Nordic Aquatic Fulvic Acid Research Articles

Effects of surface tension time-evolution for CCN activation of a complex organic surfactant.

The physical processes and time scales underlying the evolution of surface tension in atmospheric solution droplets are largely unaccounted for in present models describing cloud droplet formation. Adsorption of surface-active molecules at the surface of a solution droplet depresses the droplet surface tension but also depletes solute from the droplet bulk, which have opposing and sometimes canceling effects in cloud droplet formation. In this work, we study the effect of time-evolving surface tension for cloud droplet activation of particles composed of Nordic Aquatic Fulvic Acid (NAFA) mixed with sodium chloride (NaCl). We model the formation of cloud droplets using Köhler theory with surface tension depression and bulk/surface partitioning evaluated from two different thermodynamic surface models. Continuous ternary parameterizations were constructed from surface tension measurements of macroscopic droplets at different time steps after the formation of a droplet surface. The predicted results are compared to previous measurements of mixed NAFA-NaCl cloud condensation nuclei (CCN) activity and a bulk solution model that does not take the NAFA bulk/surface partitioning equilibrium into account. Whereas the bulk model shows a trend in cloud droplet formation following that of macroscopic surface tension depression with time, the variation with time essentially disappears when bulk/surface partitioning is taken explicitly into account during droplet activation. For all equilibrium time steps considered, the effect of surface tension depression in the NAFA-NaCl system is counteracted by the depletion of solute from the finite-sized droplet bulk phase. Our study highlights that a comprehensive data set is necessary to obtain continuous parameterizations of surface tension and other solution properties required to fully account for the bulk/surface partitioning in growing droplets. To our knowledge, no similar data set currently exists for other aqueous organic systems of atmospheric interest. Additional work is necessary to deconvolve the effects of bulk/surface partitioning in the context of time-evolution on cloud droplet activation and to determine whether the results presented here can be further generalized.

Impact of natural organic matter in water on in vitro bioactivity assays

Surface water can be contaminated with pollutants from multiple sources and contain a vast number of various chemicals. In vitro bioassays are valuable tools to assess the total bioactivity of micropollutants in water samples. Besides anthropogenic chemicals, natural organic matter (NOM) is ubiquitous in water, which also may have an impact on the bioactivity in water samples.In the present study we investigated concentration-dependent effects of Nordic Aquatic fulvic acid (NA-FA) and Nordic reservoir NOM (NR-NOM) on bioactivity measured by a panel of luciferase reporter gene assays. The assays included measurements of both induction of activities and inhibition of induced activation on aryl hydrocarbon receptor (AhR), androgen receptor (AR), estrogen receptor (ER), peroxisome proliferator-activated receptor alpha, and on the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activity as a marker of oxidative stress.At non-cytotoxic concentrations both NA-FA and NR-NOM induced AhR activity, inhibited AR activity with and without the known inducer dihydrotestosterone, inhibited Nrf2 activity, and NR-NOM induced ER activity. The results indicate that the presence of NOM in water samples may lead to false positive results for AhR activity and false positive results for AR and Nrf2 activity, when assessing inhibition of induced bioactivities from anthropogenic substances. We have demonstrated that NA-FA and NR-NOM have an impact on in vitro bioactivities and conclude that the impact of NOM in water should be considered in the evaluation of results from bioactivity assays.

Fractionation of Dissolved Organic Matter by Co-Precipitation with Iron: Effects of Composition

Interactions between dissolved organic matter (DOM) and different physical-chemical forms of iron (Fe) represent important biogeochemical processes in the organic carbon cycle. Due to the effect of climate change and anthropogenic activities such as land-use change, the loading of terrestrial DOM into aquatic systems is increasing, and thus, enhancing the organic matter-based acidity in aquatic ecosystems. While complexation of Fe with DOM and the sorption of DOM on iron oxides and (oxy)hydroxides have been reported, less is known about how co-precipitation processes might affect by DOM composition. Here the co-precipitation of two DOM standards, namely the Suwannee River Standard Humic Acid Standard II (SRHA) and Nordic Aquatic Fulvic Acid Reference (NAFA), with Fe was investigated in a pH range of 4.0–8.0. The DOM remaining after co-precipitating with Fe was systematically characterized by various analytical methods to reveal the molecular fractionation of DOM. The co-precipitation of SRHA or NAFA with Fe was enhanced by decreasing the pH, where at pH 4.0, about 70~80% DOC of SRHA or NAFA was removed at Fe(III)/C ratios higher than 0.12. The decrease in SUVA254 and the humification index (HIX) during the co-precipitation process suggests that DOM with high aromatic character was preferentially co-precipitated with Fe. DOM molecular weight influenced the selectivity to co-precipitation, with high molecular weight (HMW) DOM showing a stronger affinity. DOM co-precipitation with Fe was clearly dependent on DOM composition, showing an affinity order of terrestrial humic-like> ubiquitous humic-like> microbial humic-like components. The difference in the reactivity and the relative abundances of excitation emission matrix fluorescence combined with parallel factor analysis (EEM-PARAFAC) components explained the difference in DOC removal efficiency between SRHA and NAFA. This study provides direct insights into the effects of DOM composition on its fractionation specifically through co-precipitation with Fe, and suggests that for aquatic systems rich in iron-based (oxy)hydroxides, and for environmental redox interfaces, co-precipitation of DOM with iron might affect optical properties of the aqueous phase, and represent an important sink for terrestrially-derived organic matter.

Surface adsorption of Nordic aquatic fulvic acid on amine-functionalized and non-functionalized mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSNs) have the potential to be released into the environment and to then adsorb natural organic matter.

Cloud droplet activation of mixed model HULIS and NaCl particles: Experimental results and κ-Köhler theory

Significant amounts of humic-like substances (HULIS) are present in marine submicrometer particles. The cloud condensation nuclei (CCN) activation was investigated for marine model particles comprised of Nordic Aquatic Fulvic Acid Reference (NAFA) and sodium chloride (NaCl) in mass ratios of 100:0, 80:20, 50:50, 20:80 and 0:100 respectively. The CCN activity of NAFA was found to be represented by a κ value of 0.028. The CCN activities of the mixed particles were overestimated by volume weighted addition of the κ values of the pure compounds, which indicates that synergistic effects of the mixtures tend to lower the CCN activity. Parameterizations of water activity (aw) and surface tension (σ) versus solute concentration were obtained from measurements on aqueous solutions. The CCN activity was modeled on the basis of the parameterizations of aw and σ using Köhler theory. For the particles containing 50% or more NAFA the model overpredicted the CCN activity compared to observations. Reasonable model results were obtained by assuming a surface tension of pure water.

Measuring and modeling the hygroscopic growth of two humic substances in mixed aerosol particles of atmospheric relevance

Abstract. The hygroscopic growth of atmospheric particles affects atmospheric chemistry and Earth's climate. Water-soluble organic carbon (WSOC) constitutes a significant fraction of the dry submicron mass of atmospheric aerosols, thus affecting their water uptake properties. Although the WSOC fraction is comprised of many compounds, a set of model substances can be used to describe its behavior. For this study, mixtures of Nordic aquatic fulvic acid reference (NAFA) and Fluka humic acid (HA), with various combinations of inorganic salts (sodium chloride and ammonium sulfate) and other representative organic compounds (levoglucosan and succinic acid), were studied. We measured the equilibrium water vapor pressure over bulk solutions of these mixtures as a function of temperature and solute concentration. New water activity (aw) parameterizations and hygroscopic growth curves at 25 °C were calculated from these data for particles of equivalent composition. We examined the effect of temperature on the water activity and found a maximum variation of 9% in the 0–30 °C range, and 2% in the 20–30 °C range. Five two-component mixtures were studied to understand the effect of adding a humic substance (HS), such as NAFA and HA, to an inorganic salt or a saccharide. The deliquescence point at 25 °C for HS-inorganic mixtures did not change significantly from that of the pure inorganic species. However, the hygroscopic growth of HA / inorganic mixtures was lower than that exhibited by the pure salt, in proportion to the added mass of HA. The addition of NAFA to a highly soluble solute (ammonium sulfate, sodium chloride or levoglucosan) in water had the same effect as the addition of HA to the inorganic species for most of the water activity range studied. Yet, the water uptake of these NAFA mixtures transitioned to match the growth of the pure salt or saccharide at high aw values. The remaining four mixtures were based on chemical composition data for different aerosol types. As expected, the two solutions representing organic aerosols (40% HS/40% succinic acid/20% levoglucosan) showed lower water uptake than the two solutions representing biomass burning aerosols (25% HS/27% succinic acid/18% levoglucosan/30% ammonium sulfate). However, interactions in multicomponent solutions may be responsible for the large variation of the relative water uptake of identical mixtures containing different HSs above a water activity of 0.95. The ZSR (Zdanovskii, Stokes, and Robinson) model was able to predict reasonably well the hygroscopic growth of all the mixtures below aw = 0.95, but produced large deviations for some multicomponent mixtures at higher values.

Dissolution-Accompanied Aggregation Kinetics of Silver Nanoparticles

Bare silver nanoparticles with diameters of 82 ± 1.3 nm were synthesized by the reduction of the Ag(NH(3))(2)(+) complex with D-maltose, and their morphology, crystalline structure, UV-vis spectrum, and electrophoretic mobilities were determined. Dynamic light scattering was employed to assess early stage aggregation kinetics by measuring the change in the average hydrodynamic diameter of the nanoparticles with time over a range of electrolyte types (NaCl, NaNO(3), and CaCl(2)) and concentrations. From this the critical coagulation concentration values were identified as 30, 40, and 2 mM for NaNO(3), NaCl, and CaCl(2), respectively. Although the silver nanoparticles were observed to dissolve in all three electrolyte solutions, the aggregation results were still consistent with classical Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The dissolution of the silver nanoparticles, which were coated with a layer of Ag(2)O, was highly dependent on the electrolyte type and concentration. In systems with Cl(-) a secondary precipitate, likely AgCl, also formed and produced a coating layer that incorporated the silver nanoparticles. Aggregation of the silver nanoparticles was also examined in the presence of Nordic aquatic fulvic acid and was little changed compared to that evaluated under identical fulvic acid-free conditions. These results provide a fundamental basis for further studies evaluating the environmental fate of silver nanoparticles in natural aquatic systems.

Ligand extraction of rare earth elements from aquifer sediments: Implications for rare earth element complexation with organic matter in natural waters

The ability of organic matter as well as carbonate ions to extract rare earth elements (REEs) from sandy sediments of a Coastal Plain aquifer was investigated for unpurified organic matter from different sources (i.e., Mississippi River natural organic matter, Aldrich humic acid, Nordic aquatic fulvic acid, Suwannee River fulvic acid, and Suwannee River natural organic matter) and for extraction solutions containing weak (i.e., CH 3COO −) or strong (i.e., CO 3 2 - ) ligands. The experimental results indicate that, in the absence of strong REE complexing ligands in solution, the amount of REEs released from the sand is small and the fractionation pattern of the released REEs appears to be controlled by the surface stability constants for REE sorption with Fe(III) oxides/oxyhydroxides. In the presence of strong solution complexing ligands, however, the amount and the fractionation pattern of the released REEs reflect the strength and variation of the stability constants of the dominant aqueous REE species across the REE series. The varying amount of REEs extracted by the different organic matter employed in the experiments indicates that organic matter from different sources has different complexing capacity for REEs. However, the fractionation pattern of REEs extracted by the various organic matter used in our experiments is remarkable consistent, being independent of the source and the concentration of organic matter used, as well as solution pH. Because natural aquifer sand and unpurified organic matter were used in our experiments, our experimental conditions are more broadly similar to natural systems than many previous laboratory experiments of REE-humic complexation that employed purified humic substances. Our results suggest that the REE loading effect on REE-humic complexation is negligible in natural waters as more abundant metal cations (e.g., Fe, Al) out-compete REEs for strong binding sites on organic matter. More specifically, our results indicate that REE complexation with organic matter in natural waters is dominated by REE binding to weak sites on dissolved organic matter, which subsequently leads to a middle REE (MREE: Sm-Ho)-enriched fractionation pattern. The experiments also indicate that carbonate ions may effectively compete with fulvic acid in binding with dissolved REEs, but cannot out compete humic acids for REEs. Therefore, in natural waters where low molecular weight (LMW) dissolved organic carbon (DOC) is the predominant form of DOC (e.g., lower Mississippi River water), REEs occur as “truly” dissolved species by complexing with carbonate ions as well as FA, resulting in heavy REE (HREE: Er-Lu)-enriched shale-normalized fractionation patterns. Whereas, in natural terrestrial waters where REE speciation is dominated by organic complexes with high molecular weight DOC (e.g., “colloidal” HA), only MREE-enriched fractionation patterns will be observed because the more abundant, weak sites preferentially complex MREEs relative to HREEs and light REEs (LREEs: La-Nd).

Assessing the trihalomethane formation potential of aquatic fulvic and humic acids fractionated using thin-layer chromatography

The significance of this research is the application of thin-layer chromatography (TLC) to fractionate well-characterized aquatic humic materials coupled with the novel evaluation of the trihalomethane formation potential (THMFP) of the fractionated materials. Disinfection by-products such as trihalomethanes (THMs) form when natural water is treated by chlorination. Nordic Aquatic and Suwannee River fulvic and humic acids, obtained from the International Humic Substances Society, were prepared at pH 6 and 9 and fractionated on silica gel plates using a mobile phase consisting of methanol and ethyl acetate (2:1, v:v). Based on retention factor ( R f) values, three common fractions were identified in all substances examined. Additionally, other fractions were noted that were characteristic of specific humic substances. Each of the three primary fractions derived from Nordic Aquatic fulvic acid at pH 6 demonstrated the potential to contribute to formation of THMs. This research provides data to support the hypothesis that differences in the chemical structure and composition of natural organic matter (NOM) significantly affect the potential to react with chlorine to form THMs.

Adsorbability and photocatalytic degradability of humic substances in water on Ti-modified silica

From the viewpoint of development of a removal agent for humic substances, we prepared Ti-modified silica gel, SiO 2–Ti, from titanium alkoxide and microsized silica gel. The prepared silica agent was investigated in adsorption and photocatalytic degradation of humic substances in water. In these experiments, four humic substances, commercially available Wako humic acid (Wako-HA), Nordic aquatic humic acid (Nordic-HA), Nordic aquatic fulvic acid (Nordic-FA), and Suwannee river fulvic acid (Suwannee-FA), were used, and Freundlich constants ( K F and 1 / n ) and photodegradation rates were evaluated. Wako-HA, which has the highest aromaticity ratio [Ar–OH]/[COOH] and molecular weight, had the highest adsorbability ( K F = 17.5 ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.67 ) but the lowest photodegradability (<80%). On the other hand, Suwannee-FA, which has the lowest aromaticity, [Ar–OH]/[COOH] ratio, and molecular weight, afforded lesser adsorbability ( K F = 7.1 ( mg / g ) ( L / mg ) 1 / n , 1 / n = 0.39 ) but the highest photodegradability (>99%). Nordic-HA and Nordic-FA afforded adsorbabilities similar to that for Suwannee-FA, and medium photodegradabilities between those for Wako-HA and Suwannee-FA. Adsorption and photodegradation capacities of SiO 2–Ti were improved with increased Ti content and phosphorescence emission amount, respectively. From XRD analysis, we found that the structure of anatase-type TiO 2 features the Ti modifiers of SiO 2–Ti. Therefore, humic substance molecules effectively interact with the Ti modifiers and are decomposed by OH radicals generated in situ. We hope that SiO 2–Ti will be used as a photodegradation catalyst in water purification plants.

Hygroscopic properties of two model humic-like substances and their mixtures with inorganics of atmospheric importance.

Water-soluble macromolecular polyacids can play a potentially important role in the hygroscopic properties of atmospheric aerosols. These acids have molecular structures similar to natural fulvic acids (FA) (or humic acids) and are referred to as humic-like substances (HULIS). In this study, the hygroscopicity of HULIS and the mixture of HULIS and sodium chloride (NaCl) and that of HULIS and ammonium sulfate (AS) aerosols at a mass ratio of 1:1 are studied using two natural FA: the Nordic Aquatic Fulvic Acid (NAFA) and the Suwannee River Fulvic Acid (SRFA) as model compounds in an electrodynamic balance. NAFA and SRFA both absorbed and desorbed water reversibly without crystallization and retained water at a relative humidity (RH) < 10%. NAFA and SRFA have a mass growth ratio of 1.25 and 1.45 from RH = 10% to RH = 90%, respectively. However, these results are different from those of another natural FA (the Nordic River Fulvic Acid Reference) in the literature. The differences are possibly due to the differences in the chemical composition of the natural FA, which depends on their sources and the isolation methods. These results suggest that a standardization of the isolation methods of HULIS is needed for better understanding of their atmospheric properties and environmental impacts. In general, the deliquescence and crystallization RH of FA-inorganic mixtures are comparable with those of their respective pure inorganic species. Since FA are less hygroscopic than NaCl and AS, all mixtures absorb less water compared to their respective pure inorganic species of equal particle mass. The FA-AS mixtures have a larger water uptake than the sum of those of the FA and AS individually following a simple additivity rule as noninteracting species at RH = 90%. This enhancement effect increases as the RH decreases. There is no such enhancement effect for the FA-NaCl mixtures until RH is below 90%. These results reveal that the effect of the interactions between FA and inorganic species on the water uptake of the mixtures, in general, is a function of RH.