Microcalorimetric studies of perchlorate on heat production by hepatocytes and mitochondria isolated from Carassius auratus

As a new threat to environment all through the world, perchlorate (ClO(4)(-)) was predominantly a thyrotoxin, and its toxic manifestations in non-thyroid were also documented. However, little is known about the effects of ClO(4)(-) on cell and organelle. Therefore, the present study was designed to investigate the effects of ClO(4)(-) on hepatocytes and mitochondria isolated from Carassius auratus from the direct viewpoint of energy by using the microcalorimetric method. The metabolic thermogenic curves of hepatocytes and mitochondria at 25°C were obtained. And the thermokinetic parameters, such as growth rate constant (k), inhibitory ratio (I), maximum thermal power (P(max)) and total thermal effect (Q(total)) have been calculated. The results indicated that the toxicity of ClO(4)(-) on hepatocytes was relevant to the concentration of ClO(4)(-). However, 10-100mgL(-1)ClO(4)(-) stimulated the metabolic activity of mitochondria and the toxicity of ClO(4)(-) on mitochondria only occurrenced when treated with higher concentration of ClO(4)(-). This study shown that mitochondria has a major impact on the metabolic thermogenic of hepatocytes, but not the only factor. Meanwhile, it demonstrated that microcalorimetry was a powerful tool for understanding biological processes and studying on the toxic action of environmental contaminants in cell or subcellular level.     

Microcalorimetric studies on the metabolism of Chlorella vulgaris

The heat output of the non-growth metabolism of Chlorella vulgaris has been determined using an LKB-2277 BioActivity Monitor. The experimental results indicate that there is a turn-point on the metabolic thermogenic curves, which can be divided into two parts, an early phase and a later phase. For the early phase, there is a linear relationship between the metabolic power (P) and the cell concentration (C), and that the heat output produced by a single cell's metabolism (P0) depends on the cell concentration (C) and is inhibited by the cell density, the thermokinetic equation of their metabolism is dP/dt = k0, k0 = 0.     

Fixed-bed study for lanthanide (La, Eu, Yb) ions removal from aqueous solutions by immobilized Pseudomonas aeruginosa: experimental data and modelization

A fixed-bed study was carried out by using cells of Pseudomonas aeruginosa immobilized in polyacrylamide gel as a biosorbent for the removal of lanthanide (La, Eu, Yb) ions from aqueous solutions. The effects of superficial liquid velocity based on empty column, particle size, influent concentration and bed depth on the lanthanum breakthrough curves were investigated. Immobilized biomass effectively removed lanthanum from a 6 mM solution with a maximum adsorption capacity of 342 micromolg(-1) (+/-10%) corresponding closely to that observed in earlier batch studies with free bacterial cells. The Bohart and Adams sorption model was employed to determine characteristic parameters useful for process design. Results indicated that the immobilized cells of P. aeruginosa enable removal of lanthanum, europium and ytterbium ions from aqueous effluents with significant and similar maximum adsorption capacities. Experiments with a mixed cation solution showed that the sequence of preferential biosorption was Eu3+ > or = Yb3+ > La3+. Around 96+/-4% of the bound lanthanum was desorbed from the column and concentrated by eluting with a 0.1 M EDTA solution. The feasibility of regenerating and reusing the biomass through three adsorption/desorption cycles was suggested. Neural networks were used to model breakthrough curves performed in the dynamic process. The ability of this statistical tool to predict the breakthrough times was discussed.     

Bioaccumulation of lanthanum and cerium and their effects on the growth of wheat (Triticum aestivum L.) seedlings

Through short-term exposure (7-d exposure), long-term exposure (16-d exposure) and exposure-recovery (7-d exposure + 9-d recovery), the bioaccumulation and distribution of La and Ce and their effects on growth of wheat seedlings were studied. Addition of La (0.5-25 mg/l) and Ce (0.5-25 mg/l) to the culture medium individually and in combination inhibited primary root elongation, reduced the dry weight of roots and shoots and the content of mineral elements (Ca, Mg, K, Cu, Zn). The damage increased with an increase in the concentrations of La and Ce in culture medium. Relative damage ratio increased with an increase in concentrations of La and Ce in the culture medium and with exposure time. Comparing exposure-recovery groups with long-term exposure groups, primary root lengths, dry weight of roots and shoots and the content of five mineral elements were higher. The accumulation of La and Ce in the seedlings was positively correlated with the concentrations of La and Ce in the culture medium and with exposure time. Bioaccumulation factors of La and Ce in roots were much higher than those of shoots. The uptake rates of La and Ce by the plants were much higher than the translocation rates from roots to shoots. The accumulation and distribution of La and Ce in the seedlings in exposure-recovery groups showed that there was very little excretion through metabolism during the recovery period, but redistribution occurred throughout the whole plant. No apparent selective uptake was found between La and Ce by the plants when they were applied in combination.     

Effect of La3+ on the activities of antioxidant enzymes in wheat seedlings under lead stress in solution culture

In order to improve the plant ability to resist lead stress, effect of 0.05 mg/l La(NO₃)₃ on the activities of catalase (CAT), superoxide dismutase (SOD), the level of malondialdehyde (MDA) in wheat seedlings under lead stress was studied. The effect of La³⁺ on plant growth, chlorophyll content in wheat seedlings after adding 0, 50, 100 mg/l Pb(NO₃)₃ to the nutrient solution for 12 days was observed. The plants were grown in nutrient solution in a strictly controlled climate growth room. Effects of La³⁺ (with La treatment) compared with check groups was evidently observed. The activities of SOD and CAT in root were enhanced 0.45–1.69 times and 33.20–77.77% respectively and MDA content was reduced 11.05–27.49% in root after treatments from the second day till the end of the experiment. The activities of SOD and CAT was found to be increased slightly (P<0.05) and MDA content decreased in shoot and root of wheat seedlings by La³⁺ under lead stress within five days after treatments compared with Pb1 and Pb2 groups. It was assumed that antioxidant enzymes was found to be increased by La(NO₃)₃, the antioxidant potential of the wheat seedlings to resist lead stress enhanced. It is suggested that La³⁺ could be used to resist lead stress at the beginning under stress while the stress was not so serious.     

Biochemical interaction of six OP delayed neurotoxicants with several neurotargets

Five organophosphorous insecticides: Leptophos, EPN, Cyanofenphos, trichloronate and salithion proved to cause irreversible ataxia not only to chicken but also to mice and sheep. TOCP was included as a reference. Cyanofenphos blocked the catecholamine B-receptor binding activity with 3H-norepinephrine at a level similar to that of the specific inhibitor propranolol in the mouse heart preparation. In the lamb heart preparation, the B-receptor was more sensitive to Leptophos, salithion and TOCP than to propranolol. The six compounds and their oxons were screened for their in-vitro inhibition to monamine oxidase (MAO), acetyl cholinesterase (AChE) and neurotoxic esterase (NTE) in the brain of either mouse, lamb or chicken. It is believed that their AChE inhibition stands for their acute toxicity, while NTE inhibition is responsible for their paralytic ataxia.     

Removal of metal ions from the complexed solutions in fixed bed using a strong-acid ion exchange resin

Fixed bed removal of equimolar metal ions (Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺) from aqueous solutions using a strong-acid resin was examined. The solution contained a water-soluble complexing agent including ethylenediaminetetraacetic acid, nitrilotriacetic acid, and citric acid. Experiments were performed under different solution pH and molar concentration ratios of complexing agent to the total metals. It was shown from batch studies that the equilibrium exchange of metals and the resin mainly depended on solution pH, and partly on the type of complexing agent used. A mass transfer model was proposed to describe the breakthrough curves of the resin bed, which contained two parameters (τ and k) estimated from the observed breakthrough data. The calculated breakthrough curves agreed well with the measured ones (standard deviation <6%). In fixed bed tests at low pH (=2), the type of complexing agent had little effect on the breakthrough data. For a given complexing agent, the metal with a larger overall formation constant (K_f) showed a smaller exchange capacity. For a given metal ion, the complexing agent with a larger K_f also revealed a smaller exchange capacity.     

Background levels and dietary intake of PCDD/Fs in domestic and imported meat in South Korea

A survey was conducted in South Korea to determine residual levels and dietary intake of polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) from meat. Altogether 119 domestic and 164 imported samples of beef, pork, and chicken were examined. The mean levels of PCDD/Fs in upper bound were 0.21, 0.22, and 0.04pg WHO-TEQ/g fat for beef, pork, and chicken, respectively. The low level of PCDD/Fs in chicken probably resulted from the low fat content in the samples used. The samples were separated into domestic and imported products in order to investigate the sources of contamination. PCDFs were the more dominant congeners in domestic beef and were similar to those found from emission of incineration. However, the congener profiles of domestic beef and incineration were difficult to compare because the environmental fate and animal metabolism were involved. The upper bound dietary intake of PCDD/Fs from beef, pork and chicken was calculated to be 0.04pg/WHO-TEQ/kgbw/day. The combined consumption of beef, pork, and chicken was found to be 84.8g per day for a person weighing 60kg and represented 5.7% of their total daily food intake.     

Surface properties and catalytic performance of La(1-x)Sr(x)FeO(3) perovskite-type oxides for methane combustion

La(1-x)Sr(x)FeO(3) (x=0.0-1.0) perovskites were prepared and tested for the combustion of methane. X-ray diffraction (XRD) patterns revealed the presence of a single perovskite structure for substitutions 0x0.3, however Fe(2)O(3), SrCO(3) and SrFeO(3) phases were observed for substitutions x>0.3. The results of activity test indicate that with La(1-x)Sr(x)FeO(3) as the catalyst, the combustion of methane can take place at low temperatures around 400 degrees C. Partial substitution of La with Sr increases the activity and an optimal substitution fraction (x=0.5) exists in the La(1-x)Sr(x)FeO(3) catalysts. Catalyst activity can be well correlated to the product of the specific surface area and atomic ratio of Fe to La+Sr on the catalyst surface. Experimental results of O(2)-TPD and CH(4)-TPD in the range of 350-500 degrees C indicate that the amount of oxygen desorbed from the La(1-x)Sr(x)FeO(3) catalysts is far larger than that of methane. Therefore, it can be proposed that the catalytic oxidation of CH(4) over these catalysts proceeds with the surface reaction between CH(4) in the gas phase and the adsorbed O(2). Addition of water vapor or CO(2) to the feed inhibited catalyst activity, but the inhibition was reversible and became negligible at high reaction temperature.     

Biochemical interaction of six op delayed neurotoxicants with several neurotargets

Abstract

Five organophosphorous insecticides: Leptophos, EPN, Cyano‐fenphos, trichloronate and salithion proved to cause irreversible ataxia not only to chicken but also to mice and sheep. TOCP was included as a reference. Cyanofenphos blocked the catecholamine B‐receptor binding activity with ³H‐norepinephrine at a level similar to that of the specific inhibitor propranolol in the mouse heart preparation. In the lamb heart preparation, the B‐receptor was more sensitive to Leptophos, salithion and TOCP than to propranolol. The six compounds and their oxons were screened for their in‐vitro inhibition to monamine oxidase (MAO), acetyl cholinesterase (AChE) and neurotoxic esterase (NTE) in the brain of either mouse, lamb or chicken. It is believed that their AChE inhibition stands for their acute toxicity, while NTE inhibition is responsible for their paralytic ataxia.     

Validation of model calculation of ammonia deposition in the neighbourhood of a poultry farm using measured NH3 concentrations and N deposition

Substantial emission of ammonia (NH₃) from animal houses and the related high local deposition of NH₃-N are a threat to semi-natural nitrogen-deficient ecosystems situated near the NH₃ source. In Denmark, there are regulations limiting the level of NH₃ emission from livestock houses near N-deficient ecosystems that are likely to change due to nitrogen (N) enrichment caused by NH₃ deposition. The models used for assessing NH₃ emission from livestock production, therefore, need to be precise, as the regulation will affect both the nature of the ecosystem and the economy of the farmer. Therefore a study was carried out with the objective of validating the Danish model used to monitor NH₃ transport, dispersion and deposition from and in the neighbourhood of a chicken farm. In the study we measured NH₃ emission with standard flux measuring methods, NH₃ concentrations at increasing distances from the chicken houses using passive diffusion samplers and deposition using ¹⁵N-enriched biomonitors and field plot studies. The dispersion and deposition of NH₃ were modelled using the Danish OML-DEP model. It was also shown that model calculations clearly reflect the measured NH₃ concentration and N deposition. Deposition of N measured by biomonitors clearly reflected the variation in NH₃ concentrations and showed that deposition was not significantly different from zero (P < 0.05) at distances greater than 150–200 m from these chicken houses. Calculations confirmed this, as calculated N deposition 320 m away from the chicken farm was only marginally affected by the NH₃ emission from the farm. There was agreement between calculated and measured deposition showing that the model gives true estimates of the deposition in the neighbourhood of a livestock house emitting NH₃.     

Disruption of hepatic mitochondrial bioenergetics is not a primary mechanism for the toxicity of methoprene - relevance for toxicological assessment

Methoprene (isopropyl(2E,4E)-11-methoxy-3,7,11-trimethyl-2,4-dodecadienoate) is an insect growth regulator generally used to control insect populations by preventing insect maturation. So far, the effects of the insecticide on mitochondrial bioenergetics were not investigated. In the present work, liver mitochondria from Wistar rats were isolated and features of mitochondrial physiology were characterized in the presence of methoprene. High concentrations of methoprene, in the range of 40-100 nmol/mg of protein could decrease the transmembrane electric potential (Delta Psi) developed by mitochondria and, at the highest concentration, methoprene prevented complete Delta Psi repolarization after ADP addition. The effect was more evident using succinate than with ascorbate+TMPD as substrate. State 3 respiration was approximately 60% inhibited by 80 nmol of methoprene/mg of protein, while state 4 respiration, within the same range of methoprene concentrations, showed a slight increase, when both glutamate-malate and succinate were used as substrates. Additionally, FCCP-stimulated respiration was inhibited to an extent comparable to the effect on state 3, which suggests an interaction of methoprene with the respiratory chain, more evident with glutamate/malate as substrate. The activity of complex I (NADH-ubiquinone oxidorreductase) and that of the segment comprehending complexes II and III (succinate-cytochrome c reductase) were decreased in the presence of methoprene (approximately 60% and 85% of inhibition, respectively, with 300 nmol of methoprene/mg of protein), while the activities of cytochrome c oxidase and ATPase do not seem to be affected. Furthermore, the action of methoprene on the mitochondrial permeability transition was also studied, showing that the insecticide (in the range of 30-80 nmol mg(-1) of protein) decreases the susceptibility of liver mitochondria to the opening of the transition pore, even in non-energized mitochondria. These results lead to the conclusion that methoprene interference with hepatic mitochondrial function occurs only for high concentrations, which implies that the noxious effects of the insecticide reported for a number of non-target organisms are not fully attributable to mitochondrial effects. Therefore, it seems that mitochondrial activity does not represent the primary target for methoprene toxic action.     

The influence of lindane and lindane metabolites on microsomal and mitochondrial ATPase in vitro

In vitro investigations of the influence of lindane and its metabolites were performed on microsomal and mitochondrial ATPases from liver, kidney and brain of rat and mouse. The microsomal Na+-K+-ATPases in rat liver were inhibited by the tested substances. An increase of activity was observed only with 2.5 X 10(-5) M gamma-HCH. Effects on the microsomal Na+-K+-ATPase from kidney and brain of rat were also indicated. The mitochondrial enzyme in rat liver was stimulated by all the compounds tested at concentrations of 10(-4) M - 10(-2) M. The effects on mitochondrial enzymes from kidney and brain varied in dependence on the tested substances. In the microsomes and mitochondria of mouse an influence on the Na+-K+-ATPases similar to the effects on the preparations from organs of rat was evident.     

Isolation and identification of beta-nitrostyrene from smoked chicken

Extraction and identification of beta-nitrostyrene from smoked chicken is described. Commercially obtained smoked chicken was homogenised and extracted with chloroform-methanol (2:1). The extracts were fractioned by silicic acid column chromatography. The purified extract using thin-layer chromatography was identified by a colour reaction (this qualitative method for some nitrated compounds is developed this time), high pressure liquid chromatography and gas chromatography/mass spectrometry. The concentration of beta-nitrostyrene in the smoked chicken was 94 ppb. The average recovery of added beta-nitrostyrene was 107%. However, the toxicity of this material was not tested in the present paper.     

Adsorption and desorption of 2,4,6-trichlorophenol onto and from ash as affected by Ag+, Zn2+, and Al3+

Metal cations and organic pollutants mostly co-exist in the natural environment. However, their interactions in adsorption processes have yet to be adequately addressed. In the current study, the effect of inorganic cations with different charges (Ag⁺, Zn²⁺, and Al³⁺) on the adsorption and desorption of 2,4,6-trichlorophenol (TCP) onto and from processed ash derived from wheat (Triticum aestivum L.) straw was investigated. The adsorption and desorption of TCP were both nonlinear; the isotherm and kinetics curves fitted well using the Freundlich equation and a pseudo-second-order model, respectively. The presence of Ag⁺ promoted TCP adsorption, while Zn²⁺ and Al³⁺ reduced TCP adsorption onto ash. The desorption of TCP from ash showed obvious hysteresis, and the presence of Ag⁺, Zn²⁺, and Al³⁺ caused the desorption to be less hysteretic. The suppression of TCP adsorption by Zn²⁺ and Al³⁺ was ascribed to the partial overlapping of adsorption groups between TCP and metal ions. Al³⁺ had a stronger inhibition effect than that of Zn²⁺ due to its higher binding capacity and larger hydrated ionic radius than those of Zn²⁺. Enhanced adsorption of TCP onto ash by Ag⁺ was ascribed to its ability to reduce the competitive adsorption of water molecules on ash surface by replacing the original ions, such as Na⁺ and Ca²⁺, and compressing the hydrated ionic radius of these metal ions. In addition, Ag⁺ was able to bind with the aromatic organic compounds containing π-electrons, which resulted in a further increase of TCP adsorption by ash.     

Biochemical changes produced by beta- and gamma-hexachlorocyclohexane isomers in albino rats

Administration of beta- and gamma-isomers of hexachlorocyclohexane (HCH) at 800 ppm dietary level for 2 weeks to albino rats produced noticeable hepatocellular damage as indicated by elevations in serum aminotransferases and decreases in hepatic soluble enzymes. Although serum total LDH activity was not altered, the LD5 isoenzyme was proportionately higher in the HCH isomers treated animals. Treatment of rats with beta- and gamma-isomers of HCH increased the hepatic glucose-6-phosphate dehydrogenase and aldolase activities suggesting a higher rate of glucose oxidation. Liver glucose-6-phosphatase activity was decreased in these animals indicating inactivation of gluconeogenesis in liver. Dietary beta- and gamma-HCH decreased the liver mitochondrial DNP/Mg++/Ca++-activated ATPases thus affecting the energy metabolism. An unaltered ratio of DNP/Mg++-ATPase, a study of swelling pattern of hepatic mitochondria, and NAD+ permeability test suggested the maintenance of structural integrity of mitochondrial membrane in these pesticide fed animals. Liver microsomal Na+,K+-ATPases were lower in these animals.     

Fluorescence fingerprints and Cu2+-complexing ability of individual molecular size fractions in soil- and waste-borne DOM

Land spreading of organic materials introduces large amounts of dissolved organic matter (DOM) into the soil. DOM has the ability to form stable complexes with heavy metals and can facilitate their transport towards the groundwater. The effects on soil processes are difficult to assess, because different DOM components might react differently towards metal ions. The objective of this study was to investigate the fluorescence signature and the Cu2+-binding capacity of individual molecular size fractions of DOM from various sources. DOM extracted from leaf compost, chicken manure, sugar cane vinasse and a fulvic hypercalcaric cambisol was fractionated by the means of dialysis into four molecular size classes: MW<500, 50012000-14000 Da. Vinasse and leaf compost contained around 80% and 70%, respectively, of the total organic carbon in the fractions with low molecular weight (MW<3500 Da); in chicken manure and soil these fractions accounted for 40% and 50% only. Fluorescence was highest in the fraction MW>12000 Da for leaf compost, chicken manure and soil. The opposite result was obtained for vinasse, where the fractions with low molecular weight showed highest fluorescence intensities, distinguishing it from all other samples. Vinasse showed the greatest ability to bind Cu2+ with a resulting complex concentration of 6.31mgl(-1) while in contact with an excess of Cu2+. Leaf compost, soil and chicken manure followed with 2.69, 1.12, and 0.85mgl(-1), respectively. Within vinasse, the fraction MW<500 Da was able to form the most DOM-Cu complexes, indicating the importance of low molecular weight fractions in metal binding.     

Enhanced photocatalytic degradation of VOCs using Ln3+-TiO2 catalysts for indoor air purification

Two types of lanthanide ion-doped titanium dioxide (Ln3+-TiO2) catalysts including La3+-TiO2 and Nd3+-TiO2 were prepared by a sol-gel method. The effects of the lanthanide ion doping on the crystal structure, surface area, adsorption properties, pore size distribution, and surface chemical state of the catalysts were investigated by means of XRD, BET, and XPS. As results, the crystal size decreased significantly, while the specific surface area, t-plot total surface area, micropore volume, and the total pore volume increased owing to the lanthanide ion doping. The nitrogen adsorption-desorption isotherms of the catalysts showed that the N2 adsorption ability of the Ln3+-TiO2 catalysts was better than the TiO2 catalyst. Among them, the 0.7% Ln3+-TiO2 catalysts demonstrated the highest adsorption ability. The photocatalytic activity of the catalysts was investigated in the experiments of the photocatalytic degradation of benzene, toluene, ethylbenzene and o-xylene (BTEX) in a gaseous phase. The photocatalytic efficiency of the TiO2 catalysts with the lanthanide ion doping was remarkably enhanced by BTEX removal. The 1.2% Ln3+-TiO2 catalysts achieved the highest photocatalytic activity. The enhanced photodegradation of BTEX is possibly due to the improved adsorption ability and the enhanced electron-hole pairs separation due to the presence of Ti3+ on the surface of Ln3+-TiO2 catalysts and the electron transfer between the conduction band/defect level and lanthanide crystal field state.     

Thermochemical studies of the toxic actions of heavy metal ions on Rhizopus nigricans

By using a LKB2277 BioActivity Monitor (heat conduction microcalorimeter), stopped-flow method, the thermogenetic curves of Rhizopus nigricans growth at 25 degrees C inhibited by four kinds of heavy metal ions are determined, parameters such as growth rate constants k, inhibitory ratio I, half inhibitory concentration IC50 et al. are obtained. The experimental results show that heavy metal ions can inhibit Rhizopus nigricans growth obviously, low concentration of Cu2+ has promoting action. The inhibitory sequence is Cd2+ > Hg2+ > Pb2+ > Cu2+, half inhibitory concentration of them are Cd+ 0.8 micro g x ml(-1), Hg2+ 1.7 micro g x ml(-1), Pb2+ 48.0 micro g x ml(-1), Cu2+ 110 micro g x ml(-1). This microclorimetric bioassay for acute cellular toxicity is based on metabolic heat evolution from cultured cells. The assay is quantitative, inexpensive, and versatile; moreover, toxicological information can be obtained with cell from other species of interest.     

Cesium migration in Hanford sediment: a multisite cation exchange model based on laboratory transport experiments

Cs+ transport experiments carried out in columns packed with uncontaminated Hanford formation sediment from the SX tank farm provide strong support for the use of a multisite, multicomponent cation exchange model to describe Cs+ migration in the Hanford vadose zone. The experimental results indicate a strong dependence of the effective Cs+ Kd on the concentrations of other cations, including Na+ that is present at high to extremely high concentrations in fluids leaking from the Hanford SX tanks. A strong dependence of the Cs+ Kd on the aqueous Cs+ concentration is also apparent, with retardation of Cs+ increasing from a value of 41 at a Cs+ concentration of 10(-4) M in the feed solution to as much as 282 at a Cs+ concentration of 5x10(-7) M, all in a background of 1 M NaNO3. The total cation exchange capacity (CEC) of the Hanford sediment was determined using 22Na isotopic equilibrium exchange in a flow-through column experiment. The value for the CEC of 120 microeq/g determined with this method is compatible with a value of 121.9 microeq/g determined by multi-cation elution. While two distinct exchange sites were proposed by Zachara et al. [Geochim. Cosmochim. Acta 66 (2002) 193] based on binary batch exchange experiments, a third site is proposed in this study to improve the fit of the Cs+-Na+ and Cs+-Ca+ exchange data and to capture self-sharpened Cs+ breakthrough curves at low concentrations of Cs+. Two of the proposed exchange sites represent frayed edge sites (FES) on weathered micas and constitute 0.02% and 0.22% of the total CEC. Both of the FES show a very strong selectivity for Cs+ over Na+ (K(Na-Cs)=10(7.22) and 10(4.93), respectively). The third site, accounting for over 99% of the total CEC, is associated with planar sites on expansible clays and shows a smaller Na+-Cs+ selectivity coefficient of 10(1.99). Parameters derived from a fit of binary batch experiments alone tend to under predict Cs+ retardation in the column experiments. The transport experiments indicate 72-90% of the Cs+ sorbed in experiments targeting exchange on FES was desorbed over a 10- and 24-day period, respectively. At high Cs+ concentrations, where sorption is controlled primarily by exchange on planar sites, 95% of the Cs+ desorption was desorbed. Most of the difficulty in desorbing Cs+ from FES is a result of the extremely high selectivity of these sites for Cs+, although truly irreversible sorption as high as 23% was suggested in one experiment. The conclusion that Cs+ exchange is largely reversible in a thermodynamic sense is supported by the ability to match Cs+ desorption curves almost quantitatively with an equilibrium reactive transport simulation. The model for Cs+ retardation developed here qualitatively explains the behavior of Cs+ in the Hanford vadose zone underneath a variety of leaking tanks with differing salt concentrations. The high selectivity of FES for Cs+ implies that future desorption and migration is very unlikely to occur under natural recharge conditions.