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PubMed1994

Domoic acid induced release of [3H]GABA in cultured chick retina cells.

The effect of the neurotoxin domoic acid (DOM), a structural analogue of kainic acid, on the release of [3H]gamma-aminobutyric acid (GABA) and on the [Ca2+]i was studied in cultured chick retina cells. DOM stimulated dose-dependently the release of [3H]GABA with an EC50 of 2.5 microM. In Ca(2+)-containing medium (1 mM), DOM (5 microM) increased the [Ca2+]i by about 190 nM and evoked the release of 11.8 +/- 1.3% of the intracellular [3H]GABA, while in the absence of extracellular Ca2+ DOM induced the release of only 7.9 +/- 1.4% of the accumulated [3H]GABA. The Ca(2+)-independent release of [3H]GABA was blocked by the non-competitive inhibitor of the GABA carrier 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5,6-tetrahydro-3-py ridine- carboxylic acid hydrochloride (NNC-711), but a component of Ca(2+)-dependent release remains. DOM evoked Ca(2+)-independent release of [3H]GABA was significantly depressed in the absence of external Na+ and completely blocked by the non-selective antagonist of the non-NMDA glutamate receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Similarly, CNQX decreased the [Ca2+]i response to DOM, whereas L(+)-2-amino-3-phosphonopropionic acid (L-AP3), an antagonist of the metabotropic glutamate receptors, was without effect. MK-801 did not affect the release of [3H]GABA stimulated by DOM. Taken together our results indicate that DOM evokes both Ca(2+)-dependent and Ca(2+)-independent release of [3H]GABA, most likely by activating kainate receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

PubMed2004

Physiological action of dissolved organic matter in rainbow trout in the presence and absence of copper: sodium uptake kinetics and unidirectional flux rates in hard and softwater.

We investigated the physiological effects of dissolved organic matter (DOM) on sodium (Na+) transport in juvenile Oncorhynchus mykiss (approximately 2.5 g) in the presence and absence of simultaneous acute exposure to copper (Cu2+; 0, 70, and 300 microg l(-1)). Trout were acclimated in either hardwater (approximately 1000 microM Ca2+) or softwater (approximately 100 microM Ca2+), and DOM was tested at approximately 8 mg C l(-1) using a natural (NOM) and a commercial (AHA) source. Ion transport was evaluated based on kinetics estimates (maximum Na+ uptake rates, Jmax; substrate affinity, Km) and unidirectional flux measurements (Jin, Jout, Jnet). Jmax was higher and unidirectional flux rates were greater in softwater-acclimated trout. Fish exposed to DOM alone in hardwater exhibited an increased Na+ transport capacity indicated by both the kinetics (67% higher Jmax for AHA) and Jin measurements (153% higher for AHA and 125% higher for NOM). In softwater, the effects of DOM alone on kinetic parameters and unidirectional flux rates were negligible. Cu2+ affected Na+ uptake by a mixed-type inhibition (both non-competitive and competitive). In hardwater, only Km was increased (i.e., affinity decreased), whereas in softwater, Km was increased and Jmax was decreased, with more marked effects at the higher Cu2+ level. In hardwater, the stimulatory effect of AHA on Jmax persisted even in the presence of 300 microg l(-1) Cu2+, whereas both AHA and NOM prevented the increase in Km caused by Cu2+; these effects were reflected in Jin measurements. In softwater, AHA helped to protect against the increased Km caused by high Cu2+, but there was no protection against the inhibition of Jmax. Unidirectional flux measurements indicated that in softwater, Cu2+ inhibited Jin at 70 microg l(-1), whereas at 300 microg l(-1) Cu2+, Jout was also stimulated. Fish were more affected by Cu2+ in softwater, as indicated by the inability to control diffusive losses of Na+ and a reduced ability to take up Na+, but in the presence of DOM, losses were better controlled at the end of 6 h exposure. We conclude that DOM has direct effects on the gills, as well as protecting fish against acute Cu2+ toxicity. This occurs because DOM complexes Cu2+, and because it acts on the transport and permeability properties of the gills. These effects differ depending on both water hardness and the nature of the DOM source.

Adaptation, Physiological↗

PubMed2004

An independent prediction of the effect of dissolved organic matter on the transport of polycyclic aromatic hydrocarbons.

The transport of polycyclic aromatic hydrocarbons (PAH) in porous media in the presence of dissolved organic matter (DOM) was predicted with a transport bicontinuum model using independently obtained relationships to derive transport parameters for describing the effect of PAH binding to the DOM. The sorption constants of PAHs to soil and their binding constants to DOM were derived from basic correlations with K(ow) (indicator of hydrophobicity). The kinetic (rate) constants were derived from previously published correlations with K(p) (sorption constant). The independently obtained sorption and rate constants were corrected for binding to DOM and were used to predict the breakthrough curves (BTC) of contaminants in the presence and the absence of DOM. Column results confirmed the independently predicted BTC of PAHs in the presence of DOM that did not sorb to the solid phase, as well as the effect of DOM on the rate of the sorption and desorption processes. These findings confirm the ability to quantitatively describe how DOM facilitates transport of contaminants in the subsurface using independently derived parameters.

Absorption↗

PubMed2005

Development and application of functional assays for freshwater dissolved organic matter.

A series of 11 standardised, reproducible, assays have been developed of physico-chemical functions of dissolved organic matter (DOM) in freshwaters. The assays provide quantitative information on light absorption, fluorescence, photochemical fading, pH buffering, copper binding, benzo(a)pyrene binding, hydrophilicity and adsorption to alumina. To obtain DOM for the assays, a 45 L sample of filtered freshwater was rotary-evaporated to reduce the volume to ca. 500 cm3. The concentrate was then passed through a strong cation exchanger, in the Na+ form, to remove alkaline-earth cations, and then through 0.7 and 0.2 microm filters. Eight samples, two each from a lake and three streamwaters, were processed. The yields of dissolved organic carbon (DOC) ranged from 70% to 107% (average 91%). The samples of DOM, stored in the dark at 4 degrees C, retained their functional assay characteristics for up to 7 months. When assaying the concentrates, parallel assays were performed with Suwannee River fulvic acid (SRFA), as a quality control standard. For most of the assays, the results for eight freshwater DOM samples are similar to those obtained with SRFA, the chief exception being the greater hydrophilicity of the DOM samples. For eight of the assays, variability among the DOM samples is significantly (p < 0.01) greater than can be explained by analytical error, i.e. by comparison with results for the SRFA quality standard; the three exceptional assays are photochemical fading, copper binding and benzo(a)pyrene binding. The two lakewater samples studied gave the most extreme assay results, probably because of the influence of phytoplankton-derived DOM. Significant correlations of hydrophilicity and adsorption with optical absorbance may mean that some DOM functional properties can be predicted from comparatively simple measurements.

Benzo(a)pyrene↗

PubMed2006

Adsorption of Cu(II) to schwertmannite and goethite in presence of dissolved organic matter.

Sorption processes involving secondary iron minerals may significantly contribute to immobilisation of metals in soils and surface waters. In the present work the effect of dissolved organic matter (DOM) from a concentrated bog-water on the adsorption of Cu(II) onto schwertmannite (Fe8O8(OH)6SO4) and goethite (alpha-FeOOH) has been studied. The acid/ base behaviour of DOM up to pH 6 was explained by assuming a diprotic acid with a density of carboxylate groups of 6.90 microeq (mg C)(-1). The resulting acidity constants, recalculated to zero ionic strength were pK(0)a1 = 3.61 and pK(0)a2 = 5.34. The uptake of DOM to schwertmannite and goethite was highest at low pH although adsorption was significant also under mildly alkaline conditions. Adsorption to the two minerals was similar although at high pH more DOM was adsorbed to schwertmannite than to goethite. DOM enhanced the adsorption of Cu(II) at moderately low pH in the goethite system but there was no effect of DOM in the case of schwertmannite. The presence of Cu(II) resulted in a decreased adsorption of DOM to goethite at weakly acidic pH and increased adsorption at high pH. In the case of schwertmannite, Cu(II) did not affect DOM uptake.

Adsorption↗

PubMed2003

Polydisperse adsorbability composition of several natural and synthetic organic matrices.

The polydisperse composition of nine dissolved organic materials (DOMs) from two river water sources, one ground water source, two biologically treated wastewater sources, and two commercial sources was analyzed based on their adsorbabilities by activated carbon. For each DOM, batch adsorption isotherms measured for both TOC and UV260 were analyzed using an overall isotherm model derived from the IAST-Freundlich expression. By accounting for the heterogeneity of each DOM with a log-normal distribution of the Freundlich parameter (K), its adsorption behavior was characterized with only four parameters (including three fitting ones). The average adsorptive strength (KM) and heterogeneity (sigma) determined for all DOMs, which were defined by the mean value and the standard deviation of the log-normal distribution of the Freundlich K, changed over the ranges 2.5-62.2 and 0.22-0.97 (mg/g)/(mg/l)(1/n), respectively, when the TOC index was used. Among all DOMs studied, a river water DOM at the upper stream was found least heterogeneous: the Freundlich K of its organic constituents varied in the range 10.8-190 (mg/g)/(mg/l)(1/n), as compared to a commercial humic acid that exhibited the broadest Freundlich K distribution of 0.01-1494.3 (mg/g)/(mg/l)(1/n). KM and sigma, along with other two parameters (the Freundlich exponent 1/n and the nonadsorbable organic fraction parameter Cnon/CT0), changed with both indices of TOC and UV260 in a regular manner, indicating that UV-absorbing organic molecules possessed adsorbabilities different from non-UV-absorbing ones. Also based on HPSEC chromatograms measured for solutions before adsorption, the molecular weight composition of all DOMs was also assessed and the molecular size impacts on adsorption characteristics of DOMs were briefly discussed.

Adsorption↗

PubMed2002

Age-related changes in tolerance to the marine algal excitotoxin domoic acid.

During an incident of toxic mussel poisoning, the epileptogenic excitotoxin domoic acid (DOM) was associated with lasting neurological deficits mainly in older patients (), suggesting supersensitivity to excitotoxins is a feature of brain aging. Here, hippocampal slices from young (3 months) and aged (26-29 months) Sprague Dawley rats were assessed by CA1 field potential analysis before and after preconditioning with DOM. In naïve slices from young animals, DOM produced initial hyperexcitability followed by significant dose-dependent reductions in population spike amplitude during prolonged application. Following toxin washout, only small changes in neuronal activity were evident during a second application of DOM, suggesting that a resistance to the effects of DOM occurs in hippocampal slices which have undergone prior exposure to DOM. This inducible tolerance was not antagonized by the NMDA receptor blockers APV or MK-801, nor was it diminished by the group I, II or III mGluR blockers AIDA, CPPG and EGLU. Likewise, neither the AMPA/KA blocker CNQX nor the VSCC blocker nifedipine were effective in blocking tolerance induction in young slices. Field potential analysis revealed significant age-related reductions in CA1 EPSP strength, population spike amplitude and paired-pulse inhibition, but aged slices did not differ in sensitivity to DOM relative to young. However, aged CA1 failed to exhibit any tolerance to DOM following preconditioning, suggesting that a loss of inducible neuroprotective mechanisms may account for increased sensitivity to excitotoxins during aging.

Aging↗

PubMed2002

Characterization of dissolved organic matter in effluents from wastewater treatment plants.

Dissolved organic matter (DOM) in effluents from sewage and human-wastes treatment plants (STPEs and HWTPEs) was fractionated using resin adsorbents into six classes: aquatic humic substances (AHS), hydrophobic bases (HoB), hydrophobic neutrals (HoN), hydrophilic acids (HiA), hydrophilic bases (HiB), and hydrophilic neutrals (HiN). DOM-fraction distribution varied substantially depending on the kind of wastewater and the type of treatment process. AHS and HiA dominated in all effluents, collectively accounting for more than 55% of the DOM measured as dissolved organic carbon (DOC). In particular, HiA were the most abundant fraction in the effluents, constituting 32-74% of the DOM. AHS appeared to be the second most dominant fraction and varied considerably, accounting for 3-28% of the DOM. The HoN fraction also varied from 0-21%. AHS, HoN, and HiA were the fractions that changed substantially and differed characteristically among the samples studied. The ratios of ultraviolet absorbance to DOC (UV: DOC ratio) in all effluents exhibited a common relationship: AHS> total DOM > HiA. Nevertheless, the ratios were substantially different between STPEs and HWTPEs and among HWTPEs. For HWTPEs, the effluent from the chemical coagulation process had the highest UV: DOC ratios. On the other hand, the effluent from the ultrafiltration and activated carbon adsorption processes had the lowest ratios. Molecular size distribution of the effluents was determined by size exclusion chromatography and found to exhibit a relatively narrow size range and low weight-averaged molecular weights ranging from 380 to 830 g mol(-1). The weight-averaged molecular weight of DOM increased as the UV: DOC ratio of total DOM increased.

Chromatography↗

PubMed2002

Factors affecting the adsorption capacity of dissolved organic matter onto activated carbon: modified isotherm analysis.

Effects of aqueous phase Ca(II) concentrations and pH levels on the adsorption capacity of dissolved organic matters (DOMs) as well as the capacity dependency on the sources and types of DOMs and activated carbons (ACs) were examined. The Ca(II) effect was studied for three coal-based ACs having different pore size distributions (PSDs) and for three DOMs contained in three water samples. For each water sample, four working solutions prepared by adding different dosages of Ca(II) (0-1.5 mM) were used. For the water sample whose adsorption capacity was least affected by Ca(II), the effect of pH was subsequently examined for four water pH levels (pH = 5.5-10) and these three ACs. Isotherm data were analyzed in terms of a modified isotherm model selected from three models developed for normalizing isotherms of heterogeneous organic mixtures. The Ca(II) effect depended obviously on the DOMs used. For all three ACs, increasing Ca(II) greatly enhanced the adsorption capacity of a commercial humic acid. However, the capacity of the DOM in a naturally colored surface water source was much less affected and that of the DOM remaining after precoagulation was not affected. The DOM-Ca(II) interactions, rather than the AC-Ca(II) interactions, seemed to be the predominant mechanism that controlled the extent of the Ca(II)'s impact. Water pH greatly affected the adsorption of the surface water DOM remaining after precoagulation. This effect seemed to be attributed to pH's capability in changing ACs' charge characteristics reflected by zeta-potentials. The adsorption capacity increased as the water pH decreased and was well correlated as a function of pH and the volume of AC pores in sizes of 30-100 A. ACs having more pores in this size region generally exhibited larger adsorption capacities.

Adsorption↗

PubMed2003

Dissolved organic matter effects on the performance of a barrier to polycyclic aromatic hydrocarbon transport by groundwater.

In order to contain the movement of organic contaminants in groundwater, a subsurface sorption barrier consisting of sand or clay minerals coated with a cationic surfactant has been proposed. The effectiveness of such a sorption barrier might be affected by the presence of dissolved organic matter (DOM) in the groundwater. To study the impact of DOM on barrier performance, a series of batch experiments were performed by measuring naphthalene and phenanthrene sorption onto sand coated with cetylpyridinium chloride (CPC) and bentonite coated with hexadecyltrimethylammonium bromide (HDTMA) in the presence of various concentrations of DOM. The overall soil-water distribution coefficient (K*) of naphthalene and phenanthrene onto CPC-coated sand decreased with increasing DOM concentration, whereas the K* of the compounds onto HDTMA-coated bentonite slightly increased with increasing DOM concentration. To describe the overall distribution of polycyclic aromatic hydrocarbons (PAHs) in the systems, a competitive multiphase sorption (CMS) model was developed and compared with an overall mechanistic sorption (OMS) model. The modeling studies showed that while the OMS model did not explain the CPC-coated sand experimental results, a model that included competitive sorption between DOM and PAH did. The experimental results and the modeling study indicated that there was no apparent competition between DOM and PAH in the HDTMA-coated bentonite system, and indicated that in groundwater systems with high DOM, a barrier using HDTMA-coated bentonite might be more effective.

Adsorption↗

PubMed2003

Effect of dissolved organic matter and bacteria on contaminant transport in riverbank filtration.

A mathematical model for the transport of hydrophobic organic contaminants in an aquifer under simplistic riverbank filtration conditions is developed. The model considers a situation where contaminants are present together with dissolved organic matter (DOM) and bacteria. The aquifer is conceptualized as a four-phase system: two mobile colloidal phases, an aqueous phase, and a stationary solid phase. An equilibrium approach is used to describe the interactions of contaminants with DOM, bacteria, and solid matrix. The model is composed of bacterial transport equation and contaminant transport equation. Numerical simulations are performed to examine the contaminant transport behavior in the presence of DOM and bacteria. The simulation results illustrate that contaminant transport is enhanced markedly in the presence of DOM and bacteria, and the impact of DOM on contaminant mobility is greater than that of bacteria under examined conditions. Sensitivity analysis demonstrates that the model is sensitive to changes of three lumped parameters: K+1 (total affinity of stationary solid phase to contaminants), K+2 (total affinity of DOM to contaminants), and K+3 (total affinity of bacteria to contaminants). In a situation where contaminants exist simultaneously with DOM and bacteria, contaminant transport is mainly affected by a ratio of K+1/K+2/K+3, which can vary with changes of equilibrium distribution coefficient of contaminants and/or colloidal concentrations. In riverbank filtration, the influence of DOM and bacteria on the transport behavior of contaminants should be accounted to accurately predict the contaminant mobility.

Bacteria↗

PubMed2003

Binding of mercury(II) to aquatic humic substances: influence of pH and source of humic substances.

Conditional distribution coefficients (K(DOM')) for Hg(II) binding to seven dissolved organic matter (DOM) isolates were measured at environmentally relevant ratios of Hg(II) to DOM. The results show that K(DOM') values for different types of samples (humic acids, fulvic acids, hydrophobic acids) isolated from diverse aquatic environments were all within 1 order of magnitude (10(22.5 +/-1.0)-10(23.5 +/- 1.0)) L kg(-1)), suggesting similar Hg(ll) binding environments, presumably involving thiol groups, for the different isolates. K(DOM') values decreased at low pHs (4) compared to values at pH 7, indicating proton competition for the strong Hg(II) binding sites. Chemical modeling of Hg(II)-DOM binding at different pH values was consistent with bidentate binding of Hg(II) by one thiol group (pK(a) = 10.3) and one other group (pK(a) = 6.3) in the DOM, which is in agreement with recent results on the structure of Hg(II)-DOM bonds obtained by extended X-ray absorption fine structure spectroscopy (EXAFS).

Environmental Monitoring↗

PubMed2004

Effects of dissolved organic matter surrogates on the partitioning of 17beta-estradiol and p-nonylphenol between synthetic membrane vesicles and water.

Partition coefficients of two estrogenic compounds, 17beta-estradiol (E2) and p-nonylphenol (NP), between synthetic membrane vesicles (K'lipw values) and water were determined using equilibrium dialysis to evaluate the potential biological uptake of these compounds with and without the presence of dissolved natural organic matter (DOM) surrogates, Suwannee River fulvic acid, dialyzed Aldrich humic acid, and polyphenolic tannic acid. Overall, K'lipw values for E2 and NP reduced by 20-30% with the increase of DOM concentration from 0 to approximately 4 mg of C/L, a typical DOM concentration in the aquatic environment. This trend for E2 and NP is similar to that obtained by other researchers for moderately hydrophobic compounds including polycyclic aromatic hydrocarbons with three or four rings. A three-phase compartment model with three independent interactions, the sorption of E2 or NP by DOM surrogate (Koc), the sorption of DOM surrogates by membrane vesicles (KlipDOM), and the partition of E2 or NP by membrane vesicles (Klipw), was proposed, and K'lipw values for E2 or NP in the presence of DOM were calculated. The model predicted the decrease in Klipw values with the increase of DOM concentration, and the predictions using the three linear interactions agreed satisfactorily with the experimental results at relatively lower concentration of DOM.

Estradiol↗

PubMed2005

Photochemical oscillation of Fe(II)/Fe(III) ratio induced by periodic flux of dissolved organic matter.

Variation of iron species in the UV-irradiated aqueous solution was examined in the presence of various dissolved organic matter (DOM). Under the irradiation at constant light intensity, a regular oscillation in the ratio of Fe(II) to total iron, Fe(II)/Fe(t), was observed when DOM was periodically added into the solution. In each cycle, the Fe(II)/Fe(t) ratio increased initially and then decreased with concomitant degradation of DOM. The Fe(II)/Fe(t) ratio approached a constant value after the DOM was completely mineralized. The period and amplitude of the oscillation were dependent on DOM structure and its initial concentration, but the ultimate photosteady state was not affected by DOM. It was revealed that both DOM and photoreactive Fe(III) species were indispensable for the fluctuation in Fe(II)/Fe(t) ratio. The ultimate photosteady state originated from the equilibrium between Fe(III) photoreduction and aerobic Fe(II) photooxidation induced simultaneously by UV irradiation. It was the DOM that disturbed these two opposite processes, leading to the oscillation in Fe(II)/ Fe(t) ratio under UV irradiation.

Iron↗

PubMed2006

Arsenite and arsenate binding to dissolved humic acids: influence of pH, type of humic acid, and aluminum.

The fate of arsenic in the aquatic environment is influenced by dissolved natural organic matter (DOM). Using an equilibrium dialysis method, conditional distribution coefficients (Dom) for As(III) and As(V) binding onto two commercial humic acids were determined at environmentally relevant As/dissolved organic carbon (DOC) ratios and as a function of pH. At all pH values, As(V) was more strongly bound than As(III). Maximum binding was observed around pH 7, which is consistent with H+ competition for binding sites at low pH values and OH- competition for the arsenic center at high pH. For both oxidation states, Dom values increased with decreasing As/DOC ratios. Dom values were fitted as a function of the As/DOC ratio for As(III) and As(V). Compared to the aquatic humic acid, the terrestrial humic acid had a higher affinity for arsenic binding with 1.5-3 times higher Dom values under the same conditions. Al3+ in excess to arsenic successfully competed for strong binding sites at low As/DOC ratios. Under environmentally relevant conditions, about 10% of total As(V) may be bound to DOM, whereas >10% of As(III) is bound to DOM at very low As/DOC ratios only. Binding of arsenic to DOM should be considered in natural systems.

Aluminum↗

PubMed2001

Spectrophotometric determination of polyacrylamide in waters containing dissolved organic matter.

Using polyacrylamide (PAM) to reduce soil erosion in irrigated land has increased rapidly in recent years. A simple and reliable method to measure the PAM concentration in waters containing dissolved organic matter (DOM) is of great importance in assessing the fate and efficiency of PAM application. In this research, an analytical method to determine the PAM concentration of waters with correction for DOM interference was developed and tested. The method is based on a combination of determining the total concentration of amide groups by the N-bromination method (NBM) and determining the DOM content spectrophotometrically. The total concentration of amide groups of both PAM and DOM was determined by NBM at 570 nm. The DOM moiety, which is proportional to DOM concentration, was determined by spectrophotometry using a UV 254-nm wavelength. The actual PAM concentration of a water sample (soil extract containing PAM in this study) was obtained from NBM readings subtracted by the interferential DOM contribution using a correction curve. Analysis of PAM in two soil-water samples showed that the recoveries ranged from 94 to 100.3% for the 2 mg/L PAM sample and from 98.4 to 101.4% for the 10 mg/L PAM sample with various DOM concentrations. The coefficients of variation were <6% in all cases.

Acrylic Resins↗

PubMed2007

Adsorption kinetics of natural dissolved organic matter and its impact on arsenic(V) leachability from arsenic-loaded ferrihydrite and Al-ferrihydrite.

The present work was broadly divided into two parts: first, the efficiency of synthetically prepared ferrihydrite and Al-ferrihydrite to adsorb dissolved organic matter (DOM) was tested as a function of time, pH and ionic strength and its effects on specific surface area was found. In the second part, the effect of DOM concentration and solution pH was studied to elucidate the influence of this two parameters on As(V) leachability from As(V) loaded ferrihydrite and Al-ferrihydrite. It was found that both pH and ionic strength had significant influence on DOM adsorption. The behavior and magnitude of adsorption was significantly different for both the materials. In general, the efficiency of Al-ferrihydrite to adsorb DOM was better compared to ferrihydrite. Results indicated that ligand exchange was the dominant interaction mechanism for DOM adsorption on ferrihydrite and Al-ferrihydrite. The study also suggested a strong potential for DOM to mobilize As(V) from the studied materials. At pH 5.0, DOM concentrations of 2.5 and 5.0 mg C/L had negligible effect on As(V) leachability. With increasing DOM concentration from 10 to 30 mg C/L, increased the As(V) leachability into the solution. Net release from ferrihydrite was up to 1.07 mg/g (5.75%) of the total adsorbed arsenic. The corresponding figure for Al-ferrihydrite was 1.47 mg/g (6.30%). As the primary mechanisms for the arsenic release from solid phases we identified two different types of mechanisms i.e., dissolution of the solid phase and competition between arsenic and organic anions for sorption sites.

Adsorption↗

PubMed1985

Dopamine receptors on dispersed bovine anterior pituitary cells.

The dopamine antagonist [3H]-domperidone-[3H]-DOM-bound to a single class of high-affinity (Kd = 1.24 +/- 0.14 nM) and saturable receptors on dispersed bovine anterior pituitary (AP) cells. The binding of [3H]-DOM was stereoselective and reversible with agonists and antagonists. Dopamine competitions for [3H]-DOM binding modeled best for a single site consistent with an interaction with a homogeneous population of receptors. The mean number of specific binding sites labeled by [3H]-DOM was 53,000 per cell in dispersed AP cells consisting of 42% lactotrophs. Dispersed bovine AP cells attached to extracellular matrix within 3 h, and prolactin secretion from these cells was effectively inhibited by dopamine. Several observations suggested that [3H]-DOM-labeled receptors on dispersed bovine AP cells were restricted to the outer plasma membrane and not internalized. These included (1) the rapid and complete dissociation of specific [3H]-DOM binding; (2) the ability of treatment with acid or proteolytic enzymes to entirely remove specifically bound [3H]-DOM, and (3) the lack of effect of metabolic inhibitors on specific [3H]-DOM binding.

Animals↗