Activity coefficients of salts in highly concentrated protein solutions. II. Potassium salts in isoionic bovine serum albumin solutions

Mean activity coefficients of different potassium salts KX (X = F-, Cl-, Br-, I-, NO3-, SCN-) have been measured in concentrated isoionic bovine serum albumin (BSA) solutions, by use of the EMF method with ion-exchange membrane electrodes. These solutions may be regarded as simple model systems for the cytoplasm of living cells as far as the influence of the macromolecular component on the activity coefficients of the salts is concerned. Two series of measurements have been carried out: (a) varying the amount of salt from 0.01 to 0.5 molal and maintaining the BSA concentration constant at 20 wt% and (b) varying the protein concentration up to 25 wt% and keeping the salt concentration constant at 0.1 molal. For all salts studied, the mean activity coefficients in the protein-salt solutions increase as the salt concentration rises, when the protein concentration is maintained constant. In the series of measurements (b) the activity coefficients of all salts change linearly with the protein concentration. Marked qualitative differences, however, were observed depending on the anion species, which could be interpreted in terms of specific ion binding of X- to the protein molecule. By taking into account BSA-bound 'non-solvent' water, the results were analyzed in terms of numbers of anions bound per BSA molecule. Comparison with the results of Scatchard, obtained at low protein concentrations, showed only a very small electrostatic effect of the BSA-(X-)v polyions on the activity coefficient of the salts at higher protein and salt concentrations.     

Activity coefficients of KCl in highly concentrated protein solutions

As a contribution to the understanding of the thermodynamic state of single salts in living systems, the activity coefficients of KCl were determined in concentrated bovine serum albumin (BSA) solutions. The concentration range studied was 0.01 to 0.5 M KCl and zero to 18% wt BSA, thus amply covering physiological conditions. The activity coefficients of the salt were measured using the EMF method with ion exchange membrane electrodes. Keeping the salt concentration constant, the activity coefficients of the salt decrease linearly with protein concentration, the effect being more pronounced for low salt content. The maximal deviations of the activity coefficients with respect to those in pure salt solution amount to ca. 40% for 0.01 M KCl and 18% wt BSA. The results were interpreted on the assumption of the superposition of three effects i.e. water bound to BSA molecules as non-solvent water, specific Cl^– ion binding and the electrostatic interactions of the polyions with the salt ions. In view of the results it can be concluded that only a small portion of simple intracellular ions are bound, based on the assumption that the cytoplasm of living cells may be regarded as a concentrated protein-salt solution.     

Conformational change of poly-N epsilon-glutaryl-L-lysine and poly-N epsilon-succinyl-L-lysine in aqueous salt solutions

The conformational changes of poly-N^ε-glutaryl-L -lysine (PGL) and poly-N^ε-succinyl-L -lysine (PSL) in various salt solutions were studied by use of ORD and potentiometric titration measurements. The addition of alkali metal salts to the fully ionized PGL or PSL solution caused helix formation. The helical content of the polymers increases in the following sequences: at salt concentration 0–2 M, CsCl < KCl < LiCl < NaCl; and at 2–3 M, LiCl < CsCl < KCl ～ NaCl. The preferential binding of the solvent components with various alkali metal salts of PGL or PSL was measured in LiCl, NaCl, and KCl solutions by means of equilibrium dialysis and differential refractometry. It was found that with increasing salt concentration, the polymers were preferentially hydrated in NaCl and KCl soultions; however the salt was preferentially bound to the polymers in LiCl solution. Such preferential binding was suggested to be closely related to conformational change. The addition of CaCl₂ to polymer solutions led to the stabilization of the helical structure of PGL or PSL.     

Molecular dynamic simulations study of the effect of salt valency on structure and thermodynamic solvation behaviour of anionic polyacrylate PAA in aqueous solutions

The effect of salt concentration and valency on intermolecular structure and solvation thermodynamic properties of aqueous solution containing polyacrylicacid (PAA) chains and multi-valent salts calcium chloride (CaCl₂) and aluminium chloride (AlCl₃) as a function of charge density was investigated using atomistic molecular dynamic simulations with explicit solvent. Salt-free solution favours the self-association of uncharged (acidic form) PAA chains facilitated by inter-chain hydrogen bonds. The ionised (charged) PAA chains are not associated in salt-free aqueous solutions and undergo self-association in the salt solutions due to bridging effect induced by condensed salt ions in agreement with scattering investigations available in literature. The collapse behaviour of PAA in presence of CaCl₂ and re-expansion behaviour of PAA chains in case of AlCl₃ salt solutions are observed. The rigidity of PAA chains decrease with increase in salt concentration, in agreement with experimental results available in literature. The trivalent salt favours relatively the greater extent of shrinking of PAA chains as well as inter-chain interactions as compared to divalent salts as evident from radius-of-gyration, H-bond and pair-wise solvation enthalpy data. The conformation and hydration behaviour of the acid form of PAA chains are not significantly altered by added salt ions. The hydration behaviour of ionised PAA chains is significantly reduced by added salts due to screening effect of the condensed salt ions. The pair correlation functions of solutions species such as Ca²⁺, Al³⁺, Na⁺ and Cl^? with respect to PAA oxygen show the greater affinity of PAA units with the higher valency Al³⁺ ions over Ca²⁺ and Na⁺ in solution. With increase in concentration of AlCl₃ and CaCl₂ salts, a decrease in effective charge density of ionised PAA chains is observed from the existence of unfavourable PAA–water, PAA–Ca²⁺ and PAA–Al³⁺ interactions.     

Sodium and chloride ions contribute synergistically to salt toxicity in wheat

The effects of supplying excess mineral salts, involving sodium as a cation and a range of counteranions, including chloride, on the growth and photosynthetic capacity of a salt susceptible bread wheat were studied. Plant performance was much more affected by the NaCl treatment than by the same concentration of either of the two component ions. With the exception of K⁺, other alkali metal chlorides also greatly inhibit plant growth and the electron flow through photosystem 2. The ranking of toxicity of these cations is Li⁺>Na⁺>K⁺. The synergistic effect of sodium (and other alkali and alkaline earth metals) and chloride shows that neither of these ions alone is responsible for salt stress induced damage.     

Ion‐dependent metabolic responses of Vicia faba L. to salt stress

Salt‐affected farmlands are increasingly burdened by chlorides, carbonates, and sulfates of sodium, calcium, and magnesium. Intriguingly, the underlying physiological processes are studied almost always under NaCl stress. Two faba bean cultivars were subjected to low‐ and high‐salt treatments of NaCl, Na₂SO₄, and KCl. Assimilation rate and leaf water vapor conductance were reduced to approximately 25–30% without biomass reduction after 7 days salt stress, but this did not cause severe carbon shortage. The equimolar treatments of Na⁺, K⁺, and Cl^? showed comparable accumulation patterns in leaves and roots, except for SO₄^2? which did not accumulate. To gain a detailed understanding of the effects caused by the tested ion combinations, we performed nontargeted gas chromatography–mass spectrometry‐based metabolite profiling. Metabolic responses to various salts were in part highly linearly correlated, but only a few metabolite responses were common to all salts and in both cultivars. At high salt concentrations, only myo‐inositol, allantoin, and glycerophosphoglycerol were highly significantly increased in roots under all tested conditions. We discovered several metabolic responses that were preferentially associated with the presence of Na⁺, K⁺, or Cl^?. For example, increases of leaf proline and decreases of leaf fumaric acid and malic acid were apparently associated with Cl^? accumulation.     

Density gradient proportionality constants for a number of aqueous binary solutions

A computer program, based upon the method of Trautman, has been developed to calculate density-gradient proportionality constants, β⁰, as a function of density for any salt for which density and activity coefficient data are available. Results are given for twenty 1:1 electrolytes at 25°C. These salts are the chlorides, bromides, iodides, and nitrates of the five alkali cations. The program is available for use for any other salt and for a variety of temperatures if the necessary data can be found or measured. Between six and eleven centrifuge runs at different densities were performed fur each of seven of these salts experimentally to determine β⁰. In general, the experimental and theoretical values agree within 3% except at the extremes of density. This demonstrates the validity of the computer program and is the first extensive demonstration that the thermodynamic calculation of density gradients is correct. Five new quadratic relationships between refractive index and density are given.     

Dependence of the intracellular concentrations of univalent ions and hydrogenase activity on the salt composition and pH of the medium in the haloalkaliphilic sulfate-reducing bacterium <Emphasis Type="Italic">Desulfonatronum thiodismutans</Emphasis>

It has been shown that the intracellular concentrations of Na⁺, K⁺, and Cl^? ions in Desulfonatronum thiodismutans depend on the extracellular concentration of Na⁺ ions. An increase in the extracellular concentration of Na⁺ results in the accumulation of K⁺ ions in cells, which points to the possibility that these ions perform an osmoprotective function. When the concentration of the NaCl added to the medium was increased to 4%, the concentration gradient of Cl^? ions changed insignificantly. It was found that D. thiodismutans contains two forms of hydrogenase—periplasmic and cytoplasmic. Both enzymes are capable of functioning in solutions with high ionic force; however they exhibit different sensitivities to Na⁺, K⁺, and Li⁺ salts and pH. The enzymes were found to be resistant to high concentrations of Na⁺ and K⁺ chlorides and Na⁺ bicarbonate. The cytoplasmic hydrogenase differed significantly from the periplasmic one in having much higher salt tolerance and lower pH optimum. The activity of these enzymes depended on the nature of both the cationic and anionic components of the salts. For instance, the inhibitory effect of NaCl was less pronounced than that of LiCl, whereas Na⁺ and Li⁺ sulfates inhibited the activity of both hydrogenase types to an equal degree. The highest activity of these enzymes was observed at low Na⁺ concentrations, close to those typical of cells growing at optimal salt concentrations.     

The equivalent conductivity of aqueous salt-free solutions of DNA: Influence of univalent counterions

The equivalent conductivity of salt-free solutions of deoxyribonucleates of alkali metals and ammonium obtained by filtering an isoionic DNA solution through a cation exchanger in the corresponding form has been investigated in the concentrations range of 1 × 10^?4 to 4 × 10^?3M. For all counterions investigated there is a linear dependence of the equivalent conductivity on \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt {C_p} $\end{document}, where C_p is the nucleic phosphorus concentration. The limiting equivalent conductivity of deoxyribonucleates increases linearly with the limiting mobility of a counterion. By extrapolation to the zero mobility of the counterion, we have obtained the limiting mobility of a macroion, which is equal to 19 × 10^?4 Sm m² equiv.^?1, which is in good agreement with the literature data for denatured DNA obtained by the method of a moving boundary. It is shown that the degree of binding of counterions calculated from the conductometric data in diluted DTA solutions in independent of the nature of the univalent counterion. The degree of dissociation of H⁺-DNA in the isoionic solution calculated with allowance for the fraction of unprotonated bases practically coincides with this value for salts of DNA. The parameter of Manning's theory calculated from the experimental data corresponds to the distance between phosphates along the chain of the macroion, which is equal to 6.7 Å. We attribute the smaller value of this distance as compared with the theoretical one for denatured DNA to the aggregation of macroions.     

Effect of inorganic salts on free radicals production by near UV irradiation of frozen aqueous solutions of adenine and its derivatives

The addition of Na and Ca chlorides to adenine (A), adenosine (Ado) and adenosine diphosphate solutions at pH 5.3 has been shown to result in intensification of EPR signals in samples irradiated by near UV at 77 K and appearance of signals of Cl ₂ ^?? and peroxyl radicals. The peroxyl radicals contribution can exceed 30% of total amount of paramagnetic products. The addition of inorganic phosphate reduces the contribution of peroxyl radicals. Possible mechanisms of the processes involved are discussed.     

Prospects of Inducing Resistance in Fodder Species against Toxic Ions and Metals

ABSTRACT

Experiments were carried out with various salts and their combinations to ascertain the impact of these salts on seedling traits of fodder species and to identify tolerant species. Length-based traits showed a repressed effect, whereas weight-based traits were increased under salt stress. Furthermore, accumulation of Na⁺, Ca²⁺, and Cl^? ions and metals (Cu²⁺, Fe²⁺, and Al³⁺) increased in various organs of seedlings due to various salt treatments. Contrastingly, K⁺, K⁺/Na⁺, and Ca²⁺/Cl^? decreased, showing priority for specific salts. Seedling traits, such as shoot length sensitivity and shoot biomass, provide an effective mean of selection for tolerant or susceptible genotypes. Diverse types of tolerance mechanisms were present in cultivars to detoxify the effect of ions and metals. Cultivars that showed low susceptibility index, high shoot biomass, and high metal concentration were salt includers and could be utilized for bioremediation of the affected areas, whereas tolerant cultivars that showed low susceptibility index, metals concentration, and comparable shoot biomass to that of the control were salt excluders and could be utilized for fodder purposes.     

Cations and Anions as Modifiers of Ryanodine Binding to the Skeletal Muscle Calcium Release Channel

Rate and equilibrium measurements of ryanodine binding to terminal cysternae fractions of heavy sarcoplasmic reticulum vesicles demonstrate that its activation by high concentrations of monovalent salts is based on neither elevated osmolarity nor ionic strength. The effect of the ions specifically depends on their chemical nature following the Hofmeister ion series for cations (Li⁺ < NH⁺ ₄ < K⁻∼ Cs⁺≤ Na⁺) and anions (gluconate⁻ < Cl⁻ < NO₃ ⁻∼ ClO₄ ⁻∼ SCN⁻) respectively, indicating that both are involved in the formation of the salt-protein complex that can react with ryanodine. Activation by rising salt concentrations exhibits saturation kinetics with different dissociation constants (25–11 m) and different degrees of cooperativity (n= 1.5–4.0) for the respective salts. Maximal second order binding rates between 40,000 and 80,000 (m ⁻¹· sec⁻¹) were obtained for chlorides and nitrates of 1a group alkali ions with the exception of lithium supporting only rates of maximally 10,000 (M⁻¹· sec⁻¹). The nitrogen bases, NH⁺ ₄ and Tris⁺, in combination with chloride or nitrate, behave divergently. High maximal binding rates were achieved only with NH₄NO₃. The dissociation constants for the ryanodine–protein complexes obtained by measurements at equilibrium proved to depend differently on salt concentration, yet, converging to 1–3 nm for the applied salts at saturating concentrations. The salts do not affect dissociation of the ryanodine protein complex proving that the effect of salts on the protein's affinity for ryanodine is determined by their effect on the on-rate of ryanodine binding. ATP and its analogues modify salt action resulting in elevated maximal binding rates and reduction or abolition of binding cooperativity. Linear relations have been obtained by comparing the rates of ryanodine binding at different salt concentrations with the rates or the initial amplitudes (15 sec) of salt induced calcium release from actively loaded heavy vesicles indicating that the various salts promote specifically and concentration dependently channel opening and its reaction with ryanodine. Received: 9 February 1998/Revised: 24 April 1998     

Interaction of hemoglobin with salts: Effects on the functional properties of human hemoglobin

Oxygen isotherms of human hemoglobin measured in distilled water and in solutions of different inorganic salts in the concentration range from below 10^?3 m to above 1·5 m at neutral pH indicate that the oxygen affinity decreases with increasing salt concentration in the lower range of ionic strength; above the physiological range, there is in most cases a further decrease in oxygen affinity, but this varies with the nature of the salt and, in some instances, the affinity goes through a maximum.The effect of cations, which is opposite to that of anions, operates primarily in the higher concentration range; i.e. above 0·1 m. This effect is especially large for Li⁺, Ca²⁺ and Mg²⁺.The alkaline Bohr effect depends strongly on anion concentration, being displaced towards higher pH values and being reduced in magnitude as chloride concentration is increased. On the other hand, the acid Bohr effect, observed below pH 6, appears to be independent of chloride concentration from 6 × 10^?2 m to 2 m.The overall heat of oxygenation has been determined for the isoionic protein as well as at different concentrations of chloride and phosphate. The average intrinsic heat of reaction of hemoglobin with oxygen in solution is found to be ?14·6 kcal/mol of O₂.     

Theoretical and experimental studies on freezing point depression and vapor pressure deficit as methods to measure osmotic pressure of aqueous polyethylene glycol and bovine serum albumin solutions

For survival in adverse environments where there is drought, high salt concentration or low temperature, some plants seem to be able to synthesize biochemical compounds, including proteins, in response to changes in water activity or osmotic pressure. Measurement of the water activity or osmotic pressure of simple aqueous solutions has been based on freezing point depression or vapor pressure deficit. Measurement of the osmotic pressure of plants under water stress has been mainly based on vapor pressure deficit. However, differences have been noted for osmotic pressure values of aqueous polyethylene glycol (PEG) solutions measured by freezing point depression and vapor pressure deficit. For this paper, the physicochemical basis of freezing point depression and vapor pressure deficit were first examined theoretically and then, the osmotic pressure of aqueous ethylene glycol and of PEG solutions were measured by both freezing point depression and vapor pressure deficit in comparison with other aqueous solutions such as NaCl, KCl, CaCl(2), glucose, sucrose, raffinose, and bovine serum albumin (BSA) solutions. The results showed that: (1) freezing point depression and vapor pressure deficit share theoretically the same physicochemical basis; (2) theoretically, they are proportional to the molal concentration of the aqueous solutions to be measured; (3) in practice, the osmotic pressure levels of aqueous NaCl, KCl, CaCl(2), glucose, sucrose, and raffinose solutions increase in proportion to their molal concentrations and there is little inconsistency between those measured by freezing point depression and vapor pressure deficit; (4) the osmotic pressure levels of aqueous ethylene glycol and PEG solutions measured by freezing point depression differed from the values measured by vapor pressure deficit; (5) the osmotic pressure of aqueous BSA solution measured by freezing point depression differed slightly from that measured by vapor pressure deficit.     

Is salinity tolerance related to Na accumulation in Upland cotton (Gossypium hirsutum) seedlings?

Physiological responses to salt stress were studied in two cotton cultivars previously selected on the basis of growth under salinity. Plants were grown in nutrient solutions under controlled conditions. In the first experiment, the genotypes were grown at different salt concentrations (0, 100 and 200 mt M NaCl) and growth rates, water contents and ion accumulation were determined. In a second experiment, both genotypes were grown at the same salt concentration (200 mt M NaCl). Dry matter partitioning in individual leaves, stem and roots, water contents, specific leaf area (SLA), ion accumulation (K⁺, Na⁺, Cl^–) and leaf water potentials were measured. Finally, an experiment with low salt levels (2.7 and 27 mt M NaCl) was run to compare K and Na⁺ uptake and distribution.There were no differences in growth between the cultivars in the absence of salt stress, whereas under stress genotype Z407 had higher leaf area and dry matter accumulation than P792. Leaf water potential and leaf water content were lower in cv P792 than in cv Z407. There were no significant differences in the levels of Cl^– accumulation between genotypes. The main feature of the tolerant genotype (Z407) was a higher accumulation of Na⁺ in leaves and an apparent capacity for K⁺ redistribution to younger leaves.We postulate that the higher tolerance in Z407 is the result of several traits such as a higher Na⁺ uptake and water content. Adaptation through adequate, but tightly controlled ion uptake, typical of some halophytes, matched with efficient ion compartmentation and redistribution, would result in an improved water uptake capacity under salt stress and lead to maintenance of higher growth rates.     

The influence of potassium and sodium ions on the negative pasteur effect in Brettanomyces claussenii custers

Summary The present article deals with the negative Pasteur effect in Brettanomyces claussenii Custers, i.e. with the inhibition of the alcoholic fermentation under anaerobic conditions and its stimulation in presence of atmospheric oxygen.As distinct from the negative Pasteur effect in resting cells of Saccharomyces species the effect in Br. claussenii is not specific for cell suspensions prepared with succinic acid-succinate buffer but may at Ph 4.5–4.6 in addition be demonstrated in resting cells suspended in distilled water or phosphate buffer as well as in buffer solutions of a great number of organic acids and their alkali salts, e. g. in acetic acid-acetate, propionic acid-propionate, oxalic acid-oxalate, malonic acid-malonate, fumaric acid-fumarate, malic acid-malate, d-tartaric acid-tartrate, and citric acid-citrate mixtures.The aerobic fermentation of glucose by resting cells of Br. claussenii is quite sensitive to potassium and sodium ions. In all systems examined, except the succinic acid-succinate buffer and the buffer solutions inhibiting the fermentation completely or practically completely, the rate of the aerobic fermentation is considerably increased on increasing the concentration of the potassium ions and decreasing that of the sodium ions. Under anaerobic conditions the alcoholic fermentation is insusceptible to the ions mentioned.Because of the fact that the influence of the potassium ions or of the K⁺/Na⁺ ratio upon the rate of fermentation is comparatively large under aerobic conditions but small or even negligible under anaerobic conditions, the magnitude of the negative Pasteur effect will under the proper conditions be determined by the potassium ion concentration or by the ratio between the concentrations of the potassium and sodium ions. The negative Pasteur effect obtained in a buffer of an acid and its potassium salt may be considerably larger than that observed in a buffer of the same acid and its sodium salt. In solutions containing a mixture of the potassium and sodium salts in addition to an acid the magnitude of the negative Pasteur effect will increase with increasing potassium ion concentration and decreasing sodium ion concentration at constant total molar concentration of the alkali ions.To Professor Dr. E. G. Pringsheim with best wishes on his 80th birthday.     

Effect of Ionic Composition of Suspending Solution on Virus Adsorption by a Soil Column

The effect of various electrolytes on the adsorption of poliovirus was measured in 250-cm-long soil columns with ceramic samplers at different depths. Viruses suspended in deionized water moved much farther through the soil than those suspended in tap water, whereas movement in sewage water was intermediate. The salt content of the tap water and sewage water promoted virus adsorption, but evidently the organic compounds in sewage retarded adsorption. When viruses were suspended in chloride solutions of K⁺, Na⁺, Ca⁺, and Mg²⁺, virus adsorption increased as the cation concentration and valence increased. The depth of virus penetration was related to the ionic strength of the solutions. Virus penetration data for NO₃⁻, SO₄²⁻, and H₂PO₄⁻ salts of K⁺, Na⁺, and Ca²⁺ indicated that other anions were more effective than Cl⁻ in promoting virus adsorption. Also, NH₄⁺ was more effective than other cations in limiting the penetration depth of viruses. It seems that ions composed of radicals are more effective than ions composed of single atoms in promoting virus adsorption. Al³⁺ was the most effective ion in limiting virus penetration, probably owing to flocculation of the viruses. Adding AlCl₃ concentrations to secondary sewage effluent to provide an Al³⁺ concentration of 0.1 mM reduced the virus penetration depth to 40 cm. These studies show that the ionic composition of the suspending solutions must be considered in predicting virus penetration depths, and it may be practical to add low concentrations of a flocculating agent such as AlCl₃ to sewage water to limit virus movement through very porous soils.     

Stimulation of the salt receptor of the blowfly. III. The alkali halides

Application of solutions of each of the alkali halides to the tip of a labellar sensillum of the blowfly elicited a repetitive neural discharge from the salt receptor. The records were qualitatively similar to those for NaCl. For each of the alkali chlorides and sodium halides, the shapes of the curves of the response of the salt receptor as a function of concentration were similar to that for NaCl. The alkali halides exhibited a regular pattern of relative stimulating effectiveness for the salt receptor. The effectiveness of the anions increased monotonically with atomic number. The effectiveness of the cations was greatest for potassium and declined as the atomic number was increased or decreased. This hierarchy for stimulating effectiveness was maintained at all tested molarities. The response to a mixture of two salts appeared to be an average of those to the single salts at concentrations equal to the total concentration of the mixture. Cross-adaptation was observed between the alkali halides. The results indicate that an explanation of stimulation of the salt receptor must apply to all the salts tested and that both the anion and the cation affect a salt's stimulating effectiveness.     

Effects of caecal ligation and saline acclimation on plasma concentration and organ mass in male and female Pekin ducks,Anas platyrhynchos

Summary The intestinal caeca reabsorb urinary sodium chloride (NaCl) and water (Rice and Skadhauge 1982). Free water may be generated if the reabsorbed NaCl is secreted via salt gland secretion (Schmidt-Nielsen et al. 1958). Therefore ceacal ligation should (a) reduce hingut NaCl and water reabsorption, (b) enhance the increase in plasma osmolality during saline acclimation, and (c) affect drakes more than ducks. Twelve Pekin drakes and 13 Pekin ducks, Anas platyrhynchos, were caecally ligated or sham operated before acclimation to 450 mmol · 1 NaCl. Body mass, hematocrit, plasma osmolality, and inonic concentrations of plasma, cloacal fluid, and salt gland secretion were measured after each increase in drinking water salinity. Osmoregulatory organ masses were determined. Caecal ligation did not effect plasma osmolality or ion concentrations of plasma, cloacal fluid, or salt gland secretion, but reduced salt gland size in ducks. Drakes and ducks drinking fresh water had the same hematocrit, plasma osmolality, and plasma concentrations of Na⁺ and Cl^–. In both sexes exposure to 75 mmol · 1^-1 NaCl significantly decreased plasma [Na⁺] and doubled cloacal fluid [Na⁺]. Exposure to 450 mmol · 1^-1 NaCl decreased body mass and increased hematocrit, plasma [Na⁺], [Cl^–], and plasma osmolality (more in drakes than in ducks); cloacal fluid osmolality nearly doubled compared to freshwater-adapted ducks, due mainly to osmolytes other than Na⁺ and Cl^–. The [Cl^–] in salt gland secretion only slightly exceeded drinking water [Cl^–].Abbreviations AVT antiduretic hormone - CF cloacal fluid - ECFV extraoellular fluid volume - FW freshwater acclimated - Hct hematocrit - MDWE mean daily water flux - [Na ⁺]_cf cloacal fluid sodium concentration - [Na ⁺]_pl plasma sodium concentration - Osm _cf cloacal fluid osmolality - Osm _pl plasma osmolality - SGS salt gland secretion - TBW total body water     

Effects of road salts on groundwater and surface water dynamics of sodium and chloride in an urban restored stream

Road salts are a growing environmental concern in urban watersheds. We examined groundwater (GW) and surface water (SW) dynamics of Na⁺ and Cl^? in Minebank Run (MBR), an urban stream in Maryland, USA. We observed an increasing salinity trend in this restored stream. Current baseflow salinity does not exceed water quality recommendations, but rapid “first flush” storm flow was approximately one-third that of seawater. Comparisons between the upstream and downstream study reaches suggest that a major interstate highway is the primary road salt source. A heavily used road parallels most of MBR and was an additional source to GW concentrations, especially the downstream right bank. A baseflow synoptic survey identified zones of increased salinity. Downstream piezometer wells exhibited increases in salt concentrations and there was evidence that Na⁺ is exchanging Ca²⁺ and Mg²⁺ on soils. SW salt concentrations were generally elevated above GW concentrations. Salinity levels persisted at MBR throughout the year and were above background levels at Bynum Run, a nearby reference stream not bisected by a major highway, suggesting that GW is a long-term reservoir for accumulating road salts. Chronic salinity levels may be high enough to damage vegetation and salinity peaks could impact other biota. Beneficial uses and green infrastructure investments may be at risk from salinity driven degradation. Therefore, road salt may represent an environmental risk that could affect aquatic biota and limit the effectiveness of costly resource management and restoration efforts.