Correlation of poly(methylene)-rich amorphous aliphatic domains in humic substances with sorption of a nonpolar organic contaminant phenanthrene

Effect of organic carbon structures on the degradation of nonylphenol by hydrogen peroxide in sediment-water system

A laboratory experiment is conducted to investigate the effects of organic carbon (OC) from riverine and marine sediments on the degradation of ring-14 C-labeled nonylphenol (14 C-NP) by hydrogen peroxide (H2 O2 ). Researchers have isolated demineralized OC (DM) before and after oxidation, namely, DM and resistant OC (ROC) fractions, respectively. The structures of DM and ROC are characterized using solid-state 13 C nuclear magnetic resonance. Unstable structures (O-alkyl, OCH3 /NCH, and COO/NC=O) show a significant and positive correlation with the degradation of 14 C-NP (R2  > 0.73, p < 0.05), thus suggesting that the NP absorbed in the unstable structures is easily degraded because of the decomposition of unstable components. The stable structures (alkyl C and non-protonated aromatic C [Arom C─C]) exhibit a significant and negative correlation with the degradation of 14 C-NP (R2  > 0.69, p < 0.05), thus suggesting that the NP absorbed and protected in these resistant structures is minimally degraded. The significant correlations among the degradation kinetic parameters (Frap and Fslow ), OC structures (Falip and Farom ), and microporosity further illustrate the important protective roles of OC structures and micropores in the degradation of 14 C-NP by H2 O2 (R2  > 0.69, p < 0.05). The parent NP fraction that desorbed into the aqueous solution or extracted is completely degraded, indicating preferential degradation of the easily desorbed NP. This study provides important insights into the NP degradation mechanism in sediment-water systems, particularly regarding sediment OC structures and microporosity.

Compositional changes in the humin fraction resulting from the long-term cultivation of an Irish grassland soil: Evidence from FTIR and multi-NMR spectroscopies

Soil humin (HN), a major long-term sink for carbon in the pedosphere, plays a key role in the global carbon cycle, and has been less extensively studied than the humic and fulvic acids components. There are increasing concerns about the depletions of soil organic matter (SOM) arising from modern soil cultivation practices but there has been little focus on how HN can be altered as the result. This study has compared the HN components in a soil under cultivation for wheat for >30 years with those from an adjacent contiguous soil that had been under long-term grass for all that time. A urea-fortified basic solution isolated additional humic fractions from soils that had been exhaustively extracted in basic media. Then further exhaustive extractions of the residual soil material with dimethyl sulfoxide, amended with sulphuric acid isolated what may be called the "true" HN fraction. The long-term cultivation resulted in a loss of 53 % soil organic carbon in the surface soil. Infrared and multi-NMR spectroscopies showed the "true" HN to be dominated by aliphatic hydrocarbons and carboxylated structures, but with clear evidence for lesser amounts of carbohydrate and peptide materials, and with weaker evidence for lignin-derived substances. These lesser-amount structures can be sorbed on the soil mineral colloid surfaces and/or covered by the hydrophobic HN component or entrained within these which have strong affinities for the mineral colloids. HN from the cultivated site contained less carbohydrate and more carboxyl groups suggesting slow transformations took place resulting from the cultivation, but these were much slower than for the other components of SOM. It is recommended that a study be made of the HN in a soil under long-term cultivation for which the SOM content has reached a steady state and where HN will be expected to dominate the components of SOM.

Effect of sorption properties on the content, ecotoxicity, and bioaccumulation of polycyclic aromatic hydrocarbons (PAHs) in bottom sediments

Polycyclic aromatic hydrocarbons (PAHs) tend to accumulate in the sediment due to their high hydrophobicity. Despite PAHs have been the subject of several reviews, PAH sorption processes in bottom sediments has not been comprehensively discucorrelation coefficients between sorption parameters and contessed. Understanding the dependencies governing PAH sorption processes will allow to predict, monitor, and mitigate the ecological effects of PAH contamination and the associated risks to humans or wildlife. The objectives of the study were to assess the relationship between the sorption properties and the content of PAHs in bottom sediments and mussels. The PAH profile was dominated by higher-molecular hydrocarbons, which accounted for 73% of the total concentration of PAHs. Potentiometric studies revealed the steric-based PAH sorption mechanism that strongly depended on the presence of negatively dissociating structures such as carboxylic or phenolic functional groups. Based on the changes in Q8 values, the size-exclusion effect was more likely for 5- and 6-ring compounds. Pores < 5 µm, which had the largest share in the specific surface area, were the preferred sites for PAH sequestration and stabilization in bottom sediments. The availability of PAHs was reduced in sediments with high organic matter content. The PAH bioaccumulation factor significantly decreased with increasing TOC content in sediments. Higher mortality and growth inhibition of H. incongruens were observed in samples with high and medium TOC contents than in those with low TOC content.

Sorption of Polycyclic Musks on Soil Components of Different Aggregate Sizes: The Effect of Organic Matter-Mineral Interactions

Polycyclic musks (PCMs) in soils have been of increasing concern because of their potential characteristics of persistence, bioaccumulation, and ecological risk. However, little is known about their fate process in soil environment. Here, two PCMs namely galaxolide (HHCB) and tonalide (AHTN) were selected as sorbates to explore their sorption process in soils. Sorption batch experiments with six soils and their different aggregate fractions were carried out to elucidate the effect of organic matter-mineral interactions in different aggregate fractions on sorption of these two PCMs. The possible causes of variation in the organic carbon-normalized partition coefficient (K_oc) for HHCB and AHTN have been investigated. The strong influence of organic matter-mineral interactions on K_oc was evidenced by the large variation in K_oc on HF-treatment for both bulk soils and their different aggregate fractions. This study verified the dual effect of organic matter-mineral interactions among selected soils, and in promoting or inhibiting sorption may be related to the types of organic matter-mineral interactions. There were also interactions between soil components with different aggregate sizes, which affected the variation of K_oc in the bulk soil. This study represents a valuable contribution to the understanding of the fate processes and behaviors of HHCB and AHTN in soils and its implication on the risk assessment.

Dynamics in imidacloprid sorption related to changes of soil organic matter content and quality along a 20-year cultivation chronosequence of citrus orchards

The on-going and extensive use of neonicotinoids occur in orchards. However, it is still unknown whether and how orchard management affects soil properties, especially the contents and structure of soil organic matter during orchard development, and their further influences on neonicotinoid persistence. Here, surface soil samples were collected from the citrus orchards with different cultivation ages (1, 10, 14, and 20 years), and their physicochemical properties were determined. Changes in the chemical structure of soil organic matter (SOM) were furtherly examined using solid-state CP/TOSS ¹³C NMR. Then, the sorption isotherms of imidacloprid in these soils were investigated. The sorption coefficient (K_d) of imidacloprid at C_e of 0.05 mg/L in the orchard soils increased by 19.4-23.3%, along a 20-year chronosequence of cultivation, which should be mainly ascribed to the increase of SOM. However, the organic carbon-normalized sorption coefficient (K_oc, sorption per unit mass of OM) of imidacloprid declined with increasing cultivation ages. Moreover, the polar and aliphatic domains of SOM had a significantly positive relation to the K_oc of imidacloprid, suggesting its key role in governing imidacloprid sorption. The results highlighted that reasonable management measures could be adopted to control the occurrence and fate of neonicotinoids in soils, mainly by affecting the content and quality of SOM.

Natural and artificial humic substances to manage minerals, ions, water, and soil microorganisms

The chemistry of humic substances (HSs) occurs hidden from our sight, but is of key importance to agriculture and the environment, and nowadays even to medicine and technology. HSs are nowadays not only natural, but extracted and engineered, and in the past 20 years such products have been widely used in soil improvement and environment governance. In this review, we collate and summarize the applications and working principles of such HSs in agriculture and environmental ecology, mainly to elaborate the multiple roles of this functional polymer along with physical chemical quantification. Then several of the latest synthesis technologies, including hydrothermal humification technology (HTH), hydrothermal carbonization technology (HTC) and hydrogen peroxide oxidation technology (HOT) are presented, which were introduced to prepare artificial humic substances (A-HSs). The availability of reproducible and tunable synthetic A-HSs is a new chemical tool, and effects such as solubilization of insoluble phosphorus minerals, recovery of phosphorus, improvement of soil fertility for crop growth and reduction of toxicity of typical pollutants, can now be analyzed in detail and quantified. As a result, we can provide an effective chemical technology for utilizing biomass side products ("biowaste") to generate A-HSs of different types, thus realizing improvement in agricultural production and control of environmental pollution by the macro-synthesis of A-HSs-.

Comparison of adsorption behaviors of selected endocrine-disrupting compounds in soil

Bisphenol-A (BPA), 17α-ethinylestradiol (EE2), and 4-nonylphenol (4NP) are endocrine-disrupting chemicals (EDCs) that are useful models for studying the potential fate and transport of EDCs in soil and water environments. Two alluvial soils with contrasting physicochemical properties were used as adsorbents for this study. The Zook soil material had more organic matter and clay than the sandy loam Hanlon soil material. Batch equilibrium experiments were performed to generate adsorption isotherms, to determine the adsorption parameters, and to assess desorption hysteresis. Adsorption of BPA to both soils followed an L-type isotherm, and 4NP adsorbed to both Hanlon and Zook soils exhibited S-shape isotherms. EE2 adsorbed to the Zook soil also followed an S-shaped isotherm, but EE2 adsorbed to the Hanlon soil showed an H-type isotherm. Overall, the Sips model fit the data well, with standard errors of prediction generally ≤6%. The adsorption affinity (K_LF ) values were highest for 4NP, and BPA had the lowest hysteresis indices. The data suggest that BPA was most likely adsorbed by soil organic matter via hydrogen bonding involving its two phenolic groups. In contrast, isotherm shape, model affinity indices, lack of desorption, and molecular-scale characteristics led us to infer that 4NP was adsorbed largely by the retention of molecular clusters, perhaps in clay nanopores. Finally, the adsorption of EE2 exhibited different isotherm shapes for the two soils as well as intermediate affinity and desorption indices, suggesting that EE2 molecules could be retained both by soil organic matter and by clay.

An Overview of the Sorption Studies of Contaminants on Poly(Ethylene Terephthalate) Microplastics in the Marine Environment

Marine pollution is one of the biggest environmental problems, mainly due to single-use or disposable plastic waste fragmenting into microplastics (MPs) and nanoplastics (NPs) and entering oceans from the coasts together with human-made MPs. A rapidly growing worry concerning environmental and human safety has stimulated research interest in the potential risks induced by the chemicals associated with MPs/NPs. In this framework, the present review analyzes the recent advances in adsorption and desorption studies of different contaminants species, both organic and metallic, on MPs made of Poly(Ethylene terephthalate). The choice of PET is motivated by its great diffusion among plastic items and, unfortunately, also in marine plastic pollution. Due to the ubiquitous presence of PET MPS/NPs, the interest in its role as a vector of contaminants has abruptly increased in the last three years, as demonstrated by the very high number of recent papers on sorption studies in different environments. The present review relies on a chemical engineering approach aimed at providing a deeper overview of both the sorption mechanisms of organic and metal contaminants to PET MPs/NPs and the most used adsorption kinetic models to predict the mass transfer process from the liquid phase to the solid adsorbent.

Importance of the structure and micropores of sedimentary organic matter in the sorption of phenanthrene and nonylphenol

The demineralized fraction (DM), lipid-free fraction (LF), nonhydrolyzable organic carbon fraction (NHC), and black carbon (BC) were isolated from five marine surface sediments, and they were characterized by elemental analysis as well as CO₂ and N₂ adsorption techniques, respectively. The NHC fractions were characterized using advanced solid-state ¹³C nuclear magnetic resonance (NMR) and x-ray photoelectron spectroscopy (XPS). Then, the sorption isotherms of phenanthrene (Phen) and nonylphenol (NP) on all of the samples were investigated by a batch technique. The CO₂ micropore volumes were corrected for the outer specific surface areas (SSAs) by using the N₂-SSA. Significant correlations between the micropore-filling volumes of Phen and NP and the micropore volumes suggested that the micropore-filling mechanism dominated the Phen and NP sorption. Meanwhile, the (O + N)/C atomic ratios were negatively and significantly correlated with the sorption capacities of Phen and NP, indicating that the sedimentary organic matter (SOM) polarity also played a significant role in the sorption process. In addition, a strong linear correlation was demonstrated between the aromatic C and the sorption capacity of Phen for the NHC fractions. This study demonstrates the importance of the micropores, polarity, and aromaticity on the sorption processes of Phen and NP in the sediments.

Effects of the structures and micropores of sedimentary organic matter on the oxidative degradation of benzo(a)pyrene by Na2S2O8

In this study, we investigated how the desorption and degradation processes of radiolabeled benzo[a]pyrene (BaP) that was aged in various marine sediments were influenced by sedimentary organic matter properties. The stable OC fraction (STOC) and the demineralized fraction (DM) were isolated and characterized via advanced solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR) and a CO₂ gas adsorption technique, respectively. Sodium persulfate preferentially removed the unstable OC fractions (USOC) and the aromatic C groups, and the residual STOC fractions were enriched with aliphatic C groups. The aliphatic C showed stronger resistance to degradation by persulfate than that of the aromatic C. A first-order kinetic model described the degradation process by sodium persulfate solutions very well (R² > 0.997). The desorption percentages, degradation percentages and rates k (h^-1) of BaP gradually decreased from the estuarine sediments to the offshore marine sediments and were highly significantly and negatively correlated with STOC-bulk, F_aliph-bulk, and V_o-bulk (R²>0.903, p < 0.01). It was demonstrated that sodium persulfate degraded not only desorbed BaP but also a portion of the bound BaP fraction that was difficult to desorb. The BaP fractions that sorbed on USOC were degraded initially; then, the fractions of BaP that were released from STOC were degraded. This study demonstrated the important roles of STOC, aliphatic moieties, and micropores in the degradation process of BaP during the Na₂S₂O₈ treatment of the sediments.

Sorption Behavior and Mechanisms of Organic Contaminants to Nano and Microplastics

Nano and microplastics (NPs/MPs) have received widespread attention in recent years. Because of their large specific surface area and hydrophobicity, NPs/MPs can adsorb various organic contaminants. This article gives a brief review of the sorption behavior of organic contaminants to NPs/MPs, summarizes the possible sorption mechanisms, and analyzes the influencing factors in the environment on the sorption behavior and mechanisms of NPs/MPs. The main mechanisms of sorption of organic contaminants to NPs/MPs are partitioning, surface sorption (hydrogen bonding, π-π interaction, electrostatic interaction, and van der Waals force), and pore filling. The sorption behavior of organic contaminants to NPs/MPs is not only affected by the properties of the NPs/MPs and the organic contaminants, but also by the solution chemistry, such as the pH, ionic strength, and dissolved organic matter.

Artificial Humic Acids: Sustainable Materials against Climate Change

Humic acid, as a natural organic matter, is widely distributed in surface soil, oceans, rivers, and other ecological environments throughout the whole earth ecosystem. Humic acid provides abundant organic carbon and helps to maintain a hydrated, pH and redox buffered environment hosting the soil microbiome. Humic acid is however also a largely ignored polymer material full of exciting functional properties, and its scale is enormous. This perspective article discusses its synthesis and management as a tool to tackle parts of the climate crisis as well its use in technological applications, as made by chemical conversion of agricultural side products to artificial humic acids.

Importance of Sporopollenin Structure and Accessibility in the Sorption of Phenanthrene by Biota Spores and Pollens

Although spores/pollens are so abundant and ubiquitous in the environment, the role of these natural organic matter concerning fate and transport of organic pollutants in the environment is neglected. Lipid-free fractions and sporopollenins were isolated from seven spores/pollens collected from lower and higher biota species and were characterized by elemental analysis, CO₂ adsorption techniques, and advanced solid-state ¹³C nuclear magnetic resonance spectroscopy. Then, the sorption isotherms of phenanthrene (Phen) on all the samples were investigated by a batch technique. The sporopollenins were a highly cross-linked polymer including alkyl carbon, poly(methylene) carbon, and aromatic carbon as well as oxygen functionalities; additionally, their sorption capacities (K_oc) for Phen reached up to 1 170 000 mL/g, suggesting that some of the sporopollenins were good biopolymeric sorbents for the removal of hydrophobic organic contaminants in aquatic media. A highly significant and positive correlation between the sorption capacity of Phen and the aliphaticity of the sporopollenins suggested that their structure was critical to Phen sorption. Meanwhile, the (O + N)/C atomic ratios and polar groups were significantly and negatively correlated with the sorption capacity of Phen, indicating that accessibility also played a significant role in the sorption process. Moreover, variable correlations between the sorption capacities (K_oc) and the micropore volumes of the spore/pollen fractions were observed. This study sheds light on the importance of the polarity, microporosity, and structure of sporopollenins in the sorption process of Phen.

Comparative analysis on the sorption kinetics and isotherms of fipronil on nondegradable and biodegradable microplastics

Biodegradable plastics have been introduced and widely used as a promising alternative to traditional nondegradable plastics. However, the differences in sorption behavior of pesticides on nondegradable and biodegradable microplastics has been insufficiently studied. Here, four types of nondegradable [polyethylene (PE), polystyrene (PS), polyvinyl chloride (PVC), polypropylene (PP)] and two types of biodegradable [polylactic acid (PLA), polybutylene succinate (PBS)] microplastics were selected to investigate the sorption mechanism of fipronil based on their sorption kinetics and isotherms. The results indicated that the sorption rates of PLA and PBS were much higher than those of PE, PP, PVC and PS and that the sorption capacities of fipronil on microplastics followed the order of PBS > PLA > PP > PE > PS > PVC. The sorption kinetics followed a pseudo-second-order kinetics model (R² = 0.953-0.998) for all tested microplastics. External mass transport and intraparticle diffusion were the main rate controlling steps of the sorption of fipronil on microplastics. Furthermore, isotherm results indicated that a Langmuir model provided the best fit for fipronil sorption on PE, PS, PVC and PP (R² = 0.997-0.999), while a Freundlich model was the most appropriate model for PLA and PBS (R² = 0.998-0.999). The presence of surface O-containing functional groups and the spatial arrangement of rubbery domains are likely to affect the sorption process. The results from this work suggest that microplastics, especially biodegradable ones, may play an important role in the fate and transport of pesticides, and their effects on soil organisms (e.g., earthworms) require further investigation.

Effects of compositions, chemical structures, and microporosity of sedimentary organic matter on degradation of benzo(a)pyrene by hydrogen peroxide

We investigated how the degradation of 7-¹⁴C-BaP aged in sediments by H₂O₂ treatment was influenced by the chemical structures, compositions, and microporosity of sedimentary organic carbon (SOC). Unstable OC (USOC), stable OC (STOC), mineral-protected OC (MOC), and chemically resistant OC (ROC) fractions were fractionated. The chemical structures and microporosity of the ROC fractions were characterized by ¹³C solid-state nuclear magnetic resonance (NMR) and CO₂ adsorption technique, respectively. A first-order, two-compartment kinetics model described the degradation process very well (R² > 0.980). The BaP degradation ratios increased with the increasing USOC contents and decreased with the increasing ROC contents. The BaP parent compound in the aqueous solution was almost completely degraded. The considerable portions of oxidized intermediates were detected in different SOC fractions, which represented either oxidized intermediates or parent compounds. The very good multivariate regressions among the degradation kinetics parameters, SOC structures and micropore volumes demonstrated that ROC-bulk, aliphatic moieties, and microporosity played crucial roles in protecting sorbed BaP from being degraded by H₂O₂. The results showed that ROC, aliphatic moieties, and microporosity played vital roles in Bap degradation process in sediments during H₂O₂ treatment, which is reported for the first time in this study.

Synchrotron infrared microspectroscopy reveals the roles of aliphatic and aromatic moieties in sorption of nitroaromatic compounds to soils

A consensus on the role of organic carbon moieties as the sorptive domains for nonionic organic compounds in soils is lacking due to the extremely complicated compositions of soil matrices. In this study, synchrotron radiation-based infrared microspectroscopy (IMS) was applied to in situ probe the distributions of four nitroaromatic compounds with varying hydrophobicity (namely, 1,3-dinitrobenzene, 1,5-dinitronapthalene, 3-nitrophenanthrene and 6-nitrobenzo[a]pyrene) and their associations with aliphatic and aromatic organic carbon moieties in soils. The technique revealed that both nitro group (NO₂) from the nitroaromatic compounds and organic carbon moieties were unevenly distributed in the soils at the micron scale. The spatial distribution of nitro groups was positively correlated with that of aromatic carbon (C=C) (r>0.804, p<0.01), indicating that the aromatic moieties of soil organic carbon play a key role in sorption of nitroaromatic compounds to soils. Neither nitro groups nor aromatic carbon showed a close relationship with aliphatic carbon (CH) in the spatial distribution in the soils. Meanwhile, the nitro groups from 1,3-dinitrobenzene and 1,5-dinitronapthalene exhibited a significant correlation with clay minerals (OH) in their distributions (r>0.629, p<0.01) in the soils and the correlation became insignificant for the other two compounds with high hydrophobicity. This study for the first time provides micron-scale spectroscopic evidence for the roles of organic carbon moieties in the sorption of nonionic organic compounds to soils.

Comparison between Soil- and Biochar-Derived Humic Acids: Composition, Conformation, and Phenanthrene Sorption

Biochar-derived organic matter (BDOM) plays an important role in determining biochar's application potential in soil remediation. However, little is known about the physicochemical properties of BDOM and its sorption of hydrophobic organic compounds (HOCs). Humic acids (HAs) were extracted from oxidized biochars produced from plant straws and animal manures at 450 °C, and their sorption of phenanthrene, a representative of HOCs, was investigated. The organic carbon recovery of biochar-derived HAs (BDHAs) was 13.9-69.3%. The ¹³C NMR spectra of BDHAs mainly consisted of aromatic and carboxylic C, while those of soil-derived HAs (SDHAs) contained abundant signals in aliphatic region. BDHAs and SDHAs had comparable CO₂ cumulative surface areas. BDHAs were found to exhibit higher phenanthrene sorption than SDHAs. After the removal of amorphous aromatic components, the logK_oc values of BDHAs were significantly decreased, implying that amorphous aromatic C regulated phenanthrene sorption by BDHAs. In contrast, aliphatic moieties dominated phenanthrene sorption by SDHAs, as evidenced by the enhanced sorption after the removal of amorphous aromatics. This study clearly demonstrated the contrasting characteristics and sorption behaviors of BDHA and SDHA, indicating that biochar addition and subsequent weathering could greatly affect native organic matter properties and the fate of HOCs in biochar-amended soils.

Importance of the structure and nanoporosity of organic matter on the desorption kinetics of benzo[a]pyrene in sediments

The desorption kinetics and mechanism were investigated using a Tenax extraction technique on different sediments spiked with radiocarbon-labeled benzo[a]pyrene (BaP). Five sedimentary fractions were sequentially fractionated, and the only nonhydrolyzable organic carbon fractions (NHC) were characterized using advanced solid-state ¹³C nuclear magnetic resonance spectroscopy (NMR), improved six end-member model, and a CO₂ gas adsorption technique. The sediments contained high percentages of algaenan and/or sporopollenin but low percentages of black carbon and lignin. A first-order, two-compartment kinetics model described the desorption process very well (R² > 0.990). Although some of the organic carbon fractions were significantly related to the desorption kinetics parameters, the NHC fractions showed the highly significant correlation. Moreover, the nanoporosity or specific surface area (SSA) of the NHC fractions was highly related to their OC contents and aliphatic C (R² = 0.960, p < 0.01). The multiple regression equations among the desorption kinetics parameters, structural parameters, and nanoporosity were well established (R²=>0.999). Nanoporosity and aromatic C were the dominant contributors. Furthermore, the enhanced percentages of desorbed BaP at elevated temperatures significantly showed a linear regression with the structure and nanoporosity. To our knowledge, the above evidence demonstrates for the first time that the transfer (or diffusion) of BaP in the nanopores of condensed aromatic components is the dominant mechanism of the desorption kinetics of BaP at organic matter particle scale.

Advanced solid-state NMR spectroscopy of natural organic matter

Solid-state NMR is essential for the characterization of natural organic matter (NOM) and is gaining importance in geosciences and environmental sciences. This review is intended to highlight advanced solid-state NMR techniques, especially a systematic approach to NOM characterization, and their applications to the study of NOM. We discuss some basics of how to acquire high-quality and quantitative solid-state ¹³C NMR spectra, and address some common technical mistakes that lead to unreliable spectra of NOM. The identification of specific functional groups in NOM, primarily based on ¹³C spectral-editing techniques, is described and the theoretical background of some recently-developed spectral-editing techniques is provided. Applications of solid-state NMR to investigating nitrogen (N) in NOM are described, focusing on limitations of the widely used ¹⁵N CP/MAS experiment and the potential of improved advanced NMR techniques for characterizing N forms in NOM. Then techniques used for identifying proximities, heterogeneities and domains are reviewed, and some examples provided. In addition, NMR techniques for studying segmental dynamics in NOM are reviewed. We also briefly discuss applications of solid-state NMR to NOM from various sources, including soil organic matter, aquatic organic matter, organic matter in atmospheric particulate matter, carbonaceous meteoritic organic matter, and fossil fuels. Finally, examples of NMR-based structural models and an outlook are provided.

New Evidence for High Sorption Capacity of Hydrochar for Hydrophobic Organic Pollutants

This study investigated the sorption potential of hydrochars, produced from hydrothermally carbonizing livestock wastes, toward organic pollutants (OPs) with a wide range of hydrophobicity, and compared their sorption capacity with that of pyrochars obtained from conventional dry pyrolysis from the same feedstock. Results of SEM, Raman, and ¹³C NMR demonstrated that organic carbon (OC) of hydrochars mainly consisted of amorphous alkyl and aryl C. Hydrochars exhibited consistently higher log K_oc of both nonpolar and polar OPs than pyrochars. This, combined with the significantly less energy required for the hydrothermal process, suggests that hydrothermal conversion of surplus livestock waste into value-added sorbents could be an alternative manure management strategy. Moreover, the hydrochars log K_oc values were practically unchanged after the removal of amorphous aromatics, implying that amorphous aromatic C played a comparable role in the high sorption capacity of hydrochars compared to amorphous alkyl C. It was thus concluded that the dominant amorphous C associated with both alkyl and aryl moieties within hydrochars explained their high sorption capacity for OPs. This research not only indicates that animal-manure-derived hydrochars are promising sorbents for environmental applications but casts new light on mechanisms underlying the high sorption capacity of hydrochars for both nonpolar and polar OPs.

Novel Phenanthrene Sorption Mechanism by Two Pollens and Their Fractions

A pair of pollens (Nelumbo nucifera and Brassica campestris L.) and their fractions were characterized by elemental analysis and advanced solid-state (13)C NMR techniques and used as biosorbents for phenanthrene (Phen). Their constituents were largely aliphatic components (including sporopollenin), carbohydrates, protein, and lignin as estimated by (13)C NMR spectra of the investigated samples and the four listed biochemical classes. The structure of each nonhydrolyzable carbon (NHC) fraction is similar to that of sporopollenin. The sorption capacities are highly negatively related to polar groups largely derived from carbohydrates and protein but highly positively related to alkyl carbon, poly(methylene) carbon, and aromatic carbon largely derived from sporopollenin and lignin. The sorption capacities of the NHC fractions are much higher than previously reported values, suggesting that they are good sorbents for Phen. The Freundlich n values significantly decrease with increasing concentrations of poly(methylene) carbon, alkyl C, aromatic moieties, aliphatic components, and the lignin of the pollen sorbents, suggesting that aliphatic and aromatic structures and constituents jointly contribute to the increasing nonlinearity. To our knowledge, this is the first investigation of the combined roles of alkyl and aromatic moiety domains, composition, and accessibility on the sorption of Phen by pollen samples.

Characterization and phthalate esters sorption of organic matter fractions isolated from soils and sediments

The sorption of two phthalate esters (PAEs) and phenanthrene (PHE) by different natural organic matter fractions (NOMs) was examined. The surface area of the NOMs correlated positively with the starting decomposition temperature (SDT), implying increased number of micropores with the rise of condensation. Sorption of PHE on nonhydrolyzable carbons (NHCs) and other NOMs was respectively dependent on aromatic and aliphatic C contents. Likely physical blocking of the aliphatic moieties and input of black carbon materials led to elevated sorption capacity for PHE of aromatic domains in the NHCs. Sorption of PAEs by NOMs excluding NHCs was jointly regulated by hydrophobic partitioning and H-bonding interactions. The SDT of the NOMs correlated negatively with the Koc when SDT ≥304 °C, likely because the highly condensed domains may impair the availability of amorphous moieties for sorption. This study highlights the influence of domain accessibility of NOMs on sorption of hydrophobic organic contaminants.

Effect of organic carbon chemistry on sorption of atrazine and metsulfuron-methyl as determined by (13)C-NMR and IR spectroscopy

Soil organic matter (SOM) content is the major soil component affecting pesticide sorption. However, recent studies have highlighted the fact that it is not the total carbon content of the organic matter, but its chemical structure which have a profound effect on the pesticide's sorption. In the present study, sorption of atrazine and metsulfuron-methyl herbicides was studied in four SOM fractions viz. commercial humic acid, commercial lignin, as well as humic acid and humin extracted from a compost. Sorption data was fitted to the Freundlich adsorption equation. In general, the Freundlich slope (1/n) values for both the herbicides were <1. Except for atrazine sorption on commercial humic acid, metsulfuron-methyl was more sorbed. Desorption results suggested that atrazine was more desorbed than metsulfuron-methyl. Lignin, which showed least sorption of both the herbicides, showed minimum desorption. Sorption of atrazine was best positively correlated with the alkyl carbon (adjusted R (2) = 0.748) and carbonyl carbon (adjusted R (2) = 0.498) but, their effect was statistically nonsignificant (P = 0.05). Metsulfuron-methyl sorption showed best positive correlation with carbonyl carbon (adjusted R (2) = 0.960; P = 0.05) content. Sorption of both the herbicides showed negative correlation with O/N-alkyl carbon. Correlation of herbicide's sorption with alkyl and carbonyl carbon content of SOM fractions suggested their contribution towards herbicide sorption. But, sorption of metsulfuron-methyl, relatively more polar than atrazine, was mainly governed by the polar groups in SOM. IR spectra showed that H-bonds and charge-transfer bonds between SOM fraction and herbicides probably operated as mechanisms of adsorption.

Interactions between natural organic matter and organic pollutants as revealed by NMR spectroscopy

Natural organic matter (NOM) plays a critical role in regulating the transport and the fate of organic contaminants in the environment. NMR spectroscopy is a powerful technique for the investigation of the sorption and binding mechanisms between NOM and pollutants, as well as their mutual chemical transformations. Despite NMR relatively low sensibility but due to its wide versatility to investigating samples in the liquid, gel, and solid phases, NMR application to environmental NOM-pollutants relations enables the achievement of specific and complementary molecular information. This report is a brief outline of the potentialities of the different NMR techniques and pulse sequences to elucidate the interactions between NOM and organic pollutants, with and without their labeling with nuclei that enhance NMR sensitivity.

Impact of reference geosorbents on oral bioaccessibility of PAH in a human in vitro digestive tract model

Former studies on human oral bioaccessibility of polycyclic aromatic hydrocarbons (PAH) from natural soil samples using human in vitro digestive tract models (physiologically based extraction tests, PBET) show highly variable results (0-100% of mobilized PAH). Apart from other factors, the type and amount of present geosorbents are assumed to be significant for the degree of desorption/release of PAH into the digestive juice. Therefore, in this study, the reference geosorbents pure quartz sand, Na-montmorillonite clay, Pahokee peat, and charcoal "Sommerhit" were spiked with selected deuterated PAH and employed as single materials in a PBET. Lowest bioaccessibility was determined in charcoal, representing black carbon (0.1 ± 0.1 % for ∑10 PAH-d) in contrast to higher bioaccessibility in peat (6.4 ± 2.2%) and clay (4.8 ± 1.1%). Highest bioaccessibility was determined in sand (26.9 ± 7.5%). The results show a systematic impact of heterogeneous geosorbents on human oral bioaccessibility of PAH and particularly black carbon acting as a very strong geosorbent that reduces human health risk.

Biosorption of nonylphenol by pure algae, field-collected planktons and their fractions

Algal samples were fractionated into lipid (LP), lipid free (LF), alkaline nonhydrolyzable carbon (ANHC), and acid nonhydrolyzable carbon (NHC) fractions, and were characterized by the quantitative (13)C multiCP NMR technique. The biosorption isotherms for nonylphenol (NP) were established and compared with previously published data for phenanthrene (Phen). The log KOC values are significantly higher for the field-collected plankton samples than for the commercial algae and cultured algae samples, correlating with their lipid contents and aliphatic carbon structure. As the NHC fraction contains more poly(methylene) carbon, it exhibits a higher biosorption capacity. The sorption capacities are negatively related to the polarity index, COO/N-C=O, polar C and O-alkyl C concentrations, but are positively related to the H/O atomic ratios and poly(methylene) carbon. The higher sorption capacities observed for NP than for Phen on the investigated samples are explained by specific interactions such as hydrogen bonding and π-π interaction.

Role of structure and microporosity in phenanthrene sorption by natural and engineered organic matter

Natural sorbents including one humic acid (HA), humins (HMs), nonhydrolyzable carbons (NHCs), and engineered sorbents (biochars) were subject to bleaching to selectively remove a fraction of aromatic C. The structural properties and sorption isotherm data of phenanthrene (Phen) by original and bleached sorbents were obtained. Significant correlations between Phen Koc values by all sorbents and their organic carbon (OC)-normalized CO2 cumulative surface area (CO2-SA/OC) suggested that nanopore-filling mechanism could dominate Phen sorption. After bleaching, natural sorbents still contained large amounts of aromatic C, which are resistant to bleaching, suggesting that they are derived from condensed or nonbiodegradable organic matter (OM). After eliminating the effect of aromatic C remaining in the bleached samples, a general trend of increasing CO2-SA/OC of natural sorbents with increasing aliphaticity was observed, suggesting that nanopores of natural sorbents are partially derived from their aliphatic moieties. Conversely, positive relationships between CO2-SA/OC or Phen logKoc of engineered sorbents and their aromaticity indicated the aromatic structures of engineered sorbents primarily contribute to their nanopores and dominate their sorption of HOCs. Therefore, this study clearly demonstrated that the role of structure and microporosity in Phen sorption is dependent on the sources of sorbents.

Sorption selectivity in natural organic matter probed with fully deuterium-exchanged and carbonyl-13C-labeled benzophenone and 1H-13C NMR spectroscopy

Specific functional-group or domain interactions of fully deuterium-exchanged, carbonyl-(13)C-labeled benzophenone and different types of natural organic matter (NOM) were investigated through two-dimensional (1)H-(13)C heteronuclear correlation NMR spectroscopy. The sorbents included Beulah-Zap lignite, type II kerogen (IL-6), Pahokee peat, Amherst humic acid, and a polystyrene-poly(vinylmethyl ether) (PS-PVME) blend. PS-PVME consists of PS and PVME chains that are mixed on a scale of <5 nm. The NOM sorbents all consist predominantly of a mixed aromatic-alkyl or aromatic-O-alkyl matrix that is homogeneous on the 3 nm scale, as evidenced by fast equilibration of aromatic and alkyl (1)H magnetization. In addition, Beulah lignite and IL-6 kerogen exhibit small fractions of distinct polymethylene (CH2)n domains, and Pahokee peat contains significant fractions of polar and nonpolar alkyl domains. Benzophenone-((13)C═O)-d10 shows proximity to both aromatic rings and alkyl segments in all samples but preferentially interacts with aromatic rings in PS-PVME and Beulah lignite, possibly due to π-π electron donor-acceptor interactions. The data for IL-6 kerogen are also compatible with preferential location of benzophenone near the alkyl-substituted edges of aromatic rings, while in Pahokee peat, clear signatures of benzophenone affinity to both aromatic-rich and nonpolar alkyl domains have been detected. Amherst humic acid shows evidence of some affinity to polar alkyl segments but which is weaker than that to aromatic rings. Our results indicate that specific interactions of the sorbate and the presence of domains in the sorbent influence the magnitude and selectivity of sorption.

Impact of the simulated diagenesis on sorption of naphthalene and 1-naphthol by soil organic matter and its precursors

Soil organic matter (SOM) in a peat soil, humic acid, and humin and their precursors (i.e., cellulose and lignin) were treated at high temperature (250 and 400 °C) with high pressure in a sealed platinum reaction kittle to simulate the influence of diagenesis on their composition and structure, and impact of the simulated diagenesis on sorption behaviors of hydrophobic organic compounds (HOCs) (i.e., naphthalene and 1-naphthol) by these samples was investigated. High temperature and pressure treatment greatly influenced chemical composition and physical properties of the original samples and their sorption for both naphthalene and 1-naphthol. Sorption of naphthalene by all samples was jointly regulated by hydrophobic and π-π interactions with their alkyl and aromatic carbon moieties, which was derived from the positive correlation between total hydrophobic carbon content of all sorbents and their organic carbon content-normalized sorption coefficients (Koc) for this compound (p = 0.075). However, sorption of 1-naphthol by the tested sorbents was governed by hydrogen bonding with their O-containing polar functionalities, as derived from the positive correlation between Koc values of 1-Naph and their polarity index ((O+N)/C). Difference in sorption mechanisms of naphthalene and 1-naphthol by the original and treated samples noted the great influence of chemical composition of sorbates on their interaction and essential roles of specific interactions (e.g., hydrogen bonding) in sorption of polar compound (i.e., 1-naphthol) to these sorbents. Surface area (SA) and porosity data of sorbents obtained from N2 sorption-desorption isotherms at 77 K showed that new SA and pores were created during the diagenetic process of all original samples, which provided substantial sorption sites and thus enhanced sorption of naphthalene and 1-naphthol. Among all tested samples, physicochemical properties of cellulose were most strongly affected by the simulated diagenetic process, and impact of such a process on its sorption intensity for the tested compounds was the most significant. The characterization data of the treated sorbents showed that the high temperature and pressure treatment similarly simulated the naturally occurring diagenesis of SOMs and their precursors, which is a first attempt. These findings are valuable for better understanding of the sorption behaviors of HOCs to SOM and its precursors as affected by diagenesis, which in turn is critical for elucidating the transport and fate of HOCs in the environment.

Biosorption of phenanthrene by pure algae and field-collected planktons and their fractions

The biosorption isotherms for phenanthrene (Phen) by cultured algae, field-collected plankton, and market algae samples (OSs) and their fractions (lipid-LP, lipid free carbon-LF, alkaline nonhydrolyzable carbon-ANHC, and acid nonhydrolyzable carbon-NHC) were established. All the biosorption isotherms are well fitted by the Freundlich model. The biosorption isotherms for the ANHC and NHC fractions are nonlinear and for the other fractions are linear. It was found that the NHC fractions are chemically and structurally different from other fractions by using elemental analysis and Fourier transformed infrared spectroscopy (FTIR), consisting mainly of aliphatic polymethylene carbon. The average KOC values for Phen at Ce=0.005Sw are 10706±2768mLg(-1) and 95843±55817mLg(-1) for the bulk market algal samples and their NHC isolates, respectively. As the NHC fraction for Porphyra contains higher polymethylene carbon than that for Seaweed or Spirulina, it exhibits higher biosorption capacity. Moreover, the logKOC values are significantly higher for the field-collected samples than for the market algae and cultured algae samples. The multivariate correlation shows that the logKOC values are positively related to the LP contents, and negatively to the C/N ratios for the original algal samples. Furthermore, the logKOC values are negatively related to the polarity indices (O/C and O+N/C) for the original samples and their fractions excluding LP fractions. These observations help to understand the role of polarity, LP and NHC fractions, and aliphatic structures in the biosorption of Phen, which requires more attention in the examination of sorption processes in the natural environment.

Isolation and characterization of different organic matter fractions from a same soil source and their phenanthrene sorption

Four humic acids (HAs) including de-ashed HAs (D-HAs), two humins (HMs), nonhydrolyzable carbons, and demineralized fraction (DM) were isolated separately from two soils and characterized detailedly; then their sorption of phenanthrene (Phen) was examined. The sequence of removal of HAs and minerals affected molecular composition of HMs. After de-ashing, thermal stability of HAs was improved; however, sorption (logKoc) also decreased due to removal of amorphous alkyl-C. Significant correlations between CO2 surface area of HAs with their sorption coefficients (n and Koc) suggested that pore filling could dominate Phen sorption. Alkyl-C could facilitate elevated thermal stability of OM and Phen sorption, supporting that thermal stability of OM was correlated with Phen sorption. The OM fraction composed of aromatic moieties (AMs) did not produce the highest logKoc, providing strong evidence to dispute the dominant role of AMs in Phen sorption. No correlations between the Koc values of Phen by all tested sorbents and their bulk or surface polarity were observed, suggesting that the role of bulk or surface polarity of OM fractions in regulating Phen sorption was dependent on soil sources. This work shows the major influence of bulk and surface composition of OM and amorphous alkyl-C isolated from a soil sample on hydrophobic organic compounds sorption.

Impact of organic matter properties on sorption domains of phenanthrene on chemically modified geosorbents and synthesized charcoals

To study the impact of organic matter (OM) properties on different sorption domain of hydrophobic organic contaminants, phenanthrene sorption on chemically modified geosorbents and synthesized charcoals (SCs) was investigated and explored using Dual-Mode model (DMM). Sorption of phenanthrene on two geosorbents, peat and lignite, and their modified forms by hydrolysis, oxidation, and oximation, as well as on three SCs with different pyrolytic degrees changed were significantly affected by the aromaticity (A) and polarity index (PI) of OM. Positive correlation between OM normalized parameter of Langmuir sorption capacity of DMM (S(DM)/f(OM)) and A×PI(-1) was observed. To distinguish the deviation of DMM, S(DM) was corrected by assigning the Langmuir affinity parameter (b(DM)) of DMM to the high energy Langmuir affinity parameter (b(H)) in Dual-Langmuir model (DLM). More significant correlation was observed between A×PI(-1) and corrected S(DM), which confirms that the nonpolarity and aromaticity of sorbent OM contribute much to the hydrophobic organic contaminants sorption with high energy. Besides, the partition coefficient of linear domain of DMM normalized by OM (K(P)/f(OM)) was positively related to PI(-1) rather than negatively related to PI, suggesting that PI(-1) is more suitable than -PI to evaluate the nonpolarity of sorbent OM.

Sorption selectivity in natural organic matter studied with nitroxyl paramagnetic relaxation probes

Sorption site selectivity and mechanism in natural organic matter (NOM) were addressed spectroscopically by the sorption of paramagnetic nitroxyl compounds (spin probes) of different polarity, TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) and HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl). The sorbents were Pahokee peat, Beulah-Zap lignite, and a polystyrene-poly(vinyl methyl ether) (PS-PVME) polymer blend representing the mixed aliphatic-aromatic, polar-nonpolar character of NOM. Nuclear-electron spin interaction serves as an efficient relaxation pathway, resulting in attenuation of the (13)C-CP/TOSS NMR signal for (13)C nuclei in proximity to the N-O· group (r(-6) dependence). In the natural solids the spin probes sorbed more specifically (greater isotherm nonlinearity) and had lower rotational mobility (broader electron paramagnetic resonance signals) than in PS-PVME. Titration with spin probe indicated almost no selectivity for the different carbon functional groups of PS-PVME, and little to no selectivity for the different carbon moieties of Pahokee and Beulah, including aromatic, alkyl, O-alkyl, di-O-alkyl, and O-methyl. In any case, sorption site selectivity of spin probes to NOM was always weaker than partition selectivity found in model solvent-water (toluene, hexadecane, anisole, octanol) and cellulose-water systems. The results indicate little or no preferential sorption in NOM based on functional group chemistry or putative microdomain character, but rather are consistent with the filling of pores whose walls have an average chemical environment reflecting the bulk chemical composition of the solid. This work demonstrates for the first time the use of paramagnetic probes to study sorption specificity.

In-situ molecular-level elucidation of organofluorine binding sites in a whole peat soil

The chemical nature of xenobiotic binding sites in soils is of vital importance to environmental biogeochemistry. Interactions between xenobiotics and the naturally occurring organic constituents of soils are strongly correlated to environmental persistence, bioaccessibility, and ecotoxicity. Nevertheless, because of the complex structural and chemical heterogeneity of soils, studies of these interactions are most commonly performed indirectly, using correlative methods, fractionation, or chemical modification. Here we identify the organic components of an unmodified peat soil where some organofluorine xenobiotic compounds interact using direct molecular-level methods. Using (19)F→(1)H cross-polarization magic angle spinning (CP-MAS) nuclear magnetic resonance (NMR) spectroscopy, the (19)F nuclei of organofluorine compounds are used to induce observable transverse magnetization in the (1)H nuclei of organic components of the soil with which they interact after sorption. The observed (19)F→(1)H CP-MAS spectra and dynamics are compared to those produced using model soil organic compounds, lignin and albumin. It is found that lignin-like components can account for the interactions observed in this soil for heptafluoronaphthol (HFNap) while protein structures can account for the interactions observed for perfluorooctanoic acid (PFOA). This study employs novel comprehensive multi-phase (CMP) NMR technology that permits the application of solution-, gel-, and solid-state NMR experiments on intact soil samples in their swollen state.

Sorption of atrazine and ametryn by carbonatic and non-carbonatic soils of varied origin

Sorption of two s-triazines, atrazine and ametryn, by carbonatic soils, Histosols, Spodosols and Oxisols was examined. Linear isotherms were observed and sorption coefficients (K(d)) of both compounds were significantly lower (α = 0.05) onto carbonatic soils compared to non-carbonatic soils. Furthermore, among carbonatic soil types, the marl-carbonatic soils had the lowest sorption affinities. K(d) and organic carbon content were highly correlated, suggesting predominant influence of organic carbon in the sorption of the s-triazine, except in Oxisols and Spodosols where variations suggest other factors. Upon removal of organic matter (OM) using sodium hypochlorite and hydrogen peroxide, the K(d) values were reduced by ~90%, indicating minimal contribution of mineral surfaces. Thus OM compositional differences likely explain the large variation in s-triazine sorption within and between soil orders. This study highlights the need to consider OM composition in addition to quantity when determining pesticide applications rates, particularly for carbonatic soils.

Sorption of four hydrophobic organic compounds by three chemically distinct polymers: role of chemical and physical composition

The sorption behavior of four hydrophobic organic contaminants (HOCs) (i.e., phenanthrene, naphthalene, lindane, and 1-naphthol) by three types of polymers namely polyethylene (PE), polystyrene (PS), and polyphenyleneoxide (PPO) was examined in this work. The organic carbon content-normalized sorption coefficients (K(oc)) of phenanthrene, lindane, and naphthalene by PEs of same composition but distinct physical makeup of domains increased with their crystallinity reduction (from 58.7 to 25.5%), suggesting that mobility and abundance of rubbery domains in polymers regulated HOC sorption. Cross-linking in styrene-divinylbenzene copolymer (PS2) created substantial surface area and porosity, thus, K(oc) values of phenanthrene, lindane, naphthalene, and 1-naphthol by PS2 were as high as 274.8, 212.3, 27.4, and 1.5 times of those by the linear polystyrene (PS1). The K(oc) values of lindane, naphthalene, and 1-naphthol by polar PPO were approximately 1-3 orders of magnitude higher than those by PS1, and PPO had comparable sorption for phenanthrene but higher sorption for naphthalene and 1-naphthol than PS2. This can be a result that a portion of O-containing moieties in PPO were masked in the interior part, while leaving the hydrophobic domains exposed outside, therefore demonstrating the great influence of the spatial arrangement of domains in polymers on HOC sorption.

Effect of lipids on sorption/desorption hysteresis in natural organic matter

The chemical composition and physical conformation of natural organic matter (NOM) play a major role in regulating its capacity to retain hydrophobic organic compounds. Naphthalene and phenanthrene were used to study the correlations between sorption/desorption isotherm nonlinearity and compositional data obtained from quantitative (13)C solid-state DPMAS NMR spectroscopy for soil and peat organic matter with or without lipids. Sorption experiments were conducted using a batch equilibration method. Desorption experiments were carried out immediately following the sorption experiments by three successive decant-refill cycles. Hysteresis was observed in all samples. Nonlinear sorption behavior was increased by removal of lipids from the NOM. The hysteresis index, obtained from the ratio of the Freundlich exponents (N values) for the desorption and sorption isotherms, was lower in the lipid-extracted NOM samples than in the same samples without lipid extraction. The relationship between the extent of hysteresis and the characteristics of the (13)C DPMAS NMR spectra indicates that altering NOM composition through lipid extraction not only increased the proportion of aromatic-C content, but also increased sorption/desorption hysteresis. Our data also suggest that the hysteresis index is negatively related to aromaticity.

Mobile aliphatic domains in humic substances and their impact on contaminant mobility within the matrix

Using a novel NMR option, magic angle spinning pulsed field gradient (MAS PFG) NMR, the mobility of aliphatic domains in humic substances in the presence of toluene (about 4.5 wt. %) has been monitored. Results show a strong correlation between the diffusivities of the mobile aliphatic chains and those of the adsorbed toluene molecules in the matrix as a function of temperature. Particularly, a strong influence of structural relaxation of the humic matrix on the diffusivity of toluene is observed. Our findings confirm that the aliphatic domains in humic substances play an important role in the mobility of sorbed contaminants within this matrix. These findings further confirm the potential of MAS PFG NMR method in monitoring diffusion processes in particulate humic substances.

Peroxidase-catalyzed stabilization of 2,4-dichlorophenol in alkali-extracted soils

Horseradish peroxidase- (HRP) mediated stabilization of phenolic contaminants is a topic of interest due to its potential for remediation of contaminated soils. This study evaluated the sorption of 2,4-dichlorophenol (DCP) and its HRP-mediated stabilization in two alkali-extracted soils. Alkali extraction reduced the soil organic matter (SOM) contents of the geomaterials and enriched the residual SOM with humin C. Sorption of DCP on these sorbents was complete within 1 d. However, most of the sorbed DCP was removed from the geomaterials by water and methanol, suggesting weak solute-sorbent interactions. The addition of HRP resulted in the generation of DCP polymerization products (DPP), which partitioned between the aqueous and solid phases. The DPP phase distribution was rapid and complete within 24 h. Between 70 and 90% of the added DCP was converted to DPP and up to 43% of the initial aqueous phase contaminant was transformed into a residue that was resistant to extraction with methanol. Bound residues of DPP increased with initial aqueous phase solute concentration and remained fairly constant after 7 d of contact. Contaminant stabilization was noted to be high in the humin-mineral geomaterial. Results illustrate that HRP may be effective in stabilizing phenolic contaminants in subsoils that are likely to contain SOM enriched in humin C.

Tetracycline sorption to coal and soil humic acids: an examination of humic structural heterogeneity

The sorption properties of tetracycline were compared between a coal humic acid (CHA) and a soil humic acid (SHA) under various solution chemistry conditions. Structural characteristics of the two humic acids were quantified in detail by elemental analysis, solid-state (13)C nuclear magnetic resonance (NMR), acid-base titration, and Zeta potential measurement. The CHA consists primarily of poly(methylene)-rich aliphatics with more aromatic C--O and higher negative surface charge, while SHA is mainly composed of young material residues of lignin, carbohydrates and peptides, and oxidized charcoal. At pH 5 the sorption affinities of tetracycline to SHA and CHA were very close, but remarkably stronger than that to functionality-free model polymeric sorbents (polyethylene and polystyrene). Meanwhile, despite the much lower hydrophobicity, tetracycline displayed stronger sorption to the humic acids than nonpolar, nonionic 1,3,5-trichlorobezene. It is thus concluded that specific complexation (H--bonding and cation exchange) with the humic functionality overwhelmed hydrophobic effect in sorption when tetracycline was dominated by the zwitterion. Furthermore, modifying solution chemistry conditions (pH, ionic strength of NaCl and CaCl2, and the presence of Zn2+) generally caused more prominent effects on tetracycline sorption to CHA than to SHA, which was attributed to the higher surface charge of CHA. Results of this research demonstrate the importance of the structural nature of humic acids in antibiotic sorption.

Identifying components in dissolved humic acid that bind organofluorine contaminants using (1)H{(19)F} reverse heteronuclear saturation transfer difference NMR spectroscopy

Interactions between dissolved peat humic acid and two structurally dissimilar organofluorine compounds, perfluoro-2-naphthol and perfluoro-octanoic acid, are probed using a novel (1)H{(19)F} Nuclear Magnetic Resonance (NMR) Spectroscopy technique based on the Saturation Transfer Difference (STD) experiment. This technique is used here to show selectively only those regions of the (1)H NMR spectrum of humic acid that arise from chemical constituents interacting with perfluorinated organic compounds. This approach provides a tool for high-resolution analysis of interactions between contaminants and soil organic matter (SOM) directly at the molecular level. Soil organic matter is a chemically heterogeneous mixture, and traditional techniques used to study sorption or binding phenomenon are unable to resolve multiple processes occurring simultaneously at distinct chemical moieties. Here, multiple interaction domains are identified based on known chemical constituents of humic acid, most notably from lignin- and protein-derived material. Specifically, perfluoro-2-naphthol is shown to interact with lignin, protein, and aliphatic material; however, preference is exhibited for lignin-derived domains, while perfluoro-octanoic acid exhibits near exclusive preference for the protein-derived domains of humic acid.

New option for characterizing the mobility of organic compounds in humic acids

A new NMR option for monitoring the mobility of organic contaminants in SOM in the solid state has been successfully applied for the first time. This recently available noninvasive technique, magic angle spinning pulsed-field gradient (MAS PFG) NMR, combines both NMR spectroscopy and diffusometry to selectively monitor the diffusion of compounds sorbed in porous media or polymer matrices. Using this technique, the diffusion of toluene in humic acid particles has been studied. Measurements were performed under varying temperatures from 25 to 80 degrees C. The obtained diffusion coefficients were found to be in good agreement with those obtained from computer simulations reported elsewhere. Our results show a strong influence of the interaction of toluene with humic acid on its diffusion in the matrix even at elevated temperatures of up to 80 degrees C. The Arrhenius plot of the diffusivities shows a decrease in the activation energy of diffusion above 50 degrees C by a factor of 3. This change of activation energy is attributed to a structural change in the humic acid matrix that influences the mobility of toluene.

The effect of solvent-conditioning on soil organic matter sorption affinity for diuron and phenanthrene

The effect of solvent-conditioning on the sorption of diuron and phenanthrene was investigated. The organic carbon-normalized sorption coefficients (K(OC)) for diuron and phenanthrene (determined from single initial concentrations of 0.8mgL(-1) and 1.5mgL(-1), respectively) were consistently higher following solvent-conditioning of a whole soil with five organic solvents (acetonitrile, acetone, methanol, chloroform and dichloromethane). The relative increase in K(OC) was inversely related to the polarity of the conditioning solvent (i.e. greater increases in K(OC) were observed for the least polar solvents: chloroform and dichloromethane). The effect of solvent-conditioning on the sorption properties of the same soil that had been lipid-extracted using accelerated solvent extraction (ASE) was also investigated. Since lipid extraction involves treatment with a non-polar solvent (95:5 dichloromethane:methanol) one may have expected no further increase in K(OC) on solvent-conditioning. On the contrary, the lipid-extracted soil exhibited very similar increases in K(OC) as the whole soil. This demonstrated that lipid removal and solvent-conditioning, which both increased K(OC) for this soil, are quite separate phenomena.

Differences in PAH desorption and sediment organic matter composition between non-vegetated and recently vegetated fuel-oiled sediments

We assessed the desorption behavior of pyrene, chrysene, phenanthrene, and tri-alkylated (C3) phenanthrene/anthracenes for non-vegetated and recently vegetated (< 2 yrs) fuel-oiled sediments collected from the Indiana Harbor Canal (IHC), Gary, IN. Bulk sediment and humin were analyzed for PAH concentrations, organic matter composition, and PAH desorption behavior. PAH desorption isotherms and kinetics were determined using batch aqueous extractions and a two compartment, first-order kinetic model Vegetated sediments contained more plant carbon and were more nonpolar and less oxidized than non-vegetated sediments. Desorption kinetics indicated that PAH desorption was primarily controlled by a slow PAH-desorbing fraction (F2) of IHC sediments. However, in vegetated sediments, particularly humin, PAH release from a faster PAH-desorbing fraction (F1) increased as did the rates (k2) of PAH desorption from the dominant slow PAH-desorbing fraction (F2). We propose that vegetation provides aliphatic, nonpolar carbon to IHC sediments that facilitates more rapid PAH desorption from bulk sediment and humin.

Relative role of aliphatic and aromatic moieties as sorption domains for organic compounds: a review

The sorption behavior of hydrophobic organic compounds (HOCs) in the environment has been the focus of numerous studies. In most of them, the role of aliphatic domains in sorption has been ignored, even although aliphatic components make up a significant portion of the soil organic matter (SOM). The objective of this review is to elucidate the role of the molecular descriptors--aromaticity and aliphaticity--of natural and engineered sorbents as sorption domains for HOCs in the environment. The data, collected from a large and diverse literature data set, show that phenanthrene, like other HOCs, has a strong affinity for aliphatic SOM domains. In many cases, sorption coefficients are higher than those with aromatic-rich sorbents. No significant correlations between either aromaticity or aliphaticity and sorption affinity were recorded for such a large and diverse data set. On the basis of the data set from our literature review of natural and engineered sorbents, we conclude that (i) aliphatic structures must be considered in the evaluation of HOC-sorption processes in the environment; (ii) neither aromaticity nor aliphaticity of SOM alone can be used to predict the sorption affinity of sorbents having wide and diverse properties; and (iii) these molecular descriptors are valuable for relatively homogeneous and chemically similar sorbents.

The effect of lipids on the sorption of diuron and phenanthrene in soils

The influence of lipids on the sorption of diuron and phenanthrene to soils was investigated. Accelerated solvent extraction (ASE) was used to extract lipids from twelve soil horizons. Extractable lipids accounted for 3-13% of organic C. The organic carbon-normalized sorption coefficients (K(OC)) for diuron and phenanthrene were consistently higher for the lipid-extracted soils than for the whole soils (average of 31% for diuron and 29% for phenanthrene), indicating that lipids compete for or block sorption sites on the organic matter. Sorption experiments on one pair of HF-treated soils indicated that the blocking effects of minerals and lipids are independent, since lipid extraction and HF-treatment combined increased K(OC) by more than either treatment alone. Lipids extracted from whole and HF-treated soils were very similar in composition, consisting predominantly of long-chain polymethylene structures. K(OC) of the lipid itself was lower than for any of the whole soils and soil fractions (lipid extracted and HF-treated) for diuron, but higher for phenanthrene. Solid-state (13)C NMR spectra of the HF-treated soils before and after lipid extraction indicated that 15-20% of alkyl C was removed by ASE and that no other structures were affected.