Purpose Biomass burning smoke-derived dissolved organic matter (BBS-DOM) is annually deposited in massive quantities into terrestrial ecosystems, yet its impacts on heavy metal geochemistry in acidic soils remain poorly characterized. Methods We investigated the 3-month dynamic effects of six BBS-DOMs derived from alfalfa, pinewood, and corn straw combustion on Cu(Ⅱ) adsorption in an acidic soil, combining UV-Vis, EEM-PARAFAC and FT-ICR MS. Results Feedstock-specific bidirectional effects strongly modulated by aging: alfalfa-BBS-DOM consistently promoted Cu(Ⅱ) adsorption, with 4648 L·kg − 1 K d in unaged soil and remaining 7.8 ~ 8.4-fold higher than control throughout incubation; pinewood/corn straw-BBS-DOM initially inhibited or had no significant promotive effect on soil Cu(Ⅱ) adsorption, with K d increasing by 187.2%~206.8% in the first month but returning to control levels after 3 months. Molecular characterization revealed alfalfa-BBS-DOM was dominated by nitrogen-enriched large humic-like matters (CHON and CHONP compounds), while pinewood/corn straw-BBS-DOM mainly consisted of oxygen-rich polyphenol-like matters dominated (CHO compounds). Mechanistically, these divergent effects arise from the coupled regulation of aqueous-phase complexation and soil-surface interactions on Cu(Ⅱ) adsorption: protonated amino (-NH 2 ) groups in alfalfa-BBS-DOM inhibit soluble DOM-Cu(Ⅱ) complex formation in the aqueous phase, while negatively charged -SO 3 − , -H 2 PO 3 − , and -COO − groups enable alfalfa-BBS-DOM to strongly adsorb to soil surfaces; the adsorbed alfalfa-BBS-DOM retains these negatively charged functional groups, which attract Cu(Ⅱ) ions. Conversely, -COOH and phenolic-OH groups in pinewood/corn straw-BBS-DOM form soluble aqueous complexes with Cu(Ⅱ). Conclusion This study provides a mechanistic basis for heavy metal risk assessment in wildfire-affected ecosystems.

Tire wear particles (TWPs), a ubiquitous class of microplastics, have recently been recognized as a contaminant of emerging concern. Aging profoundly alters the physicochemical characteristics of TWPs; consequently, may impact the molecular properties of dissolved organic matter leached from these particles (TWP-DOMs). In this study, TWPs were aged using different approaches (photo-oxidation (UV radiation), chemical-oxidation (Fenton and H2O2), acidic or basic treatment (HCl or NaOH), and photo-chemical oxidation (UV combined with H2O2 (UV/H2O2)). A multi-analytical approach integrating FTIR, TEM, Fluorescence spectrum, Raman, and twodimensional correlation spectroscopy (2D-COS) was employed to elucidate aging-induced alterations in the properties of TWPs and/or TWP-DOMs. The results demonstrated that HCl-or NaOH-treated TWPs exhibited more pronounced surface cracking and/or structural defects than photo-oxidation and chemical oxidation. Meanwhile, the oxidation treatments (Fenton, H2O2, UV, and UV/H2O2) promoted the formation of more oxygen-containing groups on TWP surfaces than HCl-or NaOH-treatment, with the sequential group change of-OH-*C-O-*C-OH during the aging process. Herein, the UV-oxidation introduced more than 2 times the O content into TWP surfaces in comparison with other oxidation processes. Spectral characteristics of TWP-DOMs obtained from FTIR and Fluorescence spectrum analysis showed that the aging enhanced the aromaticity and humification of TWP-DOMs. Generally, the photo-aging appeared to decrease the molecular size of DOMs released from TWPs, while the acidic or basic treatment resulted in the contrary tendency. Furthermore, although the release sequence and abundances of organic components from TWPs varied with the aging approaches, the aging treatment transformed tryptophan-like protein components (the predominant component in the untreated TWP-DOM) into humic-like substances (the main components in the aged TWP-DOMs). Our findings expand the understanding of the critical role of aging in evaluating the environmental fate of TWPs and TWP-derived DOMs.

Pyrolysis of tea waste to produce biochar (BC) for soil modification offers a promising reuse strategy. However, the short-term application of BC can enhance soil organic carbon (SOC) mineralization, and the economic viability of this BC across its lifecycle (from production to field application) remains unclear. In this study, Fe-modified tea waste BC (FBC) was produced at 300-900 °C to enhance SOC sequestration over 180 days, alongside an evaluation of their economic benefits. Compared with unmodified BC, FBC produced at 600 °C (FBC600) and 900 °C (FBC900) significantly increased SOC content, with increments of 1770-1800 mg/kg at 15-60 days and 660-830 mg/kg at 60-180 days. This enhancement was attributed to two factors: first, the highly aromatic structures of FBC600 and FBC900 were associated with the abundance of putative autotrophic taxa, with Fe potentially facilitating fresh SOC synthesis by these bacteria; second, dissolved organic C (DOC) decreased by 417-436 mg/kg in FBC-amended soils, which was approximately twice the cumulative mineralized C, indicating that enhanced DOC adsorption further contributed to SOC sequestration. Spectral analysis suggested preferential adsorption of small aromatic protein-like molecules in FBC600- and FBC900-amended soils. Life cycle assessment revealed significant economic benefits for both FBC600 and FBC900, with overall revenues of 674.63 USD/ton and 721.04 USD/ton, respectively, alongside net CO2 emission reductions of 1432.12 kg/ton and 1098.16 kg/ton. This study highlights a valuable approach for tea waste reuse that offers both economic advantages and mitigation of the short-term SOC mineralization commonly induced by BC application.

As an effective soil amendment, biochar can reduce the adverse effects and environmental impacts of neonicotinoid pesticides. Rhamnolipid, an active and common biosurfactant in soil systems, may alter the co-transport behaviors of biochar colloids and pesticides. Nevertheless, biosurfactant-mediated changes in pesticide mobility in soils affected by biochar colloids are currently lacking. Herein, the single or combined effects of biochar colloids and rhamnolipid on the transport properties of dinotefuran (DTF, a typical neonicotinoid pesticide) in soil matrix were investigated. When the influents contained biochar colloids, the DTF transport was reduced, primarily via colloid-associated DTF deposition and pesticide bound to the deposited colloids on porous media surfaces. Meanwhile, rhamnolipid also restrained DTF mobility because of its bridging effect (i.e., this biosurfactant mediated DTF-soil binding through molecular bridging). However, rhamnolipid notably diminished the suppressed influences of biochar colloids on DTF transport because of the decrease of colloid-associated DTF retention and the high mobility of free DTF. Moreover, the degree of rhamnolipid's weakened effects was related to the solution pH values (i.e., the influences declined as the pH values increased). Because rhamnolipid exhibited greater inhibition effects on the binding abilities of colloids to pesticide molecules under lower pH conditions (pH 5.0), leading to more free DTF mobility. The results underscore the critical roles of ubiquitous biosurfactants in the fate and risks of pesticides when biochar is used as an amendment for contaminated soil.

Owing to the extensive use of solid fuels (e.g., coal, charcoal, and biomass), massive smoke dissolved organic matters (SDOMs) are produced. They are not only deteriorate atmosphere, but eventually deposit into water and soil environments, and interact with pollutants (e.g., heavy metals (HMs)), further altering the environmental fate and risks of HMs. However, the distinct molecular complexing mechanisms of SDOMs from various solid fuels combustion toward HMs still remains unknown. This study investigated the distinct molecular complexing mechanisms with Cu(II) and Cd(II)) (0-100 mu mol/L) for SDOMs (10 mg-C/L) from coal, charcoal, and biomass based on Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), two dimensional fluorescence excitation-emission matrix (EEM) and Fourier transform infrared spectroscopy (FTIR). Notably, various SDOMs exhibited evidently different molecular complexing characteristics with HMs. Fluorescence quenching/enhancing ratio showed that humic-like matters in biomass SDOMs (28.7-51 %) were significantly combined with HMs, and polyphenols in coal and charcoal SDOMs (7.3-38.4 %) were significantly combined with HMs. Coal-derived SDOM was rich in CHOS compounds (-SO3H group) which played a dominant role in the binding capacity toward HMs, with the binding sequence preceded CHON and CHONP compounds. Charcoal-derived SDOM featured N-containing compounds (-NH2 group), which formed H-bonds with S-/P-containing compounds and competed against HMs binding, leading highly aromatic CHO compounds to preferentially interact with HMs via cation-pi effect. Biomass-derived SDOMs possessing the maximum CHO compounds which provided more multi-oxygen coordination sites for HMs complexing, but CHON, CHOS and CHOP compounds interacting with HMs preceded CHO compounds. The complexing order of functional groups followed phenol-O->S=O/P-O/-NH > aromatic C=C > -OH. This study elucidated distinct molecular mechanisms of various SDOMs binding with HMs according to their molecular compositions and functional group types. The results are essential to understanding and controlling the geochemistry process and environmental fate of various solid fuels-derived SDOM-HMs complexes in surface environments.

Owing to the worldwide wildfire, the environmental process of polycyclic aromatic hydrocarbons (PAHs) in soil is inevitably affected by the co-deposition of biomass-burning-smoke dissolved organic matters (BBS-DOMs), which have significantly different molecular characteristics from soil-DOMs. However, to date, the molecular-level interactions among PAHs, BBS-DOMs, and soil remain a significant knowledge gap. Hence, this study used FT-ICR-MS and multi-spectrometers to comprehensively investigate their molecular-level interactions. This study revealed that the binding coefficient, Kd, of PAHs on BBS-DOMs (2.36 × 104∼7.40 × 104 L/kg) was about 100 times that for PAHs binding onto soils (2.07 × 102∼8.39 × 102 L/kg), owing to the abundant aromatic CHO, CHON, and CHONP molecules of BBS-DOMs, which were responsible for this stronger interaction. Additionally, the spectral index (SUVA254) of BBS-DOMs could be effectively used to predict the sorption capacities of PAHs onto DOMs, with the prediction models of log10Kd = 0.0946SUVA254+3.969 and log10Kd = 0.0991SUVA254+4.006 (r > 0.95, p < 0.01) for phenanthrene and pyrene, respectively. Interestingly, though BBS-DOMs input (0.1 wt%) significantly increased the dissolved organic carbon content of soil, their input significantly increased rather than decreased the sorption of PAHs onto soils, with Kd increased by 10∼35%. The FT-ICR-MS and other spectral results revealed that the small phenolic structure-containing molecules (e.g., polyphenols, lignin, and tannin) in BBS-DOMs were preferentially bound to soil. These preferentially binding molecules enhanced the interaction between PAHs and soils by the additional molecular bridging effect of π-π electron donor-acceptor interaction. These results give crucial evidence to understand the environmental fate and risk of BBS-DOMs and PAHs co-deposition into soils after a wildfire.

The deposition of biomass-burning smoke-derived dissolved organic matters (BBS-DOMs) poses challenges to water treatment in wildfire areas. This study innovatively investigated the molecular binding between BBS-DOMs and clays (kaolinite and montmorillonite) and its interaction with tetracycline adsorption using Fourier transform-ion cyclotron resonance-mass spectrometry and various other spectral analyses. Herein, the amine-containing molecules (CHON, CHONP, and CHONSP compounds) in BBS-DOMs were the dominant adsorbed components on kaolinite with limited binding sites (specific surface area (SSA): 17.9 m(2)/g; pH(pzc): 3.8) by forming strong hydrogen-bonds and electrostatic attraction. Conversely, montmorillonite exhibits sufficient binding sites (SSA: 63.5 m(2)/g; pH(pzc): 2.7) to allow simultaneous interaction with both amine-containing and polyphenolic molecules (CHO compounds) in BBS-DOMs. Intriguingly, with increasing tetracycline concentration, the strong-enhancing effect of BBS-DOMs (<= 1.0 mg/L tetracycline) transformed to weak-enhancing/inhibiting effects (>= 10.0 mg/L tetracycline) on tetracycline adsorption. This transition is due to the shift in primary compositions of BBS-DOMs binding with clays from large aromatic molecules (humic-like molecules) (the average proportion of dissolved state increased from 13.5 % to 40.0 %) to polyphenol- and aromatic amides/(oligo)peptide-like molecules (the average proportion of dissolved state decreased from 77.5 % to 38.8 %). The results suggested that at the environment-relevant concentration of tetracycline (<1.0 mg/L), BBS-DOMs could significantly enhance its adsorption onto clays. Furthermore, within the pH range of 3.0-10.0, the enhancing-effect of BBS-DOMs was maximum at pH 4.0. These results provided a crucial data-support for elucidating the molecular mechanism of BBS-DOMs-affected adsorption of tetracycline onto clays, and contribute to optimizing the water treatment processes in wildfire areas by clays application.

Metalated porous ionic polymers featuring multiple active sites show significant potential for carbon dioxide (CO2) fixation. However, general and efficient strategies to enhance their catalytic efficiency still remain to be developed. Herein, carbon nanotube-multifunctional ionic polymer core-shell composite (CNT@P(TBr-Py)ZnBr2) was easily prepared by a solvothermal radical copolymerization strategy, followed by metallization with ZnBr2. Characterization revealed that the synthesized composite exhibited a distinct core-shell tubular nano- structure, with CNT serving as the core, and multifunctional polymer containing Lewis acid (Zn), nucleophilic Br- and CO2-philic triazine groups as the shell. Furthermore, the composite displayed broad pore size distribution and large average pore size. Impressively, CNT@P(TBr-Py)-ZnBr2 delivered an outstanding catalytic efficiency in the cycloaddition of CO2 to epichlorohydrin, surpassing the control catalysts poly(triazine-based vinyl ionic liquid) (PTBr), bipyridine-functionalized porous ionic polymer (P(TBr-Py), and ZnBr2 metalated P(TBr-Py) (P (TBr-Py)-ZnBr2) by factors of 5.4, 5.8, and 1.3, respectively. At 140 degrees C, a high turnover frequency (TOF) of 11174 h- 1 and a 93.4 % yield of target cyclic carbonate were achieved in the absence of any additional co-catalyst. This exceptional catalytic performance of CNT@P(TBr-Py)-ZnBr2 can be mainly attributed to its unique core-shell structure, along with the synergistic catalytic effect of its multifunctional active sites. Also, the reaction can proceed smoothly under near-ambient conditions (30 degrees C, 1 bar CO2), though a longer reaction time was required. Additionally, CNT@P(TBr-Py)-ZnBr2 demonstrated a wide range of substrate compatibility and excellent recycling stability. This work therefore presents a viable approach for designing efficient and multifunctional ionic polymer-based catalysts for CO2 fixation.

Understanding the roles of low-molecular-weight organic acids (LMWOAs) in the transformation of chemical speciation of heavy metals in contaminated soil amended by biochar is of great significance for assessing the effectiveness of this carbonaceous amendment. The impacts of citric acid (a typical LMWOA) on the redistribution of Cd in contaminated soil amended by different amounts of biochar (1–5

The size fractionation of colloids is an important process while they migrate through porous media. To date, the information about the contribution of the size fractionation of clay colloids on heavy metal mobility during their co-transport process is limited. Herein, taking montmorillonite as a typical clay mineral, the size fractionation characteristics (> 2.0 mu m, 1.2-2.0 mu m, 0.45-1.2 mu m, 0.1-0.45 mu m, and < 0.1 mu m) of colloidal montmorillonite particles after passing through saturated sand and their different contribution to Pb2+ transport were investigated. The results indicated that the extent of Pb2+-mobilizing ability of colloids at pH 7.0 was higher than that at pH 5.0, ascribed to more Pb2+ adsorbed to the colloids and greater mobility of colloids at higher pH values. Generally, the contribution of colloid size fractions on Pb2+ mobility followed the order of (> 2.0 mu m) > (< 0.1 mu m) > 0.45-1.2 mu m > 0.1-0.45 mu m approximate to 1.2-2.0 mu m, which depended on the colloid size distribution in the effluents (i.e., the larger proportion of fractions exhibited greater contribution to the enhancement of Pb2+ mobility in this work). However, the relative contaminant-mobilizing abilities of different colloid size fractions (obtained by normalizing the fraction-facilitated Pb2+ breakthrough with the respective fraction breakthrough) increased with the decrease in colloid size, which stemmed from the relatively higher mobility and greater metal-binding capacities of smaller size fractions. Additionally, the differences in the relative contaminant-mobilizing abilities of different fractions decreased with decreasing sand grain sizes (20-40 mesh (0.425-0.85 mm), 40-60 mesh (0.25-0.425 mm), and 60-80 mesh (0.178-0.25 mm)), which was related to the different mobility of the colloid size fractions. In summary, these findings indicate that size fractionation of natural colloids plays a critical role in heavy metal mobility and retention in groundwater systems.

Forest fire (mainly wood burning) and crop residue burning (mainly herb burning) are two ways to produce biomass burning smoke water-soluble organic matters (BBS-WSOMs), largely altering atmospheric light absorption. However, their molecular characteristics-dependent light absorption remains unknown. Hence, this study combined Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) analysis with UV-Vis spectrum to deeply investigate the different molecules-dependent light absorption of wood- and herb-derived BBS-WSOMs from different burning temperatures. The results showed that at the tested burning temperatures (300 and 600 degrees C), biomass types showed a stronger influence on the light absorption at 200-550 nm than burning temperatures. Herb-derived BBS-WSOMs had a stronger light absorption than wood-derived BBSWSOMs. This was because in herb-derived BBS-WSOMs, more conjugated diene structures or more CHO compounds of low molecular mass and high aromaticity were responsible for their light absorption at 200-300 nm, and more CHON compounds (mainly nitroaromatics compounds) were responsible for their light absorption at 365-550 nm. The CHO/CHOS compounds in wood-derived BBS-WSOMs and CHON compounds in herb-derived BBS-WSOMs were respectively responsible for their light absorption at 365-550 nm. Interestingly, O-containing groups played an increasingly important role in enhancing light absorption with the increasing wavelength at 220-275 nm, while highly aliphatic structure with low O content played an increasingly important role in enhancing light absorption with the increasing wavelength at 365-550 nm. This study is beneficial for deeply understanding the different molecules-dependent light absorption of BBS-WSOMs, having significant implications in atmospheric environment management and quality control.

It is widely recognized that remediating cadmium (Cd)-contaminated sediments using biochar (BC) can significantly influence plant growth and development. However, the efficiency of such remediation often diminishes in field trials compared to greenhouse experiments, likely due to limited comprehension of the BC addition on the plant-sediment-microbe interaction. In this study, a 56-day pot experiment demonstrated that BC application offered (i) enhanced plant root length and biomass, (ii) increased proline content, (iii) improved photosynthetic capacity (e.g., total chlorophyll content), and (iv) mitigated oxidative stress (e.g., decreased the peroxidase (POD) and (CAT) activity, and increased superoxide dismutase (SOD) activity). The increased SOD allowed better scavenging of reactive oxygen species (ROS) in leaves (the primary site of ROS generation), thereby alleviating leaf growth retardation. Notably, the translocation factor of Cd significantly reduced to 0.0034 in BC-amended sediments, under high-Cd toxicity. Qualitative and quantitative analysis identified that BC facilitated the Cd binding ability on the wall of the root cells (up to 85.67 ± 0.88 %) by increasing the adsorption capacity of matrix polysaccharides. Furthermore, the bioavailable Cd proportion in sediments was markedly reduced after BC addition. BC also increased the relative abundances of bacteria, such as Desulfuromonadia and Alteromonadaleswhich were involved in Cd immobilization, and enhanced microbial adaptability to Cd-stress by boosting genetic and environmental information processing functions. The mechanisms on how BC reduced the bioavailable Cd in sediment was dependent on both BC and root presence. These findings demonstrated that BC application is an effective strategy for remediating Cd-contaminated coastal wetlands, offering significant benefits for environmental health and human well-being.

With increasing wildfire and crop residue burning, organic P in biomass burning smoke-derived dissolved organic matters (BBS-DOMs), as an important source of atmospheric P, plays a growingly crucial role in P cycling on the Earth's surface. However, the limited understanding of the molecular characteristics of this organic P hampers our ability to comprehend its environmental stability and cycling processes. To address this knowledge gap, this study synthesized various BBS-DOMs and used FT-ICR-MS to analyze their molecular characteristics and potential environmental stabilities. Herein, CHOP compounds (the capital letters in these compound names indicate their elemental compositions) were the dominant organic P component in most BBS-DOMs, followed by CHONP and CHONSP compounds. However, high content of N in biomass enabled CHONP compounds to become the primary component during the burning process. Furthermore, CHOP compounds exhibited higher polarity and aliphaticity, lower molecular mass and aromaticity than CHONP and CHONSP compounds. Among these compounds, CHOP compounds predominantly existed as hydrolysis-available P (phosphate esters with three P-O-C/H groups), accounting for >76% of the total organic P. Differently, CHONP and CHONSP compounds exhibited comparable oxidation-available P (containing P-C bond or incompletely oxidized P) and hydrolysis-available P levels. These findings suggested that CHOP compounds had a lower environmental stability and shorter turnover cycle than CHONP and CHONSP compounds. Additionally, the (cellulose + hemicellulose)/lignin ratio of biomass and the burning temperature co-regulated the aromatic degree and available state of organic P compounds in BBS-DOMs. This study provides critical molecular-level insights into the biogeochemical process of atmospheric P from biomass burning.

While low molecular weight organic acids (LMWOAs) are commonly used to enhance the dissolution and bioavailability of polycyclic aromatic hydrocarbons (PAHs) in soils, a comprehensive mechanistic framework is lacking. In this study, four representative organic acids (formic, acetic, citric, and oxalic acids) were systematically evaluated to their efficacy in promoting PAH desorption from a long-term contaminated soil, with particular emphasis on elucidating the governing mechanisms and environmental implications. The results demonstrated that these organic acids increased the release of PAHs and dissolved organic carbon (DOC) by 1.17-1.90 fold and 1.12-17.39 fold, respectively, compared to the NaCl control. The ratio of desorbed PAHs per unit of DOC followed the order: acetic acid > formic acid ≫ citric acid ≥ oxalic acid. Citric and oxalic acids solubilized significantly more Fe3+ and Al3+ (bridging cations between minerals and soil organic matter, SOM) than formic and acetic acids, thereby releasing larger amounts of dissolved organic matter (DOM) with relatively high molecular weights. However, additional solubilization of Fe3+ and Al3+ had negligible effects of on PAH desorption. The dominant mechanisms governing PAH desorption included Ca2+ dissolution and the disruption of negative charge-assisted hydrogen bonds, (-)CAHB, within SOM (including both intermolecular and intramolecular linkages). From the perspective of maintaining soil fertility and mitigating global climate change, formic/acetic acids outperform citric/oxalic acids in PAH desorption. The key advantage is that they release less biodegradable DOM, which reduces the risk of increased CO2 emissions and helps preserve SOM.

Previous studies have demonstrated that immobilized cadmium carbonate (CdCO3) materials were prone to decomposition in acidic environments (pH < 5.6), potentially causing secondary pollution. To address this limitation, a novel bio-CaCO3 material was developed using microbially induced carbonate precipitation (MICP) technology. This material effectively adsorbed cadmium (Cd) onto its surface during the remineralization to form bio-CaCO3-Cd. Subsequently, the composite material (bio-CaCO3-CdCO3) was synthesized by leveraging its unique urease activity. This core-shell structured material not only exhibits high Cd2+ capture capability but also maintains stability under acidic conditions, achieving 56.2 %-96.3 % Cd2+ immobilization at pH levels ranging from 3.5 to 5.6. Urease activity analyses revealed that bio-CaCO3-0.1M, synthesized with 0.1 M CaCl2 and urea, exhibited 23-fold higher urease activity compared to samples prepared under 1.2M conditions. Cd2+ tolerance tests further confirmed that bio-CaCO3-0.1M maintained a removal efficiency of ∼90 % across Cd2+ concentrations ranging from 10 to 100 mg/L. Additionally, X-ray diffraction (XRD) and Scanning electron microscope (SEM) analyses validated that bio-CaCO3-0.1M initially adsorbs Cd2+ to form CdCO3, then utilized urease activity to drive re-biomineralization. Energy dispersive spectroscopy (EDS) tests indicated a reduction of Cd2+ contents in the crystal surface from 9.75 % to 0.05 %, following the remineralization. Notably, a comprehensive evaluation through cost-benefit analysis revealed that the bio-CaCO3 system can generate enormous economic and social benefits, which proved the reasonableness of assumptions and the feasibility of large scale application. This unique core-shell structure significantly enhanced practical applications, and provided a green and sustainable strategy to mitigate secondary pollution associated with the re-leaching of mineralized heavy metals in extreme environments.

Soil is the foundation of agriculture, and the world’s farmers depend on soil to produce about 95% of the food we eat [...]

The frequent wildfire induces abundant biomass-burning smoke water-soluble organic matter (BBS-WSOM) deposition, subsequently profoundly influencing heavy metal mobility in the ground-surface systems. The complex molecular components in BBS-WSOMs may play heterogeneous roles in heavy metal transport. Herein, BBS-WSOMs were produced from pinewood sawdust (PW), alfalfa (AL), and corn straw (CS) at burning temperatures of 300 degrees C and 600 degrees C. These BBS-WSOMs were subsequently employed to evaluate the heterogeneous contributions of different molecular components to the heavy metal (Cd2 + and Zn2+) mobility in water-saturated sand based on the combination of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), fluorescence spectrum, and two-dimensional (2D) correlation spectroscopy. The results illustrated that the proportion of molecular components in BBS-WSOMs was unaffected by the transport process. Interestingly, AL WSOMs (mainly composed of CHON molecules) showed higher mobility than PW-and CS-WSOMs (mainly composed of CHO molecules). However, PW-and CS-WSOMs exhibited more enhanced effects on Cd2+ mobility, while AL-WSOMs had a greater effect on Zn2+ transport, which was attributed to the strong interactions of CHO-Cd2+ and CHON-Zn2+, respectively. The fluorescence variations and molecular analysis demonstrated that the small aromatic molecules (polyphenol and aromatic protein-like substances) in BBS-WSOMs gave a primary contribution to the mobility of both Cd2+ and Zn2+. The findings are beneficial for an in-depth understanding of the different roles of organic components of BBS-WSOMs in the risk and mobility behaviors of heavy metals in subsurface environments.

The deposition of biomass-burning smoke water-soluble organic matter (BBS-WSOM) significantly affects the environmental behavior of heavy metals in aqueous environments. However, the interactions between BBS-WSOM and heavy metals at the molecular level remain unknown. This study combined FT-ICR-MS, fluorescence spectrum, FTIR, and two-dimensional correlation spectroscopy to anatomize the molecular characteristics of BBS-WSOM binding with Cd(II). The results show that CHO and CHOP compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225nm and 275nm/Em: 325nm, and abundant proteins or CHON compounds were responsible for the fluorescence response of BBS-WSOM at Ex: 225~250nm/Em: 350~450nm and Ex: 300~350nm/Em: 350~450nm, which was very different from the fluorescence molecules in natural organic matters. Fluorescence change after Cd(II) addition indicated that CHOP and CHOS compounds enhanced BBS-WSOM binding with Cd(II). Differently, the CHON compounds could weaken the binding of other compounds with Cd(II). Different compounds binding with Cd(II) generally followed the order: CHON/CHOS compounds>CHOP compounds>CHO compounds, and the chemical groups binding with Cd(II) generally followed the prioritization: -COO->-NH/S=O>P=O/P-O>aromatic ring>C=O>C-OH of phenol/alcohol>C-O-C. This study provides a profound insight into the interaction between BBS-WSOM and Cd(II) at the molecular level.

Using biochar as a soil amendment is a newly developed approach that effectively reduces the adverse effects of neonicotinoid pesticides. Low-molecular-weight organic acids (LMWOAs), as active organic substances in the soil rhizosphere environment, may impact the co-mobility features of pesticides and biochar colloids. However, the influences of organic acids on biochar colloid-mediated transport of neonicotinoid pesticides in soils have not been systematically performed. In this study, the influences of three typical LMWOAs, such as citric acid, tartaric acid, and acetic acid, on the mobility features of nitenpyram (NTP, a common neonicotinoid pesticide) in the absence or presence of biochar colloids in saturated soil were explored. Generally, the results clarified that biochar colloids inhibited NTP mobility at pH 5.0 or 7.0 due to the deposition of colloid-associated NTP and the additional active deposition sites for contaminants caused by the adsorbed biochar colloids on soil surfaces. However, LMWOAs facilitated NTP mobility under experimental conditions, which stemmed from the steric effect, the competitive deposition between organic acids and pesticide molecules, and the preventing interaction between pesticide molecules and soil organic matter induced by surface LMWOA coating on soil. Interestingly, LMWOAs weakened the inhibitory effects of biochar colloids on NTP transport due to the enhanced free NTP mobility and the colloid-associated NTP transport. Meanwhile, the extent of the effects of LMWOAs was highly dependent on organic acid types (acetic acid < tartaric acid < citric acid), biochar types, and solution pH values. This observation was strongly related to the different properties of LMWOAs and the inhibitory influences of LMWOAs on the affinities of different biochar colloids toward NTP as affected by pH values. The results help understand the fate of neonicotinoid pesticides in soil amended with biochar.

Biomass-pyrogenic smoke dissolved organic matter (BPS-DOM) can co-deposit with polycyclic aromatic hydrocarbons (PAHs), thereby altering their environmental behavior and fate in surface environments. However, the heterogeneous molecular characteristics of BPS-DOM binding with PAHs remain unclear. This study systematically elucidates the binding characteristics of PAHs (phenanthrene and pyrene), with various molecular compositions in BPS-DOM, utilizing FT-ICR MS and fluorescence variation analysis. CHO compounds in BPS-DOM, characterized by high aromaticity and abundant CO bonds, significantly enhance PAHs binding by promoting π-π electron donor-acceptor interactions. In contrast, CHON compounds with higher aliphaticity inhibit pyrene binding by competing for binding sites on BPS-DOM. Furthermore, the binding sequence of different fluorescent molecules follows the order of CHO→CHOS→CHON for phenanthrene and CHO→CHON→CHOS for pyrene. This was primarily due to the larger conjugated aromatic structures of CHO compounds, which provide stronger π-π interaction sites for PAHs binding. The difference in binding sequences between phenanthrene and pyrene is primarily attributed to phenanthrene's reliance on π-π electron donor-acceptor interactions induced by -SO and -N = O, while pyrene binding depended on π-π interactions driven by larger conjugated aromatic structures. These results provide an important theoretical foundation for further understanding the molecular-level interactions between BPS-DOM and PAHs.