Water Ionic Strength Research Articles

EFFECT OF WATER IONIC STRENGTH ON CALCIUM AND MAGNESIUM DESORPTION FROM SOME CALCAREOUS SOILS IN NINEVEH PROVINCE

A laboratory study was conducted to determine desorption behavior of Ca+2 and Mg+2 from of solid phase and dissolution of their holding minerals by using quiet water flow of different ionic strength and SAR constructed by miscible displacement technique via two Aridisols disturbed soil columns sampled from Fadhlia and Hamdania locations in Nineveh province northern of Iraq for 10 irrigation cycles elongated for 240 minute, and also to determine Ca+2&Mg+2 and desorption coefficient rates at 298˚ Kelvin. Results referred two desorption process pathways. First denoted to contributing of exchangeable phase in desorption process and enrichment of soil solution with a highly desorption rate. Second stage denotes to dissolution of minerals holding Ca+2&Mg+2 which supply soil solution for long period by water ionic strength action in presence of in common ion. Parabolic diffusion and power function models appeared high significant of desorption process. Water of high ionic strength 11.2×10-5 mole.L-1 gave highest desorption capacity 456.4 c.mole.kg-1 in comparison with that of low ionic strength 1.12×10-5 mole.L-1 24.9 c.mole.kg-1. Highest desorption coefficient rate 35.51 mg. kg-1.mint-½ in Fadhlia location for water of high ionic strength while it reduced to 2.225 mg. kg-1.mint-½ for low water ionic strength. Desorption coefficient rate in Fadhlia was higher than that in Hamdania location due to difference of waters ionic strength.

Control of hydrogen bubble plume during electrolysis of water

Hydrogen bubble plumes are generated from the cathode during electrolysis. The plume formation mechanism contributes to the control of bubble diameters and alignment in solvent. The generation of hydrogen bubbles (HBs) and oxygen bubbles (OBs) from electrodes was observed in tap water and saline using a high-speed microscope. Bubble diameter changes were analysed from the obtained microscopic images, and the growth kinetics of HBs and OBs were compared. The result showed that plume formation was primarily dependent on ion strength of water and not voltage to the electrode. HB diameter change in plume was proportional to the distance from the cathode in tap water. Such correlation between HB diameter and distance from the cathode was not observed in saline. By simultaneous observation of HBs and OBs attached to the electrodes, the increase in HB diameter was faster than that of OB. The kinetic properties in HBs and OBs were proportional to (time)1/2 and (time)1, respectively, suggesting that the diffusion of oversaturated hydrogen gas and pressure difference at OB surfaces were dominant. Based on these results, HB plume formation was determined by the lower gas solubility and mass density of HB than that of OB, as well as controlled by voltage and ionic strength of water.

The establishment of a new culture of Hyalella azteca that would permit toxicity tests to be conducted on low-ionic strength waters.

The objective of the present study was to establish a culture of Hyalella azteca that could be used for laboratory toxicity testing in low–ionic strength waters with electrical conductivities of <200 μS/cm. A wild strain of H. azteca was collected from Twin Lake, a small seepage lake with an electrical conductivity of 81 ± 27 μS/cm located on the property of Chalk River Laboratories in Chalk River, Canada. To determine the minimum aqueous ion requirements for an optimal culturing medium for the Twin Lake strain, Twin Lake was monitored for water quality and ionic content over 4 yr. Water quality parameters were averaged and used to formulate a medium containing NaHCO3, CaCl2, MgSO4, KCl, NaBr, NaF, and LiCl, with an electrical conductivity of 89 ± 3 μS/cm. By evaluating survival and reproduction, it was concluded that this artificial medium promoted survival and supported reproduction (10 ± 4 neonates/female/wk) of the Twin Lake amphipod. The Twin Lake strain of H. azteca can, therefore, be maintained in laboratory settings, and this allows for toxicity testing to be conducted on low–ionic strength waters. Environ Toxicol Chem 2019;38:585–590. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Biochar particle aggregation in soil pore water: the influence of ionic strength and interactions with pyrene.

The beneficial properties of biochar have led to its increasing application to soils for environmental management. Despite its stability in soil, biochar can physically disintegrate into smaller particles, which can then be relocated from the application area. Biochar transport is strongly dependent on the biochar particle size and aggregation, with the extent of aggregation depending on the chemistry of the soil pore water. Biochar has a strong sorption affinity for polyaromatic hydrocarbons (PAHs) such as pyrene, which can also affect its transport. We therefore investigated biochar particle aggregation in solutions of different ionic strengths (ultrapure water, 0.01 M CaCl2, and 0.1 M CaCl2) with suspensions of biochar particles, and with suspensions of biochar particles loaded with pyrene (0.2 and 3.6 g kg-1). Increasing the pyrene concentration in ultrapure water resulted in an increase in the biochar particle size, an effect that was more pronounced following equilibration for 28 days than following equilibration for only 24 hours. Biochar particle aggregation in solutions containing both pyrene and 0.01 M CaCl2 was greatly enhanced compared to aggregation in similar solutions with no pyrene. However, the influence of pyrene became negligible at high CaCl2 concentrations (0.1 M CaCl2). To determine the fate of biochar in soil, both the presence of PAHs and the influence of the pore water's ionic strength therefore need to be taken into account.

Brine-Dependent Recovery Processes in Carbonate and Sandstone Petroleum Reservoirs: Review of Laboratory-Field Studies, Interfacial Mechanisms and Modeling Attempts

Brine-dependent recovery, which involves injected water ionic composition and strength, has seen much global research efforts in the past two decades because of its benefits over other oil recovery methods. Several studies, ranging from lab coreflood experiments to field trials, indicate the potential of recovering additional oil in sandstone and carbonate reservoirs. Sandstone and carbonate rocks are composed of completely different minerals, with varying degree of complexity and heterogeneity, but wettability alteration has been widely considered as the consequence rather than the cause of brine-dependent recovery. However, the probable cause appears to be as a result of the combination of several proposed mechanisms that relate the wettability changes to the improved recovery. This paper provides a comprehensive review on laboratory and field observations, descriptions of underlying mechanisms and their validity, the complexity of the oil-brine-rock interactions, modeling works, and comparison between sandstone and carbonate rocks. The improvement in oil recovery varies depending on brine content (connate and injected), rock mineralogy, oil type and structure, and temperature. The brine ionic strength and composition modification are the two major frontlines that have been well-exploited, while further areas of investigation are highlighted to speed up the interpretation and prediction of the process efficiency.

Comparing electron- and hole transporting semiconductors in ion sensitive water- gated transistors

We present a systematic study comparing different solution-processed semiconductors in cation- sensitive water- gated thin film transistors (WGTFTs): A hole transporting semiconducting polymer (rrP3HT), and an electron- transporting precursor- route metal oxide (ZnO). To allow comparison, we used the same ionophore to sensitise the gate contact for both semiconductors. We find both organic hole transporter and inorganic electron transporter have their relative merits, and drawbacks, in ion- sensitive WGTFTs. Hole transporting rrP3HT WGTFTs show low hysteresis under water- gating and give super- Nernstian sensitivity. However, rrP3HT responds to ionic strength in water even when WGTFTs are not sensitised, compromising selectivity. Electron transporting ZnO WGTFTs show higher mobility, but also stronger hysteresis, and sub- Nernstian response. However, ZnO WGTFTs show little response to ionic strength when not sensitised. We rationalise the super- versus- sub- Nernstian sensitivities via a capacitive amplification/attenuation effect. Our study suggests that the optimum semiconductor material for ion- selective WGTFTs would be a precursor- route inorganic hole transporting semiconductor.

Coupling of chemical and hydromechanical properties in bentonite

Bentonite plays a key role as buffer/backfill in many engineered barrier concepts for nuclear waste repositories and is required to perform over long periods of time. Swelling pressure and porosity distribution, two of the crucial properties for the performance of bentonite, vary with the chemical environment. This contribution reviews available data, explores a simple coupling model, and applies it to a fresh water/saline water scenario.Systematic swelling pressure data for bentonite or montmorillonite under controlled chemical conditions are scarce. Evaluation of literature data shows that swelling pressure drops by 75% when increasing ionic strength of the equilibrated NaCl electrolyte from 0 to 3 M for an effective montmorillonite dry density corresponding to 1500 kg/m3 (MX-80 bentonite). In contrast, swelling pressure of CaCl2-equilibrated montmorillonite drops only by 40% for the same ionic strength increase. Cation occupancy strongly affects swelling pressure at densities below 1500 kg/m3 (monovalent vs. divalent), and ionic strength still controls swelling pressure at higher density.The chemical influence on the pore size/shape distribution in confined constant-volume systems is poorly investigated. The presence and quantity of a “free” porosity containing charge-balanced electrolyte (not affected by charged clay surfaces) in highly compacted clay systems is debated. Experimental data states different average montmorillonite interlayer distances at different ionic strengths at constant dry density. Assuming a constant volume for solids and electrolyte, any change in interlayer volume must be compensated by a corresponding change in some other type of porosity, most likely in a larger-size porosity domain. This coupling of ionic strength to porosity can explain differences in advective and diffusive transport commonly observed in clays tested with different background electrolyte concentrations, but at the same density.The existence of any effect of cation occupancy on porosity distribution has not been confirmed so far. Observed differences in advective and diffusive solute transport between Na and Ca montmorillonite might be caused by different microstructures originating from sample preparation. However, our own experimental approach avoiding such artefacts also results in transport properties dependent on the exchanger cation.Own and critically reviewed data from literature indicate a coupling of ionic strength or cation occupancy with porosity distribution. The influence of ionic strength is stronger and supported by experimental data. This HMC coupling (hydromechanical-chemical) was incorporated into a dual-porosity multicomponent reactive transport code. The code maps the complex porosity distribution into two domains: the Donnan porosity contains the porewater influenced by the negatively charged clay sheet surfaces, and has to compensate for this permanent charge with cations (representing the exchangeable cations of the clay). The Donnan porosity comprises clay interlayers and a region near clay particle outer surfaces (diffuse double layer). The Donnan porewater composition is at equilibrium with the charge-balanced “free porewater” not affected by surface charge. Both, the interlayer distance and the thickness of the diffuse double layer are assumed to depend linearly on the Debye length (dependent on ionic strength).Two reactive transport modelling examples show that equilibration time of bentonite with different ionic strength waters varies significantly. The redistribution of porosity slows down or accelerates diffusive transport.

Effect of cadmium sulphide precipitation on the partitioning of Cd isotopes: Implications for the oceanic Cd cycle

The biogeochemical cycling of cadmium (Cd) and its isotopes in the surface ocean is dominated by biological uptake into phytoplankton, while regeneration of the sinking particulate Cd governs the shapes of Cd profiles in the deeper ocean. Additionally, the water mass circulation plays an important role in the redistribution of Cd and its isotopes. Superimposed on this general cycle, it has recently been argued that cadmium sulphide (CdS) precipitation can occur in oceanic Oxygen Deficient Zones (ODZ). This has been proposed to account for the decrease in Cd/PO4 ratios and the positive Cd isotope excursion in seawater compared to sinking particles. To assess whether CdS precipitation results in a fractionation of Cd isotopes, we performed cadmium–sulphide precipitation experiments under controlled low-oxygen conditions in low (pure water) and high ionic strength (synthetic seawater) water, with variable reaction times and cadmium/sulphide ratios. Enrichment in light Cd isotopes is systematically observed in the precipitated CdS phase, in agreement with recent ab initio simulations of isotope effects associated with Cd speciation in aqueous solution. Our experimental results follow a closed-system Rayleigh fractionation model with the fractionation factor (αCdsol-CdS) for 112Cd/110Cd decreasing with increasing salinity – from 1.00026 for pure water to 1.00014 for a salinity twice that of modern seawater, indicating a salinity control on the magnitude of Cd isotope fractionation. We propose that this fractionation, varying with salinity, is controlled by isotope equilibrium between the various Cd aqueous species present in solution, with preferential involvement of free Cd2+ ion in CdS formation.The magnitude of Cd isotope fractionation in seawater (αCdsol-CdS = 1.00016) determined in our study is in accord with the Cd isotope shift observed in modern oceanic ODZ and attributed to removal by CdS. Our experiments show that CdS precipitation could have significant local impact on the cycling of Cd, and further demonstrates the utility of Cd isotopes as tracers of the sequestration of cadmium into sulphides in restricted euxinic basins, such as the Black Sea.

Natural attenuation of TiO2 nanoparticles in a fractured hard-rock

Successive transport experiments of TiO2 nanoparticles (NP) suspension through fractured hard-rock column were done in laboratory. A low ionic strength (IS) water (0.8–1.3 10−3 M) at pH ∼4.5 was used, corresponding to the chemical composition of groundwater where the rock was collected (Naizin, France). The surface charge of TiO2 NP was positive while that of rock was negative favoring NP deposition. SEM/EDX reveals that NP were retained on a broad distribution of mineral collectors along the preferential flow pathways (i.e., fractures). However, a non-negligible amount of NP (∼10%) was transferred through the rock. Divalent cation (Ca2+) was responsible for the reduction of the negative charge of the rock and thus contributed to limit the NP deposition as attested by DLVO model. Blocking of rock surfaces by NP favored NP transfer while the ripening process and the size exclusion of aggregates decreased NP mobility. Decrease of water flow favored the exchange of solutes from the immobile to the mobile water in the porous medium, which in turn favored the aggregation of the NP and led to their natural attenuation. The result evidences how slight modifications of the environmental conditions can strongly influence the fate of NP in groundwater.

The behaviour of zirconium and hafnium during water-rock interaction

Zr and Hf are two elements with same ionic charge and similar ionic size at a given coordination number. Despite the Zr/Hf ratio is quite constant in meteorites and lithospheric rocks, in natural waters can be either higher or lower compared to values of interacting minerals and rocks. Here, we reanalyze very recent published and present new data on continental and brine waters indicating that the Zr and Hf behavior is dependent on the properties of the authigenic phases formed during the water-rock interaction process. Our results show that water pH in the range between 1 and 9 and water ionic strength in the range between 0.001 and 4 mol kg−1 are responsible for the change of the Zr/Hf ratio. However, analyzing the colloidal fraction comprising Fe-oxyhydroxides, carbonate and clay minerals (occasionally gypsum and halite), obtained by ultrafiltration at the dimension between 10 kDa and 0.45 μm diameter pore, we found that the Zr/Hf molar ratio is very low and variable between 5 and 35. We propose that the dissolved Zr/Hf ratio is dependent on the morphological and electrical properties of authigenic mineral surfaces and emphasize the lack of a quantitative evaluation of the ion speciation of Zr and Hf in natural waters and brines limiting the transport prediction of Zr and Hf during the complex water-rock interaction process.

Swelling Properties of Propranolol HCl-loaded Polyvinyl Alcohol-graft-lactic Acid Hydrogel Films

This paper presented the swelling properties of propranolol HCl-loaded polyvinyl alcohol-graft-lactic acid (PPH-loaded PVA-g-LA) hydrogel films. The swelling properties including swelling-deswelling measurement and swelling behaviour in different environmental stimuli fluids such as water, various pH, and various ionic strength were determined. It was found that the swelling properties of the PPH-loaded PVA-g-LA hydrogel films depend on the LA amount addition. They had a good swelling and deswelling in water and acetone. The PPH-loaded PVA-g-LA hydrogel films showed the high swelling in the medium pH 7. Thus, the prepared PPH-loaded PVA-g-LA hydrogel films had a good swelling property that could be used to controlled drug release in pharmaceutical product.

Antagonistic Microbial Interactions: Contributions and Potential Applications for Controlling Pathogens in the Aquatic Systems.

Despite the active and intense treatment of wastewater, pathogenic microorganisms and viruses are frequently introduced into the aquatic environment. For most human pathogens, however, this is a rather hostile place, where starvation, continuous inactivation, and decay generally occur, rather than successful reproduction. Nevertheless, a great diversity of the pathogenic microorganisms can be detected, in particular, in the surface waters receiving wastewater. Pathogen survival depends majorly on abiotic factors such as irradiation, changes in water ionic strength, temperature, and redox state. In addition, inactivation is enhanced by the biotic interactions in the environment. Although knowledge of the antagonistic biotic interactions has been available since a long time, certain underlying processes and mechanisms still remain unclear. Others are well-appreciated and increasingly are applied to the present research. Our review compiles and discusses the presently known biotic interactions between autochthonous microbes and pathogens introduced into the aquatic environment, including protozoan grazing, virus-induced bacterial cell lysis, antimicrobial substances, and predatory bacteria. An overview is provided on the present knowledge, as well as on the obvious research gaps. Individual processes that appear promising for future applications in the aquatic environment are presented and discussed.

Synthesis of carboxymethylcellulose/starch superabsorbent hydrogels by gamma-irradiation

BackgroundSuperabsorbent hydrogels show a large potential in a wide array of applications due to their unique properties. Carboxymethylcellulose (CMC) is a commercially available water-soluble cellulose derivative of major interest in the hydrogel synthesis. High-energy irradiation allows the chemical crosslinking without the use of crosslinking agents, while the introduction of other natural or synthetic polymers offers a convenient way to modify the gels. In this study we examined the effect of the addition of starch, a low-cost renewable polysaccharide, on the properties of carboxymethylcellulose-based hydrogels.ResultsSuperabsorbent gels were prepared by gamma irradiation from aqueous mixtures of carboxymethylcellulose and starch. The partial replacement of CMC with starch improved the gel fraction, while a slight increase in the water uptake was also observed. However, very high starch content had a negative impact on the gelation, resulting in a decrease in gel fraction. Moreover, higher solute concentrations were preferred for the gelation of CMC/starch than for pure CMC. Hydrogels containing 30% starch showed the best properties: a water uptake of ~350 gwater/ggel was achieved with ~55% gel fraction synthesized from 15 w/w% solutions at 20 kGy. Heterogeneous gel structure was observed: the starch granules and fragments were dispersed in the CMC matrix. The swelling of CMC/starch gels showed a high sensitivity to the ionic strength in water due to the CMC component. However, the mixed gels are less sensitive to the ionic strength than pure CMC gels.ConclusionsThe introduction of starch to carboxymethylcellulose systems led to improved properties. Such gels showed higher water uptake, especially in an environment with high electrolyte concentration. CMC/starch hydrogels may offer a cheaper, superior alternative compared to pure cellulose derivative-based gels depending on the application.

PH-Metric study of picolinic acid with Cu (II), Co (II) and Fe(II)ions

pH-Metric measurements of picolinic acid were studied with Cu(II), Co (II) and Fe(II)metal ions at 0.2 M ionic strength in water by Irving-Rossotti titration technique for determination of stability constants. 1: 1 complexes were formed in present investigation in between picolinic acid (PA) and Cu (II), Co (II)and Fe(II) metal ions. Values of proton-ligand stability constant (pK) and metal-ligand stability constants log k were evaluate and compared from resultant data.

DEMONSTRATION OF CULTIVABILITY FOR A LOW IONIC STRENGTH WATERHYALELLA AZTECASTRAIN

The in-lab reproductive success of a strain of Hyalella azteca collected from Twin Lake, a water body located on the Canadian Nuclear Laboratories Chalk River Laboratories site, is sufficient to be used for effluent and (or) sediment toxicity assessments. This strain of Hyalella azteca enhances our capabilities to evaluate ecological risks in low ionic strength waters.

Investigating the Formation of a Repulsive Hydrogel of a Cationic 16mer Peptide at Low Ionic Strength in Water by Vibrational Spectroscopy and Rheology.

The cationic peptide (AAKA)4 (AK16) exhibits a high propensity for aggregation into β-sheet-like structures in spite of the high positive charge of its protonated lysine side chains. Upon incubation into an aqueous solution, the peptide maintains a metastable β-sheet-like structure with fibrillar content, the apparent stability of which increases with peptide concentration. In the presence of a sufficiently high concentration of anions, the peptide spontaneously forms a hydrogel at millimolar concentrations. Interestingly, we find that even in the absence of gel-supporting anions, the peptide is capable of forming a hydrogel in the centimolar range. Rheological data reveal that the gel is a stable elastic solid. These data show that the peptide can overcome the repulsive interactions between the positively charged ammonium groups of the lysine residues. The addition of 1 M NaCl just accelerates this process. Atomic force microscopy images of the peptide gel reveal fibrils with thicknesses between 4 and 8 nm, which suggests that they contain multiple layers of sheets. We propose that long tapes of β-sheet are arranged in fibrils via stacking of alternating interfaces induced by hydrophobic interactions between alanine side chains and by the formation of a hydrogen bonded water network between hydrophilic sides of AK16 β-sheets, which leads to the observed immobilization of the solvent in the formed hydrogel. Water immobilization is proposed as the likely cause for a significant increase in the amide I' oscillator strength of the formed β-sheet structures.

Removal of trace metal contaminants from potable water by electrocoagulation.

This study investigated the effects of four operational and environmental variables on the removal of trace metal contaminants from drinking water by electrocoagulation (EC). Removal efficiencies for five metals (arsenic, cadmium, chromium, lead and nickel) were compared under varying combinations of electrode material, post-treatment, water composition and pH. Iron electrodes out-performed aluminum electrodes in removing chromium and arsenic. At pH 6.5, aluminum electrodes were slightly more effective at removing nickel and cadmium, while at pH 8.5, iron electrodes were more effective for these metals. Regardless of electrode, cadmium and nickel removal efficiencies were higher at pH 8.5 than at pH 6.5. Post-EC treatment using membrane filtration (0.45 μm) enhanced contaminant removal for all metals but nickel. With the exception of lead, all metals exhibited poorer removal efficiencies as the ionic strength of the background electrolyte increased, particularly in the very high-solids synthetic groundwaters. Residual aluminum concentrations were lowest at pH 6.5, while iron residuals were lowest in low ionic strength waters. Both aluminum and iron residuals required post-treatment filtration to meet drinking water standards. EC with post-treatment filtration appears to effectively remove trace metal contaminants to potable water standards, but both reactor and source water parameters critically impact removal efficiency.

Soluble hydrocarbons uptake by porous carbonaceous adsorbents at different water ionic strength and temperature: something to consider in oil spills.

Nowadays, petrochemical operations involve risks to the environment and one of the biggest is oil spills. Low molecular aromatics like benzene, toluene, and naphthalene dissolve in water, and because of their toxicological characteristics, these produce severe consequences to the environment. The oil spill cleanup strategies are mainly designed to deal with the heavy fractions accumulated on the water surface. Unfortunately, very limited information is available regarding the treatment of dissolved fractions.A commercial (Filtrasorb 400) and modified activated carbons were evaluated to remove benzene, toluene, and naphthalene from water, which are the most soluble aromatic hydrocarbons, at different ionic strengths (I) and temperatures (0-0.76M and 4-25°C, respectively). This allowed simulating the conditions of fresh and saline waters when assessing the performance of these adsorbents. It was found that the hydrocarbons adsorption affinity increased 12% at a I of 0.5M, due to the less negative charge of the adsorbent, while at a high I (≃0.76M) in a synthetic seawater, the adsorption capacity decreased 21% that was attributed to the adsorbent's pores occlusion by water clusters. Approximately, 40h were needed to reach equilibrium; however, the maximum adsorption rate occurred within the first hour in all the cases. Moreover, the hydrocarbons adsorption and desorption capacities increased when the temperature augmented from 4 to 25°C. On the other hand, thermally and chemically modified materials showed that the interactions between adsorbent-contaminant increased with the basification degree of the adsorbent surface.

Silver Biotic Ligand Model (BLM): Refinement of an Acute BLM for Silver

The biotic ligand model (BLM) is a computational tool that may be used to predict toxic effect levels of metals, including Ag. The BLM considers the effect of site-specific water quality characteristics on Ag speciation and bioavailability. This provides a basis for extrapolating from laboratory waters, used for most Ag toxicity tests, to natural waters, where the bioavailability and toxicity of Ag may differ. The original version of the BLM for the acute toxicity of Ag was reviewed by the USEPA Science Advisory Board (SAB) in 1999 and they recommended the completion of additional Ag chemistry and toxicity studies to provide data to test and refine the model. This project was completed to satisfy these recommendations. A chemistry component was completed to improve the representation of Ag speciation in natural waters and to characterize the important effect of sulfide on Ag bioavailability. These investigations added to the information that was available to characterize Ag chemistry and provided a basis for updating the earlier version of the Ag BLM. The BLM was also calibrated to laboratory toxicity data that were generated for a Ag-sensitive invertebrate, Ceriodaphnia dubia, a cladoceran that had previously been tested to only a limited degree. The studies were carried out in laboratory waters in which the chemistry was systematically varied to provide a basis for calibration of the BLM to the toxicity data for C. dubia. Toxicity tests were also performed with both Pimephales promelas and C. dubia in natural water samples that were well characterized chemically, with the data then used to test the model. While the C. dubia BLM results were relatively successful at simulating the observed effect levels the P. promelas results highlighted the need for further testing and refinement of the Ag BLM as it was applied to this fish species. Physiological tests were performed to explore the apparent increase in sensitivity of P. promelas in some of the test waters that were relatively low in ionic strength. It was determined that acclimation to such low ionic strength waters, in the absence of Ag, did not significantly reduce their sensitivity to Ag. Rather, it appeared that any benefit that may have been realized by acclimation, such as an enhanced ability to upregulate ion uptake rates in low ionic strength waters, was apparently offset by a concomitant increase in the rate at which Ag was accumulated. The Ag BLM was modified to account for the effect of low ionic strength water on the sensitivity to Ag of > 4-day old P. promelas. This led to an improved ability of the BLM to predict P. promelas effect levels in the natural waters. Physiological tests were also performed to investigate the apparent species-specific protection against Ag toxicity that is provided by chloride. Investigations with P. promelas suggested that the differences in degree of protection may be related to differences in how Ag affects the ionoregulation of Na+ and Cl− by different fish species. Although questions remain with regard to chloride, it appears that the BLM is able to predict this response reasonably well, particularly for the relatively sensitive <4 day old P. promelas. In summary, the WERF program yielded an improved chemistry and toxicity database, including data over an extended range of water quality characteristics and for an additional Ag-sensitive invertebrate, thereby providing a basis for refining the acute Ag BLM and improving its overall predictive ability.This title belongs to WERF Research Report SeriesISBN: 9781780403656 (eBook)ISBN: 9781843397960 (Print)

Implementation of High-Quality Warm-White Light-Emitting Diodes by a Model-Experimental Feedback Approach Using Quantum Dot-Salt Mixed Crystals.

In this work, a model-experimental feedback approach is developed and applied to fabricate high-quality, warm-white light-emitting diodes based on quantum dots (QDs) as color-conversion materials. Owing to their unique chemical and physical properties, QDs offer huge potential for lighting applications. Nevertheless, both emission stability and processability of the QDs are limited upon usage from solution. Incorporating them into a solid ionic matrix overcomes both of these drawbacks, while preserving the initial optical properties. Here borax (Na2B4O7·10H2O) is used as a host matrix because of its lower solubility and thereby reduced ionic strength in water in comparison with NaCl. This guarantees the stability of high-quality CdSe/ZnS QDs in the aqueous phase during crystallization and results in a 3.4 times higher loading amount of QDs within the borax crystals compared to NaCl. All steps from the synthesis via mixed crystal preparation to the warm-white LED preparation are verified by applying the model-experimental feedback, in which experimental data and numerical results provide feedback to each other recursively. These measures are taken to ensure a high luminous efficacy of optical radiation (LER) and a high color rendering index (CRI) of the final device as well as a correlated color temperature (CCT) comparable to an incandescent bulb. By doing so, a warm-white LED with a LER of 341 lm/Wopt, a CCT of 2720 K and a CRI of 91.1 is produced. Finally, we show that the emission stability of the QDs within the borax crystals on LEDs driven at high currents is significantly improved. These findings indicate that the proposed warm-white light-emitting diodes based on QDs-in-borax hold great promise for quality lighting.