Sorbed Phase Research Articles

Effects of organic degradation products on the migration behaviour of radionuclides in cementitious materials

The impact of phthalates, which might be present in a cementitious repository as degradation products of superplasticisers or PVC additives, on the migration behaviour of An(III)/Ln(III) was investigated in batch sorption experiments on hardened cement paste. In the absence of organics, An(III)/Ln(III) sorb strongly on HCP with distribution ratios, Rd, of 105 to 106 L kg−1. Above a no-effect level of ~ 10–3 mol L−1 phthalate, a distinct decrease of the An(III)/Ln(III) sorption was observed with sorption reduction factors (i.e., the ratio between the Rd values without and with organic ligand) of 100 to 1000 at phthalate concentrations of 10–1 mol L−1. This sorption reduction is attributed to the effect of Ca complexation with phthalate on the stability of calcium silicate hydrate (C–S–H) phases as main sorbing phase. These results and ongoing diffusion experiments indicate an increase in the mobility of An(III)/Ln(III) in cementitious barriers with increasing phthalate concentrations.Graphical abstract

On the Sorption Mode of U(IV) at Calcium Silicate Hydrate: A Comparison of Adsorption, Absorption in the Interlayer, and Incorporation by Means of Density Functional Calculations

Calcium silicate hydrate (C-S-H) is the main product of cement hydration and has also been shown to be the main sorbing phase of actinide ions interacting with cement. U(IV) has been chosen as an exemplary actinide ion to study actinide sorption at C-S-H as U is the main element in highly active radioactive waste and because reducing conditions are foreseen in a deep geological repository for such waste. U(IV) surface adsorption, absorption in the interlayer, and incorporation into the calcium oxide layer of C-S-H has been modeled quantum mechanically, applying a density functional approach. For each sorption mode various sites have been considered and a combined dynamic equilibration and optimization approach has been applied to generate a set of representative stable sorption complexes. At the surface and in the interlayer similar U(IV) hydroxo complexes stabilized by Ca2+ ions have been determined as sorbates. Surface adsorption tends to be preferred over absorption in the interlayer for the same type of sites. Incorporation of U(IV) in the CaO layer yields the most favorable sorption site. This result is supported by good qualitative agreement of structures with EXAFS results for other actinides in the oxidation state IV, leading to a new interpretation of the experimental results.

Effect of organic compounds on the retention of radionuclides in clay rocks: Mechanisms and specificities of Eu(III), Th(IV), and U(VI)

The use of geological barriers is widely studied in the context of hazardous waste management and pollution events. In the near field of pollution sources, geological barriers endure disturbances with the concomitant release of hazardous chemicals and organic or saline plumes. In this study, we investigate the effect of organic compounds on the retention of radionuclides in contact with a sedimentary rock, namely Callovo-Oxfordian clay rock (East of Paris Basin). The retention of Eu(III), Th(IV), U(VI), was quantified at near-neutral pH, in presence of model organic compounds released from wastes and engineered barriers, e.g. ortho-phthalate, α-isosaccharinate (α-ISA), succinate, as well as high complexing compounds (oxalate, citrate, EDTA). The studied concentrations of organic compounds, eventually higher than disposal conditions, aimed at quantifying concentration ranges above which the retention of radionuclides decreases, and the underlying mechanisms occurring.A simplified surface complexation model, assuming illite as the main sorbing phase, was used for predictive modelling. The comparison with experimental results allowed the evaluation of the robustness of the surface complexation constants and of the thermodynamic database “ThermoChimie” of the Andra-RWM-Ondraf/Niras consortium, to account for speciation in solution (ThermoChimie V10a, https://www.thermochimie-tdb.com). Specific mechanisms are discussed, such as complexation of Eu(III) by α-ISA, or retention of Th(IV)/citrate complexes. U(VI) displayed a unique behaviour because of uranyl complexation by natural species under geological conditions. The low solid to liquid distribution ratio, Rd(U(VI)/COx) ~ 7.5 ± 1.6 L kg−1 decreases in presence of organic compounds, but without direct complexation by organic molecules. Indeed, the organic plume induces a disturbance of chemical equilibria in pore water of the clay rock, leading to additional complexation of uranyl by calcium and carbonates. Such effect highlights the crucial role of clay surfaces and carbonate minerals. More generally, these results provide insights on the geochemical buffers and key parameters involved during near-field disturbance of environmental media.

Modeling the Hydration-Induced Structural Transitions of the SAPO-34 Zeolite and Their Impact on the Water’s Sorbed Phase Equilibrium and Dynamics

We identified computationally a number of hydration-induced structural phases of the SAPO-34 zeolite, possessing different energetic characteristics as revealed by density functional theory calcula...

Legacy and Emerging Persistent Organic Pollutants (POPs) in Terrestrial Compartments in the High Arctic: Sorption and Secondary Sources.

Legacy persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and emerging perfluoroalkyl substances (PFASs) were measured in vegetation and soil samples collected at remote lakes in the Canadian High Arctic. Field studies were carried out in 2015 and 2016 to assess concentrations of POPs, study the relevant sorbing phases, and determine whether Arctic soils were sinks or sources of legacy POPs to the atmosphere and to neighboring lakes. The patterns of legacy POPs in vegetation and soils were dominated by low molecular weight PCB congeners along with OCPs, confirming the importance of long-range atmospheric transport. Lipid and non-lipid organic matter was a key determinant of legacy POPs in Arctic vegetation. Soil organic matter was the main descriptor of hydrophobic PCBs and OCPs in soils, while soil inorganic carbon content, was an important driver of the sorption of PFASs in soils. While contaminant concentrations were low in soil and vegetation, higher PCBs and PFOS organic and inorganic carbon-normalized concentrations were found at Resolute Lake indicating the presence of local sources of contamination. Comparison of fugacities of PCBs in soil and air from Resolute Lake indicated soils as net sources of PCBs to the atmosphere.

Iron Isotope Fractionations Reveal a Finite Bioavailable Fe Pool for Structural Fe(III) Reduction in Nontronite.

We report on stable Fe isotope fractionation during microbial and chemical reduction of structural Fe(III) in nontronite NAu-1. (56)Fe/(54)Fe fractionation factors between aqueous Fe(II) and structural Fe(III) ranged from -1.2 to +0.8‰. Microbial (Shewanella oneidensis and Geobacter sulfurreducens) and chemical (dithionite) reduction experiments revealed a two-stage process. Stage 1 was characterized by rapid reduction of a finite Fe(III) pool along the edges of the clay particles, accompanied by a limited release to solution of Fe(II), which partially adsorbed onto basal planes. Stable Fe isotope compositions revealed that electron transfer and atom exchange (ETAE) occurred between edge-bound Fe(II) and octahedral (structural) Fe(III) within the clay lattice, as well as between aqueous Fe(II) and structural Fe(III) via a transient sorbed phase. The isotopic fractionation factors decreased with increasing extent of reduction as a result of the depletion of the finite bioavailable Fe(III) pool. During stage 2, microbial reduction was inhibited while chemical reduction continued. However, further ETAE between aqueous Fe(II) and structural Fe(III) was not observed. Our results imply that the pool of bioavailable Fe(III) is restricted to structural Fe sites located near the edges of the clay particles. Blockage of ETAE distinguishes Fe(III) reduction of layered clay minerals from that of Fe oxyhydroxides, where accumulation of structural Fe(II) is much more limited.

Kinetics and equilibrium partitioning of dissolved BTEX in PDMS and POM sheets.

Passive sampling of volatile organic chemicals from soil and groundwater is primarily important in assessing the status of environmental contamination. A group of low molecular weight pollutants usually found in petroleum fuels, benzene, toluene, ethylbenzene, and xylenes (BTEX) was studied for its kinetics and equilibrium partitioning with single-phase passive samplers using polydimethylsiloxane (PDMS) and polyoxymethylene (POM) as sorbing phase. PDMS (1mm) and POM (0.076mm) sheets were used for sorption of BTEX and concentrations were analyzed using GC-FID. The equilibrium absorption and desorption of PDMS in water was achieved after 120min while POM sheets absorbed up to 35days and desorbed in 7days. The kinetic rate constants in PDMS is higher than in POM up to 3 orders of magnitude. Logarithms of partition coefficient were determined to be in the range of 1.6-2.8 for PDMS and 2.1-3.1 for POM. The results indicate that POM is a stronger sorbent for BTEX and has slower equilibration time than PDMS. The partitioning process for both polymers was found to be enthalpy-driven by measurement of K d values at varying temperatures. K d values increase at low temperature and high ionic strength conditions. Presence of other gasoline components, as well as dissolved organic matter, did not significantly affect equilibrium partitioning. A good 1:1 correlation between the measured and the predicted concentrations was established on testing the potential application of the constructed PDMS sampler on natural soils and artificial soils spiked with gasoline-contaminated water.

Distinctive green recovery of silver species from modified cellulose: Mechanism and spectroscopic studies

The present study aimed to recover precious silver in order to identify the adsorption coupled reduction pathways that determine this process. A combination technique of adsorption and nanocrystallization was used to investigate the recovery of silver species from taurine-cellulose (T-DAC) samples. The non-synthetic route of nanocrystallization yielded spherical zero-valent silver sized ∼18nm. Rate-controlling steps were modeled by adsorption parameters by the best fit of Langmuir capacity (55mg/g), pseudo-second order curves, and exothermic chemical reactions. The T-DAC was an excellent sorbing phase for the treatment of silver-polluted waters over a broad range of pH (2.1–10.1) and varying ionic strengths (8.5–850mM, as NaCl), which are the conditions often encountered in industrial and mining effluents. A good recovery of silver (40–65%) was also obtained in the presence of Cd(II), Co(II), Cr(VI), Ni(II), and As(V) at lower or equivalent concentrations with Ag(I), either from individually added metals or from all metal ions mixed together. Desorption was compared with a series of five eluents including complexing agents. In these experiments acidified thiourea yielded 86% desorption of Ag(I). Aqueous silver reduced to metallic silver on the surface of the T-DAC samples, which was confirmed by X-ray photo electron spectroscopy.

Trace and major element associations in basaltic ash soils of El Hierro Island

Associations between major and trace elements (aqua regia) were studied in basaltic-ash soils from the island of El Hierro in order to distinguish possible non-lithological contributions to the large trace element concentration shown by the soils. Soil composition reflected the basaltic composition of the parent materials and their extended tendencies to ultrabasic and trachytic compositions. The obtained values did not differ from previously reported reference values for natural soils, pointing to a low intensity anthropic activity. Only Cd levels were above those predicted by parent materials. The large soil total phosphorus (P) concentrations were consistent with those reported for the parent materials, thus obscuring the hypothesis of the contribution of the phosphate-rich Saharan dust to soil Cd enrichment. The spatial distribution of trace and major elements helped to identify a larger concentration of trace elements in soils of the most humid zones where andic properties were more highly expressed. Anthropic influence was revealed by the association of P and Cd in a former intensive agricultural zone. The large metal concentrations could reach or exceed the Soil Quality Standards for heavy metal concentrations in relation to soil pH. Plant composition, however, did not approach hazardous levels, probably due to the effect of the organic and highly reactive mineral sorbing phases of the studied soil types.

Modeling the effect of soil structure on water flow and isoproturon dynamics in an agricultural field receiving repeated urban waste compost application

Transport processes in soils are strongly affected by heterogeneity of soil hydraulic properties. Tillage practices and compost amendments can modify soil structure and create heterogeneity at the local scale within agricultural fields. The long-term field experiment QualiAgro (INRA–Veolia partnership 1998–2013) explores the impact of heterogeneity in soil structure created by tillage practices and compost application on transport processes. A modeling study was performed to evaluate how the presence of heterogeneity due to soil tillage and compost application affects water flow and pesticide dynamics in soil during a long-term period. The study was done on a plot receiving a co-compost of green wastes and sewage sludge (SGW) applied once every 2years since 1998. The plot was cultivated with a biannual rotation of winter wheat–maize (except 1year of barley) and a four-furrow moldboard plow was used for tillage. In each plot, wick lysimeter outflow and TDR probe data were collected at different depths from 2004, while tensiometer measurements were also conducted during 2007/2008. Isoproturon concentration was measured in lysimeter outflow since 2004. Detailed profile description was used to locate different soil structures in the profile, which was then implemented in the HYDRUS-2D model. Four zones were identified in the plowed layer: compacted clods with no visible macropores (Δ), non-compacted soil with visible macroporosity (Γ), interfurrows created by moldboard plowing containing crop residues and applied compost (IF), and the plow pan (PP) created by plowing repeatedly to the same depth. Isoproturon retention and degradation parameters were estimated from laboratory batch sorption and incubation experiments, respectively, for each structure independently. Water retention parameters were estimated from pressure plate laboratory measurements and hydraulic conductivity parameters were obtained from field tension infiltrometer experiments. Soil hydraulic properties were optimized on one calibration year (2007/08) using pressure head, water content and lysimeter outflow data, and then tested on the whole 2004/2010 period. Lysimeter outflow and water content dynamics in the soil profile were correctly described for the whole period (model efficiency coefficient: 0.99) after some correction of LAI estimates for wheat (2005/06) and barley (2006/07). Using laboratory-measured degradation rates and assuming degradation only in the liquid phase caused large overestimation of simulated isoproturon losses in lysimeter outflow. A proper order of magnitude of isoproturon losses was obtained after considering that degradation occurred in solid (sorbed) phase at a rate 75% of that in liquid phase. Isoproturon concentrations were found to be highly sensitive to degradation rates. Neither the laboratory-measured isoproturon fate parameters nor the independently-derived soil hydraulic parameters could describe the actual multiannual field dynamics of water and isoproturon without calibration. However, once calibrated on a limited period of time (9months), HYDRUS-2D was able to simulate the whole 6-year time series with good accuracy.

Mechanistic investigation on the green recovery of ionic, nanocrystalline, and metallic gold by two anionic nanocelluloses

Abstract The modified cellulose (ADAC samples) used as backbone to obtain biodegradable hydrogels, which demonstrated high affinity to concentrate precious gold species. The primary foci of the study were to develop green techniques to recover Au from dilute solutions by providing the mechanistic evidences for the adsorption coupled reduction pathways. The derivatives of anionic nanocellulose were used for recovery of the ionic, nanoparticulate, and metallic forms of Au. The ADAC samples were promising sorbing phase (57 and 60 mg/g capacity) even at low pH for the treatment of the gold-polluted waters. Thermodynamically, ADAC hydrogels were remained active at moderate to higher temperature (295–333 K) in an endothermic way. Reduction of Au occurred at different stages of kinetic curves, facilitating the formation of zerovalent gold (48 and 41 nm particle size). The Au recovery minimally altered by the competing heavy metals (Cd, Co, Cr, Ni, and As), either at equivalent or lower concentrations. A significant amount of Au(III) (83–99%) regenerated by a strong complexing eluent (0.5 M thiourea in 1 M HCl), moreover thermal crystallization yielded metallic gold in an excellent amount (94%). The mechanism of adsorptive–reduction of gold-nanocellulose were investigated and characterized by the spectroscopic studies including X-ray photoelectron spectroscopy. Overall, recovery of gold in desired forms from nanocellulose can be viewed as an effective biomaterial management strategy.

Passive sampling methods for contaminated sediments: state of the science for organic contaminants.

This manuscript surveys the literature on passive sampler methods (PSMs) used in contaminated sediments to assess the chemical activity of organic contaminants. The chemical activity in turn dictates the reactivity and bioavailability of contaminants in sediment. Approaches to measure specific binding of compounds to sediment components, for example, amorphous carbon or specific types of reduced carbon, and the associated partition coefficients are difficult to determine, particularly for native sediment. Thus, the development of PSMs that represent the chemical activity of complex compound–sediment interactions, expressed as the freely dissolved contaminant concentration in porewater (Cfree), offer a better proxy for endpoints of concern, such as reactivity, bioaccumulation, and toxicity. Passive sampling methods have estimated Cfree using both kinetic and equilibrium operating modes and used various polymers as the sorbing phase, for example, polydimethylsiloxane, polyethylene, and polyoxymethylene in various configurations, such as sheets, coated fibers, or vials containing thin films. These PSMs have been applied in laboratory exposures and field deployments covering a variety of spatial and temporal scales. A wide range of calibration conditions exist in the literature to estimate Cfree, but consensus values have not been established. The most critical criteria are the partition coefficient between water and the polymer phase and the equilibrium status of the sampler. In addition, the PSM must not appreciably deplete Cfree in the porewater. Some of the future challenges include establishing a standard approach for PSM measurements, correcting for nonequilibrium conditions, establishing guidance for selection and implementation of PSMs, and translating and applying data collected by PSMs. Integr Environ Assess Manag 2014;10:167–178. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC.

Selenium(IV) Uptake by Maghemite (γ-Fe2O3)

The mechanism of selenium(IV) uptake by maghemite was investigated on both the macroscopic and the molecular level. Maghemite nanoparticles exhibited fast adsorption kinetics toward selenium(IV). Batch experiments showed a decreased sorption with increasing pH (3.5-11). Ionic strength variations (0.01 to 0.1 M NaCl) had no significant influence on selenium(IV) uptake. Electrophoretic mobility measurements revealed a significant shift toward lower values of the isoelectric point of maghemite upon selenium(IV) uptake, suggesting the formation of inner-sphere surface complexes. At the molecular level, using X-ray Absorption Fine-Structure Spectroscopy (EXAFS), the formation of both bidentate binuclear corner-sharing ((2)C) and bidentate mononuclear edge-sharing ((1)E) inner-sphere surface complexes was observed, with a trend toward solely (1)E complexes at high pH. The absence of a tridentate surface complex as observed for arsenic(III) and antimonite(III) might be due to the relatively small size of the Se(IV)O3 unit. These new spectroscopic results can be implemented in reactive transport models to improve the prediction of selenium migration behavior in the environment as well as its monitoring through its interaction with maghemite or maghemite layers at the surface of magnetite. Due to its chemical stability even at low pH and its magnetization properties allowing magnetic separation, maghemite is a promising sorbing phase for the treatment of Se polluted waters.

Uptake and toxicity of polycyclic aromatic hydrocarbons in terrestrial springtails—studying bioconcentration kinetics and linking toxicity to chemical activity

Passive dosing applies a polymer loaded with test compound(s) to establish and maintain constant exposure in laboratory experiments. Passive dosing with the silicone poly(dimethylsiloxane) was used to control exposure of the terrestrial springtail Folsomia candida to six polycyclic aromatic hydrocarbons (PAHs) in bioconcentration and toxicity experiments. Folsomia candida could move freely on the PAH-loaded silicone, resulting in exposure via air and direct contact. The bioconcentration kinetics indicated efficient uptake of naphthalene, anthracene, and pyrene through air and (near) equilibrium partitioning of these PAHs to lipids and possibly the waxy layer of the springtail cuticle. Toxicities of naphthalene, phenanthrene, and pyrene were related to chemical activity, which quantifies the energetic level and drives spontaneous processes including diffusive biouptake. Chemical activity-response relationships yielded effective lethal chemical activities (La50s) well within the expected range for baseline toxicity (0.01-0.1). Effective lethal body burdens for naphthalene and pyrene exceeded the expected range of 2 to 8 mmol kg(-1) fresh weight, which again indicated the waxy layer to be a sorbing phase. Finally, chemical activities were converted into equilibrium partitioning concentrations in lipids yielding effective lethal concentrations for naphthalene and phenanthrene in good correspondence with the lethal membrane burden for baseline toxicity (40-160 mmol kg(-1) lipid). Passive dosing was a practical approach for tightly controlling PAH exposure, which in turn provided new experimental possibilities and findings.

A Two-Component Mass Balance Model for Calibration of Solid-Phase Microextraction Fibers for Pyrethroids in Seawater

Determination of the analyte-specific distribution coefficient between the aqueous and sorbing phases is required for estimation of the aqueous-phase concentration of the analyte of interest using polymeric materials. Poly(dimethylsiloxane)-coated solid-phase microextration (PDMS-SPME) fiber-water partition coefficient (K(f)) values for eight common-use pyrethroids were determined using a two-compartment mass balance model and parameters determined in experimental seawater microcosms. Mass balance, epimerization, and aqueous-phase degradation (i.e., hydrolysis) were characterized using gas chromatography-negative chemical ionization mass spectrometry to facilitate K(f) estimation. Of the eight pyrethroids, only bifenthrin exhibited increasing sorption on the SPME fiber over the entire time-series exposure, indicating that its K(f) value could be estimated through a stable-compound model. The remaining pyrethroids were found to be unstable (half-life of <22 days), underscoring the importance of accounting for degradation in estimating K(f). The two-compartment model explained the experimental time-series data for bifenthrin (R(2) > 0.98) and the remaining unstable pyrethroids (R(2) > 0.7), leading to estimated values of log K(f) between 5.7 and 6.4, after correcting for residual dissolved organic carbon (DOC) in the experimental seawater. These K(f) values can be used to determine freely dissolved pyrethroid concentrations in the pg/L range using PDMS-SPME in fresh or seawater matrices under equilibrium conditions in laboratory or field applications.

On the Impact of Sorbent Mobility on the Sorbed Phase Equilibria and Dynamics: A Study of Methane and Carbon Dioxide within the Zeolite Imidazolate Framework-8

The presented work aims at exploring the influence of the mobility of the sorbent framework on both the equilibrium and the kinetic properties of the sorbed phase by means of molecular dynamics computer experiments under isochoric–isothermal and isobaric–isothermal statistical ensembles for several host model options, combined by Widom averaging along the entire trajectory of the host–guest system toward rigorously obtained sorbate isotherms within a fully flexible lattice. The methodology is adapted to the study of the self-diffusivity and the collective (Maxwell–Stefan and transport) diffusivities of carbon dioxide (CO2) and methane (CH4) within the zeolite imidazolate framework-8 (ZIF-8). The simulation predictions are compared with measurements from pulsed-field gradient nuclear magnetic resonance (PFG NMR), as well as with recently conducted infrared microscopy (IRM) experiments elaborated on the basis of the current modeling in the flexible ZIF-8. The modeling results reveal a significant influence ...

The method of definition of the effective thermodynamic parameters of trace metals sorbed forms in bottom sediments from sequential extraction data

Citation: Lipatnikova, O.A., D. V. Grichuk, O. V. Sokolova (2011), The method of definition of the effective thermodynamic parameters of trace metals sorbed forms in bottom sediments from sequential extraction data, Vestn. Otd. nauk Zemle, 3, NZ6065, doi:10.2205/2011NZ000195. Application of thermodynamic modeling to forecast of trace metals migration in water ecosystems is difficult because bottom sediments composition in reservoirs is very changeable and uncertain. We offer the alternative approach for solving similar problems. It is based on use of empirical information about distribution of mobile and potentially mobile forms of trace elements. Such type of information can be received using sequential extraction scheme (for example Tessier scheme). Effective thermodynamic parameters for certain object are calculated from this data. System «pore water – solid phase» of bottom sediments is considered as multicomponent system in thermodynamic model. It includes aqueous phase, individual solid phases and principal sorbing phases (clay minerals, iron and manganese hydroxides and organic matter) assumed as ideal solid solutions. The coefficients of trace metals selectivity with respect to calcium for the main sorbed forms were calculated based on the results of the analysis of extracts from the solid phase of bottom sediments and pressed pore waters. Based on these coefficients, the imaginary increments of the Gibbs free energy Δg°(T) for the sorbed forms were calculated. The quantity Δg°(T) CaX=0 was taken as a reference point of the imaginary Δg°. We performed the calculation of metal distribution between sorbents and pore solution using the calculated effective thermodynamic parameters. The thermodynamic calculations accurately reproduce the empirically obtained trace metals distribution in bottom sediments.

Thermodynamic modeling of heavy metal forms in bottom sediments: By the example of the Ivankovsky Reservoir

The technique of thermodynamic modeling for interactions in system “pore water-solid phase of bottom sediments” is suggested (including dissolved and sorbed forms of heavy metals). The main sorbent phases (clay minerals, iron and manganese hydroxides, and organic matter) are presented as multi-component ideal solid solutions. The capacities of sorbing phases are calculated according to the results of selective extraction by the Tessier scheme supplemented with determination macro-cations. The selectivity constants and free energy of metal bonding (Fe, Mn, Zn, Cu, Ni, Pb, Co, and Cd) with sorbing phases are calculated for bottom sediments of various compositions within the Ivankovsky Reservoir and the estimation of their natural variations is given.

Preliminary indications from atomic force microscopy of the presence of rapidly-formed nanoscale films on aquifer material surfaces

The objective of this study was to determine if there is a nanoscale surface film on aquifer-like materials exposed to deep groundwaters, as has previously been found on surfaces exposed to surface and soil waters. Such surface films will modify surface properties that are so important in determining the mobility of many groundwater pollutants. Muscovite mica was used because a) it is a good analogue for the main sorbing phases of many clastic aquifers and b) its cleavage planes are atomically flat allowing high resolution imaging. Freshly-cleaved muscovite plates were exposed to groundwater from a sandstone aquifer for 30 min, and surface properties (morphology, coverage, roughness and tip–substrate force interactions) were measured using atomic force microscopy (AFM). A patchy surface film of several nanometres in depth, incorporating larger separate particles, was found on the mica surface. This film was associated with significantly increased roughness values and AFM probe–sample interaction forces compared with pure water and inorganic (synthetic groundwater) solution controls. Although the results reported are preliminary in nature, if confirmed, such films are likely to affect sorption reactions, surface-facilitated redox interactions, non-aqueous phase liquid wetting angles, and colloid–pathogen–rock attachment, and will thus be of importance in understanding natural attenuation and migration of dissolved, non-aqueous and particulate phases in groundwaters.

Nonlinear sorption of nonreactive components during polluted-groundwater flow in soils

When polluted groundwater flows in soils, some components are sorbed by the solid phase. A mathematical model of sorption incorporates the description of equilibrium between the mobile and sorbing phases (isotherm) and the kinetics of mass transport, which controls the tailing of the pollution front. In the case of nonlinear isotherms, the sorption and desorption are governed by different types of isotherms, resulting in histeresis effects or essential difference between the shapes of pollutant fronts. Moreover, the sorption has a damping effect, i.e., it smoothes concentration variations on the soil surface caused by seasonal variations and other factors.