Sorption-desorption Hysteresis Research Articles

Water Sorption and Structural Properties of Human Airway Mucus in Health and Muco-Obstructive Diseases.

Muco-obstructive diseases change airway mucus properties, impairing mucociliary transport and increasing the likelihood of infections. To investigate the sorption properties and nanostructures of mucus in health and disease, we investigated mucus samples from patients and cell cultures (cc) from healthy, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) airways. Atomic force microscopy (AFM) revealed mucin monomers with typical barbell structures, where the globule to spacer volume ratio was the highest for CF mucin. Accordingly, synchrotron small-angle X-ray scattering (SAXS) revealed more pronounced scattering from CF mucin globules and suggested shorter carbohydrate side chains in CF mucin and longer side chains in COPD mucin. Quartz crystal microbalance with dissipation (QCM-D) analysis presented water sorption isotherms of the three types of human airway mucus, where, at high relative humidity, COPD mucus had the highest water content compared to cc-CF and healthy airway mucus (HAM). The higher hydration of the COPD mucus is consistent with the observation of longer side chains of the COPD mucins. At low humidity, no dehydration-induced glass transition was observed in healthy and diseased mucus, suggesting mucus remained in a rubbery state. However, in dialyzed cc-HAM, a sorption-desorption hysteresis (typically observed in the glassy state) appeared, suggesting that small molecules present in mucus suppress the glass transition.

Removal of per- and polyfluoroalkyl substances by activated hydrochar derived from food waste: Sorption performance and desorption hysteresis

Carbonaceous materials, derived from waste biomass, have proven to be a viable and appealing alternative for removing emerging micro-pollutants, such as per- and polyfluoroalkyl substances (PFAS). To assess the feasibility and efficacy of using material derived from food waste to alleviate PFAS pollution, this study prepared activated hydrochar (AHC) for sorbing ten PFAS, including five perfluoroalkyl carboxylic acids (PFCA; C4–C8), three perfluoroalkyl sulfonic acids (PFSA; C4, C6, C8), and two emerging PFAS, namely hexafluoropropylene oxide dimer acid (commercial name GenX, an alternative to perfluorooctanoic acid (PFOA)) and 6:2 fluorotelomer sulfonic acid (6:2 FTS). The results demonstrated that AHC possessed a relatively high specific surface area (207 m2/g) and hydrophobic surface properties. At environmentally relevant concentrations (40 μg/L), the sorption partition coefficients (log Kd) of PFAS on AHC ranged from 2.33 to 6.49 L/kg. Notably, GenX exhibited a lower log Kd value (2.33 L/kg) than PFOA (3.88 L/kg). The AHC showed favorable sorption performance for all tested PFAS, with log Kd values surpassing other reported sorbents (e.g., 0.83 for GenX on pyrochar, and 2.83 for PFOA on commercial biochar). Additionally, desorption hysteresis was observed for all PFAS, except for PFOA, and was particularly pronounced in PFBA, GenX, and 6:2 FTS at high initial concentrations, with Hysteresis Index (HI) values varying from 0.31 to 1.45, 0.68 to 1.88, and 0.51 to 1.85, respectively. Given its robust sorption capacity and desorption hysteresis toward PFAS, AHC is expected to be a favorable candidate for remediating PFAS-contaminated water. This study underscores, for the first time, the potential of food waste-derived hydrochar as an efficient sorbent for alleviating PFAS contamination, and further study is needed to investigate the sorption and desorption behaviors of PFAS on AHC at various environmental conditions.

Construction of 2D/2D Mesoporous WO3/CeO2 Laminated Heterojunctions for Optimized Photocatalytic Performance.

Photocatalytic elimination of antibiotics from the environment and drinking water is of great significance for human health. However, the efficiency of photoremoval of antibiotics such as tetracycline is severely limited by the prompt recombination of electron holes and slow charge migration efficacy. Fabrication of low-dimensional heterojunction composites is an efficient method for shortening charge carrier migration distance and enhancing charge transfer efficiency. Herein, 2D/2D mesoporous WO3/CeO2 laminated Z-scheme heterojunctions were successfully prepared using a two-step hydrothermal process. The mesoporous structure of the composites was proved by nitrogen sorption isotherms, in which sorption-desorption hysteresis was observed. The intimate contact and charge transfer mechanism between WO3 nanoplates and CeO2 nanosheets was investigated using high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy measurements, respectively. Photocatalytic tetracycline degradation efficiency was noticeably promoted by the formation of 2D/2D laminated heterojunctions. The improved photocatalytic activity could be attributed to the formation of Z-scheme laminated heterostructure and 2D morphology favoring spatial charge separation, confirmed by various characterizations. The optimized 5WO3/CeO2 (5 wt.% WO3) composites can degrade more than 99% of tetracycline in 80 min, achieving a peak TC photodegradation efficiency of 0.0482 min-1, which is approximately 3.4 times that of pristine CeO2. A Z-scheme mechanism is proposed for photocatalytic tetracycline by from WO3/CeO2 Z-scheme laminated heterojunctions based on the experimental results.

A thermodynamic theory of sorption in glassy polymers

Sorption of vapors by glassy polymers is known to have properties that are different from those typical for sorption by rubbery polymers or liquids. Despite an importance for many practical applications, this difference is still not fully understood. We developed a thermodynamic theory for description of penetrant activity in the glassy state. The presented approach considers the glass transition in terms of a second order phase transition and utilizes heat capacity changes for calculation of thermodynamic activity. The formalism developed here explains a deviation of penetrant activity in the glassy state from equilibrium values. Moreover, the sorption-desorption hysteresis can be explained in thermodynamic terms as well. We demonstrate that not only the heat capacity change of the polymer, but also the heat capacity change of the penetrant should be considered to understand the difference between three cases: sorption by equilibrium liquid, absorption by glass and desorption from glass.The theory presented here is tested on experimental data on water sorption by maltodextrin and bovine submaxillary gland mucin. A very good fitting of the experimental data for both sorption and desorption cases is demonstrated. The values of heat capacity increments of the components obtained by fitting the penetrant activity data can be used to get new insights into the non-equilibrium properties of glassy materials.

Fibre Individualisation and Mechanical Properties of a Flax-PLA Non-Woven Composite Following Physical Pre-Treatments

Pre-treatments for plant fibres are very popular for increasing the fineness of bundles, promoting individualisation of fibres, modifying the fibre-matrix interface or reducing water uptake. Most pre-treatments are based on the use of chemicals and raise concerns about possible harmful effects on the environment. In this study, we used physical pre-treatments without the addition of chemical products. Flax tows were subjected to ultrasound and gamma irradiation to increase the number of elementary fibres. For gamma pre-treatments, a 20% increase in the number of elementary fibres was quantified. The biochemical composition of pre-treated flax tows exhibited a partial elimination of sugars related to pectin and hemicelluloses depending on the pre-treatment. The hygroscopic behaviour showed a comparable decreasing trend for water sorption-desorption hysteresis for both types of pre-treatment. Then, non-woven composites were produced from the pre-treated tows using poly-(lactid) (PLA) as a bio-based matrix. A moderate difference between the composite mechanical properties was generally demonstrated, with a significant increase in the stress at break observed for the case of ultrasound pre-treatment. Finally, an environmental analysis was carried out and discussed to quantitatively compare the different environmental impacts of the pre-treatments for composite applications; the environmental benefit of using gamma irradiation compared to ultrasound pre-treatment was demonstrated.

Water vapor sorption-desorption hysteresis in glassy surface films of mucins investigated by humidity scanning QCM-D

HypothesisInvestigating the origin of water sorption-desorption hysteresis in glassy biopolymers is important for understanding the properties of biological barriers, such as the mucus epithelium. In general, hysteresis is a result of a complex interplay between diffusion of water and relaxation of the polymer matrix. Our hypothesis is that for thin films, typical for quartz crystal microbalance with dissipation monitoring (QCM-D) experiments performed in gas phase with defined relative humidity, the diffusion limitation is eliminated and hysteresis results only from relaxation of the polymer matrix. ExperimentsWe use a recently developed humidity scanning (HS) QCM-D method to obtain water sorption-desorption isotherms of mucin films under controlled conditions where water diffusion is not the limiting factor, neither in the vapor phase nor in the glassy mucin film. FindingsWe present new results on the water sorption-desorption behavior of glassy mucin films with nanoscale thicknesses. Despite the fact that water diffusion is not the limiting factor, the sorption-desorption branches show clear hysteresis effects that are similar to those typically observed in bulk samples. The hydration-induced glass transition, resolved from monitoring the rheological behavior of the films, is shown to be in excellent agreement with the onset of the sorption-desorption hysteresis. We suggest that the hysteresis effect is related to a difference in dynamical and structural properties of the glassy materials depending on the hydration history of the films.

Evaluation study for phosphorus mobilisation-release behaviour on different marine sediments: focus on phosphate sorption characteristics

Environmental contextPhosphorus is a key nutrient element associated with eutrophication in aquatic ecosystems. We studied phosphate sorption processes, which play a key role in phosphorus cycling, in sediments collected from 23 sites including estuary, coastal sea and aquaculture areas in China. The results show the influence of sediment type on phosphorus buffering capacity and allow better interpretation of phosphorus migration in aquatic ecosystems. AbstractPhosphorus is well known as an important nutrient element associated with eutrophication in the marine ecosystem, and its sorption on sediments plays a key role in its immobilisation in the bio-geochemical cycle. In this paper, the sorption behaviour of phosphorus onto sediments collected from 23 different sites in estuary, coastal sea and aquaculture areas of China was studied. The main aim is to determine the phosphorus sorption characteristics of these sediments thereby assessing their phosphorus buffering capacities. Both kinetic and equilibrium isotherms of the sorption and desorption of phosphorus were assessed. The resultant sorption and desorption kinetic curves fit well to a two-compartment first-order equation. The equilibration time was considered as 48h. The isotherms agreed well with the Freundlich and Langmuir equations. The hysteresis coefficient values showed an obvious sorption-desorption hysteresis. Decreasing salinity was favourable for the sorption ability in the range from 30 to 3. The mean values of the phosphorus sorption-desorption equilibrium concentration and the maximum phosphorus sorption capacity were 0.098mgL−1 and 0.086mgg−1 for sediments in the Changjiang Estuary and East China Sea shelf, and 0.138mgL−1 and 0.067mgg−1 for the sediments in the aquaculture area. The fractions of clay, calcite and organic matter influenced the sorption and retention abilities and the effects were different for sediments obtained from different origins.

Nanoengineered Sorbents To Increase the Persistence of the Allelochemical Carvone in the Rhizosphere

This study investigates the changes in sorption/desorption, dissipation, and leaching of the two enantiomeric forms of the allelochemical carvone, R-carvone and S-carvone, after amending an agricultural soil sample with two nanoengineered sorbents: biochar (BC) and organoclay (OCl). The sorption of carvone enantiomers was nonenantioselective and similarly improved by the addition of OCl and BC to the soil. However, OCl-amended soil showed reversible sorption, whereas BC-amended soil displayed sorption-desorption hysteresis. Dissipation of carvone enantiomers was enantioselective. Both amendments increased the half-life of the enantiomers in the soil. This effect was more pronounced for BC-amended soil and for S-carvone. Leaching of R- and S-carvone through soil columns was scarce in unamended soil (<7%), due to their rapid degradation during leaching, and null for OCl- and BC-amended soil, for which much of the applied R- and S-carvone remained in the top 0-5 cm of the amended soil layer. Addition of biochars and organoclays could help increase the persistence of carvone enantiomers in the rhizosphere, which may favor their use as residual pest-management substances.

Accumulated Gibbs free energy as a quantitative measure of desorption hysteresis associated with the formation of metastable states

The persistence of metastable states was proposed in the literature as one explanation for sorption-desorption hysteresis (SDH) of organic compounds on soils and sediments. When such metastable states freely exchange sorbate molecules with the surroundings and there is no spontaneous exit of a whole system from that state, it is possible to determine the extra Gibbs free energy (ΔGext) accumulated in a system due to the persistence of metastable states. A novel contribution of this paper is the characterization of SDH, in which the sorption isotherm (SI) and desorption isotherm (DI) do not close a loop, in terms of free energy needed to create "frozen", metastable states. To that end, liquid phase sorption of non-ionized sorbates is considered and by integrating over the sorption-desorption sequence, ΔGext and an integral hysteresis index (IHI) were obtained. Experimental data collected from the literature on aqueous sorption and desorption of polyaromatic hydrocarbons, triazines and ureas were examined on soils, sediments, organic matter-rich sorbents, montmorillonites and fullerene. Positive ΔGext values were obtained to quantify the thermodynamic potential for spontaneous exit from a metastable state that is not implemented due to the kinetic barriers. Relating the ΔGext values to sorbate molecular structure and sorbent properties may allow the prediction of SDH for various chemicals on sorbents in which the sorbate-induced perturbation of a sorbent matrix is believed to be a cause for the formation of persistent metastable states and the appearance of a non-closed sorption-desorption sequence.

Three Residual Benefits of Applying Phosphate Fertilizer

Core Ideas Phosphate continues to react with soil thereby decreasing its effectiveness. However, the continuing reaction conveys negative charge to the reacting particles. This reaction decreases both the buffering capacity and the rate of further reactions. Both of these changes increase the effectiveness of subsequent applications. Fertilizer P provides three benefits to subsequent crops. The first is that P not lost in produce or leachate remains in soil. However, its effectiveness usually decreases with time because the P slowly diffuses into the adsorbing particle. The second benefit stems from the resulting increased negative charge and decreased buffering capacity. We test whether this decreases the P required for a given yield. The third benefit occurs because, given enough P, the penetration reaction stops. We test whether it is then sufficient to only supply P needed by the plants. We incubated for 35 d at 60°C samples of a P–deficient soil to which we had added five levels of P. At the end of this incubation period, we measured P sorption and desorption on one set of samples of the soil. On another set, we added several different levels of P and measured plant response. On a third set, we similarly added several different levels of P but incubated soil plus the extra P for a further 3 d at 60°C before measuring plant response. Incubating the soil with P decreased the P buffering capacity and increased the effectiveness of P applications. The effects were nonlinear with greatest effect occurring at low levels of application. The incubation with P also virtually eliminated sorption–desorption hysteresis. With increasing levels of incubated P, the difference in plant response between the once–incubated and the twice–incubated treatments decreased linearly. All of the observations are consistent with slow penetration of the adsorbed P.

Comparative sorption and desorption of benzo[α]pyrene and 1,2,3-trichlorobenzene by biochar in the presence of dissolved organic matter

Sorption and desorption of benzo[α]pyrene (BaP) and 1,2,3-trichlorobenzene (TrCB) on biochar prepared from maple wood shavings heated at 500°C were studied in the presence of dissolved organic matter (DOM), including citric acid, l-phenylalanine (L-PH), and peptone. Compared to TrCB, BaP exhibited more nonlinear and stronger sorption on biochar. Nonlinearity of the sorption isotherms increased in the presence of DOM. The presence of citric acid enhanced the sorption capacity and desorption hysteresis of BaP and TrCB on biochar mainly due to the strong sorption of citric acid on the biochar surface. Moreover, there were positive relations between the concentration dependent sorption capacity coefficient (K&lt;sub&gt;d&lt;/sub&gt;) values of BaP and TrCB and the citric acid concentration (P &amp;lt; 0.01). In contrast, peptone reduced the sorption capacity and increased the sorption reversibility because of the partition of BaP and TrCB in the peptone solution. L-PH at 50–200 mg/l also leads to a decrease in the sorption capacity and irreversibility attributed to solubilization, although the sorbed L-PH on the biochar surface can slightly increase the BaP and TrCB sorption. At the same concentration, peptone leads to a higher decrease in the BaP and TrCB sorption than L-PH. Also, negative correlations were found between the K&lt;sub&gt;d&lt;/sub&gt; values of BaP and TrCB, and the L-PH and peptone concentration (P &amp;lt; 0.05). Our results may help understand the different impacts of DOM on the transport and fate of halogenated aromatic hydrocarbons in aquatic environments polluted with biochars.

Characterization of the sorption behavior and mechanism of U(VI) on sericite by batch experiments and spectroscopic techniques

This study explored the sorption behavior and mechanism of U(VI) on sericite. The surface properties of sericite were investigated, and the effects of several environmental factors on U(VI) sorption to sericite were evaluated. The experimental data were simulated by different isotherm models and kinetic models. Humic acids affects U(VI) sorption obviously while silicate promotes the process in the whole pH range. The sorption–desorption hysteresis suggests an irreversible sorption process. Spectroscopic analyses indicate that the −OH groups have an important effect in the U(VI) sorption.

Effect of shear stress and carbon surface roughness on bioregeneration and performance of suspended versus attached biomass in metoprolol-loaded biological activated carbon systems

The bioregeneration of activated carbon (AC) in biological activated carbon (BAC) systems is limited by sorption-desorption hysteresis and transport between the adsorbent and biomass. In this study, we investigated these limitations and whether a biofilm covering the AC surface is required. Consequently, BAC reactors were operated at different shear stress and AC surface smoothness, since this may affect biofilm formation. The experiments were carried out in BAC and blank reactors treating synthetic wastewater containing the pharmaceutical metoprolol.After start-up, all reactors removed metoprolol completely; however, after 840h the removal dropped due to saturation of the AC. In the blank reactors, the removal dropped to 0% while in the BAC reactors removal recovered to >99%, due to increased biological activity. During the initial phase, the metoprolol was adsorbed, rather than biodegraded. At the end, the AC from the BAC reactors had higher pore volume and sorption capacity than from the blank reactors, showing that the AC had been bioregenerated.At high shear (G=25s−1), the rough AC granules (Ra=13μm) were covered with a 50–400μm thick biofilm and the total protein content of the biofilm was 2.6mg/gAC, while at lower shear (G=8.8s−1) the rough AC granules were only partly covered. The biofilm formation at lower shear (G=8.8s−1) on smooth AC granules (Ra=1.6μm) was negligible. However, due to the presence of suspended biomass the reactor performance or bioregeneration were not reduced. This showed that direct contact between the AC and biomass was not essential in mixed BAC systems. The microbial analyses of the suspended biomass and the biofilm on AC surface indicated that metoprolol was mainly biodegraded in suspension.

Clinoptilolite and palygorskite as sorbents of neutral emerging organic contaminants in treated wastewater: Sorption-desorption studies

Water reuse for aquifer recharge could be an important route for the introduction of emerging organic contaminants (EOCs) into the environment. The installation of a Horizontal Permeable Reactive Barrier (H-PRB) could constitute a tertiary treatment process to remove EOCs from treated domestic wastewater prior to recharge activities. The sorption-desorption behaviour of six neutral EOCs present in treated domestic wastewater (acetaminophen, caffeine, carbamazepine, cotinine, 4-acetamidoantipyrine (4-AAA) and 4-formylaminoantipyrine (4-FAA)) has been evaluated. Clinoptilolite and palygorskite have been studied as sorbents to be installed in the H-PRB. Batch tests were carried out using an EOC initial concentration ranging from 5 to 100 μg L−1. Apart from acetaminophen and caffeine, both materials showed a limited sorption capacity of neutral EOCs (Kd = 0.63–5.42 L kg−1). In general, the experimental results show that EOCs exhibit a higher sorption affinity for clinoptilolite than for palygorskite. With the exception of carbamazepine, the sorption of the compounds occurs mainly by interactions with mineral surfaces as indicated by the comparison of the partition coefficients into organic matter and into mineral surfaces. According to the molecular geometry of the compounds and the sorption sequences observed, it appears that the dimensions of the organic molecules play a key role in the sorption process. All the studied EOCs exhibit irreversible sorption and sorption-desorption hysteresis.

Sorption and desorption of selected non-steroidal anti-inflammatory drugs in an agricultural loam-textured soil

Non-steroidal, anti-inflammatory drugs (NSAIDs) are widely used pharmaceutical products with analgesic and anti-inflammatory effects that are consistently detected in municipal wastewater systems and in municipal biosolids. Land application of biosolids and irrigation with reclaimed wastewater introduces these compounds into agricultural environments, which is an emerging issue of concern for ecosystem health. In this study, the sorption-desorption behaviour of four commonly consumed NSAIDs, including naproxen (NPX), ibuprofen (IBU), ketoprofen (KTF), and diclofenac (DCF), was examined in a loam textured soil exposed to either an individual-compound or a mixture of the four NSAIDs. The proportion of NSAIDs adsorbed to the soil in the mixture-compound system was 72%, 55%, 50% and 45%, for diclofenac, naproxen, ketoprofen, and ibuprofen, respectively, and differed slightly from the individual compound adsorption. Diclofenac displayed strong sorption and low desorption in both the individual-compound and mixture-compound systems. Naproxen and ibuprofen exhibited significant differences between the adsorption isotherms of the individual-compound and mixture-compound systems. Results of this study highlight differences in the sorption behaviour of NSAIDs, when present as mixtures, possibly through multilayer bonding effects or complexation with cationic metals or organo-clays from the soil. Soil organic matter (SOM) may have played a role in determining some of the interactions between the compounds but other factors associated with the mixture-compound system, such as cation bridging or multilayer cooperative adsorption. Desorption data suggests that the mechanisms involved in binding NSAIDs to the soil surface are also influence by the presence of other compounds in a mixture. A reduction in desorption was observed for all four NSAIDs in the mixture-compound system relative to the individual-compound system, but were greatest for naproxen and ibuprofen. The sorption-desorption hysteresis increased for naproxen and ibuprofen in the mixture-compound system. This study suggests that cooperative adsorption plays a role in the interaction of NSAIDs when present as mixtures rather than as individual compounds.

Impacts of water level fluctuations on the physicochemical properties of black carbon and its phenanthrene adsorption-desorption behaviors

The stability of black carbon (BC) as a slow cycling pool in the global C cycle is an important property and is likely governed by environmental conditions. Although the importance of role of the water regime in BC degradation was confirmed, direct impacts of water level fluctuations (WLF) on BC degradation were absent. This study investigated the changes in the physicochemical properties of BC and the behaviors of adsorption-desorption due to long-term WLF. The results showed that BC in the zone of WLF in soil contained higher amounts of carbon and lower amounts of oxygen, leading to contain few carboxylic functional groups and indicating that the WLF imposed on the reservoirs have altered BC decomposition, causing a decrease in mineralization. Furthermore, BC exhibited higher adsorption capacities and an apparent sorption–desorption hysteresis. Our results suggested that WLF has an advantageous role in preventing BC decomposition. Such protection has significance for the stability of BC in soils as well as for its effects on global C cycling and HOCs sorption. Understanding the decomposition mechanisms, dynamics and environmental influences should provide new insights into BC degradation and cycling.

Distribution, Sorption and Desorption of Tylosin, Chlortetracycline and their Metabolites in Pig Manure

Effects of pH on sorption, desorption and hysteresis of chlortetracycline (CTCs), tylosin (TYL) and their metabolites have been studied in pig manure samples collected from different pig farms. Approximately 36% of the samples analyzed tested positive (concentration &gt; quantitative detection limit) for the antibiotics and metabolite residues. The degree of contamination depended upon the manure’s pH. The acidic TYL-positive manure samples contained TYL-A and TYL-B, while the basic TYL-positive samples contained TYL-A, TYL-ALD and TYL-D. The CTC-positive manure samples contained mostly CTC, ECTC and ACTC at acidic pH, but mostly CTC, ICTC, EICTC and EACTC at basic pH. For acidic and neutral manure samples, the logKDdes values were greater than the KDs values for TYL-B, TYL-A, TYL-ALD, CTC, ACTC, ECTC and EACTC, indicating sorption-desorption hysteresis. TYL-D, ICTC and EICTC did not exhibit sorption-desorption hysteresis. At acidic and neutral pH, the residues remained solid-bound, but an increase in pH decreased hysteresis, resulting in greater leaching and contamination of the environment. Thus, environmental pH may determine the antibiotics and metabolite leaching in freshwater at or away from the site of production. In addition, analysis of the parent antibiotic residues may not provide an accurate assessment of the environmental health.

Non-equilibrium passive sampling of hydrophobic organic contaminants in sediment pore-water: PCB exchange kinetics

This study investigates the isotropic exchange kinetics of PCBs for polyethylene (PE) passive samplers in quiescent sediment and develops a novel non-equilibrium passive sampling method using PE with multiple thicknesses. The release and uptake kinetics of PCBs in quiescent sediment are reproduced by a 1-D diffusion model using sediment diffusion parameters fitted with the data from actual measurements. From the sediment diffusion parameters observed for uptake and release kinetics, it is seen that the uptake kinetics are distinctly slower than the release kinetics, most likely because of the sorption-desorption hysteresis of PCBs in the study sediment. Despite the presence of the anisotropic PCB exchange kinetics, a performance reference compound (PRC)-based method, which is grounded on the assumption of isotropic exchange kinetics, estimated the freely dissolved aqueous concentrations (Cfree) of PCBs in sediment pore-water with less than a factor of two error for the study sediment. The novel method developed in this study using PE with multiple thicknesses also gives reasonable estimates of Cfree, demonstrating its potential as another option for non-equilibrium passive sampling for hydrophobic organic contaminants in sediment pore-water.

Study of the chloride transport in unsaturated concrete: Highlighting of electrical double layer, temperature and hysteresis effects

In this paper, we suggest a modelling of chloride ingress in unsaturated concretes. The originality of our model lies in its consideration of the electrical double layer (EDL), the temperature as well as the isotherm sorption-desorption hysteresis. In order to consider slag and fly ash effects, several concretes were considered and experimentally tested in tidal conditions. The chloride profile was simulated by a multispecies model. The simulations show that the chloride concentration increases with a negative EDL more than with a positive EDL and that this effect occurs mainly in the concrete containing slag where the overlapping is more important due to the pore size distribution. We also show that both temperature and hysteresis affect the chloride ingress at the surface more than in deeper layers of the concrete specimen most likely due to a drying effect. Finally, the results put forward a good agreement between measured and simulated chloride profiles mainly when the hysteresis is taken into account.

Effect of pH and prior phosphate application on the reaction of fluoride with soils from northern India

We investigated whether long‐term application of phosphate fertilizers, often as phosphate rock, had led to the accumulation of soluble fluoride in soil from tea estates in northern India. We also compared fluoride sorption and desorption with that of sulphate and of phosphate. We found no evidence of build‐up of soluble fluoride and ascribed this to the very heavy rainfall of about 3 m, nearly all of which occurs during a 4‐month monsoon period. Fluoride sorption was more sensitive than phosphate or sulphate sorption to the build‐up of a negative charge caused by long‐term application of phosphate fertilizers. We think that this occurred because the fluoride ion is smaller and the mean centre of charge is, therefore, located closer to the surface. When the negative charge is increased, it, therefore, experiences a greater decrease in potential than ions for which the mean centre of charge is further from the surface. When the phosphate status of the soil was low, fluoride showed sorption–desorption hysteresis. That is the desorption curve differed from the sorption curve. When the phosphate status of the soil was higher, this was not the case. Similar effects have been observed previously for both phosphate and sulphate. We had speculated that the fluoride ion, being smaller, might have been able to penetrate pores ‘blocked’ by a previous reaction with phosphate, but this did not happen. We conclude that characterizing the charge on sorbed ions, its location and especially the accumulation of a negative charge following a long‐term reaction with phosphate is important for understanding specific sorption on ions.Highlights We investigated the effects of long‐term application of phosphate rock on tea estates. We ascribed the lack of build‐up of soluble fluoride to monsoon rainfall of about 3 m. Fluoride sorption was more sensitive than phosphate or sulphate sorption to the build‐up of a negative charge caused by long‐term application of phosphate fertilizers. Characterizing the charge on sorbed ions, its location and the accumulation of a negative charge is important.