landfill leachate DOM during binding with various heavy metals were explored through the integration of molecular spectroscopic methods with chemometrics and statistic correlation analyses. The results indicate that protein substances, phenolic and discrete carboxyl groups in landfill leachate DOM were involved in the complexation with heavy metals, resulting in the formation of conjugated macromolecules/aggregates with high aromaticity and molecular weight/size. The fluorescent protein-like, fulvic acid-like, and humic-like fractions in DOM were engaged in the interaction, which were closely related to phenolic-like and carboxylic-like structure. Compared to membrane concentrates DOM, raw leachate DOM exhibited a higher binding affinity to heavy metals (especially for Cu2+, whilst the weakest was Cd2+). The integrated approach provides useful information in elucidating the binding processes of metals with landfill leachate DOM, including site heterogeneity, binding strength and functional group sequences.

Insight into bacterial role attribution in dissolved organic matter humification during rice straw composting with microbial inoculation

This study aims to investigate the effect of microbial role distribution in microbial carbon pumps on dissolved organic matter (DOM) humification during rice straw composting with microbial inoculation. Three composting groups were designed, named CK (control), B4 (with Bacillus subtilis, OR058594) and Z1 (with Aspergillus fumigatus, AF202956.1). As a result of inoculation, the composition of microbial communities was changed, so that the microorganisms that promoted DOM humification were concentrated in the responders in the microbial carbon pump. DOM was divided into three components in three composting treatments: C1, C2 and C3. After inoculation with Bacillus subtilis, the C2 component was significantly affected, while after inoculation with Aspergillus fumigatus, the C3 component was significantly affected. The results of physicochemical factors affecting the transformation of DOM fluorescence components indicated that C1, C2 and C3 were related to the abundance of the cellulose-degrading enzyme-encoding gene GH7 in CK and B4 composting. However, the C2 was susceptible to organic matter in Z1 composting. This study explored the distribution of microbial communities from a new perspective, which provided new information for analyzing DOM humification and treating agricultural straws to achieve clean conditions for environmental friendliness.

Insights into the effect of hydrochar-derived dissolved organic matter on the sorption of diethyl phthalate onto soil: A pilot mechanism study

Biowaste-derived hydrochar is an emerging close-to-natural product and has shown promise for soil improvement and remediation, but the environmental behavior of the dissolved organic matter released from hydrochar (HDOM) is poorly understood. Focusing on the typical mulch film plasticizer diethyl phthalate (DEP), we investigated the effect of HDOM on the sorption behavior of DEP on soil. The relatively low concentration of HDOM (10 mg L-1, 25 mg L-1) decreases the sorption quantity of DEP on soil, while it increases by a relatively high concentration, 50 mg L-1. The transformation from multilayer to monolayer sorption of DEP on soil occurs as the concentration of HDOM increases. The tryptophan-like substance is the main component of HDOM sorbed to soil, reaching 49.82 %, and results in competition sorption with DEP. The soil pores are blocked by HDOM, which limits the pore filling and mass transfer of DEP, but partitioning is significantly enhanced. The surface functional groups in HDOM are similar to those in soil, and chemical sorption, mainly composed of hydrogen bonding, exists but is not significantly strengthened. We identified the specific impact of HDOM on the sorption of organic pollutants on soil and provide new insights into the understanding of the environmental behavior of hydrochar.

Effects of BC on metal uptake by crops (availability) and the vertical migration behavior in soil: A 3-year field experiments of crop rotation

Biochar (BC) has been substantiated to effectively reduce the available content of heavy metals (HMs) in soil-plant system; however, the risk of biochar (BC)derived dissolved organic matter (DOM) induced metal vertical migration has not been well documented, especially in the long-term field conditions. Therefore, this study investigated HM vertical migration ecological risks and the long-term effectiveness of the amendment of biochar in the three successive years of field trials during the rotation system. The results revealed that biochar application could increase soil pH and DOM with a decrease in soil CaCl2 extractable pool for Pb, Cu, and Cd. Furthermore, the results indicated a significant decrease in acid phosphatase activities and an increase in urease and catalase activities in the soil. Cucumber was shown to be safe during a three-year rotation system in the field. These results suggest that BC has the potential to enhance soil environment and crop yields. BC derived DOM-specific substances were identified using parallel factor analysis of excitation-emission matrix in deep soil (0-60 cm). The study incorporated HM concentration fluctuations in deep soils, providing an additional interpretation of DOM and co-migration of HMs.The environmental risk associated with the increase in DOM hydrophobicity should not be ignored by employing BC for soil HM remediation applications. The study enhances understanding of biochar-derived DOM's migration and stabilization mechanisms on heavy metals, providing guidelines for its use as a soil amendment.

Replacing traditional pretreatment in one-step UF with natural short-distance riverbank filtration: Continuous contaminants removal and TMP increase relief

Scientists have been focusing on applying more natural processes instead of industrial chemicals in drinking water treatment to achieve the purpose of carbon emissions reduction. In this study, we shortened the infiltration range of riverbank filtration, a natural water purification process, to form the short-distance riverbank filtration (sRBF) which retained its ability in water quality improvement and barely influenced the groundwater environment, and integrated it with ultrafiltration (UF) to form a one-step sRBF-UF system. This naturalness-artificiality combination could realize stable contaminants removal and trans-membrane pressure (TMP) increase relief for over 30 days without dosing chemicals. Generally, both sRBF and UF played the important role in river water purification, and the interaction between them made the one-step sRBF-UF superior in long-term operation. The sRBF could efficiently remove contaminants (90 % turbidity, 60 % total nitrogen, 30 % ammonia nitrogen, and 25 % total organic carbon) and reduce the membrane fouling potential of river water under its optimum operation conditions, i.e., a hydraulic retention time of 48 h, an operation temperature of 20 °C, and a synergistic filter material of aquifer and riverbank soil. Synergistic adsorption, interception, and microbial biodegradation were proved to be the mechanisms of contaminants and foulants removal for sRBF. The sequential UF also participated in the reduction of impurities and especially played a role in intercepting microbial metabolism products and possibly leaked microorganisms from sRBF, assuring the safety of product water. To date, the one-step sRBF-UF was a new attempt to combine a natural process with an artificial one, and realized a good and stable product quality in long-term operation without doing industrial chemicals, which made it a promised alternative for water purification for cities alongside the river.

Harnessing the composition of dissolved organic matter in lagoon sediment in association with rare earth elements using fluorescence and UV-visible absorption spectroscopy

Dissolved Organic Matter (DOM) plays a pivotal role in influencing metal binding and mobility within lagoon sediments. However, there exists a gap in understanding the compositional alterations of DOM concerning Rare Earth Elements (REEs) across varying pollution gradients. This study aimed to characterize DOM and examine its relationship with REEs in sediment cores from different pollution levels in Yundang Lagoon, China using excitation-emission matrix-parallel factor analysis (EEM-PARAFAC). The results raveled four distinct fluorescent components. Among these, two correspond to humic-like substances, while the remaining two are attributed to protein-like substances. Remarkably, the prevalence of protein-like compounds was observed to exceed 58% of the total fluorescence intensity across all the investigated sites. Furthermore, a substantial discrepancy in total fluorescence intensity was detected between the Songbai Lake and the Inner and Outer Lagoon, indicating a variance in DOM content. In terms of REEs, the average concentration of total REEs was notably elevated within the Songbai Lake sediments (318.36 mg/kg) as compared to the Inner and Outer Lagoon sediments (296.36 and 278.05 mg/kg, respectively). Of significance is the enrichment of Light Rare Earth Elements (LREEs), particularly Ce, La, Pr, and Nd, over Heavy REEs (HREEs) across all surveyed locations. Intriguingly, a coherent trend emerged wherein the fluorescence intensity and LREE concentrations exhibited a synchronized increase from Outer to Inner to Songbai Lake core sediments. This observation substantiates a strong correlation between DOM content and pollution levels (p < 0.05). By shedding light on the intricate interplay between DOM and REEs within urban aquatic sediments, this study imparts novel insights which enrich our comprehension of urban environmental dynamics.

Insight into the dynamics of dissolved organic matter components under latitude change perturbation

Dissolved organic matter (DOM) which can help the transportation of nutrients and pollutants plays essential role in the aquatic ecosystems. However, the dynamics of individual DOM component under the change of latitude have not been elucidated to date. The composition and dynamics of DOM were assessed in this study. Two individual parallel factor analysis (PARAFAC) components were found in each sampling site in Heilongjiang. To further characterize the inner change of the identified PARAFAC components, two-latitude correlation spectroscopy (2DCOS) technique was applied to the excitation loadings data. Interestingly, not all the fluorophore in a PARAFAC component change in the same direction as the overall change of a component. From upstream to downstream, the peak A1 in PARAFAC component C1 showed a downward trend, but peak A2 presented an upward trend. In PARAFAC component C2, the peak T2 and peak T3 showed an inverse changing trend under latitude perturbation. Furthermore, basic nutrients parameters in Heilongjiang were also characterized in each sampling sites. The relationships between DOM and nutrients showed that component C1 made a significant contribution to chemical oxygen demand (COD) and biochemical oxygen demand (BOD5). The evolutions of DOM peak A1 and peak A2 were accompanied by the changing of Total phosphorus (TP). The findings in this study could make a contribution to explore the fate of DOM in high humic-like substance containing river.

Electric field applications enhance the electron transfer capacity of dissolved organic matter in sludge compost

Dissolved organic matter (DOM) plays an important role in heavy metal passivation and organic pollutant degradation owing to its redox ability. The structure and composition of DOM are determinants of redox ability changes during composting. Electric field-assisted aerobic composting (EAAC) has been shown to promote the degradation and humification of organic matter in compost. However, how EAAC affects the redox ability of DOM remains unclear. Hence, electron transfer capacity (ETC) of DOM extracted from EAAC was studied using the electrochemical method. Various spectral methods, such as excitation-emission matrix and ultraviolet and visible spectrophotometry were used to study the relationship of ETC with the compositional and structural changes of DOM. Results indicated that EAAC enhanced ETC of DOM at the later stage of composting, and ETC of DOM extracted from the final EAAC product was 10.4% higher than that of the control group. Spectral and correlation analyses showed that EAAC resulted in structural and compositional changes of DOM, and humification degree, aromatic compounds, molecular weight, and fulvic- and humic-like substance contents were improved in EAAC. This conversion increased ETC of DOM. Results of this study will contribute to the understanding of the redox of DOM and in expanding the application of EAAC products.

Biochar amendment combined with partial root-zone drying irrigation alleviates salinity stress and improves root morphology and water use efficiency in cotton plant

An adsorption experiment and a pot experiment were executed in order to explore the mechanisms by which biochar amendment in combination with reduced irrigation affects sodium and potassium uptake, root morphology, water use efficiency, and salinity tolerance of cotton plants. In the adsorption experiment, ten NaCl concentration gradients (0, 50, 100, 150, 200, 250, 300, 350, 400, and 500 mM) were set for testing isotherm adsorption of Na+ by biochar. It was found that the isotherms of Na+ adsorption by wheat straw biochar (WSP) and softwood biochar (SWP) were in accordance with the Langmuir isotherm model, and the Na+ adsorption ability of WSP (55.20 mg g-1) was superior to that of SWP (47.38 mg g-1). The pot experiment consisted three factors, viz., three biochar amendments (no biochar, WSP, and SWP), three irrigation strategies (deficit irrigation, partial root-zone drying irrigation - PRD, full irrigation), and two NaCl concentrations gradients (0 mM and 200 mM). The findings indicated that salinity stress lowered K+ concentration, root length, root surface area, and root volume (RV), but increased Na+ concentration, root average diameter, and root tissue density. However, biochar amendment decreased Na+ concentration, increased K+ concentration, and improved root morphology. In particular, the combination of WSP and PRD increased K+/Na+ ratio, RV, root weight density, root surface area density, water use efficiency, and partial factor productivity under salt stress, which can be a promising strategy to cope with drought and salinity stress in cotton production.

New insight into the functional group mechanism and structure-activity relationship of the complexation between DOM and Cr(III) in landfill leachate

Widespread landfills represent a significant source of groundwater contamination. Due to the unique and diverse nature of dissolved organic matter (DOM) in landfill leachate, the interaction between DOM and heavy metals, along with its quantitative evaluation, remains unknown. Consequently, we collected ten samples from various landfill types to serve as representatives for a comprehensive investigation of the mechanism involving functional groups and Cr(III) through the establishment of a quantitative structure-activity relationship (QSAR). We employed ESI FT-ICR MS, (MW) 2D-COS, and DFT calculations for this purpose. Our findings indicate that DOM from landfill leachate contains a higher proportion of CHON molecules on intensity compared to those from natural sources. The maximum complexation capacity was determined by the proportion of proteins (69%), normalized carbon average oxidation state (16%), double bond equivalence (8%), and the number of oxygen atoms (7%) in landfill leachate DOM. Besides, N-containing groups such as N = O and C-N in landfill leachate DOM with lower humification, can exhibit stronger affinities than COOH, ArOH, CO, and polysaccharide C-O groups, which are typically identified as dominant sites in natural DOM. A QSAR model incorporating four parameters demonstrated an impressive accuracy rate of 98.8%, underscoring its reliability in predicting the complexation potential of different landfill leachate DOM with Cr(III).

New insights into the sustainable use of soluble straw humic substances for the remediation of multiple heavy metals in contaminated soil

This study addresses the research gap in understanding the differences in straw decomposition and variations in humic substances (HS) extracted from various treatment conditions. The aim is to explore the potential of soluble straw HS in remediating heavy metal pollution in soils. The study characterizes straw decomposition structures using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while employing gel permeation chromatography (GPC) and fluorescence spectroscopy (EEM) to analyze the molecular weight and degree of humification of extracted straw HS. The removal efficiency of HS for heavy metals is assessed, with a focus on aerobic humic substances (AE-HS) showing the highest potential for heavy metal removal. Spectral analysis and mass spectrometry analysis reveal the role of phenolic compounds, carboxylic acids, and aromatic compounds in AE-HS, forming humates or complexes to remove heavy metals from contaminated soil. Notably, the optimized AE-HS achieved the highest removal efficiency of 96.18 %, 82.75 %, 60.43 %, and 41.66 % for cadmium, copper, zinc, and lead, respectively. This study provides new insights into the preparation of straw for use as a heavy metal remover and has implications for the use of straw humic substances in soil remediation.

Compost-derived humic and fulvic acid coupling with Shewanella oneidensis MR-1 for the bioreduction of Cr(Ⅵ)

The compost-derived humic acids (HA) and fulvic acids (FA) contain abundant active functional groups with strong redox capacity, which can function as an electron shuttles for promoting the reduction of heavy metals, thus changing the form of the pollutants in the environment and reducing their toxicity. Therefore, in this study, UV-Vis, FTIR, 3D-EEM, electrochemical analysis were applied to study the spectral characteristics and electron transfer capacity (ETC) of HA and FA. Upon analysis, the results showed an increasing trend of ETC and humification degree (SUVA254) for both HA and FA during composting. However, the aromatic degree (SUVA280) of HA was higher than FA. After 7 days of culture, 37.95% of Cr (Ⅵ) was reduced by Shewanella oneidensis MR-1 (MR-1) alone. Whereas, only if HA or FA existed, the diminution of Cr (Ⅵ) reached 37.43% and 40.55%, respectively. However, the removal rate of Cr (Ⅵ) by HA/MR-1 and FA/MR-1 increased to 95.82% and 93.84% respectively. It indicated that HA and FA acted as electron shuttles, mediating the transfer of electrons between MR-1 and the final electron acceptor, effectively facilitating the bioreduction of Cr (Ⅵ) to Cr (Ⅲ) and also determined via correlation analysis. This study suggested compost-derived HA and FA coupling with MR-1 exhibited excellent performance for the bioreduction of Cr (Ⅵ) to Cr (Ⅲ).

Exploring the mechanism of Cd uptake and translocation in rice: Future perspectives of rice safety

Cadmium (Cd) contamination in rice fields has been recognized as a severe global agro-environmental issue. To reach the goal of controlling Cd risk, we must pay more attention and obtain an in-depth understanding of the environmental behavior, uptake and translocation of Cd in soil-rice systems. However, to date, these aspects still lack sufficient exploration and summary. Here, we critically reviewed (i) the processes and transfer proteins of Cd uptake/transport in the soil-rice system, (ii) a series of soil and other environmental factors affecting the bioavailability of Cd in paddies, and (iii) the latest advances in regard to remediation strategies while producing rice. We propose that the correlation between the bioavailability of Cd and environmental factors must be further explored to develop low Cd accumulation and efficient remediation strategies in the future. Second, the mechanism of Cd uptake in rice mediated by elevated CO2 also needs to be given more attention. Meanwhile, more scientific planting methods (direct seeding and intercropping) and suitable rice with low Cd accumulation are important measures to ensure the safety of rice consumption. In addition, the relevant Cd efflux transporters in rice have yet to be revealed, which will promote molecular breeding techniques to address the current Cd-contaminated soil-rice system. The potential for efficient, durable, and low-cost soil remediation technologies and foliar amendments to limit Cd uptake by rice needs to be examined in the future. Conventional breeding procedures combined with molecular marker techniques for screening rice varieties with low Cd accumulation could be a more practical approach to select for desirable agronomic traits with low risk.

Remediation potential of magnetic biochar in lead smelting sites: Insight from the complexation of dissolved organic matter with potentially toxic elements

Magnetic biochar has been widely used in potentially toxic elements (PTEs) polluted soils due to its magnetic separation capability and synchronous immobilization for multiple metals. However, the contribution of magnetic biochar to soil dissolve organic material (SDOM) and its binding behavior with PTEs needs to be further clarified prior to its remediation application on lead smelting sites. In this study, multi-spectral techniques of excitation-emission matrix (EEM) fluorescence spectroscopy and two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) were used to explore the evolution characteristics of SDOM in the lead smelting site under the remediation of magnetic biochar, and to further analyze its affinity and binding behavior with Pb and As. Results showed that magnetic biochar significantly increased SDOM content and decreased Pb and As available content. EEM and parallel factor analysis (EEM-PARAFAC) and Self-Organizing map analysis showed that humus-like and aromatic DOM increased and microbial-derived SDOM decreased after magnetic biochar cultivation. Furthermore, 2D-FTIR-COS correlation spectroscopy analysis indicated that BDOM had a stronger binding affinity to Pb, while SDOM has a stronger binding affinity to As. The binding sequences of different DOMs to PTEs varied greatly, the carboxyl and amide groups of SDOM and BDOM showed a remarkable and rapid response. Our results enhance the insights of magnetic biochar on soil function and PTEs remediation potential, providing novel information for its environmental remediation application.

Complexation of copper algaecide and algal organic matter in algae-laden water: Insights into complex metal-organic interactions

Copper-based algicides have been widely used to suppress algae blooms; however, the release of algal organic matter (AOM) on account of cell lysis may cause significant changes in the mitigation, transformation, and bioavailability of Cu(II). In the present work, the binding characteristics of Cu(II) with AOM were explored via combinative characterization methods, such as high-performance size exclusion chromatography, differential absorption spectra analysis, and joint applications of two-dimensional correlation spectroscopy (2D-COS), as well as heterospectral 2D-COS and moving window 2D-COS analyses of UV, synchronous fluorescence, and FTIR spectra. Carboxyl groups displayed a preferential interaction to Cu(II) binding, followed by polysaccharides. The spectral changes of C]O stretching occur after the change of chromophores in complexation with Cu(II). The AOM chromophores exhibit obvious conformations at Cu(II) concentrations higher than 120 μM, while AOM fluorophores and functional groups exhibit the greatest changes at Cu(II) concentrations lower than 20 μM. All these observations have verified the presence of binding heterogeneity and indicate that AOM could interact with Cu(II) through diverse functional moieties. Therefore, our study contributes to the better understanding of the fate of Cu(II)-AOM complexes in aquatic systems.

Photochemical behaviors of dissolved organic matter in aquatic environment: Generation, characterization, influencing factors and practical application

Dissolved organic matter (DOM) widely exists in aquatic environment and plays a critical role in environmental photochemical reaction. The photochemical behaviors of DOM in sunlit surface waters have received widely attention because its photochemical effects for some coexisted substances in aquatic environment, especially for organic micropollutants degradation. Therefore, to gain a comprehensive understanding of the photochemical properties and environmental effects of DOM, we reviewed the influence of sources on the structure and composition of DOM with relevant identified techniques to analysis functional groups. Additionally, identification and quantification for reactive intermediates are discussed with a focus on influencing factors to produce reactive intermediates by DOM under solar irradiation. These reactive intermediates can promote the photodegradation of organic micropollutants in the environmental system. In future, attention should be paid to the photochemical properties of DOM and environmental effects in real environmental system and development of advanced techniques to study DOM.

Characteristics of dissolved organic matter composition in biochar: Effects of feedstocks and pyrolysis temperatures

Biochar has widely used in soil pollution remediation due to its advantages of high efficiency and environmental sustainability. Dissolved organic matter (DOM) released by biochar plays a non-negligible role in the migration and transformation of pollutants in environment, and its composition was regarded as main impact factor. In this study, 28 biochar were investigated to detect the effect of pyrolysis temperature and feedstock on DOM content and components. Results showed that the content of DOM released from biochar at low pyrolysis temperatures (300-400 ℃) was higher than that from high pyrolysis temperatures (500-600 ℃). In addition, the specific UV-Visible absorbance at 254 nm (SUVA254) results expressed that DOM from peanut shell biochar (PSBC), rice husk biochar (RHBC) and bamboo biochar (BBC) had higher humification at high temperatures. Moreover, one fulvic acid-like (C2) and two humic acid-like (C1, C3) substances were main fluorescent components of biochar-derived DOM identified by parallel factor analysis based on excitation emission matrices fluorescence spectroscopies (EEM-PARAFAC). With the increase of pyrolysis temperature, humic acid substances content gradually decreased. The correlation analysis results revealed that pyrolysis temperatures and O/C, H/C, DOM content, the biological index (BIX), humification index (HIX), C1% and C3% was negatively correlated (p < 0.001). Thus, the pyrolysis temperatures take important roles in composition of DOM released from biochar, and this research would provide a reference for the application of biochar in the environment.

Binding of Cd(II) to birnessite and fulvic acid organo-mineral composites and controls on Cd(II) availability

Manganese oxide minerals (MnOs) are major controls on cadmium (Cd) mobility and fate in the environment. However, MnOs are commonly coated with natural organic matter (OM), and the role of this coating in the retention and availability of harmful metals remains unclear. Herein, organo-mineral composites were synthesized using birnessite (BS) and fulvic acid (FA), during coprecipitation with BS and adsorption to preformed BS with two organic carbon (OC) loadings. The performance and underlying mechanism of Cd(II) adsorption by resulting BS-FA composites were explored. Consequently, FA interactions with BS at environmentally representative (5 wt% OC) increase Cd(II) adsorption capacity by 15.05-37.39% (q_m = 156.5-186.9 mg g^-1), attributing to the enhanced dispersion of BS particles by coexisting FA led to significant increases in specific surface area (219.1-254.8 m² g^-1). Nevertheless, Cd(II) adsorption was notably inhibited at a high OC level (15 wt%). This might have derived from the supplementation of FA decreased pore diffusion rate and generated Mn(II/III) competition for vacancy sites. The dominant Cd(II) adsorption mechanism was precipitation with minerals (Cd(OH)₂), and complexation with Mn-O groups and acid oxygen-containing functional groups of FA. In organic ligand extractions, the exchange Cd content decreased by 5.63-7.93% with low OC coating (5 wt%), but increased to 33.13-38.97% at a high OC level (15 wt%). These findings help better understand the environmental behavior of Cd under the interactions of OM and Mn minerals, and provide a theoretical basis for organo-mineral composite remediation of Cd-contaminated water and soil.

Molecular size-dependent compositions and lead (II) binding behaviors of two origins of organic fertilizers-derived dissolved organic matter

The application of organic fertilizers caused large amounts of dissolved organic matter (DOM) entering the soil environment and influencing the behaviors and fates of heavy metals. Here, we investigated the molecular weight-dependent (high molecular weight [HMW], 1 kDa-0.7 µm; low molecular weight [LMW], <1 kDa) compositions and lead (Pb) binding behaviors of DOM derived from sheep manure-based (SMOF) and shrimp peptide-based organic fertilizers (SPOF) using chromophoric and fluorescent spectroscopy, Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and two-dimensional correlation spectroscopy (2D-COS). Results showed that SMOF released more DOM with higher aromaticity and hydrophobicity, containing more fluvic-like components, carboxylic-rich alicyclic molecules (CRAMs) and lignin phenolic compounds compared to SPOF-DOM with more microbially-transformed heteroatom-containing compounds (CHON, CHONS and CHOS). Furthermore, there was more aromatic compounds with ample carboxyl and hydroxyl groups in HMW-DOM but abundant protein-like components and heteroatom-containing compounds (CHONS and CHOS) in LMW-DOM. SMOF-DOM exhibited more obvious MW-dependent heterogeneity in molecular components compared to SPOF-DOM with higher molecular diversity. Moreover, 2D-COS indicated phenol and carboxyl groups in SMOF-DOM and polysaccharides in SPOF-DOM exhibited superior binding affinities for Pb. Pb binding to HMW-DOM derived from SMOF first occurred in the phenolic groups in fulvic-like substances, while polysaccharides in LMW-DOM first participated in the binding of Pb. In contrast, irrespective of MWs, polysaccharides and humic-like substances with aromatic (CC) groups in SPOF-DOM displayed a faster response to Pb. Furthermore, the polysaccharides which preferentially participated in the binding of Pb to SPOF-DOM and SMOF-derived LMW-DOM may pose a higher risk of Pb in the environment. These results were helpful to understand the effects of sources and size-dependent compositions of DOM on the associated risks of heavy metals in the environments.

Drivers to improve metal(loid) phytoextraction with a focus on microbial degradation of dissolved organic matter in soils

Bioaugmentation of soils can increase the mobilization of metal(loid)s from the soil-bearing phases. However, once desorbed, these metal(loid)s are mostly complexed to the dissolved organic matter (DOM) in the soil solution, which can restrict their availability to plants (roots mainly taking up the free forms) and then the phytoextraction performances. Firstly the main drivers influencing phytoextraction are reminded, then the review focuses on the DOM role. After having reminding the origin, the chemical structure and the lability of DOM, the pool of stable DOM (the most abundant in the soil) most involved in the complexation of metal(loid)s is addressed in particular by focusing on carboxylic and/or phenolic groups and factors controlling metal(loid) complexation with DOM. Finally, this review addresses the ability of microorganisms to degrade metal(loid)-DOM complexes as an additional lever for increasing the pool of free metal(loid) ions, and then phytoextraction performances, and details the origin of microorganisms and how they are selected. The development of innovative processes including the use of these DOM-degrading microorganisms is proposed in perspectives.

Occurrence and source analysis of heavy metals and dissolved organic matter in Nanyi Lake, Anhui Province

Nanyi Lake is a tributary in the lower reaches of the Yangtze River and the largest freshwater lake in southern Anhui. Anthropogenic activities have significantly affected the lake with the rapid development of the surrounding economy in recent years. This study collected a total of 39 × 2 water samples of surface water and overlying water, detected the heavy metal concentrations (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd), and analyzed the spectral characteristics of the dissolved organic matter (DOM). The results demonstrated that the concentrations of heavy metals (As, Cr, Cu, Mn, Ni, Pb, Sb, Zn, Fe, Cd) in the surface water were 1.00-7.78, 0.40-5.59, 0.20-4.52, 20.00-269.50, 0.40-5.56, 0.20-5.06, 1.00-7.64, 20.00-252.50, 60.00-590.00, and 0.04-0.60, respectively (unit: μg L^-1). The risk assessment showed that the carcinogenic risks of heavy metals (As, Cr, Cd) through drinking water were ranged from 10^-7 to 10^-4a^-1 in Nanyi Lake, and Cr was the main carcinogen which should be the focus of environmental health risk management. The average personal non-carcinogenic risks of heavy metals (Cu, Mn, Ni, Pb, Sb, Zn, Fe) were ranged from 10^-9 to 10^-13a^-1, and considered to be acceptable risk level. The contour map of spatial distribution demonstrated different degrees of heavy metals (except Zn) enrichment near the Langchuan River in the East Lake District. Parallel factor analysis showed that the main components of DOM in Nanyi Lake were tryptophan like, fulvic acid like, and tyrosine like, and the dissolved organic matter was primarily derived from autogenous endogenous sources. The heavy metals Cr, Ni, Pb, Fe, Cd, and HIX in the surface water of West Lake were significantly positively correlated, among which Ni, Fe and C2 were significantly negatively correlated (P < 0.05), Mn and BIX demonstrated extremely significant positive correlations (P < 0.01), while no significant correlation was observed between heavy metals and the DOM indexes in the surface water of the East Lake. The principal component and correlation analysis showed that the heavy metals in Nanyi Lake were primarily derived from the production wastewater discharged by the surrounding industrial and mining enterprises through the rivers input, followed by the non-point source runoff input of the surrounding agricultural production and lake aquaculture.

Temperature-Dependent Molecular Evolution of Biochar-Derived Dissolved Black Carbon and Its Interaction Mechanism with Polyvinyl Chloride Microplastics

Biochar-derived dissolved black carbon (DBC) molecules are dependent on the BC formation temperature and affect the fate of emerging contaminants in waters, such as polyvinyl chloride microplastic (MP_PVC). However, the temperature-dependent evolution and MP_PVC-interaction of DBC molecules remain unclear. Herein, we propose a novel DBC-MP_PVC interaction mechanism by systematically interpreting heterogeneous correlations, sequential responses, and synergistic relationships of thousands of molecules and their linking functional groups. Two-dimensional correlation spectroscopy was proposed to combine Fourier transform-ion cyclotron resonance mass spectrometry and spectroscopic datasets. Increased temperature caused diverse DBC molecules and fluorophores, accompanied by molecular transformation from saturation/reduction to unsaturation/oxidation with high carbon oxidation states, especially for molecules with acidic functional groups. The temperature response of DBC molecules detected via negative-/positive-ion electrospray ionization sequentially occurred in unsaturated hydrocarbons → lignin-like → condensed aromatic → lipid-/aliphatic-/peptide-like → tannin-like → carbohydrate-like molecules. DBC molecular changes induced by temperature and MP_PVC interaction were closely coordinated, with lignin-like molecules contributing the most to the interaction. Functional groups in DBC molecules with m/z < 500 showed a sequential MP_PVC-interaction response of phenol/aromatic ether C-O, alkene C═C/amide C═O → polysaccharides C-O → alcohol/ether/carbohydrate C-O groups. These findings help to elucidate the critical role of DBCs in MP environmental behaviors.

Oxidation of hydrochar produced from byproducts of the sugarcane industry for the production of humic-like substances: Characterization and interaction study with Cu(II)

Humic-like substances (HLS) are molecules extracted in an alkaline medium from different materials that have not been subjected to the natural process of humification that occurs in the soil. HLS have the potential to be used as organic fertilizers due to their ability to incorporate micronutrients such as Cu(II) and Co(II); in addition, they represent an alternative for the remediation of contaminated areas due to their high affinity for metals. HLS can be extracted from hydrochar (HC) but only with low yields of approximately 5%. Therefore, the present study aimed to increase the amount of HLS extracted from the HC produced from byproducts of the sugarcane industry through the oxidation of HC with HNO₃. HLS extracted from oxidized and unoxidized HC were characterized by CHNS analysis and ¹³C CPMAS NMR. The interaction between HLS and Cu(II) was studied by molecular fluorescence quenching (EEM-PARAFAC) and applying the Ryan and Weber complexation model. The oxidation of HC with HNO₃ allowed high yields of extracted HLS of above 80%. The oxidation carried out with 30% HNO₃ for 2 h showed the best result, since the HLS_30%(2h) were extracted with a very high yield (88.3%) in a short period of time. Oxidation promoted a decrease in HLS aromaticity and an increase in oxygen and nitrogen groups. HLS showed high affinity for Cu(II), as evidenced by the high logK values (between 5.5 and 5.9). HLS extracted from oxidized HCs showed higher complexation capacity due to the greater incorporation of the oxygenated groups promoted by oxidation, which are fundamental during the interaction with metallic cations. Therefore, the oxidation of HC substantially increased the production of HLS, representing a big advance for the production of carbonaceous materials with higher added value from byproducts of the sugarcane industry produced on a large scale in Brazil.

Elevated methylmercury production in mercury-contaminated paddy soil resulted from the favorable dissolved organic matter variation created by algal decomposition

Algae-derived organic matter (AOM) may considerably regulate methylmercury (MeHg) production and accumulation in the paddy fields by changing the soil-dissolved OM (SDOM) properties. In this study, a 25-day microcosm experiment was performed to compare the responding mechanisms of MeHg production in the Hg-contaminated paddy soil-water system to the input of algae-, rice-, and rape-derived OMs. Results showed that algal decomposition could release much more cysteine and sulfate than crop straws. Compared with crop straw-derived OMs, AOM input greatly increased the dissolved organic carbon concentrations in soil but resulted in a greater decrease in tryptophan-like fractions while accelerated the formation of high-molecular-weight fractions in soil DOM. Moreover, AOM input significantly increased MeHg concentrations in the pore water by 19.43%-3427.66% and 52.81%-5846.57% compared to rape- and rice-derived OMs, respectively (P < 0.05). And, a similar MeHg changing pattern was also observed in the overlying water (10-25 d) and the soil solid-phase particles (15-25 d) (P < 0.05). Correlation analysis revealed that MeHg concentrations in the AOM-added soil-water system had significantly negative and positive relationships with the tryptophan-like C4 fraction and molecular weight (E2/E3 ratio) of soil DOM, respectively (P < 0.01). These findings suggest that AOM has a higher capacity than crop straw-derived OMs to promote MeHg production and accumulation in the Hg-contaminated paddy soils by creating a favorable soil DOM variation and providing more microbial electron donors and receptors.

Manganese oxides mediated dissolve organic matter compositional changes in lake sediment and cadmium binding characteristics

In sediment environments, manganese (Mn) minerals have high dissolved organic matter (DOM) affinities, and could regulate the changes of DOM constituents and reactivity by fractionation. However, the effects of DOM fractionation by Mn minerals on the contaminant behaviors remain unclear. Herein, the transformations of mineral phases, DOM properties, and Cd(II) binding characteristics to sediment DOM before and after adsorption by four Mn oxides (δ-MnO₂, β-MnO₂, γ-MnOOH, and Mn₃O₄) were investigated using multi-spectroscopic tools. Results showed a subtle structural variation of Mn oxides in response to DOM reduction, and no phase transformations were observed. Two-dimensional correlation spectroscopy based on synchronous fluorescence spectra and Fourier transform infrared spectroscopy indicated that tryptophan-like substances and the amide (II) N-H groups could preferentially interact with Cd(II) for the original DOM. Nevertheless, preferential bonding of Cd(II) to tyrosine-like substances and phenolic OH groups was exhibited after fractionations by Mn oxides. Furthermore, the binding stability and capacity of each DOM fraction to Cd(II) were decreased after fractionation based on the modified Stern-Volmer equation. These differences may be attributed to DOM molecules with high aromaticity, hydrophobicity, molecular weight, and amounts of O/N-containing group were preferentially removed by Mn oxides. Overall, the environmental hazard of Cd will be more severe after DOM fractionation on Mn minerals. This study facilitates a better understanding of the Cd geochemical cycle in lake sediments under the DOM-mineral interactions, and recommends being careful with outbreaks of aquatic Cd pollution when sediments are rich in dissolved protein-like components and Mn minerals.

Green synthesized hydroxyapatite for efficient immobilization of cadmium in weakly alkaline environment

The development of cost-effective passivators for the remediation of heavy metal-contaminated soils has been a research hotspot and an unsolved challenge. Herein, a novel hydroxyapatite (GSCH) was synthesized by co-precipitating distiller effluent-derived Ca with (NH₄)₂HPO₄ using straw-derived dissolved organic matter (S-DOM) as the dispersant. Batch adsorption experiments and soil incubation tests were performed to assess the immobilization efficiency of GSCH for Cd in weakly alkaline environments. As a result, GSCH showed an excellent adsorption efficiency to Cd with a maximum adsorption amount of ∼222 mg g^-1, which was fairly competitive compared to other similar previously materials reported. The kinetic data indicated that the adsorption of Cd on GSCH was a chemical and irreversible process, while the thermodynamic data revealed a spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption process. Based on mechanism analysis, both physisorption (e.g., electrostatic attraction and pore filling) and chemisorption (e.g., ion exchange and complexation) were responsible for Cd adsorption on GSCH. Particularly, the incorporated S-DOM and hydroxyapatite phase in GSCH acted synergistically in the adsorption process. The incubation results showed that GSCH application could significantly reduce the bioavailability, phytoavailability and bioaccessibility of Cd in soil by 48.4%-57.8%, 20.4%-28.6% and 12.6%-24.0%, respectively. Moreover, GSCH application also improved soil bacterial communities and enhanced soil nutrient availability. Overall, this is the first study to demonstrate the potential application value of GSCH in Cd immobilization, providing promising insights into the development of green and cost-effective hydroxyapatite-based passivators for the remediation of heavy metal-contaminated soils.

Mechanistic insights into the detoxification of Cr(VI) and immobilization of Cr and C during the biotransformation of ferrihydrite-polygalacturonic acid-Cr coprecipitates

Coupled reactions among chromium (Cr), organic matter (OM), and iron (Fe) minerals play significant roles in Cr and carbon (C) cycling in Cr-contaminated soils. Although the inhibitory effects of Cr or polysaccharides acid (PGA) on ferrihydrite transformation have been widely studied, mechanistic insights into detoxification of Cr(VI) and immobilization of Cr and C during the microbially mediated reductive transformation of ferrihydrite remain unclear. In this study, underlying sequestration mechanisms of Cr and C during dissimilatory Fe reduction at various Cr/Fe ratios were investigated. Solid-phase analysis showed that reductive transformation rates of ferrihydrite were impeded by high Cr/Fe ratio and more magnetite was found at low Cr loadings. Microscopic analysis showed that formed Cr(III) was immobilized by magnetite and goethite through isomorphous substitution, whereas PGA was adsorbed on the crystalline Fe mineral surface. Spectroscopic results uncovered that binding of Fe minerals and PGA was achieved by surface complexation of structural Fe with carboxyl functional groups, and that the adhesion order of PGA functional groups and Fe minerals was influenced by the Cr/Fe ratios. These findings have significant implications for remediating Cr contaminants, realizing C fixation, and developing a quantitative model for Cr and C cycling by coupling reductive transformation in Cr-contaminated environments.

Tracing the variation of dissolved organic matter in the two-stage anoxic/aerobic process treating swine wastewater using fluorescence excitation-emission matrix with parallel factor analysis

Swine wastewater has become one of the main agricultural pollution sources. Quantitative characterization of dissolved organic matter (DOM) is often used in various water bodies, but there are few studies on DOM analysis of swine wastewater. In this study, swine wastewater was treated by a step-feed two-stage anoxic/aerobic (SF-A/O/A/O) process. By using parallel factor (PARAFAC) analysis of fluorescence excitation-emission matrix (EEM), the main components of swine wastewater were aromatic protein-like substances (C1), tryptophan-like substances (C2), fulvic acid-like/humic-like substances (C3) and humic-like substances (C4). Protein-like substances were degraded significantly, while humic-like substances were difficult to be utilized by microorganisms. Fluorescence spectral indexes showed that the characteristics of endogenous input and humus were enhanced. Moreover, several significant correlations between DOM components, fluorescence spectral indexes and water quality indexes were observed. These findings help to understand the biochemical role and the impact of DOM in water quality monitoring and control of swine wastewater.

Insight into the evolution characteristics on molecular weight of compost dissolved organic matters using high-performance size exclusion chromatography combined with a two-dimensional correlation analysis

The information on molecular weight (MW) characteristics of DOM and relevant evolution behaviors during composting are limited. In this study, DOM extracted from co-composting of chicken manure and rice husks were comprehensively analyzed by using high-performance size exclusion chromatography (HPSEC) combined with a two-dimensional correlation spectroscopy (2D COS) to explore the evolution characteristics of MW of compost DOM. The HPSEC detected at UV of 254 nm and at fluorescence (FL) Ex/Em wavelengths (315/410, 270/455 nm) all showed a gradual increase in both weight-average and number-average MW for DOM, suggesting that the large MW fractions were continuously generated and polymerized during composting. The 2D COS applied on HPSEC-UV and -FL further identified the key active MW chromophoric (i.e., 0.5, 7.2. 9.5, 26.3, 30.7, and 83.9 kDa) and fluorophoric (i.e., 0.55 and 3.5 kDa) molecules that mainly participated in the transformation processes of compost DOM. Moreover, these active MW species were preferentially formed by the order of small to large molecules. A hetero-2D COS analysis disclosed the change sequence in the order of 0.5 and 7.2 kDa chromophores → 3.5 kDa fluorophores, and the 0.55 and 3.5 kDa fluorophores → 26.3 and 83.9 kDa chromophores.

Exploration on the role of different iron species in the remediation of As and Cd co-contamination by sewage sludge biochar

Numerous studies have explored the adsorption of cadmium (Cd) and arsenic (As) by iron (Fe)-modified biochar, but few studies have examined in-depth the similarities and differences in the adsorption behavior of different iron types on Cd and As. In this study, sewage sludge biochar (BC) was co-pyrolyzed with self-made Fe minerals (magnetite, hematite, ferrihydrite, goethite, and schwertmannite) to treat Cd and As co-contaminated water. The adsorption of Cd and As on the Fe-modified biochar was further analyzed by adsorption kinetics, adsorption isotherms, and adsorption thermodynamics combined with a series of characterization experiments. Both SEM-EDX and XRD results confirmed the successful loading of iron minerals onto BC. Both adsorption kinetics and adsorption isotherms experiments showed that the adsorption of Cd and As by BC and the other five Fe-modified biochar was mainly controlled by chemical interactions. The results also indicated that goethite biochar (GtBC) was the most effective for the adsorption of Cd among the five Fe-modified biochar. Ferrihydrite biochar (FhBC) formed more diverse complexes, coupled with the relatively stronger electrons accepting ability, thus making it more effective for As adsorption than the others. Additionally, GtBC and hematite biochar (HmBC) were found effective for the adsorption of both Cd and As, whereas MBC was not found effective for either metal. Furthermore, combined with XPS results, the adsorption of Cd by the materials was mainly governed by Cd²⁺-π interactions, complexation precipitation, and co-precipitation, while oxidation reactions also existed for As.

Pyrolysis Atmospheres and Temperatures Co-Mediated Spectral Variations of Biochar-Derived Dissolved Organic Carbon: Quantitative Prediction and Self-Organizing Maps Analysis

Biochar-derived dissolved organic carbon (BDOC), as a highly activated carbonaceous fraction of biochar, significantly affects the environmental effect of biochar. This study systematically investigated the differences in the properties of BDOC produced at 300-750 °C in three atmosphere types (including N₂ and CO₂ flows and air limitation) as well as their quantitative relationship with biochar properties. The results showed that BDOC in biochar pyrolyzed in air limitation (0.19-2.88 mg/g) was more than that pyrolyzed in N₂ (0.06-1.63 mg/g) and CO₂ flows (0.07-1.74 mg/g) at 450-750 °C. The aliphaticity, humification, molecular weight, and polarity of BDOC strongly depended on the atmosphere types as well as the pyrolysis temperatures. BDOC produced in air limitation contained more humic-like substances (0.65-0.89) and less fulvic-like substances (0.11-0.35) than that produced in N₂ and CO₂ flows. The multiple linear regression of the exponential form of biochar properties (H and O contents, H/C and (O+N)/C) could be used to quantitatively predict the bulk content and organic component contents of BDOC. Additionally, self-organizing maps could effectively visualize the categories of fluorescence intensity and components of BDOC from different pyrolysis atmospheres and temperatures. This study highlights that pyrolysis atmosphere types are a crucial factor controlling the BDOC properties, and some characteristics of BDOC can be quantitatively evaluated based on the properties of biochar.

Mobilization of colloids during sediment resuspension and its effect on the release of heavy metals and dissolved organic matter

Natural colloids are important in mobilizing pollutants in aquatic environments. This study investigated the mobilization and aggregation of natural colloids during the sediment resuspension and re-sedimentation processes using nanoparticle tracking analysis. The metals and organic matter in overlying water were divided and examined in dissolved (<0.45 μm), colloidal (3 kDa - 0.45 μm), and truly dissolved (<3 kDa) forms. Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) was used to characterize the dissolved organic matter (DOM). In overlying water, most natural colloids were < 200 nm before resuspension. An evident mobilization of colloids and an increase in colloid size were observed during resuspension. The formation of particles (>0.45 μm) and decreases of small colloids (<200 nm) indicated that resuspension promoted the aggregation of colloids. Mobilization of colloids was accompanied by increases in concentrations of Fe, Al, and organic carbon in colloidal fractions, which could be related to the formation of mineral-organic complexes under an oxic environment. The release of DOM from sediments mainly contributed to the truly dissolved humic-like fraction, and colloidal organic carbon accounted for, on average, 20 % of the total dissolved organic carbon (DOC). Fe and Al had the highest colloidal proportions as they are major compositions of inorganic colloids. Substantial removal of dissolved Al, Fe, Pb, and Zn occurred when colloids aggregated in the overlying water. Although the adsorption of suspended particles may also decrease the concentrations of dissolved metals, the increased proportions of colloidal metals indicated a possible role of colloids in this process. These findings provide insight into the behavior of colloids during the resuspension process and indicate that the aggregation of colloids could promote the removal of dissolved matter.

Unveiling the Role of Dissolved Organic Matter on the Hg Phytoavailability in Biochar-Amended Soils

Biochar can effectively reduce the phytoavailability of mercury (Hg) in soil, but the mechanisms are not fully understood. In this study, the dynamic changes in Hg content adsorbed by the biochar (BC-Hg), Hg phytoavailability in the soil (P-Hg), and soil dissolved organic matter (DOM) characteristics were determined over a 60-day treatment period. Biochar obtained at 300 °C, 500 °C and 700 °C reduced the P-Hg concentration assessed by MgCl2 extraction by 9.4%, 23.5% and 32.7%, respectively. However, biochar showed a very limited adsorption on Hg, with the maximum BC-Hg content only accounting for 1.1% of the total amount. High-resolution scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) results showed that the proportion of Hg atoms in biochar after 60 d was barely detectable. Biochar treatment can shift soil DOM toward higher aromatic content and molecular weight. Additionally, the addition of high-temperature biochar increased more humus-like components, but low-temperature biochar increased more protein-like components. Correlation analysis and partial least squares path modeling (PLS-PM) showed that biochar promoted humus-like fractions formation to reduce the Hg phytoavailability. This research has deepened the understanding of the mechanisms by which biochar stabilizes Hg in agricultural soils.

Fabrication of PA-PEI-MOF303(Al) by Stepwise Impregnation Layer-by-Layer Growth for Highly Efficient Removal of Ammonia

NH₃ is a typical alkaline gaseous pollutant widely derived from industrial production and poses great risks to humans and other biota. Metal-organic frameworks (MOFs) have excellent adsorption capacities relative to materials traditionally used to adsorb NH₃. However, in practice, applications of MOFs as adsorbents are restricted because of its powder form. We prepared a polyamide (PA) macroporous polyester substrate using an emulsion template method and modified the surface with polyethylenimine (PEI) to improve the MOF growth efficiency on the substrate. The difficulty of loading the MOF because of the fast nucleation rate inside the PA macroporous polyester substrate was solved using a stepwise impregnation layer-by-layer (LBL) growth method, and a PA-PEI-MOF303(Al) hierarchical pore composite that very efficiently adsorbed NH₃ was successfully prepared. The PA-PEI-MOF303(Al) adsorption capacity for NH₃ was 16.07 mmol·g^-1 at 298 K and 100 kPa, and the PA-PEI-MOF303(Al) could be regenerated repeatedly under vacuum at 423 K. The NH₃ adsorption mechanism was investigated by in situ Fourier transform infrared spectroscopy and by performing two-dimensional correlation analysis. Unlike for the MOF303(Al) powder, the formation of multi-site hydrogen bonds between Al-O-Al/C-OH, N-H, -OH, C=O, and NH₃ in PA-PEI-MOF303(Al) was found to be an important reason for efficient NH₃ adsorption. This study will provide a reference for the preparation of other MOF-polymer composites.