Presence Of Suwannee River Humic Acid Research Articles

Interaction between functionalized multiwalled carbon nanotubes and MS2 bacteriophages in water

Fate and transport of carbon nanomaterials can be strongly dependent on the interaction with secondary particulates in the aquatic systems. Bio-particulates in water, e.g., viruses with charged and hydrophobic surface moieties, may profoundly influence the interfacial behavior and hence the environmental fate of nanomaterials (and vice versa). This study systematically evaluates the interfacial interaction of acid-functionalized multiwalled carbon nanotubes (MWNTs) with MS2 bacteriophages, or heteroaggregation behavior of these particulates, under mono- and di-valent cations and with Suwannee River humic acid (SRHA). Results indicate that the highest concentration of MS2 (i.e., MWNT:MS2 of 100:1) renders exceptional stability of MWNTs, even in high salinity conditions. However, at lower MS2 concentrations (i.e., MWNT:MS2 of 1000:1 and 10,000:1), the suppression of MWNT heteroaggregation rate is not as significant. The observed enhanced stability is likely caused by the preferential attachment of the MS2 capsids onto MWNT surfaces, which is mediated by electrostatic attraction (between negatively charged oxygen-containing moieties on MWNTs and positively charged amino acid residues on MS2 surfaces) and/or by MS2 capsids with positive hydropathy index (indicating strong hydrophobicity). Presence of SRHA also shows stability enhancement; however, at lower MS2 concentrations, SRHA dominated the heteroaggregation behavior. These results implicate that preferential interaction between virus capsids (i.e., MS2 and may be other waterborne viruses) and carbonaceous nanomaterials may influence environmental transport of both in aquatic environments.

Surfactant-Wrapped Multiwalled Carbon Nanotubes in Aquatic Systems: Surfactant Displacement in the Presence of Humic Acid.

Sodium dodecyl sulfate (SDS) facilitates multiwalled carbon nanotube (MWCNT) debundling and enhances nanotube stability in the aqueous environment by adsorbing on the nanotube surfaces, thereby increasing repulsive electrostatic forces and steric effects. The resulting SDS-wrapped MWCNTs are utilized in industrial applications and have been widely employed in environmental studies. In the present study, MWCNTs adsorbed SDS during ultrasonication to form stable MWCNTs suspensions. Desorption of SDS from MWCNTs surfaces was then investigated as a function of Suwannee River Humic Acid (SRHA) and background electrolyte concentrations. Due to hydrophobic effects and π-π interactions, MWCNTs exhibit higher affinity for SRHA than SDS. In the presence of SRHA, SDS adsorbed on MWCNTs was displaced. Cations (Na(+), Ca(2+)) decreased SDS desorption from MWCNTs due to charge screening effects. Interestingly, the presence of the divalent calcium cation facilitated multilayered SRHA adsorption on MWCNTs through bridging effects, while monovalent sodium reduced SRHA adsorption. Results of the present study suggest that properties of MWCNTs wrapped with commercial surfactants will be altered when these materials are released to surface waters and the surfactant coating will be displaced by natural organic matter (NOM). Changes on their surfaces will significantly affect MWCNTs fate in aquatic environments.

Disaggregation of silver nanoparticle homoaggregates in a river water matrix

Silver nanoparticles (Ag NPs) could be found in aquatic systems in the near future. Although the interplay between aggregate formation and disaggregation is an important factor for mobility, bioavailability and toxicity of Ag NPs in surface waters, the factors controlling disaggregation of Ag NP homoaggregates are still unknown. In this study, we investigated the reversibility of homoaggregation of citrate coated Ag NPs in a Rhine River water matrix. We characterized the disaggregation of Ag NP homoaggregates by ionic strength reduction and addition of Suwannee River humic acid (SRHA) in the presence of strong and weak shear forces. In order to understand the disaggregation processes, we also studied the nature of homoaggregates and their formation dynamics under the influence of SRHA, Ca2+ concentration and nanoparticle concentration.Even in the presence of SRHA and at low particle concentrations (10μgL−1), aggregates formed rapidly in filtered Rhine water. The critical coagulation concentration (CCC) of Ca2+ in reconstituted Rhine water was 1.5mmolL−1 and was shifted towards higher values in the presence of SRHA. Analysis of the attachment efficiency as a function of Ca2+ concentration showed that SRHA induces electrosteric stabilization at low Ca2+ concentrations and cation-bridging flocculation at high Ca2+ concentrations. Shear forces in the form of mechanical shaking or ultrasound were necessary for breaking the aggregates. Without ultrasound, SRHA also induced disaggregation, but it required several days to reach a stable size of dense aggregates still larger than the primary particles.Citrate stabilized Ag NPs may be in the form of reaction limited aggregates in aquatic systems similar to the Rhine River. The size and the structure of these aggregates will be dynamic and be determined by the solution conditions. Seasonal variations in the chemical composition of natural waters can result in a sedimentation-release cycle of engineered nanoparticles.

TiO2 nanoparticle sorption to sand in the presence of natural organic matter

The sorption properties of TiO2 nanoparticles (NPs) on sand were investigated in the presence of Suwannee River humic acid (SRHA) as a surrogate for natural organic matter. SRHA drastically reduced the sorption preference regardless of the initial pH and ionic strength of the solution. Despite the higher SRHA loading onto sand versus the TiO2 NPs, the consequent zeta (ζ)-potential drop was more significant in the TiO2 NPs, indicating that the decreased sorption should be primarily ascribed to the fraction of SRHA sorbed onto the TiO2 NP surfaces. The hindering effect of SRHA on the sorption increased with SRHA concentration, but stabilized at the concentration equivalent to full surface coverage of the TiO2 NPs and sand in the reaction system. Interaction force measurements indicated that SRHA inhibits the approach of the TiO2 NPs to the sand surface, as expected by the Derjaguin–Landau–Verwey–Overbeek calculation. However, the adhesion force of TiO2 NPs to sand was not critically affected by the presence of SRHA. TiO2 NP sorption to natural sand was limited as to the acid-treated sand in the presence of SRHA, implying that the organics dissolved from natural sand might facilitate the transport of TiO2 NPs in aquifers by inhibiting TiO2 NP sorption to aquifer materials.

Influence of humic acid on the transport behavior of bacteria in quartz sand

The significance of natural organic matter (NOM) on the transport of bacteria in packed porous media (quartz sand) was examined in both NaCl and CaCl 2–NaCl mixing solutions at pH 6.0. Three representative cell types (with EPS), Rhodococcus sp. QL2 (Gram-positive, non-motile), Escherichia coli BL21 (Gram-negative, non-motile), and E. coli C3000 (Gram-negative, motile), were utilized to systematically determine the influence of NOM (Suwannee River humic acid (SRHA)) on cell transport behavior. To investigate the significance of SRHA on transport of bacteria without EPS on cell surfaces, experiments for treated cells with the removal of EPS from cell surfaces were also performed. The breakthrough plateaus for all examined bacteria with the presence of SRHA (1 mg L −1) in solutions were higher than those with the absence of SRHA under all examined conditions, indicating that the presence of SRHA in solutions enhanced cell transport regardless of cell types (Gram-negative or Gram-positive), motility (non-motile or motile), presence or absence of EPS on cell surfaces, and solution chemistry (ionic strength and ion valence). Zeta potentials for bacteria and quartz sand with the presence of SRHA were similar as those without SRHA present in solutions, suggesting that SRHA did not alter the surface charge of bacteria or sand, thus the enhanced cell transport by SRHA was not likely driven by alteration in the surface charge of either cell or quartz sand. SRHA pre-equilibration experiments demonstrated that the site competition by a portion of SRHA and the repelling deposition by suspended SRHA contributed to the decreased cell deposition observed with the presence of SRHA in bacteria suspension.

Influence of Ca 2+ and Suwannee River Humic Acid on aggregation of silicon nanoparticles in aqueous media

Silicon nanoparticles (NPs) have potential applications in many fields including microelectronics, biomedical imaging, and most recently energetics. Even though silicon NPs are thought to be harmless, their full impact on the environment and human health needs further investigation due to their potential increased use and recent toxicity data. Various techniques were used to characterize silicon NPs that are being considered for use in energetics. These techniques included dynamic light scattering (DLS), electron microscopy (EM), X-ray diffraction (XRD) and atomic force microscopy (AFM). Experiments were also conducted on the early stage aggregation kinetics of silicon NPs in the presence of Ca 2+ and Suwannee River Humic Acid (SRHA). The addition of SRHA in the presence of Ca 2+ resulted in increased attachment efficiencies and decreased critical coagulation concentration (from 0.4 to 0.1 M). The enhanced aggregation was attributed to bridging generated by SRHA aggregates as evidenced by selected area electron diffraction (SAED) and energy dispersive spectroscopy (EDS). SAED verified the bridging to be amorphous phase comprised of humic substances rather than artifacts of silicon crystallites. Element distribution analyses were also used in the delineation of the silicon NP aggregation mechanisms in the absence and presence of SRHA.

Uptake of Neutral Metal Complexes by a Green Alga: Influence of pH and Humic Substances

We have examined the influence of pH and a natural humic acid on the short-term uptake (<40 min) of a neutral, lipophilic metal complex by a unicellular freshwater alga, Pseudokirchneriella subcapitata. Cadmium diethyldithiocarbamate ([Cd(DDC)2]0) was used as a model lipophilic metal complex and Suwannee River Humic Acid (SRHA) was chosen as a representative aquatic humic acid (6.5 mg C L−1). Under the experimental conditions virtually all the Cd was expected to be present as the lipophilic complex ([Cd]T = 0.38 nM; [DDC] 1 μM; [Cd2+] <10−15 M; pH 7.0, 6.0, or 5.5). Uptake of [Cd(DDC)2]0 proved to be sensitive to pH changes. It was lower at pH 6.0 and 5.5 than at pH 7.0. To our knowledge, this is the first demonstration of reduced uptake of a lipophilic metal complex at low pH. The presence of SRHA also affected uptake, either by binding the lipophilic complex in solution and reducing its bioavailability (pH 7.0) or by increasing the permeability of the algal membrane (pH 5.5).