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Nitrate pollution is a global environmental problem, and mean nitrate levels have risen by an estimated 36% in global waterways since 1990. Tracing nitrate sources is important for water quality management, and nitrate isotopes (δ15N-NO3− and δ18O-NO3−) are commonly used for this purpose because of the different isotopic compositions of different sources. However, the impact of nitrate sorption on matrix and desorption from matrix on N and O isotopic composition of nitrate in liquid phase has not been well clarified. To explore the mechanism for the changes in nitrate concentration and isotopes in liquid phase during sorption and desorption, this study took a shale sample (enriched in clay minerals and commonly exposed in the Earth), conducted a series of laboratory experiments for nitrate sorption and desorption, and studied the impact of sorption and desorption on nitrate N and O isotopic composition in liquid phase. The results showed that the shale sample exhibited a rapid sorption and desorption rate for nitrate in the surface water samples, with the nitrate concentration in the solution decreasing from 14.3 mg/L to 4.1 mg/L within 5 min. The sorption data fit the Langmuir model better than that of the Freundlich model. The maximum possible sorption (Qmax) for the shale sample was estimated to be 46 μg/g. Preliminary laboratory experiments showed that changes in δ15N-NO3− values were not obvious, and changes in δ18O-NO3− values in liquid phase were minor during sorption and desorption of the shale sample, suggesting that nitrogen isotopic fractionation can be neglected, and the sorption of nitrate by the shale sample has a very limited impact on the distribution of nitrate isotopes in liquid phase. However, the impact of nitrate desorption on the nitrate isotopes in liquid phase depends on the isotopic composition of exchangeable nitrate in the solid phase, which may be related to antecedent water–rock interactions. This study provides important information for elucidating the evolution mechanism of nitrate and its isotopic compositions following sorption-desorption, and is conducive to revealing the nitrogen cycle law in the environment. [ABSTRACT FROM AUTHOR]

We investigate the diffusion phenomenon of particles in the vicinity of a spherical colloidal particle where particles may be adsorbed/desorbed and react on the surface of the colloidal particle. The mathematical model comprises a generalized diffusion equation to govern bulk dynamics and kinetic equations which can describe non-Debye relaxations and is used for the colloid's surface. For the reaction processes, we also consider the presence of convolution kernels, which offer the flexibility of describing a single process or process with intermediate reactions before forming the final species. Our analysis focuses on analytical and numerical calculations to obtain the particles' behavior on the colloidal particle's surface and to determine how it affects the diffusion of particles around it. The solutions obtained show various behaviors that can be connected to anomalous diffusion phenomena and may be used to describe the ever-richer science of colloidal particles better. [ABSTRACT FROM AUTHOR]

We determined the distribution, fate, and health hazards of dimethenamid-P, metazachlor, and pyroxasulfone, the effective pre-emergence herbicides widely used both in urban and agricultural settings globally. The rate-determining phase of sorption kinetics of these herbicides in five soils followed a pseudo-second-order model. Freundlich isotherm model indicated that the herbicides primarily partition into heterogeneous surface sites on clay minerals and organic matter (OM) and diffuse into soil micropores. Principal component analysis revealed that soil OM (R2, 0.47), sand (R2, 0.56), and Al oxides (R2, 0.33) positively correlated with the herbicide distribution coefficient (Kd), whereas clay (R2, ‒ 0.43), silt (R2, ‒ 0.51), Fe oxides (R2, ‒ 0.02), alkaline pH (R2, ‒ 0.57), and EC (R2, ‒ 0.03) showed a negative correlation with the Kd values. Decomposed OM rich in C=O and C–H functional groups enhanced herbicide sorption, while undecomposed/partially-decomposed OM facilitated desorption process. Also, the absence of hysteresis (H, 0.27‒0.88) indicated the enhanced propensity of herbicide desorption in soils. Leachability index (LIX, < 0.02–0.64) and groundwater ubiquity score (GUS, 0.02‒3.59) for the soils suggested low to moderate leaching potential of the herbicides to waterbodies, indicating their impact on water quality, nontarget organisms, and food safety. Hazard quotient and hazard index data for human adults and adolescents suggested that exposure to soils contaminated with herbicides via dermal contact, ingestion, and inhalation poses minimal to no non-carcinogenic risks. These insights can assist farmers in judicious use of herbicides and help the concerned regulatory authorities in monitoring the safety of human and environmental health. [ABSTRACT FROM AUTHOR]

Purpose: Iron- and aluminum-dominated red-lateritic soils suffer from poor phosphorus (P) use efficiency due to the fixation of added P. Methods: The present investigation was conducted to study P sorption–desorption kinetics and to minimize the hysteresis indices of three acidic red-lateritic soils of West Bengal by amending with lime and/or organics like vermicompost or biochar either singly or in combination @ 10% (w/w). Results: Except for the rate constant for slow sorption (k2), the application of lime or organics in general significantly decreased all the kinetic parameters over their respective control during sorption but increased during the desorption process. About 75% of P adsorption occurred within the first 2-h period of investigation. In limed soils, more than 70% of P adsorption occurred by fast sites. The highest rate constant values (k1) for fast sorption sites were associated with the treatment receiving biochar. Irrespective of soil and treatment, more than 50% P desorption occurred from fast desorption sites. In general, the highest initial desorption rate was observed in the treatment receiving biochar either alone or in combination with vermicompost and with or without lime. In all the cases, the highest hysteresis index (> 82%) was observed in the control treatment, indicating the extent sorbed P remained in a non-diffusible form in non-amended soil. Conclusion: Application of organics in the form of biochar with the recommended dose of lime caused a maximum reduction in the hysteresis index value and thus can be regarded as the best P management strategy for acidic red and lateritic soils. [ABSTRACT FROM AUTHOR]

We investigate the diffusion phenomenon of particles in the vicinity of a spherical colloidal particle where particles may be adsorbed/desorbed and react on the surface of the colloidal particle. The mathematical model comprises a generalized diffusion equation to govern bulk dynamics and kinetic equations which can describe non-Debye relaxations and is used for the colloid’s surface. For the reaction processes, we also consider the presence of convolution kernels, which offer the flexibility of describing a single process or process with intermediate reactions before forming the final species. Our analysis focuses on analytical and numerical calculations to obtain the particles’ behavior on the colloidal particle’s surface and to determine how it affects the diffusion of particles around it. The solutions obtained show various behaviors that can be connected to anomalous diffusion phenomena and may be used to describe the ever-richer science of colloidal particles better.

Analysis of available monitoring data sets on concentrations of accidentally derived dissolved radiocesium in water bodies is indicative of two major physicochemical mechanisms responsible for their seasonal variations in water bodies in the course of the year: temperature dependence of radiocesium desorption from suspended material and ion-exchange remobilization of radiocesium by ammonium cations formed during decomposition of organic matter in anoxic conditions. An equation describing seasonal variations in concentration of dissolved radiocesium in water bodies has been derived accounting for two factors: water temperature, and combined concentration of key competing cations. [ABSTRACT FROM AUTHOR]

Composites based on silicon dioxide xerogels, containing glycerin and nicotine, were prepared by means of tetraethoxysilane hydrolysis using the single-stage synthesis and two-stage sorption procedures. In the single-stage synthesis, glycerin sorption 3 : 1 by weight with respect to the sorbent was achieved. The kinetics of the release (desorption) of nicotine from an aerosol mixture with glycols has been studied. The synthesized sorbent is promising for use in aerosol generating systems, and also as carriers and means of delivery of biologically active compounds and medicines. [ABSTRACT FROM AUTHOR]

Non-ionic herbicides, such as propisochlor, are more easily retained in organic soil fractions. The presence of straw in tropical cropping systems can affect herbicide transposition to the underlying seed banks and their environmental behavior. The aim of this study was to evaluate propisochlor soil retention in the presence of soybean and sugarcane straw (0, 5 and 10 t ha−1) through radiometric techniques. Most of the applied 14C-propisochlor was retained in the soil profile (18.2–39.4%) following an extreme rainfall simulation in the presence of straw. Decreased herbicide leaching was observed in the presence of sugarcane and soybean straw (0.7–0.5%), compared with soil without straw (1.8%). Hysteresis values ranged from 0.8 to 1.0, indicating that propisochlor sorption was reversible allowing for soil seed bank effects, as well as environmental dissipation. These findings indicate that propisochlor can overcome straw barriers, although representing low groundwater contamination risks. Because of this, reduced environmental impacts following the application of this herbicide are noted for tropical cropping systems containing straw mulch. [ABSTRACT FROM AUTHOR]

Pre-emergent herbicides are applied directly in the soil or over the straw in no-till systems and can be retained, reducing the product's availability. The current study characterizes the retention of diclosulam and diuron in forage turnip (FT), buckwheat (BW), and black oat (BO) straws. Radiometric techniques evaluated the sorption–desorption and leaching processes. Spectroscopic and microscopic methods characterized chemical and morphological alterations in the straw. Sorption rates (Kf) of diclosulam and diuron followed the order BO > BW > FT. Irreversible sorption (hysteresis < 0.7) occurs to diclosulam applied to BO straw. The BO straw showed porous structures, indicating physical entrapment of the herbicides. Straw fragments (<1 mm) increased the sorption of herbicides. The increase in straw amount (2.5 to 5 t ha−1) reduced herbicide leaching to 18.8%. Interactions between chemical groups (C-Cl, C-F, and C-N) from herbicides with straw characterize a chemical barrier. The present research suggests that entrapment and chemical interaction are involved in the sorption–desorption process of herbicides, such as diclosulam and diuron, in the straw matrix, directly interfering with their availability in the environment. This process can reduce the herbicide environmental risk but can decrease weed control efficiency. [ABSTRACT FROM AUTHOR]

The relevance of the research is determined by the current active exploitation of hydrothermal systems as an alternative energy source using renewable energy resources, for the extraction of rare metals, the development of ecological, health-improving and extreme tourism. Identification of the types of hydrothermal fields, geological conditions and patterns of their formation and modern activity are necessary for a correct assessment of their practical use. Daginsky thermomineral field, the hydrogeochemical features of which not yet well understood, is known in the north of Sakhalin Island. The aim of the work is to obtain new data on the physical-chemical parameters of thermomineral waters of the Daginsky field and to conduct a comparative analysis of the hydrogeochemical characteristics of its different sites (North, Central, South), and also to propose a model explaining the origin and patterns of formation of the chemical composition of the research waters. Objects: thermomineral waters of the Daginsky field (Sakhalin Island). Methods. Chemical analytical researches of the thermomineral waters were carried out at the Center for the Collective Use of the Institute of Marine Geology and Geophysics Far Eastern Branch Russian Academy of Sciences. The electrical conductivity of the research waters was determined by conductometric method, pH was determined by the potentiometric method. The surface temperatures of the waters in the thermomineral springs were measured using a digital thermometer. The concentrations of Na+, K+, Ca2+, Mg2+, Li+, Cl–, SO42–, NO2–, NO3–, Br– were determined by the method of ion chromatography; concentrations of HCO3– and CO32– were determined by the titrimetric method; content of the boron and silicon were determined by the spectrophotometric method. The content of organic and inorganic carbon, as well as total nitrogen was determined by high-temperature catalytic oxidation. Reservoir temperatures of thermomineral waters were calculated using hydrochemical geothermometers – K-Mg, Na-K, Mg-Li, Na-Li, SiO2. Results. The article presents the results of modern hydrogeochemical researches of the Daginsky field, conducted from 2014 to 2019. It has been established that spatial hydrogeochemical heterogeneity is observed on the territory the field. This heterogeneity is expressed in the differences in the physical-chemical characteristics of thermomineral waters (the surface temperatures, the value of total dissolved solids, and the concentration of main components of the water-salt composition) in its different sites (Northern, Central and Southern). The waters in the three sites have the same Cl-Na composition, but in the Southern and Central sites they have higher concentrations of Na+, HCO3–, Si, and in the Northern – K+, Ca2+, Mg2+, SO42–, B. The waters of the springs of the Northern site are also characterized by higher salinity (2–8 times) and lower values of surface temperatures (mainly by 10–15 °С) compared to the waters of the springs of the Southern and Central sites. Based on the obtained hydrogeochemical data, a model for the formation of thermomineral waters of the Daginsky field is proposed, which includes three «end members». According to this model, the formation of the research waters occurs as a result of mixing of mature brackish groundwaters of the North Sakhalin artesian basin, which are presumably developed in the lower part of the Nutovskaya suite, with modern fresh meteoric waters during their infiltration in the feeding area of the artesian basin, as well as salty seawaters of the Nyisky Bay in the area of discharge of thermomineral waters. The share of fresh infiltration waters of meteoric genesis in thermomineral waters can range from 15 to 80 %, the share of seawaters can be up to 30 %. The processes in the «water–rock–gas–organic matter» system have a significant impact on the chemical composition of the research waters: sulfate reduction, cation exchange and sorption-desorption. Reservoir temperatures for the Daginsky field are predominantly 60–100 °С, which corresponds to a depth of about 2–3 km.

The HEC-Adip-Na sorbent has been synthesized by the esterification reaction between hydroxyethylcellulose (HEC) and adipic anhydride followed by saponification with NaHCO3 for the removal of Cr(III) and Ni(II) from aqueous solution. Surface charge on the sorbent was evaluated by zero-point charge pH analysis and was found to be 5.0 which indicated the presence of negative charge on its surface. The sorption experiments were conducted in batches and found that the uptake of targeted metal ions was predominantly dependent on pH, sorbent dose, metal ions concentration, contact time, and temperature. The sorption isotherm indicated that sorption has occurred through the exchange of ions via chemisorption and maximum sorption capacity (Qmax) was 156 mg/g for Cr(III) and 79 mg/g for Ni(II) according to Langmuir isotherm. Uptakekinetics revealed that the sorption rate was too rapid and achieved equilibrium within the first 30 min. Thermodynamic studies suggested the spontaneous and exothermic nature of the sorption. Moreover, HEC-Adip-Na was appeared as generable. Conclusively, HEC-Adip-Na is a material of superb choice for the purification of water. [ABSTRACT FROM AUTHOR]

The use of herbicide mixtures is widely adopted by farmers in agriculture worldwide. Glyphosate and ametryn are herbicides commonly applied in tank mixtures, increasing the spectrum of weed control in sugarcane crops. After application, herbicides can reach the soil layer, which is susceptible to retention, transport, and degradation processes. Herbicide interactions in mixtures may affect their bioavailability and persistence in soil, leading to different behavior in the environment compared to when applied alone. This study evaluated the sorption-desorption and transformation of 14C-glyphosate and 14C-ametryn in soil when applied alone or in a tank mixture. The sorption of 14C-ametryn in soil was increased by 25% when mixed with glyphosate (14C-ametryn + glyphosate). This increase in sorption was not evident for 14C-glyphosate when mixed with ametryn (14C-glyphosate + ametryn). The amount desorbed of 14C-ametryn (20%) applied alone was higher than in a mixture (10%). Both herbicide's mineralization half-live time (MT 50) was influenced when applied in mixtures. 14C-glyphosate applied alone showed lower MT 50 (55 days) compared to 14C-glyphosate + ametryn (119 days). 14C-ametryn also showed lower MT 50 when applied alone than when applied with glyphosate (>120 days in both cases). These results suggest that the presence of ametryn in mixture with glyphosate decreases the desorption and mineralization of both herbicides, potentially affecting their bioavailability for weed root absorption and degradation in environment. • Herbicides are commonly combined in herbicide mixtures for weed control in sugarcane crops. • Radiometric techniques were employed to study herbicide behavior in soil. • Soil retention of both herbicides was increased by mixing ametryn with glyphosate. • Herbicide bioavailability in the soil affects weed control and degradation. [ABSTRACT FROM AUTHOR]

Nanoformulations have been used to improve the delivery of fertilizers, pesticides, and growth regulators, with a focus on more sustainable agriculture. Nanoherbicide research has focused on efficiency gains through targeted delivery and environmental risk reduction. However, research on the behavior and safety of the application of these formulations in cropping systems is still limited. Organic matter contained in cropping systems can change the dynamics of herbicide–soil interactions in the presence of nanoformulations. The aim of this study was to use classical protocols from regulatory studies to understand the retention and mobility dynamics of a metribuzin nanoformulation, compared to a conventional formulation. We used different soil systems and soil with added fresh organic material. The batch method was used for sorption–desorption studies and soil thin layer chromatography for mobility studies, both by radiometric techniques. Sorption parameters for both formulations showed that retention is a reversible process in all soil systems (H~1.0). In deep soil with added fresh organic material, nanoformulation was more sorbed (14.61 ± 1.41%) than commercial formulation (9.72 ± 1.81%) (p < 0.05). However, even with the presence of straw as a physical barrier, metribuzin in nano and conventional formulations was mobile in the soil, indicating that the straw can act as a barrier to reduce herbicide mobility but is not impeditive to herbicide availability in the soil. Our results suggest that environmental safety depends on organic material maintenance in the soil system. The availability can be essential for weed control, associated with nanoformulation efficiency, in relation to the conventional formulation. [ABSTRACT FROM AUTHOR]

Pre-emergent herbicides are applied directly in the soil or over the straw in no-till systems and can be retained, reducing the product’s availability. The current study characterizes the retention of diclosulam and diuron in forage turnip (FT), buckwheat (BW), and black oat (BO) straws. Radiometric techniques evaluated the sorption–desorption and leaching processes. Spectroscopic and microscopic methods characterized chemical and morphological alterations in the straw. Sorption rates (Kf) of diclosulam and diuron followed the order BO > BW > FT. Irreversible sorption (hysteresis < 0.7) occurs to diclosulam applied to BO straw. The BO straw showed porous structures, indicating physical entrapment of the herbicides. Straw fragments (−1) reduced herbicide leaching to 18.8%. Interactions between chemical groups (C-Cl, C-F, and C-N) from herbicides with straw characterize a chemical barrier. The present research suggests that entrapment and chemical interaction are involved in the sorption–desorption process of herbicides, such as diclosulam and diuron, in the straw matrix, directly interfering with their availability in the environment. This process can reduce the herbicide environmental risk but can decrease weed control efficiency.

Pydiflumetofen, a fungicide of the class of succinate dehydrogenase inhibitors, can disrupt energy metabolism by inhibiting the synthesis of succinate dehydrogenase, thus effectively inhibiting pathogenic fungal growth and related yield losses.We studied the adsorption and desorption behaviors and interaction mechanisms of pydiflumetofen in eight different arable soils by the infrared spectroscopy and batch equilibrium method. Pydiflumetofen adsorption and desorption property of soils conformed with the Freundlich isotherm model and the values for the adsorption capacity KF-ads were in the range of 14.592–102.610. The adsorption constants (KF-ads) exhibited a significantly positive and linear correlation (p

This novel study investigated the behavior and fate of chlorothalonil in terms of kinetics, sorption‒desorption and leaching potential in urban landscape soils using batch experiments. The pseudo-second-order model well described the sorption kinetics of chlorothalonil in urban soils. Consequently, chlorothalonil was partitioned into heterogeneous surfaces of soil following the Freundlich isotherm model. According to PCA, soil organic matter (OM), silt, clay, and oxides of Al and Fe exhibited a significant positive correlation (P < 0.05) with chlorothalonil Kd (P < 0.05), while sand content and soil pH showed a negative correlation at P < 0.05. In soils, decreased sorption of chlorothalonil was also due to the presence of undecomposed or partly decomposed OM, whereas increased sorption could be attributed to the combined effect of OM with C = O and C–H groups, silt, clay, Al and Fe oxides and hydrophobicity of the fungicide. Also, HI, GUS, LIX and Kd of four among nine urban soils indicated that chlorothalonil has a great potential for leaching into the groundwater from the soil surface, posing an unintended threat to non-target biota and food safety. Therefore, utmost care must be taken while applying chlorothalonil in urban landscapes, particularly on impervious surfaces, to minimize the impact on the ecosystem. [ABSTRACT FROM AUTHOR]

Nanoformulations have been used to improve the delivery of fertilizers, pesticides, and growth regulators, with a focus on more sustainable agriculture. Nanoherbicide research has focused on efficiency gains through targeted delivery and environmental risk reduction. However, research on the behavior and safety of the application of these formulations in cropping systems is still limited. Organic matter contained in cropping systems can change the dynamics of herbicide–soil interactions in the presence of nanoformulations. The aim of this study was to use classical protocols from regulatory studies to understand the retention and mobility dynamics of a metribuzin nanoformulation, compared to a conventional formulation. We used different soil systems and soil with added fresh organic material. The batch method was used for sorption–desorption studies and soil thin layer chromatography for mobility studies, both by radiometric techniques. Sorption parameters for both formulations showed that retention is a reversible process in all soil systems (H~1.0). In deep soil with added fresh organic material, nanoformulation was more sorbed (14.61 ± 1.41%) than commercial formulation (9.72 ± 1.81%) (p < 0.05). However, even with the presence of straw as a physical barrier, metribuzin in nano and conventional formulations was mobile in the soil, indicating that the straw can act as a barrier to reduce herbicide mobility but is not impeditive to herbicide availability in the soil. Our results suggest that environmental safety depends on organic material maintenance in the soil system. The availability can be essential for weed control, associated with nanoformulation efficiency, in relation to the conventional formulation.

Characteristics of phenanthrene and pyrene's sorption and desorption on two local soils in solutions of simulated groundwater, simulated lung fluid, and simulated saliva were studied with batch equilibrium experiments to understand the fate of PAHs in the karst region of southwestern China and to assess the environmental exposure and the health risk of PAHs. The results showed that the sorption and desorption isotherms of phenanthrene and pyrene on two target soils in the three solution systems could be adequately described by the Freundlich model, while the fitted isotherm parameters for the simulated groundwater solution distinguished notably from those for the simulated body fluid solutions. For the sorption experiments, in the simulated groundwater, the n values were 0.722 and 0.672 for phenanthrene and were 0.724 and 0.663 for pyrene, respectively, on the yellow soil and the limestone soil; The log KF values were 3.118 and 3.323 for phenanthrene and were 3.648 and 3.846 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.622 to 0.836 and from 0.590 to 0.865, respectively, and the log KF values of phenanthrene and pyrene ranged from 2.845 to 3.327 and from 3.344 to 3.779, respectively. For the desorption experiments, in the simulated groundwater, the n values were 0.662 and 0.744 for phenanthrene and were 0.702 and 0.647 for pyrene, respectively, on the yellow soil and the limestone soil. The log KF values were 3.666 and 3.686 for phenanthrene and were 4.128 and 4.225 for pyrene, respectively, on the yellow soil and the limestone soil. In the simulated body fluids, the n values for phenanthrene and pyrene ranged from 0.612 to 0.668 and from 0.631 to 0.819, respectively, and the log KF values of phenanthrene and pyrene ranged from 3.134 to 3.407 and from 3.533 to 3.839, respectively. The limestone soil had relatively higher log KF values but lower KOC values compared to those of the yellow soil, indicated that the nature of sorbent soils played the dominant role in sorption and desorption behaviors of PAHs. The experimental results showed a remarkable differences in sorption and desorption behaviors of PAHs in simulated body fluids and groundwater. The nonlinearities of measured isotherms and the measured sorption capacities of soils in simulated body fluids were significantly lower than corresponding those in the simulated groundwater, and HI values for simulated body fluids systems were significantly smaller than corresponding those for the simulated groundwater systems. The results underscore cautions in assessing environmental exposure and health risks of PAHs based on their sorption–desorption data in simulated groundwater as this is traditionally done. [ABSTRACT FROM AUTHOR]

• Preparation and characterization of sulfur-impregnated attapulgite (ATPS). • Sorption/desorption of Hg2+ ions onto/from ATPS. • Low pH favours the adsorption of Hg2+ onto the ATPS surface. • Coexisting anions have diverse controls on Hg2+adsorption capacity. Present study proposed a sorption and desorption approach of aqueous mercury ion (Hg2+) on sulfur impregnated attapulgite (ATPS) adsorbent. Morphological characterization of natural and impregnated ATP confirmed the mesoporous nature of ATPS-adsorbents. The presence of various types of functional groups on the surface of ATPS was confirmed by using the zeta-potential measurement, X-ray fluorescence (XRF), and FT-IR analysis. Batch adsorption tests were carried out to detect the optimum condition of temperature for sulfur impregnation, and the results illustrated that the best adsorbent (ATPS-500) produced via the impregnation at 500 °C, with the highest equilibrium uptake of Hg2+ at initial pH 7. Different parameters like solution pH o , initial concentration of mercury (C o), temperature (T), contact time (t) and the effect of co-existing ions were optimized. Optimum pH and equilibrium contact time at the optimum dose of adsorbent (m) = 0.02 g in 50 mL and C o = 2.0 mg L −1 were found to be pH~5 and 24 h at T = 313 K for ATPS-500.The best representation of adsorption kinetic was followed by the pseudo-first order kinetic model. The adsorption of Hg2+ions onto ATPS-500 was found to be endothermic. The heat of adsorption and changes in the entropy of Hg2+ions sorption on ATPS-500 were determined as 10.35 kJ mol−1 and 0.16 kJ mol−1 K −1, respectively. Thermal regeneration represented that ATPS-500 was used for five desorption–sorption cycles with excellent efficiency of Hg2+ in each cycle. [Display omitted] [ABSTRACT FROM AUTHOR]

We study the influence of alloying with chromium on the structure and phase composition of the Ti47.5Zr30Mn22.5 eutectic alloy and its hydrogen sorption-desorption. It is shown that the addition of chromium to the alloy changes the type of crystal lattice of the Laves phase from the C14 hexagonal phase to the C15 cubic, which does not affect the hydrogen-sorption properties. It is demonstrated that hydrides obtained on the basis of the C14 and C15 Laves phases have different thermal stabilities. [ABSTRACT FROM AUTHOR]

We studied the adsorption-desorption of Cu, Mn, Pb and Zn in Maipo river basin, one of the most perturbed rivers in Chile, and thus determined its tolerance to the addition of these metals into the sediments and the possibility of transferring the metals from the sediments to the water column. Sediments were sampled from six sites from the river basin and characterized by their pH, electrical conductivity, organic carbon, total organic carbon, water soluble phosphorus and texture. Batch sorption and kinetics experiments were conducted to obtain the retained amounts onto the sediment samples. The initial concentration of trace elements in the sediment was quantified by AAS. The metals were present in most of the sites. Sorption parameters such as Kd and Koc were determined. Metals were adsorbed in the sediment, with Mn showing the lowest affinity, Kd and Koc values and Freundlich constant (nf) support these results. Desorption less than 1% were observed for Cu, while Pb and Zn ranged from 0.6% to 6.8% and those for Mn ranged from 0% to 17.6% across sites. The tolerance of the Maipo River to metal adsorption in sediments was as follows: Pb Cu Zn Mn. Desorption analysis showed that both Zn and Mn could be transferred from the sediment to the water column. The strongest correlation occurs between the pH and Kd-Pb, indicating that at higher pH values, the Pb adsorption was unfavorable, while the correlation was moderate for Cu, Mn and Zn. On the other hand, there are positive correlations between pairs of metals such as Mn-Cu, Zn-Cu, and Zn-Mn, indicating the competition of these metals for the adsorbent sites. The high concentration of Mn found in the sediment and the possibility of being transferred to the water column, due to its easy of desorption, suggest concern due to its potential risk to aquatic biota. [ABSTRACT FROM AUTHOR]

Purpose: Huge amounts of radiocesium, radiostrontium, and fission products were released into the atmosphere during the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident. Therefore, it is necessary to determine the distribution coefficient of Cs and Sr in the soil-water system around FDNPP from the viewpoint of their migration. Materials and methods: The determination of sorption coefficient Kd(S) as well as desorption coefficient Kd(D) for Cs and Sr has been carried out in the present study using the laboratory batch method. In this experiment, stable Cs and Sr were used for sorption on contaminated Fukushima soil samples and groundwater collected in proximity to the soil sample sites. Different soil parameters were measured to understand their effect on the sorption and desorption processes. Desorption experiments were carried out on some selected contaminated soil samples. Results and discussion: Kd(S)-Cs and Kd(S)-Sr varied from 65 to 2100 L/kg and 15 to 130 L/kg, respectively. Kd(D)-Cs and Kd(D)-Sr varied between 75–2500 and 10–120 L/kg, respectively. High values of sorption coefficients for Cs indicate sorption capacity of soils for Cs is more than Sr. For Cs, Kd(D) was higher than Kd(S) whereas for Sr, Kd(S) was either equal to or higher than Kd(D). A moderate Pearson's correlation of (Kd) Cs and Sr with exchangeable cations (Al, K, Mg, and Na) supported that ion exchange sorption mechanism is significant. There is enhanced Cs sorption compared to Sr due to the presence of biotite, kaolinite and smectite minerals resulting in high mobility of Sr in the Fukushima environment. Conclusions: We concluded retention capacity of Fukushima soils for Cs is moderately stronger than Sr, which supports Sr is more mobile in the environment. [ABSTRACT FROM AUTHOR]

In Hawaii, past use of arsenical pesticides has left elevated levels of arsenic (As) in some soils. Sorption isotherms of an Andosol and an Acrisol showed that the former required 1100 mg/kg, and the latter 300 mg/kg of added As to maintain 0.20 mg As/L in solution, the maximum allowable As level in streams/rivers in Hawaii. Greenhouse experiments were conducted on an Andosol (315 mg/kg total As), which was amended with 0, 5 g/kg compost, 5 g Fe/kg as amorphous Fe(OH)3, or 250 mg P/kg as Ca(H2PO4)2, and on a low-As (15 mg/kg) Acrisol, which was spiked with 0, 150 or 300 mg As/kg as Na2HAsO4.7 H2O. Brake fern (Pteris vittata L.) was used as the test plant. Arsenic concentration in the fern fronds averaged 355 mg/kg in the Andosol, and 2610 and 1270 mg/kg (from consecutive plantings, 2 and 12 months after As addition, respectively) in the Acrisol spiked with 300 mg/kg of As. Chemical reactions, as suggested by sequential extractions, likely controlled the availability and uptake of soil As. Mehlich-3 extraction could be used to identify As-contaminated soils and potential phytoremediation as it correlated well with bioaccessible As and with As in fern fronds.

Partitioning of metals between the soil solid phase and the solution is an important topic in environmental sciences because it determines the metal transfers to aquifers and biological organisms. Complexation of metals with ligands in the soil solution strongly influences the sorption/desorption (SD) of metals, in particular that of the free ion. Because the latter is the metal species principally absorbed by biological organisms, the bioavailability of a metal is better reflected by the soil-solution distribution coefficients of the free ion as compared to that of the total metal (sum of the free ion and of the complexes). The present work proposes a modeling approach to determine the distribution coefficients for the free ion and for the metal complexes from SD experiments. The method does not require estimating the mobile pool of the metal sorbed onto the solid phase by any chemical extraction as the modeling relies on the variation of the sorbed metal, which is experimentally exactly estimated from the variation of the amount of metal in solution during the SD experiment. Tested for cadmium (Cd), the model reproduced very well the SD curves observed for the total metal. For any solution:soil ratio including that at field soil moisture, the model gives estimates of important variables including the distribution coefficient for the free ion, the complex, the ligands and the total metal, the concentration of these species in the soil solution and onto the solid phase. The model can be applied as long as the range of the concentration investigated allows to assume a linear sorption of the metal. [ABSTRACT FROM AUTHOR]

Abstract Cadmium and Ni chemical reactivities in soils are highly dependent on various soil properties. In this study, batch sorption-desorption experiments were carried out to quantify the potential of different soils to retain and release of Cd and Ni. Results revealed that several soil characteristics control Cd and Ni sorption-desorption where, the mutual effects of pH, CEC, soil carbon, clay, silt, and CaCO 3 contents govern their behavior in soils. Sorption of Cd and Ni was found to be concentration dependent. The studied soils exhibited higher Ni sorption capacities than Cd (Ni- S max > Cd- S max). Statistical relationships between soil properties and Langmuir parameters were achieved by stepwise regression analysis. Simulations of Cd and Ni kinetic reactions were performed using a multireaction model (MRM). Cadmium and Ni exhibited sorption-desorption kinetics and hysteresis in the soils and were well simulated by MRM. The highest reversible reaction rate and low hysteresis for Cd and Ni were associated with the low soil sorption capacities. Whereas, a strong nonsingularity of sorption-desorption isotherms was observed for soils with high CaCO 3 contents. Highlights • Kinetic of Cd and Ni sorption-desorption in different soils were investigated. • Soils with low Cd and Ni sorption depicted little hysteresis. • All soils exhibited higher affinity to sorb Ni than Cd. • Soils having CaCO 3 exhibited nonsingularity and limited release. • Cd and Ni sorption-desorption were well fitted using a multireaction model. [ABSTRACT FROM AUTHOR]

A study was carried out to remove/recover ammonium (NH 4 +) from residual effluents in tertiary treatment by sorption/desorption processes onto a natural clinoptilolite zeolite (NZ) in batch and fixed-bed column systems. Batch equilibrium and kinetic experiments were performed at different loading of NZ and contact time intervals, respectively. The results obtained in batch were fitted by the Freundlich and Langmuir isotherms and mass action law model. The Freundlich isotherm showed better agreement with experimental data than the Langmuir model. The isotherm studies revealed a type III with a maximum capacity of 2.8 ± 0.2 mg/g at 40 mgNH 4 +/L. Moreover, the data from the fixed-bed column studies was well fitted by a mass transfer model, considering the intraparticle diffusion resistance given by the linear driving force model (LDF). Finally, the capacity of NH 4 + recovery of activated zeolite was measured experimentally and by a robust dynamic desorption model. The column desorption results demonstrated that higher recoveries (92–99.99%) were observed when increasing the flow rate to 0.12 mL/min. The uniqueness of this study is its capability to simulate both the sorption and desorption processes of the naturally derived sorbent for the effective removal and recovery of NH 4 +-N from real wastewater stream. [Display omitted] [ABSTRACT FROM AUTHOR]

Nowadays, developing a multifunctional platform with the ability to detect and remove heavy metal ions remains a huge challenge in the field of environmental pollution control. Herein, L -cysteine functionalized novel polystyrene microspheres with special fluorescent scattering effect are constructed by simple one-step reaction. This multifunctional platform is very attractive in terms of mercury ion removal and detection. To achieve the purpose of removal, polystyrene- L -cysteine (PS-LCYS) have a lot of active sites (-SH/-NH 2 /-OH), which can coordinate with Hg2+ to form new complexes (PS-LCYS-Hg2+). Interestingly, fluorescent scattering was enhanced with the addition of Hg2+, indicating PS-LCYS can be used to detect Hg2+. As expected, this strategy achieved a low detection limit of 85 nM in a wide range of 50–1700 μM. At the same time, target-induced aggregation rendered the effective embedding and encapsulation of Hg2+ by PS-LCYS, showing good absorption of 92.69–94.32% within 10 min. And the maximum Hg2+ absorption capacity of PS-LCYS was estimated to be 1314 mg/g. What's more, this platform can be regenerated and reused with the treatment of EDTA, achieving 88.54% removal rate after 7 circulations. This multifunctional platform not only realized high sensitivity detection, but also can absorb a large number of mercury ions in the water environment in a short time. After repeated use, PS-LCYS still maintained good detection and adsorption performance. Therefore, the platform had the potential to solve the problem of heavy metal ion pollution. • This new strategy have the dual function of detection and removal Hg2 +. • PS-LCYS achieved LOD of 85 nM and obtained removal of 92.69–94.32% within 10 min. • This multifunctional platform achieved 88.54% removal rate after 7 circulations. • The maximum sorption capacity of PS-LCYS was estimated to be 1314 mg/g. [ABSTRACT FROM AUTHOR]

Activated carbon (AC) from palm empty fruit bunches has been prepared, and this material was then used to adsorb Cr(VI) from a solution. Characterization of the AC was conducted by detection of its functional groups, determination of total volatile compounds (VC) content and its iodine number. Study on sorption-desorption kinetics was conducted by comparing results of evaluations of several models with proposed reversible second order model using the data produced in this work. Results of the works showed that the AC had similar characters compared with the AC produced by previous researchers. Application of the kinetics models on sorption Cr(VI) onto the AC showed that nearly all of the models gave a good linearity. However, only the proposed model had a good relation with Langmuir isotherm, with respectively sorption (ks) and desorption (kd) constants were 5.75 x 10-4 L.mg‑1.min-1 and 2.20 x 10-3 min-1; maximum sorption capacity, qm = 20.00 mg.g-1; and equilibrium constant, K from kinetics experiment (0.261 L.mg-1) was comparable with the result from the isotherm experiment (0.269 L.mg-1). Hence, using this model, kinetics and Langmuir parameters can probably be determined from a single kinetics data experiment.

Abstract Contamination of groundwater with toxic arsenic (As) has become an emerging health and environmental problem around the world, which has seen significant attention amongst the scientists for development of new sorbents to remediate As-contaminated water. Here, we explored the arsenate (As(V)) and arsenite (As(III)) sorption to natural water melon rind (WMR), xanthated WMR and citric acid-modified WMR in aqueous solutions, and determined potential of the most potent sorbent for As removal in groundwater. Xanthated WMR (X-WMR) showed relatively higher As(V) and As(III) removal than the citric acid modified WMR (CA-WMR) and natural WMR. The maximum As(III) (99%) and As(V) (98%) removal was obtained at pH 8.2 and 4.6, respectively, by X-WMR at 4 mg L−1 initial As(V) and As(III) concentrations and sorbent dose of 1 g L−1. Langmuir isotherm model best fitted (R 2 of up to 0.96) the data both for As(III) and As(V) sorption to X-WMR. Sorption kinetics of As(V) and As(III) was well described (R 2 of up to 0.99) by the pseudo second-order model on surface of the X-WMR. Thermodynamic investigations revealed that As(V) and As(III) sorption was endothermic and spontaneous. The FTIR spectroscopy depicted the presence of different surface function groups (OH, COOH, S-bearing (C=S, S=O and S–S)) which were involved in As(V) and As(III) sequestration on the sorbents examined here. Significantly, X-WMR showed (up to 49%) greater As(III) and As(V) sorption than that of natural WMR. Our results demonstrated that X-WMR efficiently removed 94%–100% (n = 16) of As from As-contaminated drinking well water which possessed detectable concentrations of some anions (e.g., SO 4 , CO 3 , HCO 3). This study highlights that the X-WMR has potential to remove As, notably As(III), from solutions and drinking water, and might be utilized as a reactive medium for the treatment of As-contaminated water. Graphical abstract Unlabelled Image Highlights • Water melon rind (WMR) was tested for arsenic removal potential from water. • Xanthated WMR removed up to 99% of As(III)/As(V) in solutions. • Langmuir and pseudo second-order models provided the best fits for As(III) and As(V). • FTIR spectra showed arsenic sequestration with surface functional groups of sorbents. • Xanthated WMR successfully removed 94–100% arsenic from drinking well water. [ABSTRACT FROM AUTHOR]

NaF is one of the most important sorption materials used in the UF6 purification, the stability of the complex formed after NaF absorbed UF6 was investigated by in situ Raman spectroscopy. The desorption behavior of UF6 from NaF adsorbent was examined by FT-IR, which show that UF6 did not desorb significantly from the NaF adsorbent until the temperature was above 200 °C, and the maximum desorption rate was reached at approximately 330 °C. Na2UF8 was hydrolyzed to form UO2F2·nH2O when it exposed to air containing moisture, there existed two desorption peaks for the air-exposed Na2UF8 complex in a fluorine atmosphere, one appeared at approximately 325 °C, attributed to the decomposition of UF6 from Na2UF8, and another was located at approximately 401 °C, attributed to the conversion of UO2F2 to UF6 by fluorine and the subsequent release of UF6. [ABSTRACT FROM AUTHOR]

To examine the Sb(III) retention by three soils with different properties (Ferrosol, Primosol and Isohumosol), kinetic batch experiments were carried out for Sb(III) adsorption–desorption, followed by Sb release using a sequential extraction procedure. In addition, hydroxides, organic matter, and humic substances were selectively removed by washing the soil with oxalate, sodium dithionate–citrate–bicarbonate, H 2 O 2 , and NaOH. The effects of removing these substances on Sb(III) retention were investigated by comparing the Sb distribution coefficients and desorption rates. The results indicated that exogenous Sb(III) was adsorbed onto all three soils rapidly at first and then more slowly. After 168 h of adsorption, most of the adsorbed Sb(III) was irreversibly retained in stable fractions by the Ferrosol. Oxidation reactions negatively affected Sb(III) retention by the Primosol and Isohumosol, and a large proportion of the Sb adsorbed remained mobilizable. The oxalate washing markedly enhanced Sb retention but the sodium dithionate–citrate–bicarbonate washing decreased Sb retention in all three soils. The H 2 O 2 and NaOH washings affected Sb retention by the Ferrosol more than Sb retention by the Primosol and Isohumosol. Changes in the pH and hydroxides caused by the washing strongly affected Sb sorption–desorption. The results improve our understanding of the mobility and bioavailability of exogenous Sb(III) in soils and might benefit future remediation option of Sb-contaminated soils. [ABSTRACT FROM AUTHOR]

Management of phosphorus (P) loss in soils with heavy manure application requires improved understanding of the transformation characteristics of soil P. Influences of manure application on the forms and sorption-desorption characteristics of P in surface (0–30 cm) and subsurface (30–60 cm) layer of a calcareous soil were investigated in a six-year field trial in comparison to chemical fertilizer application. Hedley fractionation and P K-edge X-ray absorption near-edge structure spectroscopy were used to determine the soil P forms. Manure (M) and chemical fertilizer (F) treatments resulted in P accumulation in two soil depths, but the total P accumulation in surface soil with M treatment was significantly lower than F treatment with similar P surplus. Compared to control, M and F treatments were significantly increased the proportion of labile P at both depths. In surface soil, M treatment significantly decreased stable Ca-associated P proportion and increased Fe-associated P and inositol hexakisphosphate proportions. The accumulation and transformation of P in M treatment distinctly decreased P sorption maximun, sorption coefficient and buffer capacity, and increased the degree of P saturation and P desorption relative to F treatment. The soil properties of pH, organic carbon (OC), total nitrogen (TN), Mehlich-3 extractable Ca and Fe, and phytase in surface soil and pH, OC, TN, Mehlich-3 extractable Ca and dehydrogenase in subsurface soil had significant effects on the compositions of soil P ( P  < 0.05), respectively. Lowered pH due to manure application mainly contributed to P transformation and release in the calcareous soil. [ABSTRACT FROM AUTHOR]

Tundra soils account for 50% of global stocks of soil organic carbon (SOC), and it is expected that the amplified climate warming in high latitude could cause loss of this SOC through decomposition. Decomposed SOC could become hydrologically accessible, which increase downstream dissolved organic carbon (DOC) export and subsequent carbon release to the atmosphere, constituting a positive feedback to climate warming. However, DOC export is often neglected in ecosystem models. In this paper, we incorporate processes related to DOC production, mineralization, diffusion, sorption-desorption, and leaching into a customized arctic version of the dynamic ecosystem model LPJ-GUESS in order to mechanistically model catchment DOC export, and to link this flux to other ecosystem processes. The extended LPJ-GUESS is compared to observed DOC export at Stordalen catchment in northern Sweden. Vegetation communities include flood-tolerant graminoids ( Eriophorum ) and Sphagnum moss, birch forest and dwarf shrub communities. The processes, sorption-desorption and microbial decomposition (DOC production and mineralization) are found to contribute most to the variance in DOC export based on a detailed variance-based Sobol sensitivity analysis (SA) at grid cell-level. Catchment-level SA shows that the highest mean DOC exports come from the Eriophorum peatland (fen). A comparison with observations shows that the model captures the seasonality of DOC fluxes. Two catchment simulations, one without water lateral routing and one without peatland processes, were compared with the catchment simulations with all processes. The comparison showed that the current implementation of catchment lateral flow and peatland processes in LPJ-GUESS are essential to capture catchment-level DOC dynamics and indicate the model is at an appropriate level of complexity to represent the main mechanism of DOC dynamics in soils. The extended model provides a new tool to investigate potential interactions among climate change, vegetation dynamics, soil hydrology and DOC dynamics at both stand-alone to catchment scales. [ABSTRACT FROM AUTHOR]

Up to hundreds of milligrams per kilogram (dry weight) of nonylphenol (NP) reportedly entered the soil and sediment through the agricultural reuse of biosolids, pesticide application, etc. Organic pollutants in soil could not only further trigger groundwater contamination via leaching (that highly depends upon sorption-desorption and degradation phenomena) but also harm food safety by crop uptake (that mainly rests with the bioavailability of pollutants in soil). Thus, we first investigated the effects of earthworm casts (EWCs) on the sorption-desorption, degradation, and bioavailability of NP in soil under laboratory microcosm conditions, and then, analyzed the FT-IR spectra of EWC and soil samples (with and without EWC). The application of EWC could notably increase the sorption capacity of soils for NP and in turn significantly inhibited the desorption of NP from soil; responsively lengthened the half-time of NP in the soil; and reduced the uptake and translocation of NP in tomato seedlings and promoted their growth during the first 3 weeks. Finally, FT-IR spectra of EWC and soil samples indicated that the application of EWC increased the content of N, P, and organic matter in soil. [ABSTRACT FROM AUTHOR]

Calcined hydrotalcite can be applied to remove anionic contaminants from aqueous systems such as antimony species due to its great anion exchange capacity and high surface area. Hence, this study evaluated antimonite and antimonate sorption–desorption processes onto calcined hydrotalcite in the presence of nitrate, sulfate and phosphate. Sorption and desorption experiments of antimonite and antimonate were carried out in batch equilibrium and the post-sorption solids were analyzed by X-ray fluorescence (EDXRF). Sorption data were better fitted by dual-mode Langmuir–Freundlich model ( R 2 > 0.99) and desorption data by Langmuir model. High maximum sorption capacities were found for the calcined hydrotalcite, ranging from 617 to 790 meq kg −1 . The competing anions strongly affected the antimony sorption. EDXRF analysis and mathematical modelling showed that sulfate and phosphate presented higher effect on antimonite and antimonate sorption, respectively. High values for sorption efficiency ( SE = 99%) and sorption capacity were attributed to the sorbent small particles and the large surface area. Positive hysteresis indexes and low mobilization factors ( MF > 3%) suggest very low desorption capacity to antimony species from LDH. These calcined hydrotalcite characteristics are desirable for sorption of antimony species from aqueous solutions. [ABSTRACT FROM AUTHOR]

The purpose of this study was to compare thermal and mechanical properties of different materials based on vegetal aggregates and clay in order to characterize the performances of four different biocomposites with a view to valorizing agricultural waste. The samples analyzed were manufactured with four different plant-based aggregates (rape straw, sunflower bark, sunflower pith and a mix of sunflower pith and bark) at a same binder/aggregate ratio. These materials revealed a wide range of densities and thermo-mechanical properties. As expected, increasing the material’s density gave a higher compressive strength while at the same time increasing thermal conductivity. [ABSTRACT FROM AUTHOR]

Cyclodextrins (CDs) can improve the apparent solubility and bioavailability of a variety of organic compounds through the formation of inclusion complexes; accordingly, they are suitable for application in innovative remediation technologies of contaminated soils. However, the different interactions in the tertiary system CD/contaminant/soil matrix can affect the bioavailability of the inclusion complex through the possible sorption of CD and CD complex in the soil matrix, as well as with the potential of the sorbed CD to form the complex, concurrent with the desorption processes. This work focuses in changes produced by three different CDs in soil sorption-desorption processes of chlorpyrifos (CPF), diazinon (DZN), and chlorothalonil (CTL), and their major degradation products, 3,5,6-trichloro-2-pyridinol (TCP), 2-isopropyl-6-methyl-4-pyrimidinol, and hydroxy-chlorothalonil (OH-CTL). Cyclodextrins used were β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Mβ-CD), and 2-hydroxypropyl-β-cyclodextrin (HPβ-CD). The studied soils belong to the orders Andisol, Ultisol, and Mollisol with different organic matter contents, mineral composition, and pH. The apparent sorption constants were significantly lower for the three pesticides in the presence of all CDs. The highest displacement of sorption equilibria was produced by the influence of Mβ-CD, with the most pronounced effect for CPF, a pesticide strongly sorbed on soils. The same was obtained for TCP and OH-CTL, highlighting the need to assess the risk of generating higher levels of groundwater contamination with polar metabolites if degradation rates are not controlled. The highest desorption efficiency was obtained for the systems CPF-β-CD, DZN-Mβ-CD, and CTL-Mβ-CD. Since the degree of adsorption of the complex is relevant to obtain an increase in the bioavailability of the contaminant, a distribution coefficient for the complexed pesticide in all CD-soil-pesticide system was estimated by using the apparent sorption coefficients, the stability constant for each CD-pesticide complex, and the distribution coefficients of free pesticide. [ABSTRACT FROM AUTHOR]

Risk-based approaches to managing contaminated land, rather than approaches based on complete contaminant removal, have gained acceptance as they are likely to be more feasible and cost effective. Risk-based approaches aim to minimise risks of exposure of a specified contaminant to humans. However, adopting a risk-based approach over alternative overly-conservative approaches requires that associated uncertainties in decision making are understood and minimised. Irrespective of the nature of contaminants, a critical uncertainty is whether there are potential risks associated with exposure to the residual contaminant fractions in soil to humans and other ecological receptors, and how they should be considered in the risk assessment process. This review focusing on hydrophobic organic contaminants (HOCs), especially polycyclic aromatic hydrocarbons (PAHs), suggests that there is significant uncertainty on the residual fractions of contaminants from risk perspectives. This is because very few studies have focused on understanding the desorption behaviour of HOCs, with few or no studies considering the influence of exposure-specific factors. In particular, it is not clear whether the exposure of soil-associated HOCs to gastrointestinal fluids and enzyme processes release bound residues. Although, in vitro models have been used to predict PAH bioaccessibility, and chemical extractions have been used to determine residual fractions in various soils, there are still doubts about what is actually being measured. Therefore it is not certain which bioaccessibility method currently represents the best choice, or provides the best estimate, of in vivo PAH bioavailability. It is suggested that the fate and behaviour of HOCs in a wide range of soils, and that consider exposure-specific scenarios, be investigated. Exposure-specific scenarios are important for validation purposes, which may be useful for the development of standardised methods and procedures for HOC bioaccessibility determinations. Research is needed to propose the most appropriate testing methods and for assessing potential risks posed by residual fractions of HOCs. Such investigations may be useful for minimising uncertainties associated with a risk-based approach, so that consideration may then be given to its adoption on a global scale. This review critically appraises existing information on the bioavailability of HOC residues in soil to establish whether there may be risks from highly sequestered contaminant residues. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) usually coexist with heavy metals (HMs) in soil. MPs can influence HMs mobility and bioavailability, but the underlying mechanisms remain largely unexplored. Here, polyethylene and polypropylene MPs were selected to investigate their effects and mechanisms of sorption-desorption, bioaccessibility and bioavailability of cadmium (Cd) in paddy soil. Batch experiments indicated that MPs significantly reduced the Cd sorption in soil (p < 0.05). Accordingly, soil with the MPs had lower boundary diffusion constant of Cd (C 1 = 0.847∼ 1.020) and the Freundlich sorption constant (K F = 0.444–0.616) than that without the MPs (C 1 = 0.894∼ 1.035, K F = 0.500–0.655). X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses suggested that the MPs reduced Cd chemisorption, by covering the soil active sites and thus blocking complexation of Cd with active oxygen sites and interrupting the formation of CdCO 3 and Cd 3 P 2 precipitates. Such effects of MPs enhanced about 1.2–1.5 times of Cd bioaccessibility and bioavailability in soil. Almost the same effects but different mechanisms of polyethylene and polypropylene MPs on Cd sorption in the soil indicated the complexity and pervasiveness of their effects. The findings provide new insights into impacts of MPs on the fate and risk of HMs in agricultural soil. [Display omitted] • PE and PP microplastics (MPs) reduce Cd2+ chemisorption in soil. • The MPs reduce Cd boundary diffusion. • The MPs cover active oxygen sites on soil particles. • The MPs show a dilution effect on Cd2+ sorption to soil. • The MPs enhance desorption and bioaccessibility of Cd2+ in soil. [ABSTRACT FROM AUTHOR]

Sorption-desorption processes govern the movement of all chemicals including pesticides in soils. The present investigation was undertaken to study the sorption-desorption of imidacloprid, using a batch method, on soils of five different location of India. Sorption data were fitted to Freundlich isotherm. The log K value was the highest for loam type soil (1.830) and the lowest for clay type soil (1.661). The value of 1/n was the maximum for silt loam soil (0.909) but minimum for loam soil (0.723). Simple correlation analysis indicated that among soil properties only electrical conductivity showed a higher but marginally non-significant negative correlation with log K (r = -0.826) indicating that higher concentration of solutes solutes are conducive to low sorption capacity of soil. The desorption data conformed to two surfaces Freundlich desorption isotherm. The values of 1/n1' corresponding to easily desorbed fraction of imidacloprid showed significant negative correlation with soil pH (r = -0.886, significant at p ≤0.05) but significant positive correlation with clay content (r = 0.980, significant at p ≤0.01). The desorption index for easily desorbed fraction of imidacloprid (n1’/n) also had significant negative correlation with soil pH (r = 0.953, significant at p ≤0.05). From cumulative desorption data, it appeared that bioavailability of imidacloprid would be lower in neutral soil than acidic or alkaline soils.

Quercus cerris is an important oak species extended in large areas of Eastern Europe and Minor Asia that has a thick bark which is not utilized at all. The sorption performance of cork from Quercus cerris bark with four polycyclic aromatic hydrocarbons (PAHs) (acenaphthene, fluorene, phenanthrene, and anthracene) was investigated. Quercus cerris cork was characterized for elemental analysis, acidic groups, and summative chemical composition, and the results were compared with Quercus suber cork. A Microtox® test was carried out to test for the release of any toxic compounds into the solution. All isotherms fit the Freundlich model and displayed linear n values. Quercus cerris exhibited a high efficiency for sorption of PAHs for the studied concentrations (5 to 50 µg/L) with 80-96% removal, while the desorption isotherms showed a very low release of the adsorbed PAHs (

Azimsulfuron is an acidic herbicide with a high water solubility which makes risk of groundwater contamination a concern. Various wood based biochars produced at different pyrolysis temperatures were characterized along with their sorption capacity for the herbicide azimsulfuron. In addition, we compared sorption on biochars with sorption on mineral sorbents such as clay minerals and iron oxides. In biochar formed at high temperatures (500 °C and 700 °C), FT-IR studies confirmed the increase in aromaticity. Scanning electron microscope (SEM) images of the biochars showed differences in the macroporous structure and lower size pores at higher temperatures. SSA (Specific Surface Area) of the biochars increased with pyrolysis temperature and, for all different biochars, this resulted in higher sorption of azimsulfuron. In the case of mineral sorbents, sorption is not related to SSA. Higher sorption is observed in a montmorillonite, of lower SSA, than in mixture of clay minerals with 30% smectite (w/w). On the contrary as with the clays, sorption on the two iron oxyhydroxides increased with SSA. Desorption studies showed hysteresis. Leaching studies showed no effect on azimsulfuron retention on soil column amended with apple wood biochar, while a reduction of azimsulfuron in leachates in soil columns amended with the modified montmorillonite and alder wood biochar (500 °C). Total retention was shown for alder wood biochar. [ABSTRACT FROM AUTHOR]