High affinity sorption domains in soil are blocked by polar soil organic matter components

Soil Organic Matter Composition and pH as Factors Affecting Retention of Carbaryl, Carbofuran and Metolachlor in Soil

The majority of studies concerning the environmental behavior of hydrophobic pollutants in soil consider soil organic matter (SOM) content as a main factor influencing chemical retention, whereas the composition of SOM and its individual fraction share are often neglected. In the present paper, carbaryl, carbofuran and metolachlor retention by loamy sand and loam topsoil materials is compared and referred to humic acids (CHA) and the residual carbon (CR) content of SOM. Additionally, the sorption-desorption behavior of agrochemicals in soils was tested at a pH of three to seven. Calculated isothermal parameters point to favorable, spontaneous and physical pesticide sorption. Groundwater ubiquity score (GUS) indexes confirmed the low leaching ability of metolachlor on soils and moderate of carbofuran. The high affinity of carbaryl to CR may explain its pronounced sorption in loam soil and the lowest percolation potential. Carbofuran retention in soils was associated with montmorillonite (Mt) and CR fractions. Meanwhile, metolachlor uptake was related to humic acid and Mt content of the soils. Lower pH enhanced retention of the agrochemicals, except for carbaryl sorption in sandy loam soil. Results of this study highlight that SOM composition and mutual share of individual organic carbon fractions alongside pH may play a crucial role in predicting non-ionic pesticide behavior in soil.

Chemodiversity of soil organic matters determines biodegradation of polychlorinated biphenyls by a graphene oxide-assisted bacterial agent

A promising strategy for degrading persistent organic pollutants (POPs) in soil is amendment with nanomaterial-assisted functional bacteria. However, the influence of soil organic matter chemodiversity on the performance of nanomaterial-assisted bacterial agents remains unclear. Herein, different types of soil (Mollisol soil, MS; Ultisol soil, US; and Inceptisol soil, IS) were inoculated with a graphene oxide (GO)-assisted bacterial agent (Bradyrhizobium diazoefficiens USDA 110, B. diazoefficiens USDA 110) to investigate the association between soil organic matter chemodiversity and stimulation of polychlorinated biphenyl (PCB) degradation. Results indicated that the high-aromatic solid organic matter (SOM) inhibited PCB bioavailability, and lignin-dominant dissolved organic matter (DOM) with high biotransformation potential was a favored substrate for all PCB degraders, which led to no stimulation of PCB degradation in MS. Differently, high-aliphatic SOM in US and IS promoted PCB bioavailability. The high/low biotransformation potential of multiple DOM components (e.g., lignin, condensed hydrocarbon, unsaturated hydrocarbon, etc.) in US/IS further resulted to the enhanced PCB degradation by B. diazoefficiens USDA 110 (up to 30.34%) /all PCB degraders (up to 17.65%), respectively. Overall, the category and biotransformation potential of DOM components and the aromaticity of SOM collaboratively determine the stimulation of GO-assisted bacterial agent on PCB degradation.

Novel insights into the temporal molecular fractionation of dissolved black carbon at the iron oxyhydroxide - water interface

As the most reactive and mobile fraction of black carbon, dissolved black carbon (DBC) inexorably interacts with minerals in the biosphere. Nevertheless, the research on the mechanisms and compositions of DBC assembly at the mineral-water interface remains limited. In this study, we revealed the "kinetic architecture" of DBC on iron oxyhydroxide at novel insights based on quantitative and qualitative approaches. The results indicated that high molecular weight, highly unsaturated, oxygen-rich (such as carboxyl-rich fraction, phenolics), aliphatics, and long C chains compounds were preferentially adsorbed on the iron oxyhydroxide. 2D-COS analyses directly disclosed the sequential fractionation: aromatic and phenolic groups > aliphatic groups, and few aromatics were continuously adsorbed after the rapid adsorption. Quantitative determinations identified that aromatic and phenolic components were adsorbed rapidly over the first 60 min, while aromatics achieved the dynamic equilibrium until ∼300 min, which was consistent with the 2D-COS observations. Our findings supported the hypothesis that "mineral-OM" and "OM-OM" interactions worked simultaneously, and the adsorption might be co-driven by ligand exchange, hydrophobic interactions, and other mechanisms. This work provided the theoretical basis for organic carbon storage and turnover, and it was valuable for predicting the behaviors and fates of contaminants at the soil-water interface and surface water.

Assessing the Persistence and Mobility of Organic Substances to Protect Freshwater Resources

Persistent and mobile organic substances are those with the highest propensity to be widely distributed in groundwater and thereby, when emitted at low-levels, to contaminate drinking water extraction points and freshwater environments. To prevent such contamination, the European Commission is in the process of introducing new hazard classes for persistent, mobile, and toxic (PMT) and very persistent and very mobile (vPvM) substances within its key chemical regulations CLP and REACH. The assessment of persistence in these regulations will likely be based on simulated half-life, t _1/2, thresholds; the assessment of mobility will likely be based on organic carbon-water distribution coefficient, K _OC, thresholds. This study reviews the use of t _1/2 and K _OC to describe persistence and mobility, considering the theory, history, suitability, data limitations, estimation methods, and alternative parameters. For this purpose, t _1/2, K _OC, and alternative parameters were compiled for substances registered under REACH, known transformation products, and substances detected in wastewater treatment plant effluent, surface water, bank filtrate, groundwater, raw water, and drinking water. Experimental t _1/2 values were rare and only available for 2.2% of the 14 203 unique chemicals identified. K _OC data were only available for a fifth of the substances. Therefore, the usage of alternative screening parameters was investigated to predict t _1/2 and K _OC values, to assist weight-of-evidence based PMT/vPvM hazard assessments. Even when considering screening parameters, for 41% of substances, PMT/vPvM assessments could not be made due to data gaps; for 23% of substances, PMT/vPvM assessments were ambiguous. Further effort is needed to close these substantial data gaps. However, when data is available, the use of t _1/2 and K _OC is considered fit-for-purpose for defining PMT/vPvM thresholds. Using currently discussed threshold values, between 1.9 and 2.6% of REACH registered substances were identified as PMT/vPvM. Among the REACH registered substances detected in drinking water sources, 24-30% were PMT/vPvM substances.

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.

Water-induced release of recalcitrant polycyclic aromatic hydrocarbons from soil organic matter during microwave-assisted solvent extraction

Polycyclic aromatic hydrocarbons (PAHs) in soil can be recalcitrant to solvent extraction after aging. We showed in this study that mixing a small amount of water in the extracting solvent during microwave-assisted extraction (MAE) can release recalcitrant PAHs, resulting in significant improvement in the analyzed concentrations. The improvement factor (F) for the total of 16 priority PAHs (∑PAH16) listed by the United States Environmental Protection Agency was 1.44-1.55 for field soils. By comparing the F values for different soil organic components, we demonstrated that the recalcitrant PAHs were primarily associated with biochar, humic acid (HA), and humin (HM), with the F values for ∑PAH16 of 1.94, 6.62, and 4.59, respectively. The results showed that the recalcitrant PAHs comprised a sequestered fraction and a desorption-limited fraction. NMR spectra showed that water worked alone at elevated temperature to promote hydrolysis of biochar and destroy the macromolecular structure, thus causing the release of the otherwise sequestered PAHs during MAE. The substantial reduction in F values for HA and HM after demineralization indicated sequestration of PAHs in organic-mineral complexes, which can be destroyed by hot water treatment. The release of the sequestered fraction was nonselective and independent of compound hydrophobicity. In comparison, the release of the desorption-limited fraction was positively affected by the hydrophobicity of PAHs and was facilitated by the presence of water in the extracting solvent. The results of this study provide important insights into the sequestration and release of recalcitrant PAHs in soil.

Solution-state NMR evaluation of molecular interaction between monoaromatic carboxylic acids and dissolved humic acid

Understanding the nature of interactions between the aromatic organic pollutants with dissolved humic acid (HA) is fundamental for the prediction of their environmental fate and subsequent development of efficient remediation methods. The present study employs solution-state ¹H/¹⁹F NMR methods to investigate the non-covalent interaction between aqueous peat humic acid (Aldrich HA) and monoaromatic carboxylic acids (CA), viz., 2, 6 diflourobenzoic acid (DFBA) and its non-fluorinated analog, benzoic acid (BA). NMR self-diffusion measurement of HA protons confirmed micellar nature indicating possibility of encapsulation of small molecules through host-guest interaction. ¹⁹F-¹H and ¹H-¹H saturation transfer difference (STD) experiments reveal the mode of insertion of CA into HA superstructure. The strength of interaction has been evaluated by analyzing T₁/T₂ relaxation times and self-diffusion coefficients of CA as a function of HA concentration. Association constants extracted for CA-HA complexes from NMR diffusion experiments reflected that the association between DFBA-HA (2.34 mM^-1) is significantly higher than that of BA-HA (0.97 mM^-1). The experimental outcome reiterated that substitution of -H with halogen atoms (-F in specific) to aromatic ring plays a dominant role in modulating the strength of association and mode of insertion of organic pollutants into HA superstructure. The present study emphasizes that AHA can be a potential remediating agent for organic contaminants due to its superior binding affinity compared to less humified extracted HA (EHA) from Karwar, Rajasthan, India.

Synergistic effects of unsaturated flow and soil organic matter on retention and transport of PPCPs in soils

This study examines the effects of soil organic matter (SOM) and water content on the transport of five selected pharmaceutical and personal care products (PPCPs, ibuprofen, carbamazepine, bisphenol A, tetracycline, and ciprofloxacin) in four natural soils with different SOM contents. Batch isotherm experiment results showed that SOM effect was very significant for positively charged tetracycline and ciprofloxacin (>99% adsorption, no desorption), relatively significant for non-dissociated carbamazepine and bisphenol A (17-57% adsorption, 6-71% desorption) and insignificant for negatively charged ibuprofen (4-8% adsorption, 60-87% desorption) in the soils. Transport results showed that neither tetracycline nor ciprofloxacin moved through the saturated and unsaturated soil columns, demonstrating their very limited mobility in soils as a result of significant electrostatic attraction independent of SOM and water conditions. Overall, higher SOM content and lower water content were favorable to the retention of ibuprofen, carbamazepine and bisphenol A in the soils. Breakthrough of ibuprofen, carbamazepine and bisphenol A was 100% (both saturated and unsaturated), 94% (saturated)-97% (unsaturated) and 85% (saturated)-90% (unsaturated) in SOM-removed soils; however only 78% (saturated)-57% (unsaturated), 93% (saturated)-67% (unsaturated), 11% (saturated)-0% (unsaturated) in the SOM-high soils. The effect of water content was not significant in the SOM-removed soils. The SOM could increase the kinetic (type 2) adsorption of PPCPs at the solid-water interface (SWI), and the air phase could increase the instantaneous (type 1) adsorption of PPCPs at the air-water interface (AWI). This result suggests that lowering water content could greatly enhance the adsorption of PPCPs that had high affinities to soils and vice versa. This study provides an important implication that AWI and SWI might have a nonlinear relationship in promoting the adsorption and reducing the mobility of PPCPs under unsaturated flow conditions.

Glomalin-related soil protein reduces the sorption of polycyclic aromatic hydrocarbons by soils

Large amounts of glomalin-related soil protein (GRSP) are present in the soil; however, the impacts of GRSP on the chemical process of soil polycyclic aromatic hydrocarbons (PAHs) are far under investigation. This research sought to elucidate the sorption of phenanthrene as a representative PAH by soils, including Kandiudult, TypicPaleudalf, and Mollisols with co-existing GRSP (0-50 mg/L). The results indicated that soil sorption capacities for phenanthrene reduced significantly. Notably, GRSP changed the sorption process of phenanthrene by Kandiudult, well described as the Freundlich model. In contrast, the phenanthrene sorption isotherms were well described with the Linear model for TypicPaleudalf and Mollisols. The reduced percentage of phenanthrene sorption due to GRSP addition was 7.01%-49.21%, 23.92%-68.71%, and17.26%-66.80% for Kandiudult, TypicPaleudalf and Mollisols, respectively. It was noted that GRSP has a strong capacity for phenanthrene sorption in aqueous solutions and elevates the availability of phenanthrene for microorganisms or plants. During the sorption process, the introduction of GRSP resulted in the reduction of organic matter in soils and elevated the concentrations of dissolved organic matter in solutions, which was the primary mechanism of GRSP-reduced phenanthrene sorption by soils. The findings revealed that GRSP enrichment can increase the mobility of PAHs in contaminated soils.

The quality of soil organic matter, accessed by 13C solid state nuclear magnetic resonance, is just as important as its content concerning pesticide sorption

The global increase of food production has been achieved mainly through the intensive use of inputs such as pesticides. Once released to the soil, sorption (which could be represented by Freundlich solid-water distribution coefficients - K_F) and degradation are two governing processes that determine the distribution and persistence of pesticides in the environment. In spite of the huge dataset, the only apparent generalisation is the high correlation between K_F and soil organic matter (SOM) content. However, in this work no correlation was observed between K_F and organic C content (OC) and so the obtained K_OC (K_F normalised by OC) spread out in a wide range: 1100 to 11,400 mL g^-1 for abamectin; and 30-150 mL g^-1 for atrazine, both ranges corroborate with data from literature. These high variabilities indicate that other soil components or SOM quality strongly interfere in the pesticide sorption in addition to SOM content. Seeking to estimate the influence of SOM quality in the abamectin and atrazine K_OC values, the humic acids, a fraction of the SOM, was analysed by ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) and Principal Component (PC) Regression. The first PC of ¹³C NMR spectra presented negative loadings for aliphatic compounds and positive loadings for aryl C, typical of partially oxidised pyrogenic C. Their scores showed strong correlation with the abamectin K_OC values (R² = 0.91, p < 5 10^-8) and weaker with atrazine K_OC (R² = 0.63, p < 0.0001), in addition to a smaller standardised slope: 1.01 for abamectin and 0.76 for atrazine. These results could be explained by the higher hydrophobicity of abamectin, being thus more prone to interact with the polycondensed aryl groups from the pyrogenic C. It is also important to highlight that humic acids are useful proxies for understanding the paramount interaction of SOM with pesticides.

Studies on the sorption behavior and plant uptake of pesticides in Japanese soils

To estimate pesticide residue levels in succeeding crops based on those in soils, the relationship between pesticide concentrations in komatsuna (Brassica rapa var. perviridis) and the concentrations extracted sequentially from soils using water and acetone was investigated. The concentrations of many pesticides in komatsuna shoots showed higher positive correlation with water-extractable concentrations (C _W) than total-extractable concentrations in soils, so that the C _W was available for evaluating the phytoavailability of pesticides in the soil. As a result of examining the dissipation behavior of the C _W, the dissipation of the C _W was able to be predicted by considering time-dependent soil sorption, which could be estimated using the sorption coefficients (K _d) measured by a standard batch method. Furthermore, the present study showed that the properties of soil organic carbon such as black carbon content and the molecular structure of pesticides were important for estimating the K _d values more accurately.

Sorption of oxytetracycline in particulate organic matter in soils and sediments: Roles of pH, ionic strength and temperature

Particulate organic matter (POM) is a fraction of organic matter with dissimilar properties in different soils. POM isolated from soils and sediments (wetland, oil waste field, farmlands and aquaculture pond sediment) was used to study its sorption behavior on the antibiotic oxytetracycline (OTC). Impacts of solution pH, ionic strength and temperature on the OTC sorption were studied. The sorption rates of OTC in POM from wetland (POM-w) and farmland (POM-f1, POM-f2) were rapid during the first 3 h and gradually decreased with reaction time until reaching the equilibrium. Linear sorption occurred from 3 to 12 h in POM from oil waste field land (POM-o) and aquaculture pond sediment (POM-a). The organic carbon normalized partition coefficient (k_oc) varied from 215.0 to 4493.6 L kg^-1, and it was nearly 10× higher for the POM-w, POM-f1 and POM-f2 than in the POM-o and POM-a. Sorption of OTC by POM exhibited strong pH dependence. Ionic factors affected OTC sorption in POM-f1, POM-f2 and POM-a. The sorption capacity declined >50% in a solution with Ca²⁺ compared to other ions with similar ionic strength. Sorption thermodynamics showed an entropy increasing and endothermic progress during the OTC sorption in POM, implying a spontaneous sorption process. Several mechanisms were involved in OTC sorption in POM, including hydrogen bonding, cation exchange, hydrophobic partitioning and surface complexation.

Is food type important for in vitro post ingestion bioaccessibility models of polychlorinated biphenyls sorbed to soil?

Soils are sorbents for many organic compounds and children consume relatively large amounts of soil. To improve the estimated health risks from this exposure pathway, we examined the role of co-ingested foods in determining the post-ingestion bioaccessibility (mobilization) of 18 polychlorinated biphenyls (PCBs) sorbed to 10 characterized soils. The bioaccessibility test system (DIN 19738, 2004) was an in vitro, 3-compartment, digestive tract containing salts, protein, and bile. Each soil was fortified with PCBs, then, digestive fluids appropriate to each compartment, were added sequentially. Next, digestive fluid and soil were seperated and PCB concentrations in both media were measured. This complete test system was then reduced to assess contributions of individual endogenous digestive fluid constituents (water, salts, pancreatin, bile, and mucin) and representative foods: protein (bovine serum albumin (BSA)), sugar (glucose), and fat (oleic acid). Then, the influence of increasing concentrations of BSA, glucose, and oleic acid was evaluated (individually) complete test systems. In a subset of the samples, solid phase microextraction (SPME) was used to measure freely dissolved PCBs. Across all treatments, percent soil organic carbon was the most influential bioaccessibility determinant, accounting for ≥87% of the explained variation. When evaluated individually, pancreatin, mucin, BSA, bile, and oleic acid each effectively increased PCB bioaccessibility and reduced freely dissolved PCB concentrations. This suggests competitive sorption of PCBs by organic constituents of the digestive constituents. Without sink material, intra-PCB mobilization differences were observed as freely dissolved PCB concentrations inversely correlated (p < 0.05) with their respective log K_ow's. When added to the complete digestive fluid, increasing oleic acid mass increased PCB bioaccessibility (p < 0.05), while adding more BSA or glucose did not (p > 0.05). This indicates that fat intake may be the sole consideration needed when modeling dietary contributions to bioaccessibility of soil sorbed PCBs.

Investigation of the sorption of 17α-ethynylestradiol (EE2) on soils formed under aerobic and anaerobic conditions

A study was conducted on the sorption of 17α-ethynylestradiol (EE2) on five soils formed under different redox conditions: an Arenosol (A_20) with fully aerobic conditions, two Gleysol samples (G_20 and G_40) with suboxic and anoxic conditions and two Histosols (H_20 and H_80) with mostly anoxic conditions. The soils were characterized on the basis of total organic carbon (TOC), specific surface area (SSA) and the Fourier transform infrared spectra of the humic acid and humin fractions (the soil remaining after alkali extraction) of the soil. The maximum adsorption capacity of the soils (Q_max) ranged from 10.7 to 83.6 mg/g in the order G_20 > H_20 > G_40 > A_20 > H_80, which reflected the organic matter content of the soils. The sorption isotherms were found to be nonlinear for all the soil samples, with Freundlich n values of 0.45-0.68. The strong nonlinearity found in the adsorption of the H_80 samples could be attributed to their high hard carbon content, which was confirmed by the high aromaticity of the humin fraction. The maximum sorption capacity (Q_max) of the soils did not increase indefinitely as the organic carbon content of the soils rose. There could be two reasons for this: (i) the large amount of organic matter may reduce the number of binding sites on the surface, and (ii) the decrease in SSA with increasing soil OC content may limit the ability to adsorb EE2 molecules. In anaerobic soil samples, where organic matter accumulation is pronounced, the amount of aromatic and phenolic compounds was higher than in better aerated soil profiles. Strong correlations were found between the amount of aromatic and phenolic compounds in the organic matter and the adsorption of EE2 molecules, indicating that π-π interaction and H-bonding are the dominant sorption mechanisms.

A review of the emerging treatment technologies for PFAS contaminated soils

Contamination of soils with poly- and perfluoroalkyl substances (PFAS) has become a challenging issue due to the adverse effects of these substances on both the environment and public health. PFAS have strong chemical structures and their bonding with soil makes them challenging to eliminate from soil environments. Traditional methods of soil remediation have not been successful in their reduction or removal from the environment. This paper provides a comprehensive evaluation of existing and emerging technologies for remediating PFAS contaminated soils with guidance on which approach to use in different contexts. The functions of all remediation technologies, their suitability, limitations, and the scale applied from laboratory to the field are presented as a baseline for understanding the research need for treatment in soil environments. To date, the immobilization method has been a significant part of the remediation solution for PFAS contaminated soils, although its long-term efficiency still needs further investigation. Soil washing and thermal treatment techniques have been tested at the field scale, but they are expensive and energy-intensive due to the use of a large volume of washing solvent and the high melting point of PFAS, respectively; both methods need a large initial investment for their installation. Other remediation technologies, such as chemical oxidation, ball milling, and electron beams, have been progressed in the laboratory. However, additional research is needed to make them feasible, cost-effective and applicable in the field.

Glomalin-related soil protein enhances the sorption of polycyclic aromatic hydrocarbons on cation-modified montmorillonite

This study investigated the sorption of phenanthrene (as a representative PAH) by cation-modified montmorillonites (Ca-MMT and Fe-MMT) under the influence of Glomalin-related soil protein (GRSP) fractions (EE-GRSP and T-GRSP). Batch sorption studies were carried out as a function of GRSP concentrations (0-500 mg/L), results suggested that the sorption capacities of Ca-MMT and Fe-MMT for phenanthrene were greatly enhanced. The phenanthrene sorption isotherms were in good agreement with the Linear and Freundlich models (R² = 0.886-0.999). The K_d values increased from 4.14 to 60.76 L/kg for Ca-MMT and from 15.57 to 153.80 L/kg for Fe-MMT with the GRSP concentrations adding from 0 to 500 mg/L, respectively. Furthermore, the sorption of phenanthrene was higher on Fe-MMT than that on Ca-MMT. It is believed that GRSP developed a higher sorption level on Fe-MMT, resulting in higher phenanthrene sorption. Microscopic and Spectroscopic analyses confirmed that the effects of GRSP on phenanthrene sorption were attributed to the changes in the surface structure and the hydrophobic property of montmorillonites. In the sorption process, GRSP may sorb onto montmorillonites through cation-π interaction when a bridge linkage was formed, and phenanthrene bound with GRSP mainly via π-π electron donor-accepter interaction. The findings could provide an in-depth understanding of the ecological functions of GRSP and provide new insights into the pathways of PAH transport and fate in the contaminated fields.

Effects of soil components and solution inorganic cations on interactions of imidazolium-based ionic liquid with soils

Effects of alkyl chain length of ionic liquid (IL), soil components and solution inorganic cations on a selected IL (1-methyl-3-octylimidazolium chloride, [OMIM]Cl) interaction with Chinese soils were investigated using batch sorption experiments. The results indicated that sorption energy was mainly controlled by chain length of [OMIM]Cl and contents of soil organic matter (SOM). [OMIM]Cl sorption on soils was mainly controlled by cation exchange process. Contributions of SOM and clay minerals (CMs) to [OMIM]Cl sorption were 7.3%-53.8% and 46.2%-92.7%, respectively. SOM possessed higher energy cation-exchange binding sites than CMs. To predict the sorption of [OMIM]Cl on soils, a model for the relationship between sorption coefficient (K_d) and cation exchange capacity (CEC) from soil components (SOM and CMs, i.e., CEC_SOM and CEC_CMs) as well as solution concentration (C_e) was established: LogK_d = Log(1.67*CEC_SOM + 3.22*CEC_CMs) - 0.58LogC_e. This model could provide a good prediction for sorption coefficients and the prediction errors were within 0.48 log unit. Competitive effects caused by inorganic cations followed the order of Ca²⁺ = Mg²⁺ > K⁺ > Na⁺. Concentrations and valence of coexisting ions both affect their competitive capability on [OMIM]Cl sorption. The finding of this study provided valuable information for evaluating the fate of [OMIM]Cl in soils.

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.

Sorption, transport and biodegradation - An insight into bioavailability of persistent organic pollutants in soil

Contamination of soils with persistent organic pollutants (POPs), such as organochlorine pesticide, polybrominated diphenyl ethers, halohydrocarbon, polycyclic aromatic hydrocarbons (PAHs) is of increasing concern. Microbial degradation is potential mechanism for the removal of POPs, but it is often restricted by low bioavailability of POPs. Thus, it is important to enhance bioavailability of POPs in soil bioremediation. A series of reviews on bioavailability of POPs has been published in the past few years. However, bioavailability of POPs in relation to soil organic matter, minerals and soil microbes has been little studied. To fully understand POPs bioavailability in soil, research on interactions of POPs with soil components and microbial responses in bioavailability limitation conditions are needed. This review focuses on bioavailability mechanisms of POPs in terms of sorption, transport and microbial adaptation, which is particularly novel. In consideration of the significance of bioavailability, further studies should investigate the influence of various bioremediation strategies on POPs bioavailability.

Interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and organic soil washing agents

Understanding interaction mechanisms between polycyclic aromatic hydrocarbons (PAHs) and soil-washing agents can help in choosing efficient agents which are able to desorb and solubilize PAHs. This study investigated interaction mechanisms between pyrene and four washing agents including: two dissolved organic matters (DOM) F-DOM and CRC-DOM, and two commercial bio-based surfactants BBE-1000 and Supersolv using fluorescence spectroscopy combined with multivariate curve resolution alternating regression (MCR-AR). The efficiencies of these washing agents in removing PAHs from the soil were tested in a soil washing experiment. Pyrene showed π-π interactions with F-DOM and no interaction with CRC-DOM. This could be attributed to the more aromatic structures in F-DOM compared to CRC-DOM. The two DOMs were inefficient in soil washing which might be attributed to the relatively weak effect of π-π interactions in releasing PAHs from the soil. Interaction mechanisms between pyrene and the bio-based surfactants were elucidated with MCR-AR, which resolved three spectroscopically active species from pyrene emission spectra as a function of pyrene and bio-based surfactants concentrations. These species resembled pyrene emission in a polar and nonpolar microenvironment, respectively and of an excimer. Concentration profiles retrieved by the model for the three species showed that, below the critical micelle concentration (CMC), Supersolv created more nonpolar interactions with pyrene compared to BBE-1000. In soil washing, Supersolv showed the highest efficiency in extracting PAHs from the soil. This highlighted the importance of nonpolar interactions in desorbing PAHs from soils, which could then be solubilized in micelles. This study demonstrated the potential of fluorescence spectroscopy combined with the MCR-AR model for selecting efficient soil-washing agents.

Biodegradation of high doses of commercial pesticide products in pilot-scale biobeds using olive-oil agroindustry wastes

Biobeds systems containing soil, peat and straw (SPS) are used worldwide to eliminate pesticide point-source contamination, but implantation is difficult when peat and/or straw are not available. Novel biobeds composed of soil, olive pruning and wet olive mill cake (SCPr) or its vermicompost (SVPr) were assayed at pilot scale for its use in olive grove areas. Their removal efficiency for five pesticides applied at high concentration was compared with the biobed with SPS. The effect of a grass layer on the efficiency of these biobeds was also evaluated. Pesticides were retained mainly in the upper layer. In non-planted biobeds with SCPr and SVPr, pesticides dissipation was higher than in SPS, except for diuron. In the biobed with SVPr, with the highest pesticide dissipation capacity, the removed amount of dimethoate, imidacloprid, tebuconazole, diuron and oxyfluorfen was 100, 80, 73, 75 and 50%, respectively. The grass layer enhanced dehydrogenase and diphenol-oxidase activities, modified the pesticides dissipation kinetics and favored the pesticide downward movement. One metabolite of imidacloprid, 3 of oxyfluorfen and 4 of diuron were identified by GC-MS. These novel biobeds represent an alternative to the traditional one and a contribution to promote a circular economy for the olive-oil production.

Insights into the attenuated sorption of organic compounds on black carbon aged in soil

Sorption of organic compounds on fresh black carbons (BCs) can be greatly attenuated in soil over time. We examined herein the changes in surface properties of maize straw-derived BCs (biochars) after aged in a black soil and their effects on the sorptive behaviors of naphthalene, phenanthrene and 1,3-dinitrobenzene. Dissolved fulvic and humic acids extracted from the soil were used to explore the role of dissolved organic carbon (DOC) in the aging of biochars. Chromatography analysis indicated that DOC molecules with relatively large molecular weight were preferentially adsorbed on the biochars during the aging processes. DOC sorption led to blockage of the biochar's micropores according to N₂ and CO₂ adsorption analyses. Surface chemistry of the biochars was also substantially modified, with more O-rich functional groups on the aged biochars compared to the original biochars, as evidenced by Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. The changes in both the physical and chemical surface properties of biochars by DOC led to significant attenuation of the sorption capacity and nonlinearity of the nonionic organic compounds on the aged biochars. Among the tested organic compounds, phenanthrene was the most attenuated in its sorption by the aging treatments, possibly because of its relatively large molecular size and hydrophobicity. The information can help gain a mechanistic understanding of interactions between BCs and organic compounds in soil environment.

The surface-pore integrated effect of soil organic matter on retention and transport of pharmaceuticals and personal care products in soils

This study examines a surface-pore integrated mechanism that allows soil organic matter (SOM) to influence the retention and transport of three representative pharmaceuticals and personal care products (PPCPs)-ibuprofen, carbamazepine, and bisphenol A-in agricultural soil. A series of sorption-desorption batch tests and breakthrough column experiments were conducted using manured and non-manured soils. Results show that SOM could substantially influence the environmental behaviors of PPCPs via two mechanisms: surface-coating and pore-filling. Surface-coating with molecular SOM decreases the sorption of dissociated PPCPs (e.g., ibuprofen) but increases the sorption of non-dissociated PPCPs (e.g., carbamazepine and bisphenol A), while pore-filling with colloidal SOM enhances the retention of all the PPCPs by providing nano-/micro-pores that limit diffusion. The higher retention and lower mobility of PPCPs in soil microaggregates than in bulk soils suggest that SOM content and SOM-altered soil pore structure could exert a coupled effect on PPCP retention. Differences in the elution of PPCPs with low surface tension solution (i.e., 20% ethanol) in the presence and absence of SOM indicate that PPCPs prefer to remain in SOM-filled pores. Overall, ibuprofen has a high environmental risk, whereas carbamazepine and bisphenol A could be readily retarded in agricultural soils (with a loamy clay texture). This study implies that SOM accrual (particularly pore-filling SOM) has a high potential for reducing the off-site risks of PPCPs by increasing soil nano-/micro-porosity.

Sorption mechanisms of sulfamethazine to soil humin and its subfractions after sequential treatments

Sorption mechanisms of an antibiotic sulfamethazine (SMT) to humin (HM) isolated from a peat soil and its subfractions after sequential treatments were examined. The treatments of HM included removal of ash, O-alkyl carbon, lipid, and lignin components. The HF/HCl de-ashing treatment removed a large amount of minerals (mainly silicates), releasing a fraction of hydrophobic carbon sorption domains that previously were blocked, increasing the sorption of SMT by 33.3%. The de-O-alkyl carbon treatment through acid hydrolysis greatly reduced polarity of HM samples, thus weakening the interaction between sorbents with water at the interfaces via H-bonding, leaving more effective sorption sites. Sorption of SMT via mechanisms such as van der Waals forces and π-π interactions was enhanced by factors of 2.04-2.50. After removing the lipid/lignin component with the improved Soxhlet extraction/acid hydrolysis, the organic carbon content-normalized sorption enhancement index E_oc was calculated. The results demonstrated that the E_oc-lipid for SMT (16.9%) was higher than E_oc-lignin (10.1%), implying that removal of unit organic carbon mass of lipid led to a higher increase in sorption strength than that of lignin. As each component was progressively removed from HM, the sorption strength and isotherm nonlinearity of the residual HM samples for SMT were gradually enhanced. The K_oc values of SMT by HM samples were positively correlated with their aromatic carbon contents, implying that π-π electron donor-acceptor interactions between the benzene ring of sorbate and the aromatic domains in HM played a significant role in their interactions.

Molecular composition of soil organic matter with land-use change along a bi-continental mean annual temperature gradient

Soil organic matter (SOM) is critical for maintaining soil fertility and long-term agricultural sustainability. The molecular composition of SOM is likely altered due to global climate and land-use change; but rarely are these two aspects studied in tandem. Here we used molecular-level techniques to examine SOM composition along a bi-continental (from North to South America) mean annual temperature (MAT) gradient from seven native grassland/forest and cultivated/pasture sites. Biomarker methods included solvent extraction, base hydrolysis and cupric (II) oxide oxidation for the analysis of free lipids of plant and microbial origin, ester-bound lipids from cutin and suberin, and lignin-derived phenols, respectively. Solid-state ¹³C nuclear magnetic resonance (NMR) was used to examine the overall composition of SOM. Soil cultivation was found to increase the amount of microbial-derived compounds at warmer temperatures (up to 17% increase). The cultivated soils were characterized by much lower contributions of plant-derived SOM components compared to the native soils (up to 64% lower at the coldest site). In addition, cultivation caused an increase in lignin and cutin degradation (up to 68 and 15% increase, respectively), and an increase in the amount of suberin-derived inputs (up to 54% increase). Clear differences in the molecular composition of SOM due to soil cultivation were observed in soils of varying mineral composition and were attributed to disturbance, different vegetation inputs, soil aggregate destruction and MAT. A high organic allophanic tropical soil was characterized by its protection of carbohydrates and nitrogen-containing compounds. The conversion of native to cultivated land shows significant shifts in the degradation stage of SOM. In particular, cutin-derived compounds which are believed to be part of the stable SOM pool may undergo enhanced degradation with long-term cultivation and disruption of soil aggregates. On a per year basis, the total amount of cutin decreased only at the two forest sites that were converted to pasture, likely due to cutin degradation or to changes in vegetation and litter quality associated with land-use change. Overall, our study highlights that the implementation of different agricultural management practices enhances the degradation of recalcitrant SOM compounds that may become a source of atmospheric CO₂ with increasing land-use and climate change.

Role of structure, accessibility and microporosity on sorption of phenanthrene and nonylphenol by sediments and their fractions

To better understand interaction mechanism of sediment organic matter with hydrophobic organic compounds, sorption of phenanthrene (Phen) and nonylphenol (NP) by bulk sediments and their fractions was investigated. Three surface sediments were selectively fractionated into different organic fractions, including the demineralized carbon (DM), lipid free carbon (LF), lipid (LP), and nonhydrolyzable carbon (NHC) fractions. The structure and microporosity of the isolated fractions were characterized by NMR and CO₂ adsorption techniques, and used as sorbents for Phen and NP. The calculated micropore volumes (V_o) and specific surface area (SSA) values are positively related to the concentrations of aromatic C and char for the DM, LF and NHC fractions, suggesting that aromatic moieties and char component significantly contribute to the microporosity. The LF fractions exhibit greater sorption affinity than the DM fractions do, indicating that the presence of LP could block the accessibility of sorption sites for Phen and NP. Significant and positive correlations among log K'_FOC values for Phen and NP and aromatic carbon and char contents, and V_o and SSA values suggest the aromatic moieties and microporosity dominate their sorption of HOCs by sediment organic matter (SOM). As the NHC fractions have much stronger sorption than other fractions do, they dominate the overall sorption by the bulk samples. This study indicated that the important roles of aromatic moieties, accessibility, and microporosity in the sorption of HOCs by SOM.

Bioaccessibility of nitro- and oxy-PAHs in fuel soot assessed by an in vitro digestive model with absorptive sink

Ingestion of soot present in soil or other environmental particles is expected to be an important route of exposure to nitro and oxygenated derivatives of polycyclic aromatic hydrocarbons (PAHs). We measured the apparent bioaccessibility (B_app) of native concentrations of 1-nitropyrene (1N-PYR), 9-fluorenone (9FLO), anthracene-9,10-dione (ATQ), benzo[a]anthracene-7,12-dione (BaAQ), and benzanthrone (BZO) in a composite fuel soot sample using a previously-developed in vitro human gastrointestinal model that includes silicone sheet as a third-phase absorptive sink. Along with B_app, we determined the 24-h sheet-digestive fluid partition coefficient (K_s,24h), the soot residue-fluid distribution ratio of the labile sorbed fraction after digestion (K_r,lab), and the maximum possible (limiting) bioaccessibility, B_lim. The B_app of PAH derivatives was positively affected by the presence of the sheet due to mass-action removal of the sorbed compounds. In all cases B_app increased with imposition of fed conditions. The enhancement of B_app under fed conditions is due to increasingly favorable mass transfer of target compounds from soot to fluid (increasing bile acid concentration, or adding food lipids) or transfer from fluid to sheet (by raising small intestinal pH). Food lipids may also enhance B_app by mobilizing contaminants from nonlabile to labile states of the soot. Compared to the parent PAH, the derivatives had larger K_r,lab, despite having lower partition coefficients to various hydrophobic reference phases including silicone sheet. The B_lim of the derivatives under the default conditions of the model ranged from 65.5% to 34.4%, in the order, 1N-PYR > ATQ > 9FLO > BZO > BaAQ, with no significant correlation with hydrophobic parameters, nor consistent relationship with B_lim of the parent PAH. Consistent with earlier experiments on a wider range of PAHs, the results suggest that a major determinant of bioaccessibility is the distribution of chemical between nonlabile and labile states in the original solid.

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.

Effect of Time-Dependent Sorption on the Dissipation of Water-Extractable Pesticides in Soils

The dissipation behavior of water-extractable pesticides in soils is important when assessing the phytoavailability of pesticides in soils. This process is less understood than pesticide extraction with organic solvents. To elucidate the dissipation behavior of water-extractable pesticides in soils, we conducted an incubation study using 27 pesticides and five Japanese soils. The rate of decrease of the level of pesticides in water extracts was faster in soils than that of total extracts (water extracts and acetone extracts). This suggests that time-dependent sorption contributed to the difference in the dissipation between the pesticides in water and total extracts from soils. Increased apparent sorption coefficients (Kd,app) with time were positively and significantly correlated with Kd,app values of a 0 day incubation [Kd,app(t0)]. This empirical relationship suggests that Kd,app(t0) values can predict the time-dependent increase in Kd,app and the dissipation of water-extractable pesticides in soils.

The effect of composition on stability ((14)C activity) of soil organic matter fractions from the albic and black soils

The importance of the composition of soil organic matter (SOM) for carbon (C) cycling is still under debate. Here a single soil source was used to examine the specific influence of its composition on stability ((14)C activity) of SOM fractions while constraining other influential C turnover factors such as mineral, climate and plant input. The following SOM fractions were isolated from two soil samples: four humic acids, two humins, non-hydrolyzable carbon, and the demineralized fraction. We examined the isotope ratios of SOM fractions in relation to composition (such as aliphatic and aromatic C content) using solid state (13)C nuclear magnetic resonance (NMR) and thermal analysis. The Δ(14)C values of the fractions isolated from both an albic soil (SOMs-A) and a black soil (SOMs-B) correlated negatively with their peak temperature of decomposition and the temperature where half of the total heat of reaction was evolved, implying a potential link between thermal and biogeochemical stability of SOM fractions. Aryl C contents of SOMs-A determined using (13)C NMR varied inversely with δ(15)N values and directly with δ(13)C values, suggesting that part of aryl C of SOMs-A might be fire-derived. The Δ(14)C values of SOMs-A correlated positively with aliphatic C content and negatively with aromatic C content. We therefore concluded that fire-derived aromatic C in SOMs-A appeared to be more stable than microbially-derived aliphatic C. The greater decomposition of SOMs-B fractions weakened the relationship of their Δ(14)C values with alkyl and aryl C contents. Hence, the role of the composition of SOM fractions in regulating stability might be dependent on the source of specific C forms and their stage of decomposition.

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.

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.

Properties of biomass-derived biochars: Combined effects of operating conditions and biomass types

Combined effects of operating conditions including heating temperature (200-700 °C), time (1-8h) and rate, and atmosphere (air-flow, air-limited and N2) on the physicochemical properties of biochars with pine sawdust, maize straw and sugarcane bagasse as feedstocks were investigated. The results demonstrated that production temperature and atmosphere acted as the predominant factors that determined the properties of biochars. The X-ray diffraction data confirmed the occurrence of phase transition in the biomass structures at around 400 °C. Heating time and rate showed little effect on the functional group compositions of the biochars within 8h, particularly under N2 atmosphere. In addition, the molecular weights of the biochar-derived dissolved organic carbon tended to increase with increasing temperature. Feedstock type also affected the biochar properties by the compositional differences in mineral salts and cellulose/lignin in the three biomass materials. This work provides important information for optimizing procedures for biochar production with desired properties and high yield.

The effects of organic matter-mineral interactions and organic matter chemistry on diuron sorption across a diverse range of soils

Sorption of non-ionic organic compounds to soil is usually expressed as the carbon-normalized partition coefficient (KOC), because it is assumed that the main factor that influences the amount sorbed is the organic carbon content of the soil. However, KOC can vary by a factor of at least ten across a range of soils. We investigated two potential causes of variation in diuron KOC - organic matter-mineral interactions and organic matter chemistry - for a diverse set of 34 soils from Sri Lanka, representing a wide range of soil types. Treatment with hydrofluoric acid (HF-treatment) was used to concentrate soil organic matter. HF-treatment increased KOC for the majority of soils (average factor 2.4). We attribute this increase to the blocking of organic matter sorption sites in the whole soils by minerals. There was no significant correlation between KOC for the whole soils and KOC for the HF-treated soils, indicating that the importance of organic matter-mineral interactions varied greatly amongst these soils. There was as much variation in KOC across the HF-treated soils as there was across the whole soils, indicating that the nature of soil organic matter is also an important contributor to KOC variability. Organic matter chemistry, determined by solid-state (13)C nuclear magnetic resonance (NMR) spectroscopy, was correlated with KOC for the HF-treated soils. In particular, KOC increased with the aromatic C content (R=0.64, p=1×10(-6)), and decreased with O-alkyl C (R=-0.32, p=0.03) and alkyl C (R=-0.41, p=0.004) content.

Sorption affinities of sulfamethoxazole and carbamazepine to two sorbents under co-sorption systems

The Kd of sulfamethoxazole (SMX) on activated carbon (AC) was larger than that of SMX on single-walled carbon nanotubes (SC), but the competition of SMX with carbamazepine (CBZ) for adsorption sites was weaker on AC than SC. Thus, a large Kd value does not necessarily reflect a high affinity. The analysis of the apparent sorption, competition, desorption hysteresis, and the sorption thermodynamics for SMX and CBZ did not provide sufficient information to distinguish their sorption affinities. The release of the adsorbed CBZ was not altered with SMX as the competitor, but SMX release increased significantly after CBZ addition. The higher sorption affinity of CBZ may be explained by the interactions of the CBZ benzene rings with the aromatic structures of the adsorbents. Although the thermodynamic meaning cannot be described, the release ratio of the adsorbed pollutants provides useful information for understanding pollutant sorption strength and associated risks.

Factors influencing the accumulation of organochlorine pesticides in the surface soil across the Central Tibetan Plateau, China

Forty-four soil samples were collected across the Central Tibetan Plateau (CTP) at elevations of between 3711 and 5352 m. The scatter diagram shows that the soil concentrations of organochlorine pesticides (OCPs) were associated with the altitude of sampling site, soil clay minerals, soil organic carbon (SOC) and the fine particle fractions of soil. Pearson correction analysis and principle component analysis were used to deduce the relationship between the OCP concentrations and these factors logically. It was determined that the altitude and clays functioned as the primary factors influencing OCP accumulation, and SOC was weakly related to OCPs. The fitting equation closely matches the observations in the field while only taking the altitude and clay minerals into account. Our study found that clay minerals dominated the sorption of OCPs in soil, whereas the altitude contributed to temperature-driven condensation for the accumulation of OCPs at high altitudinal CTP.

Persistent organic pollutants in soil near the Changwengluozha glacier of the Central Tibetan Plateau, China: their sorption to clays and implication

Twenty-seven soil samples were collected at ca. 5,000 m from the Changwengluozha glacier. In addition to soil components, the concentration of 23 organochlorine pesticides (OCPs) and 16 polycyclic aromatic hydrocarbons (PAHs) were analyzed. Clay minerals were found to play a key role in the accumulation of OCPs/PAHs in soil. The sorption ratio of chemical to clay was ordered in the OCPs and PAHs to the vapor pressure in a negatively correlated fashion. Because of the negative relationship between vapor pressure and the soil-air partition coefficients (KSA), it was understood that the higher sorption ratio responded to a higher KSA, which indicated the fate of the contaminants in soil. The soil near the Changwengluozha glacier functioned as a "sink" for OCPs in the decreasing order of 2,4'-DDT, 4,4'-DDD, HCB, δ-HCH, and α-HCH and for PAHs in an decreasing order of Pyr, Flu, Fl, Ace, and Acy.