Uptake Of Barium Research Articles

Uptake of barium, molybdenum, and lithium and incorporation into scallop shells: Refining proxies for primary production dynamics

AbstractBa/Cashell, Mo/Cashell, and Li/Cashell chronologies of Pecten maximus can provide information on past phytoplankton dynamics. Distinct Ba, Mo, and Li peaks in the shells are associated with algal blooms. This study evaluated the underlying hypothesis that respective element profiles reliably record variations in phytoplankton dynamics occurring within the water column. Therefore, the chemical content of scallops from the Bay of Brest, France, that lived on the sediment surface was compared to conspecific specimens living in a cage above the seafloor and compared with the phytoplankton abundance and the physicochemical properties of the water column. As demonstrated, Ba/Cashell and Mo/Cashell peaks occurred contemporaneously in specimens within the cage and on the sediment, but were higher in the latter. Furthermore, element/Ca peaks agreed with the timing of particulate Ba and Mo enrichments in the seawater. These data support the assumption of a dietary uptake of both elements. Differences in peak heights between shells living in a cage and on the seafloor were controlled by rates of filtration and biomineralization. While the timing and magnitude of Ba/Cashell peaks were linked to Ba‐containing diatoms, Mo/Cashell peaks were related to blooms of Mo‐enriched dinoflagellate and diatom aggregation events. Two episodes of slight Li enrichment occurred synchronously in cage and sediment shells. Although the exact mechanism causing such Li increases remains unresolved, the findings suggest a link to large diatom blooms or the presence of a specific diatom taxon. This study refines previously hypothesized relationships between trace element enrichments in scallop shells and phytoplankton dynamics.

Biodistribution of strontium and barium in the developing and mature skeleton of rats.

Bone acts as a reservoir for many trace elements. Understanding the extent and pattern of elemental accumulation in the skeleton is important from diagnostic, therapeutic, and toxicological perspectives. Some elements are simply adsorbed to bone surfaces by electric force and are buried under bone mineral, while others can replace calcium atoms in the hydroxyapatite structure. In this article, we investigated the extent and pattern of skeletal uptake of barium and strontium in two different age groups, growing, and skeletally mature, in healthy rats. Animals were dosed orally for 4weeks with either strontium chloride or barium chloride or combined. The distribution of trace elements was imaged in 3D using synchrotron K-edge subtraction micro-CT at 13.5µm resolution and 2D electron probe microanalysis (EPMA). Bulk concentration of the elements in serum and bone (tibiae) was also measured by mass spectrometry to study the extent of uptake. Toxicological evaluation did not show any cardiotoxicity or nephrotoxicity. Both elements were primarily deposited in the areas of active bone turnover such as growth plates and trabecular bone. Barium and strontium concentration in the bones of juvenile rats was 2.3 times higher, while serum levels were 1.4 and 1.5 times lower than adults. In all treatment and age groups, strontium was preferred to barium even though equal molar concentrations were dosed. This study displayed spatial co-localization of barium and strontium in bone for the first time. Barium and strontium can be used as surrogates for calcium to study the pathological changes in animal models of bone disease and to study the effects of pharmaceutical compounds on bone micro-architecture and bone remodeling in high spatial sensitivity and precision.

Uptake of macro nutrients, barium, and strontium by vegetation from mineral soils on carbonatite and pyroxenite bedrock at the Lillebukt Alkaline Complex on Stjernøy, Northern Norway

AbstractCarbonatite originating from the Lillebukt Alkaline Complex at Stjernøy in Northern Norway possesses favorable lime and potassium (K) fertilizer characteristics. However, enrichments of barium (Ba) and strontium (Sr) in carbonatite may cause an undesired uptake by plants when applied to agroecosystems. A field survey was carried out to compare concentrations of Ba, Sr, and macronutrients in indigenous plants growing in mineral soil developed on a bedrock of apatite–biotite–carbonatite (high in Ba and Sr) and of apatite–hornblende–pyroxenite (low in Ba and Sr) at Stjernøy. Samples of soil and vegetation were collected from three sites, two on carbonatite bedrock and one on pyroxenite bedrock. Ammonium lactate (AL)‐extracted soil samples and nitric acid microwave‐digested samples of soil, grasses, dwarf shrubs, and herbs were analyzed for element concentration using ICP‐MS and ICP‐OES. Concentrations of magnesium (Mg) and calcium (Ca) in both soil (AL) and plants were equal to or higher compared to values commonly reported. A high transfer of phosphorus (P) from soil to plants indicates that the apatite‐P is available to plants, particularly in pyroxenite soil. The non‐exchangeable K reservoir in the soil made a significant contribution to the elevated K transfer from soil to plant. Total concentrations of Ba and Sr in surface soil exhibited a high spatial variation ranging from 490 to 5,300 mg Ba kg−1 and from 320 to 1,300 mg Sr kg−1. The transfer of AL‐extractable elements from soil to plants increased in the order Ba < Sr < Ca < Mg < K, hence reflecting the chemical binding strength of these elements. Concentrations of Ba and Sr were low in grasses (≈ 20 mg kg−1), intermediate in dwarf shrubs and highest in herbs. Plant species and their affinity for Ca seemed more important in explaining the uptake of Ba and Sr than the soil concentration of these elements. The leguminous plant species Vicia cracca acted as an accumulator of both Ba (1.800 mg kg−1) and Sr (2.300 mg kg−1).

Uptake of Barium from Vermiculite by the Bacterium Pseudomonas fluorescens - New Indications for Barium as a Palaeoproxy

The apparent association of biogenic barite (BaSO 4 ) and organic matter in marine sediments has given support to the idea of using Ba as a proxy for palaeoproductivity. Despite this general acceptance only a few unicellular organisms (acantharian, diatoms) are known to incorporate barium. In this work, we show that the bacterium Pseudomonas fluorescens is able to take up barium. Because natural seawater harbors numerous bacteria many of which may take up Ba, this uptake of Ba explains why it may be considered a palaeoproxy. The introduction of this article reviews briefly what is known to date of Ba as a palaeoproxy, and what is known about bacterial interaction with Ba. Like other trace elements such as Fe, Mn and Sr, Ba can be extracted from vermiculite by Pseudomonas fluorescens and some mutants derived from it. Barium, therefore, seems to be as important a factor in bacterial metabolism as iron or other trace elements. The incorporation of Ba by living bacterial cells in the marine environment and its release from these cells upon their death and subsequent decay can contribute to Ba accumulation in marine sediments.

Elemental Markers in Elasmobranchs: Effects of Environmental History and Growth on Vertebral Chemistry

Differences in the chemical composition of calcified skeletal structures (e.g. shells, otoliths) have proven useful for reconstructing the environmental history of many marine species. However, the extent to which ambient environmental conditions can be inferred from the elemental signatures within the vertebrae of elasmobranchs (sharks, skates, rays) has not been evaluated. To assess the relationship between water and vertebral elemental composition, we conducted two laboratory studies using round stingrays, Urobatis halleri, as a model species. First, we examined the effects of temperature (16°, 18°, 24°C) on vertebral elemental incorporation (Li/Ca, Mg/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca). Second, we tested the relationship between water and subsequent vertebral elemental composition by manipulating dissolved barium concentrations (1x, 3x, 6x). We also evaluated the influence of natural variation in growth rate on elemental incorporation for both experiments. Finally, we examined the accuracy of classifying individuals to known environmental histories (temperature and barium treatments) using vertebral elemental composition. Temperature had strong, negative effects on the uptake of magnesium (DMg) and barium (DBa) and positively influenced manganese (DMn) incorporation. Temperature-dependent responses were not observed for lithium and strontium. Vertebral Ba/Ca was positively correlated with ambient Ba/Ca. Partition coefficients (DBa) revealed increased discrimination of barium in response to increased dissolved barium concentrations. There were no significant relationships between elemental incorporation and somatic growth or vertebral precipitation rates for any elements except Zn. Relationships between somatic growth rate and DZn were, however, inconsistent and inconclusive. Variation in the vertebral elemental signatures of U. halleri reliably distinguished individual rays from each treatment based on temperature (85%) and Ba exposure (96%) history. These results support the assumption that vertebral elemental composition reflects the environmental conditions during deposition and validates the use of vertebral elemental signatures as natural markers in an elasmobranch. Vertebral elemental analysis is a promising tool for the study of elasmobranch population structure, movement, and habitat use.

Precipitation of calcium, magnesium, strontium and barium in tissues of four Acacia species (Leguminosae: Mimosoideae).

Precipitation of calcium in plants is common. There are abundant studies on the uptake and content of magnesium, strontium and barium, which have similar chemical properties to calcium, in comparison with those of calcium in plants, but studies on co-precipitation of these elements with calcium in plants are rare. In this study, we compared morphologies, distributional patterns, and elemental compositions of crystals in tissues of four Acacia species grown in the field as well as in the glasshouse. A comparison was also made of field-grown plants and glasshouse-grown plants, and of phyllodes of different ages for each species. Crystals of various morphologies and distributional patterns were observed in the four Acacia species studied. Magnesium, strontium and barium were precipitated together with calcium, mainly in phyllodes of the four Acacia species, and sometimes in branchlets and primary roots. These elements were most likely precipitated in forms of oxalate and sulfate in various tissues, including epidermis, mesophyll, parenchyma, sclerenchyma (fibre cells), pith, pith ray and cortex. In most cases, precipitation of calcium, magnesium, strontium and barium was biologically induced, and elements precipitated differed between soil types, plant species, and tissues within an individual plant; the precipitation was also related to tissue age. Formation of crystals containing these elements might play a role in regulating and detoxifying these elements in plants, and protecting the plants against herbivory.

Selective ion exchange onto Slovakian natural zeolites in aqueous solutions

Ion exchange isotherms have been measured and plotted for the uptake of cesium, barium, cobalt, zinc, silver and amonium onto clinoptilolite- and mordenite-rich tuffs of Slovakian origin selectively for both the natural and near homoionic Na form as well, using the radioanalytical determination. The higher quality clinoptilolite-rich tuff has been proven to be effective for a potential radionucleides removal in native form according to the following selectivity sequence: Ag+,Ba2,Cs+>NH4+>Co2+, while parent tuff in Na exchanged variety exhibited a little different sequence according to: Ag+ > NH4+ > Ba2+ > Cs+. The raw and Na exchanged mordenite-rich tuffs proved subsequently more or less similar selectivity : Ag+ > Zn2+ > Cs+, Ba2+ > Co2+ and Ag+ > Zn2+.

Absorção de bário por plantas de arroz (Oryza sativa L.) e mobilidade em solo tratado com baritina sob diferentes condições de potencial redox

Two parallel tests were carried out to evaluate barium solubility in soils treated with barite under reducing conditions: one in leaching columns and another with potted plants cultivated with rice. Soils were treated with three doses of barite and kept at two humidity levels. The reduction (-200 mV) condition promoted an increase in barium in the geochemical fraction of higher liability, higher concentrations of barium in the leached extracts, and higher absorption by rice plants. As a result of increased uptake and accumulation of barium, the plants showed stunted growth

Effects of temperature and elemental concentration on the chemical composition of juvenile yellow perch (Perca flavescens) otoliths

Otolith microchemistry studies assume that a relationship exists between the concentration of trace elements in the environment and otolith chemical composition. Although this assumption has been tested using marine and estuarine fish in controlled laboratory experiments, the relationships among temperature, ambient elemental concentration, and otolith chemical composition for freshwater species is not well documented. Here, juvenile yellow perch ( Perca flavescens ) were reared under different concentrations of four elements (Ba, Mg, Mn, and Sr) crossed with three temperatures (10 °C, 15 °C, and 20 °C) to determine the interactive influence of ambient elemental concentrations and temperature on otolith chemical composition. Sr:Ca and Ba:Ca were significantly related to ambient elemental concentrations, but Mg:Ca and Mn:Ca were not. Although the relative influence of temperature was less than that of ambient elemental concentrations, Sr:Ca, Ba:Ca, and Mn:Ca were all influenced by either water temperature or the interaction between temperature and elemental concentration, but the direction of the temperature effect differed for each element. Patterns in our partition coefficients are consistent with the idea that uptake of strontium facilitates uptake of barium. Overall, yellow perch otolith element composition was influenced primarily by ambient Sr and Ba concentrations, but temperature could potentially confound the results of otolith microchemistry studies.

Toxicity and histopathological effects of oil-based drilling mud on edible swimming crab (<i>Callinectes amnicola</i>)

Acute static bioassay was carried out to determine the toxicity and histopathology effects of oil-based drilling mud, using the edible swimming crab, Callinectes amnicola. The drilling mud evaluated is widely and consistently applied in exploratory operations and discarded haphazardly in the myriad of water systems, which characterise the Niger Delta basin. Pronounced mortal damage occurred in crabs exposed to as low as 2% concentration by volume of the drilling mud. Histo-pathological consequences of the tested mud on the crabs included irregular tissue shape, macrophages, inflammatory cells and basiophilic spots, etc. Uptake of barium, a carcinogenic component of the drilling mud by the crabs and implications for human consumers are also discussed. Animal Production Research Avancees Vol. 3 (1) 2007: pp. 64-68

Cholesterol depletion perturbs calcium handling by rat submandibular glands

The sensitivity to cholesterol depletion of calcium handling by rat submandibular glands was investigated. The glands were digested with collagenase. After homogenization, the lysate was extracted at 4 degrees C with 0.5% Triton X-100 and the extract was submitted to an ultracentrifugation in a sucrose discontinuous gradient. A population of detergent-resistant membranes (DRM) was collected at the 5%-35% interface. The DRM had a higher content of cholesterol, saturated and long-chain fatty acids. Caveolin-1 and alpha(q/11) were located in these membranes. They were more ordered than vesicles from total cellular lysate as determined by anisotropy measurement. They disappeared after cholesterol extraction with methyl-beta-cyclodextrin (MCD). Exposure of the cellular suspension with MCD nearly abolished the response to carbachol, epinephrine, and substance P and inhibited the activation of phospholipase C (PLC) by these agonists and by sodium fluoride. MCD did not affect the mobilization of intracellular pools of calcium by thapsigargin. It increased the uptake of extracellular calcium or barium and did not inhibit the uptake of calcium after depletion of the intracellular stores of this ion. From these results, it is concluded that Triton X-100 can extract a fraction of membrane resistant to detergents. Treatment of the cells with MCD disrupts these membranes. The coupling between the heterotrimeric GTP-binding protein G(q/11) and poly-phosphoinositide-specific PLC is affected by disruption of these membrane fractions. At the opposite, the store-operated calcium channel (SOCC) is not affected by DRM-disruption.

Multiple effects of trichloroethanol on calcium handling in rat submandibular acinar cells.

The effect of trichloroethanol (TCEt), the active metabolite of chloral hydrate, on the intracellular concentration of calcium ([Ca(2+)](i)) was investigated in rat submandibular glands (RSMG) acini loaded with fura-2. TCEt (1 - 10 mM) increased the [Ca(2+)](i) independently of the presence of calcium in the extracellular medium. Dichloroethanol (DCEt) and monochloroethanol (MCEt) reproduced the stimulatory effect of TCEt but at much higher concentrations (about 6 fold higher for DCEt and 20 fold higher for MCEt). TCEt mobilized an intracellular pool of calcium, which was depleted by a pretreatment with thapsigargin, an inhibitor of the sarcoplasmic and endoplasmic reticulum calcium-dependent ATPases, but not with FCCP, an uncoupler of mitochondria. TCEt 10 mM inhibited by 50% the thapsigargin-sensitive microsomal Ca(2+)-ATPase. DCEt 10 mM and MCEt 10 mM inhibited the ATPase by 20 and 10%, respectively. TCEt inhibited the increase of the [Ca(2+)](i) and the production of inositol phosphates in response to carbachol, epinephrine and substance P. TCEt inhibited the uptake of calcium mediated by the store-operated calcium channel (SOCC). ATP and Bz-ATP increased the [Ca(2+)](i) in RSMG acini and this effect was blocked by extracellular magnesium, by Coomassie blue and by oxydized ATP (oATP). TCEt potentiated the increase of the [Ca(2+)](i) and of the uptake of extracellular calcium in response to ATP and Bz-ATP. TCEt had no effect on the uptake of barium and of ethidium bromide in response to purinergic agonists. These results suggest that TCEt, at sedative concentrations, exerts various effects on the calcium regulation: (1) it mobilizes a thapsigargin-sensitive intracellular pool of calcium in RSMG acini; (2) it inhibits the uptake of calcium via the SOCC; (3) it inhibits the activation by G protein-coupled receptors of a polyphosphoinositide-specific phospholipase C. It does not interfere with the activation of the ionotropic P2X receptors. The use of chloral hydrate should be avoided in studies exploring the in vivo responses to sialagogues.

Crystal growth and characterization of barium doped calcium tartrate tetrahydrate crystals

Calcium tartrate tetrahydrate (CTT) single crystals doped with barium were grown by controlled diffusion in silica gel at ambient temperature. The maximum uptake of barium in CTT was determined. Effect of barium dopant on the growth and morphology of CTT was studied. The grown crystals were characterized by chemical analysis, thermoanalytical techniques, X-ray diffraction and optical studies. Barium-doped CTT crystallizes in the monoclinic system. The crystals are optically biaxial and exhibit second harmonic signals greater than quartz.

Biotic and Abiotic Controls of the Barium Distribution in the Southern Ocean Water Column

Besides mixing, the dissolved barium distribution in the oceanic water column is controlled to a significant extent also by particle-solute interaction. In vi tro uptake experiments involving diatom cultures suggest that passive uptake prevails over active uptake. The overall effect of these processes is that barium behaves as a non-limiting nutrient element with ratios of dissolved over particulate concentrations varying between 100 and 1000. Uptake of barium by plankton particles eventually results in the formation of barium sulphate (baryte). There is increasing evidence that this baryte formation is closely linked with the formation of micro-environments composed of detrital organic matter, in which BaSO4 saturation is eventually reached during the process of bacterial decay (Bishop, 1988; Dehairs et al., 1980). This mechanism sets the link between oceanic baryte and oceanic productivity and as a result oceanic baryte is now increasingly recognised to represent a good proxy for palaeoproductivity (Francois e ta / . , 1995). Using an extensive data set obtained mainly from the Southern Ocean we investigated the different main processes affecting the oceanic barium cycle. For particulate barium in surface waters regional variability can be important and this is clearly associated with variation of planktonic production and biomass such as occurring, for instance, across the Polar Front Zone (PFZ). We observed that on a time scale of approximately three weeks water column stocks of micro-crystalline baryte co-vary with seasonal change in surface water productivity (Dehairs et al. 1997). This phase lag of about three weeks is consistent with the time lapse required for baryte to be formed during in vitro experiments using decaying detritus from a diatom culture. This process Department of Analytical Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050, Brussels, Belgium

Uptake and Trophic Transfer of Barium in a Terrestrial Ecosystem

At an industrial site in central Virginia, organochlorine solvents and inorganic compounds with the potential to adversely affect wildlife have been released into the environment as a consequence of past industrial activities and practices. In the course of a ecological risk assessment for the site, soil, surface water, vegetation, insect, fish, and small mammal tissues were analyzed to ascertain whether these contaminants were bioavailable and present in the food chain. Although organochlorine solvents were found in the soil, none were found higher in the food chain. Of the inorganic compounds for which chemical analyses were performed, only barium was found at above detection limits at several level trophic levels. Four hypotheses were formed to investigate the behavior of barium in the terrestrial ecosystem at this site, as follows:

Generation and characterization of iron- and barium-loaded liposomes

Previous work (Veiro and Cullis (1990) Biochim. Biophys. Acta 1025, 109–115) has shown that Ca 2+ can be accumulated into large unilamellar vesicles (LUVs) in the presence of a transmembrane pH gradient (inside acidic) and the Ca 2+-ionophore A23187. Here, the ability of A23187 to mediate the uptake of iron and barium into LUVs has been investigated. It is shown that under appropriate conditions of temperature and A23187 concentration, iron (in the form of Fe 2+) can be accumulated into EPC and DSPC/cholesterol (55:45; mol/mol) LUVs with an acidic interior. This uptake is dependent on the internal buffer concentration, with maximum levels of uptake in the range of 300 nmol of cation per μmol lipid. The DSPC-cholesterol LUV systems exhibit superior retention properties compared to the EPC systems. It is demonstrated that Ba 2+ can also be loaded by similar methods. It is also shown that the maximally loaded Fe 2+- and Ba 2+-containing LUVs exhibit increased densities. This is expressed by enhanced gravimetric properties, as an increased proportion of the loaded LUVs can be pelleted by low speed centrifugation, and by enhanced electron densities, in that the Ba 2+-loaded systems can be directly visualized employing cryo-electron microscopy.

Uptake of barium and strontium by cress ( Lepidium Sativum) in water culture and the presence of an inhibiting soluble factor

Seeds of cress were sown in various densities on plastic grids placed in half-litre dishes filled with either a dilute salt solution or distilled water. After 2 days the radionuclides 133Ba, 134Cs and 85Sr were added, and after another 5 days the plants were harvested and the radioactivity measured by γ-ray spectrometry. It was found that plants grown in low density cultures took up more than ten times the activity of Ba and Sr than plants in dense cultures. In a second experiment, plants were grown in non-radioactive medium for 5 days and then some of the plants were changed so that the sparse culture was placed in the dish which previously contained the dense sulture and vice versa. The radionuclides were then added. These plants in alternated sparse cultures concentrated less radioactivity of Ba and Sr than the corresponding non-alternated cultures. Furthermore, when water from very dense cultures on which plants had grown for a week was sterile-filtered and added to fresh cultures, it was shown that this conditioned water strongly inhibited the uptake of Ba and Sr, although the concentration of “conditioned water” was only 15% of the total volume. The difference in radionuclide concentration in the plants as a function of plant density disappeared when the concentrations of Ca and Mg in the nutrient solution were raised to 0.15 and 0.40 mM, respectively. Apparently a chelating substance, possibly excreted from the plant roots, is responsible for the inhibition of the uptake of bivalent cations, and this agent becomes saturated when bivalent cations are present at sufficiently high concentrations.

Effect of aquatic humus on uptake of zinc and barium to alga [formula omitted

Effect of aquatic humus on uptake of zinc and barium to green alga Selenastrum capricornutum Printz has been radiometrically studied using Ba-133 and Zn-65 tracers. The presence of aquatic humus decreases uptake of barium and zinc by alga. The logarithm of accumulated radioactivity of Ba-133 and/or Zn-65 is linearly proportional to logarithm of wet biomass of alga. Concentration factors for barium (1 ± 0.2) × 10 3 and zinc (15.6 ± 3.6) × 10 3 were independent of biomass production in presence of aquatic humus of TOC 1.62 mg C/1. We also found that radiobarium added in the form of BaCl 2 in absence of aquatic humus is immediately accumulated by the alga in contrast to accumulation of radiozinc added in the form of ZnCl 2. The aquatic humus also supresses the sorption of barium and zinc onto the walls of the cultivation vessels as well as the sorption onto membrane filters Millipore HAWP.

A study of barium accumulation in desmids using the Oxford scanning proton microprobe (SPM)

Within a group of unicellular freshwater algae called desmids there is a genus, Closterium, the cells of which are known to store BaSO 4 microcrystals in vacuoles situated at each end of the cell. In studies involving Closterium moniliferum cells grown in cultures containing different concentrations of BaCl 2, it was observed that the barium uptake, as measured by the Oxford SPM, was not lowest at the lowest concentrations of BaCl 2 to which the cells were exposed (0.001 and 0.01 mg/l but unexpectedly at a median concentration of 1.0 mg/l. In a second study on Closterium moniliferum cells grown in a culture containing 0.010 mg Ba/l, the rate of uptake of barium was observed to level off over a 24 h period. SPM elemental maps of Closterium cells are presented, one sample of which was grown in a normal medium and shows BaSO 4 crystals present in the terminal vacuoles, and the other sample grown in a Ba rich medium and showing BaSO 4 crystals distributed throughout the cell.

Kinetics of the Adsorption of Radionuclides on Tuff From Yucca Mountain

ABSTRACTThe sorption of simple cations in tuff is dominated by adsorption on aluminosilicates that have charged surfaces, suc as zeolites and clays. The most significant sorbing minerals present in Nevada tuff are clinoptilolite, heulandite, mordenite, and montmorillonite. The kinetics of sorption on tuffs containing the minerals clinoptilolite and montmorillonite has been determined by studying the uptake of strontium, cesium, and barium on thin tuff wafers. The rate constants for uptake of these elements on tuff are consistent with a model of sorption that is diffusion limited but where diffusion occurs in two stages. First the cations diffuse into the rock through the water-filled pore space. Next, the cations must diffuse into the much narrower channels within the aluminosilicate crystals. After they are within the zeolite framework o between the clay planes, the cations may rapidly sorb on the negatively charged surfaces. The actinide elements have a time constant for the apparent sorption that is inconsistent with this model and may have a radically different mechanism o removal from solution.