Suwannee River Research Articles

Chemical Stability and Transformation of Molybdenum Disulfide Nanosheets in Environmental Media.

Layered transition metal dichalcogenides, including molybdenum disulfide (MoS2), have previously been considered stable in the ambient environment due to the absence of dangling bonds in the electron-filled shells of the end chalcogen atoms. Here, we evaluate the chemical stability of MoS2 nanosheets fabricated by chemical exfoliation (ceMoS2) and surfactant dispersion (sMoS2). The results demonstrate that sMoS2 exhibits greater long-term persistence. Contrarily, ceMoS2 underwent progressive deterioration, in which preferential oxidation of the 1T of a mixture of 1T and 2H phases was observed. The oxidative degradation of ceMoS2 was retarded in the presence of natural organic matter (NOM), including Suwannee River natural organic matter (SRNOM) and Aldrich humic acid (ALHA), in the dark ambient condition, while the aging process of MoS2 with co-occurring ALHA was accelerated under sunlight exposure. The observed inhibition effect on the deterioration of ceMoS2 by NOM was mainly attributed to slower dissolution kinetics with rapid initial oxidation (i.e., forming Mo-O bonding) or carbon grafting, rather than prevention of the formation of secondary small suspended Mo-containing particles. The compiled results highlight that the environmental fate of MoS2 nanosheets will be regulated by the combined effects of exfoliating agents and environmentally relevant factors including organic macromolecules and sunlight exposure.

Identification of oxidative stress and estrogenic activity induced by polarity fractions of effluent organic matter.

This study evaluated oxidative stress and estrogenic activity induced by hydrophobic (HP), transphilic (TP), and hydrophilic (HL) fractions of effluent organic matter (EfOM) from municipal and industrial wastewater treatment plants. Fluorescence regional integration (FRI) analysis indicated that EfOM showed higher FRI distribution in regions II (aromatic protein-like) and IV (soluble microbial products, SMPs) than Suwannee River natural organic matter (SRNOM), which was primarily in regions III (fulvic acid-like) and V (humic acid-like). The HP and HL fractions of industrial EfOMs significantly increased catalase (CAT) and glutathione S-transferase (GST) activity and lipid peroxidation compared with those of the control (p < 0.05). Estrogenic activity was the highest in industrial EfOM followed by municipal EfOM, and both were significantly higher than that of SRNOM and the control (p < 0.05). FRI distribution in region II was significantly related to CAT, GST, and estrogenic activity (r = 0.7142, 0.7786, and 0.8107, respectively) for the HL fraction of EfOM. For the HP fraction of EfOM, regions II and IV were significantly related to estrogenic activity (r = 0.7221 and 0.6707, respectively). These findings suggest that aromatic protein-like substances and SMPs in EfOM were responsible for the observed oxidative stress and estrogenic activity.

Contrasting photoreactivity of β2-adrenoceptor agonists Salbutamol and Terbutaline in the presence of humic substances

The photodegradation reactions of two typical β2-adrenoceptor agonists, salbutamol (SAL) and terbutaline (TBL), alone, and in the presence of Aldrich humic acid (AHA) or Suwannee River fulvic acid (SRFA) were investigated by steady-state photolysis experiments, laser flash photolysis (LFP), kinetic modeling and quantum calculation. AHA and SRFA (2–20 mgC L−1) accelerated the phototransformation of both SAL and TBL. For SAL, an inhibiting effect of oxygen on the photodegradation was observed that is fully consistent with the main involvement of excited triplet states of HS (3HS*). On the contrary, oxygen drastically enhanced the photodegradation of TBL showing that 3HS* were negligibly involved in the reaction. The involvement of singlet oxygen was also ruled out because of the low reaction rate constant measured between TBL and singlet oxygen. Quantum calculations were therefore performed to explore whether oxygenated radicals could through addition reactions explain the differences of reactivity of TBL and SAL in oxygen medium. Interestingly, calculations showed that in the presence of oxygen, the addition of phenoxyl on TBL led to the formation of adducts and to the loss of TBL while the same addition reaction on SAL partly regenerated the starting compound and at the end degraded SAL less efficiently. This study is of high relevance to understand the processes involved in SAL and TBL phototransformation and the photoreactivity of HS. Moreover, our findings suggest that TBL might be a promising probe molecule to delineate the role of oxygenated radicals.

A comparison of the effects of natural organic matter on sulfidated and nonsulfidated nanoscale zerovalent iron colloidal stability, toxicity, and reactivity to trichloroethylene

Sulfidated nanoscale zerovalent iron (S-NZVI) is a new remediation material with higher reactivity and greater selectivity for chlorinated organic contaminants such as trichloroethene (TCE) than NZVI. The properties of S-NZVI and the effects of groundwater constituents like natural organic matter (NOM) on its reactivity are less well-characterized than for NZVI. In this study, S-NZVI (Fe/S mole ratio = 15) was synthesized by sonicating NZVI in a Na2S solution, yielding particles with greater surface charge, less aggregation, and higher reactivity with TCE compared to NZVI. The cytotoxicity of S-NZVI was not mitigated effectively due to the smaller size. The addition of Suwannee River humic acid (SRHA) increased the negative surface charge magnitude and dispersion stability and reduced the toxicity of both NZVI and S-NZVI significantly, but also enhanced the corrosion of particles and the formation of non-conductive film. The degradation rate constant (ksa) of both NZVI and S-NZVI was thus reduced with the increasing concentration of SRHA, which decreased by 78% and 60% to be 0.0004 and 0.0053 L m−2 h−1, respectively, with 200 mg C/L SRHA. Additionally, the performance of S-NZVI in field was evaluated to be depressed in simulated groundwater and the negative effect was exacerbated with increased concentration of SRHA. Hydro-chemical conditions like dissolved oxygen (DO), pH, and temperature also influenced the reactivity of S-NZVI. Hence, S-NZVI was a preferred candidate for in-situ remediation of TCE than NZVI. Nevertheless, the integrity of the FeS shell on S-NZVI influenced by NOM need to be considered during the long-term use of S-NZVI in groundwater remediation.

Comparison of Trihalomethane Formation Using Chlorine-Based Disinfectants Within a Model System; Applications Within Point-of-Use Drinking Water Treatment

© 2019 Clayton, Thorn and Reynolds. Point-of-use (POU) drinking water treatment systems provide solutions for communities where centralized facilities are unavailable. Effective POU systems treat and reduce the number of pathogens in POU water supplies often employing disinfection. Chlorine disinfection results in the formation of disinfection by-products (DBPs), such as trihalomethanes (THMs), through the reaction of chlorine with natural organic matter (NOM) over time. Although THMs are known to be harmful to human health, little is known about their production within POU systems. This study compares the disinfectants; Electrochemically Activated Solutions (ECAS), hypochlorous acid (HOCl), and sodium hypochlorite (NaOCl), with respect to their potential to produce THMs within POU drinking water systems. Headspace solid-phase microextraction (HS-SPME) gas chromatography mass spectrometry (GC-MS) was utilized to quantify THMs in treated water samples containing NOM (Suwannee River humic acid, 4 mg L -1 ). All disinfection treatments were matched to free chlorine concentrations of 1, 3, and 5 mg L -1 , using reaction times of 1, 5, and 10 min. THMs were produced at free chlorine concentrations of 5 mg L -1 and at reaction times of 5 and 10 min for all disinfectants. ECAS or HOCl, resulted in the formation of significantly lower total THM concentrations across all reaction times and free chlorine concentrations, compared to NaOCl. ECAS can be generated at the POU requiring only water, salt and energy for production, and this study demonstrates that its use results in reduced formation of THMs, compared with NaOCl. Further work is required to replicate these findings within scaled-up POU water treatment systems.

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.

Soil organic matter increases antimonate mobility in soil: An Sb(OH)6 sorption and modelling study

The role of organic matter (OM) in antimonate (further denoted as Sb(OH)6) mobility in soil is unclear. The objective of this study was to evaluate Sb(OH)6–OM interaction. Antimonate solid:liquid distribution coefficients (KD) were measured at low Sb concentrations in soil samples with a natural gradient in soil organic carbon (OC) that were collected from different depths of up to 3 m in two excavated soil profiles and in a subset of four soil samples with experimentally increased OM concentration from addition of Suwannee River OM. The KD values were related to soil properties by multiple linear regression and described with the CD–MUSIC model of ferrihydrite. The KD values ranged from 12 to 2800 L kg−1 and decreased strongly with increasing OC concentrations, when normalized to the amount of iron (Fe) and aluminium (Al) in acid oxalate extracts (r = −0.69; p < 0.0001). Experimentally increasing OC by ∼1.5 g kg−1 increased soluble Sb and decreased Sb(OH)6KD values by up to a factor of 8. The multiple regression model reveals that sorption of Sb(OH)6 to Fe and Al hydroxides decreases with increasing pH and increasing dissolved organic carbon concentration. This effect could be explained with geochemical modelling by the competitive and electrostatic effects of adsorbed humic substances on Sb(OH)6 surface complexation to the reactive surface sites of the Fe and Al hydroxides. Finally, both models could predict the in situ pore water Sb concentrations of unspiked samples, with a RMSE of 0.35 for the regression model and 0.43 for the geochemical model on the log10Sb concentrations. For these predictions, the 0.1 M Na2HPO4–extractable Sb concentration was measured and used to estimate the reversibly sorbed Sb pool. This study shows that increasing soil OM increases Sb(OH)6 mobility at low soil Sb concentration, likely due to competitive sorption on Fe and Al hydroxides and a process based, geochemical model was calibrated to describe Sb(OH)6 mobility in soil.

Dissolved Organic Matter Sorption and Molecular Fractionation by Naturally Occurring Bacteriogenic Iron (Oxyhydr)oxides.

Iron (oxyhydr)oxides are highly reactive, environmentally ubiquitous organic matter (OM) sorbents that act as mediators of terrestrial and aqueous OM cycling. However, current understanding of environmental iron (oxyhydr)oxide affinity for OM is limited primarily to abiogenic oxides. Bacteriogenic iron (oxyhydr)oxides (BIOs), common to quiescent waterways and soil redox transitions, possess a high affinity for oxyanions (i.e., arsenate and chromate) and suggests that BIOs may be similarly reactive for OM. Using adsorption and desorption batch reactions, paired with Fourier transform infrared spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry, this work demonstrates that BIOs are capable of sorbing leaf litter-extracted DOM and Suwannee River Humic/Fulvic Acid (SRHA/SRFA) and have sorptive preference for distinct organic carbon compound classes at the biomineral interface. BIOs were found to sorb DOM and SRFA to half the extent of 2-line ferrihydrite per mass of sorbent and was resilient to desorption at high ionic strength and in the presence of a competitive ligand. We observed the preferential sorption of aromatic and carboxylic-containing species and concurrent solution enrichment of aliphatic groups unassociated with carboxylic acids. These findings suggest that DOM cycling may be significantly affected by BIOs, which may impact nutrient and contaminant transport in circumneutral environments.

Evaluation of algal photosynthesis inhibition activity for dissolved organic matter with the consideration of inorganic and coloring constituents

The effect of waterborne ingredient on ecosystem has been of great interest. In the present study, the evaluation method using algal photosynthesis inhibition assay with dual-channel pulse amplitude modulation (PAM) system was established for a series of water samples to elucidate the potential effect of the total body of organic compounds including natural organic matter (NOM) on aquatic ecosystems. The more sensitive and less time-consuming monitoring method compared with algal growth inhibition assay was suggested, especially considering inorganic and coloring constituents. Algal photosynthesis inhibition activity was detected with high sensitivity for photosystem II (PSII) inhibitors, whereas the IC10 of the other chemicals was over the environmental standard concentration for Chlamydomonas moewusii (Chlorophyceae) and Pheodactylum tricornutum (Diatomea). The photosynthesis inhibition activity of Lake Biwa dissolved organic matter (LBDOM) and fulvic acid (LBFA) was significantly detected at ≥10 times the concentration and >10 mgC L-1, respectively, whereas prominent activity was confirmed for Suwannee River NOM (SRNOM) on the river original concentration (>30 mgC L-1) for both algae. Significant inhibition activity was detected in both algae at least in twice-concentration for water samples from a wastewater treatment pilot plant. There was no great difference in the activity between sewage secondary effluent and its filtrate with ultrafiltration (UF), and physically washing water for the UF membrane.

Composition of dissolved organic matter controls interactions with La and Al ions: Implications for phosphorus immobilization in eutrophic lakes

Applications of aluminium (Al) salt or lanthanum (La) modified bentonite (LMB) have become popular methodologies for immobilizing phosphorus (P) in eutrophic lakes. The presence of humic substances, has been shown to inhibit this form of treatment due to the complexation with La/Al. However, the effects of other dissolved organic matter (DOM), especially that derived from phytoplankton (the dominant source in eutrophic lakes) are unknown. In this study, the interaction with La/Al of Suwannee River Standard Humic Acid Standard II (SRHA) and algae-derived DOM (ADOM) were investigated and compared. Differed to SRHA which was dominated by polyphenol-like component (76.8%, C1-SRHA), majority in ADOM were protein-like substance, including 41.9% tryptophan-like component (C2-ADOM) and 21.0% tyrosine-like component (C3-ADOM). Two reactions of complexation and coprecipitation were observed between SRHA/ADOM and La/Al. Complexation dominated at low metal inputs less than 10 μM and coprecipitation was the main reaction at higher metal inputs. For ADOM, the tryptophan-like component (C2-ADOM) was the important component to react with metal. The reaction rate for C2-ADOM with La were about two-third of that for C1-SRHA, indicating that the influence of C2-ADOM was significant during the P immobilization by La/Al-based treatment in eutrophic lakes. The P removal data in the presence of ADOM confirmed the significant inhibition of ADOM. In addition, based on the composition of coprecipitates and relatively biodegradable character of tryptophan-like substances (C2-ADOM), the coprecipitation of ADOM was assumed to reduce the stability of precipitated P in eutrophic lakes. The release of P from the potential biodegradation of the coprecipitates and thus the possible decline of the performance of P immobilization by La/Al-based treatments is an important work in the future.

Combined effects of dissolved organic matter, pH, ionic strength and halides on photodegradation of oxytetracycline in simulated estuarine waters.

Estuarine waters of variable compositions are sinks for many micropollutants. The varying water properties can impact the photodegradation of organic pollutants. In this study, the combined effects of dissolved organic matter (DOM), pH, ionic strength, and halides on the photodegradation of the model organic pollutant oxytetracycline (OTC) were investigated. Suwannee River natural organic matter (SRNOM) was used as a representative DOM. The results showed that the observed photolysis rate constant (kobs) of OTC increased rapidly upon increase of pH. SRNOM induced a 11.0-17.9% decrease of the kobs for OTC. In the presence of SRNOM, the ionic strength and specific halide effects promote OTC photodegradation with a 39.2-84.2% and 7.1-28.8% increase of the kobs, respectively. The effects of SRNOM, ionic strength and halides on OTC photodegradation are pH-dependent. Direct photolysis half-lives (t1/2) of OTC were estimated in view of the more important role of direct photolysis compared to indirect photolysis. The estimated t1/2 values decreased from 187.4-206.6 d to 34.4-36.6 d as the pH increases in the Yellow River estuarine region. The results of this research demonstrate that the photodegradation rate of OTC increases rapidly in the gradient from river water to marine water in estuarine regions.

Impact of dissolved organic matter on mercury and methylmercury sorption to activated carbon in soils: implications for remediation.

Activated carbon (AC) amendments have shown promise in reducing inorganic mercury (Hg(ii) complexes, "Hg") and methylmercury (MeHg) risk in contaminated soils. However, the effectiveness of AC in Hg and MeHg immobilization has varied among studies, suggesting that site biogeochemistry might dictate efficacy. In this study, we examined the effect of dissolved organic matter (DOM) on MeHg and Hg sorption to AC. We evaluated the impact of Suwannee River Humic Acid (SRHA) on sorption to AC directly using an isotherm approach and in a soil/AC mixture using slurry microcosms. Aqueous sorption coefficients to AC (log KAC) for Hg-SRHA and MeHg-SRHA complexes were one to two orders of magnitude lower (Hg-SRHA = 4.53, MeHgSRHA = 4.35) than those for chloride complexes (HgCl2 = 6.55, MeHgCl = 4.90) and more closely resembled the log KAC of SRHA (3.64). In anoxic, sulfidic soil slurries, the KAC for sulfide species appeared stronger than for chloride or SRHA species for both Hg and MeHg. AC significantly reduced porewater concentrations of both ambient MeHg and a fresh Me199Hg spike, and the addition of up to 60 mg L-1 SRHA did not reduce sorption to AC. The AC also reduced ambient Hg and 201Hg porewater concentrations, but as SRHA concentration increased, the magnitude of solid phase sorption decreased. Speciation modeling revealed that SRHA may have impacted Hg distribution to the solid phase by reducing HgS precipitation. This study highlights the need for site-specific evaluation of AC efficacy and the value in developing biogeochemical models of AC performance for Hg control.

Analysis and Extent of Santa Fe River Flooding in North Florida Attributed to Rainfall and Wind Damage Associated with Hurricane Irma

The Santa Fe River (SFR) is within the north Florida area of the regional Floridan aquifer system. The extent of recent flood damage in the SFR and tributaries in Bradford County has been attributed to rainfall and wind damage to trees associated with Hurricane Irma, September 2017. Implications of the determined cause of a disaster can include the allocation of disaster relief funds. Bradford County, Florida obtained approximately $2.5 million from the United States Department of Agriculture’s (USDA) Natural Resources Conservation Service (NRCS) for emergency flood abatement assistance and $255,875 from the Suwannee River Water Management District (SRWMD), combined with $13,750 in-kind match provided by the county, based on the attributed cause of that damage to rainfall and winds from Hurricane Irma. On January 2, 2018, Bradford County commissioners also approved grant applications to the SRWMD for $2.2 million for Alligator Creek Flood Mitigation and for $90,250 for Hampton Lake Canal to Santa Fe River Flood Mitigation, requiring in-kind matches from the county of $110,000 and $4750, respectively. Our study analyzed historical precipitation data for the SFR Basin and headwaters from 1895 through 2017 and recorded discharge and gage heights from the United States Geological Survey (USGS) to evaluate that presumed cause of flood damage in that basin and to provide a better understanding of historical relationships between precipitation, gage data and flooding in that basin. Recorded USGS peak gage height and Digital Elevation Models (DEMs) also were used to illustrate the lateral extent and relative depth of flooding associated with an extreme precipitation event in the lower SFR vicinity of O’Leno State Park. Finally, we evaluated the condition of the trees in the SFR Basin as an indicator of long-term anthropogenic groundwater alterations. Those data and analyses did not support the conclusion that Hurricane Irma was the only cause of the magnitude and extent of SFR flooding and tree damage in Bradford County and adjacent counties. Other contributors to stream flow in the SFR basin include heavy mineral mining wastewater discharges that have exceeded the maximum discharge volume of “40 million gallons a day” (MGD) under the National Pollutant Discharge Elimination System (NPDES) permit issued by the Florida Department of Environmental Protection (FDEP) to the Chemours Company TT LLC (Chemours, formerly DuPont) for Trail Ridge mining operations. The magnitude of those discharges suggests that those discharges and extensive Trail Ridge mining in Baker, Bradford, Clay, and Duval Counties contributed to the flooding and were a factor in the tree destruction in the SFR Basin.

Hydrologic responses to projected climate change in ecologically diverse watersheds of the Gulf Coast, United States

The Gulf Coast watersheds in the United States contain some of the highest levels of biodiversity of all freshwater systems in North America. Developing environmental management policies to protect and preserve these ecosystems makes the study of the impacts of projected climate change on the future hydrologic cycle crucial. We used the Soil and Water Assessment Tool (SWAT) to estimate the potential hydrologic changes for the mid‐21st century (2050s) and the late 21st century (2080s) in the Mobile River, Apalachicola River, and Suwannee River watersheds in the Gulf Coast region of the United States. These estimates are based on downscaled future climate projections from 20 global circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). SWAT models were calibrated and validated using the multi‐algorithm, genetically adaptive multi‐objective (AMALGAM) technique in a high‐performance computing (HPC) cluster. For the Gulf Coast watersheds, the climate is projected to be warmer and wetter. Projected changes in climatic variables are likely to bring large changes in both annual and seasonal hydrologic processes within these watersheds. We found substantial decreases in mean annual streamflow under RCP8.5 during the 2080s, with up to a 13.0% decrease projected for the Suwannee River watershed compared to the present day. Summer streamflow is projected to be substantially lower during the 2080s, with up to a 25.1% decrease projected for the Suwannee River watershed, during a time of high demand of water resources for agricultural, industrial, and ecosystem services. These hydrologic projections are expected to help in making better‐informed decisions for future water resources and ecosystem management in the Gulf Coast region.

Three-wavelength cavity-enhanced albedometer for measuring wavelength-dependent optical properties and single-scattering albedo of aerosols.

The spectral dependence of aerosol light absorption (αabs) and single-scattering albedo-[ω, defined as the ratio of the scattering (αscat) and extinction coefficients (αext = αabs + αscat)]-has proven effective in classifying dominant aerosol types. It is also helpful in understanding aerosol sources, transformation, climate and environmental effects, testing aerosol models, and improving the retrieval accuracy of satellite and remote sensing data. Despite the significant progress that has been made with measurement of light absorption and ω, many of the reported instruments either operate at a fixed wavelength or can only measure a single optical parameter. Quantitative multi-parameter wavelength-dependent measurement remains a challenge. In this work, a three-wavelength cavity-enhanced albedometer was developed. The albedometer can measure multiple optical parameters, αext, αscat, αabs, and ω, at λ = 365, 532, and 660 nm, in real time. The instrument's performance was evaluated using four different type laboratory generated aerosols, including polystyrene latex spheres (PSL, non-absorbing); ammonium sulfate (AS, non-absorbing); suwannee river fulvic acid (SRFA, slightly absorbing; a proxy for light absorbing organic aerosol); and nigrosin (strongly absorbing).

A systematic investigation on the bactericidal transient species generated by photo-sensitization of natural organic matter (NOM) during solar and photo-Fenton disinfection of surface waters

In this work, the role of dissolved oxygen in the solar and the photo-Fenton-mediated E. coli inactivation process was put under scrutiny. The effect of transient species that were produced in the presence of various natural organic matter isolates (NOM), namely Suwannee River (SR) NOM, Nordic Reservoir (NR) NOM, SR Humic acid (SRHA), and SR Fulvic acid (SRFA) was studied in detail. The role of 1O2 in this reaction was systematically evaluated by modifying the O2 concentration (N2/O2 purging) and the matrix composition (10, 50, and 100% deuterium oxide (D2O) v/v). In the presence of NOM, 1O2 was generated and the enhancement of E. coli inactivation rate due to charge transfer from triplet state to molecular oxygen. The comparison between SR and NR NOM showed that for these compounds, triplet state of NOM (3NOM*), and 1O2 were the more favorable active species in E. coli inactivation, respectively. Also, the second order rate constants (kE. coli2nd) of E. coli with 3NOM*, and 1O2 were calculated by using the steady state approximation. The obtained results showed that the rate values of 1O2 related to NR NOM was ∼ 5.6 times higher than SR NOM, while the rate values of 3NOM* for SR NOM was ∼ 8.7 times higher than NR NOM. We also determined the effect of these organic matter isolates in the photo-Fenton process and its constituents (solar/Fe2+, solar/H2O2, and solar/Fe2+/H2O2). In presence of NOM, the photo-Fenton process inactivation rates increased which confirmed that the combined processes has additional pathways generated with disinfecting effect during solar exposure of bacteria.

Insights into aggregation and transport of graphene oxide in aqueous and saturated porous media: Complex effects of cations with different molecular weight fractionated natural organic matter

The stability of nanomaterials in aquatic environment is a critical factor that governs their fate and ecotoxicity. Meanwhile, the interaction between nanomaterials and ubiquitous natural organic matter (NOM) is a vital process that influences the transport and biological effects of nanomaterials in the environment. However, impacts of NOM on the aggregation and transport of two-dimensional nanomaterials, especially for the increasingly used graphene oxide (GO), are not well understood. Particularly, there is lack of exploration on potential impacts of the heterogeneous properties of NOM on GO behaviour, especially that induced by the wide molecular weight (MW) span of NOM. In this study, effects of several kinds of well-characterized MW fractionated Suwannee River NOM (Mf-SRNOMs) on the aggregation and transport of GO in aqueous media and saturated porous media were investigated. Our results suggest that the stability and migration capacity of GO under most investigated electrolyte conditions are promoted by all Mf-SRNOMs, and efficiencies of different Mf-SRNOMs are generally positively correlated with their MW. Primarily, mechanisms including MW-dependent steric hindrance and sorption of Mf-SRNOMs onto GO are critical in stabilizing GO, and thus facilitating its transport. However, the stronger sorption of higher Mf-SRNOMs onto the GO basal plane through π-π interaction further facilitated the cation bridging between both ends of Mf-SRNOM and GO, and resulted in heteroaggregation of NOM-GO. Moreover, the weight analysis indicated that despite the fact that high Mf-SRNOMs only occupied a small percentage of pristine-SRNOM, they showed a stronger contribution towards pristine-SRNOM's capacity in stabilizing GO, when compared with that of lower MW counterpart. These findings pointed out that complex effects of the heterogeneities of NOM and cations should be highly relevant when the aggregation and transport behaviour of two-dimensional nanomaterials is investigated, and NOM fractions that are highly aromatic and of a higher MW should receive greater attention.

Photocatalytic oxidation of sulfamethoxazole in the presence of TiO2: Effect of matrix in aqueous solution on decomposition mechanisms

As water matrix, inorganic anions and natural organic matter (NOM) may impact the removal of pharmaceuticals not only on the kinetics but also on the transformation products formation. In this study, the effects of initial pH, inorganic anions and NOM on the transformation pathways of sulfamethoxazole (SMX) during photocatalytic decomposition were investigated. Three pathways including hydroxylation, hydrolysis and isoxazole ring oxidation were found during SMX photocatalysis. SMX in deionized water was degraded by hydroxylation principally in alkaline situation, while hydrolysis was the main pathway in acidic condition. Almost all the pathways for SMX decomposition were suppressed when anions were added, with the inhibitory effect followed the order of HPO42− > HCO3− > SO42− > Cl− > H2PO4−. The formation of products with larger energy barrier was affected more significantly when anions were added. The products formation was also impacted by the presence of NOM isolates including “Suwannee River Humic Acid” (SRHA), “Suwannee River Fulvic Acid” (SRFA) and “Suwannee River NOM” (SRNOM). The mechanisms of hydroxylation and isoxazole ring oxidation were inhibited by NOM, with the order of SRFA > SRHA > SRNOM, due to their hydroxyl radical scavenging abilities which were related to their aromaticity degree. Most of the hydrolysis products were favored in the presence NOM, and the enhancement effect was in accordance with the sequence of SRNOM > SRFA > SRHA due to the different photoinductive abilities of the NOM isolates.

Effect of polybrominated diphenyl ethers on the formation of disinfection byproducts in the water system

Disinfection byproducts (DBPs) can be formed from many different kinds of carbon- and nitrogen-based organic materials. This study investigated DBP formation in the presence of two types of polybrominated diphenyl ethers (PBDEs), 2,2′,4,4′-tetrabromodiphenyl ether (BDE 47) and 2,2′,3,3′,4,4′,5,5′,6,6′-decabromodiphenyl ether (BDE 209). The effects of PBDEs on the formation of DBPs upon the chlorination (or chloramination) of Suwannee River humic acid (SRHA) were also evaluated. Results indicated that the chlorination of BDE 47 and BDE 209 resulted in the formation of DBPs, with 1,1,1-trichloro-2-propanone (1,1,1-TCP) being the major DBP type formed. When PBDEs were present in the SRHA solution, a lower amount of CHCl3 was formed, and more 1,1,1-TCP was produced. However, the effects of PBDEs on the formation of DBPs in the real surface water were insignificant because of the complicated water chemistry.

Determining surface chemical composition of silver nanoparticles during sulfidation by monitoring the ligand shell.

Evaluating the surface and core compositions of transforming nanoparticles (NP) represents a significant measurement challenge but is necessary for predicting performance in applied systems and their toxicity in natural environments. Here, we use X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy to characterize both the surface and core ofpolyvinyl pyrollidone-silver nanoparticles in the presence of two Suwannee River fulvic acid (FA) standards and humic acid (HA) during sulfidation, the predominant transformation pathway in environmental systems. Only by using data from both spectroscopic methods was a clear relationship established between AgNP core composition and FA affinity established, where concomitant loss of FA was observed with Ag2S formation. Using XPS to measure AgNP surface composition, overlapping trends from XPS on FA I desorption from the AgNP surface as function of surface sulfidation were observed with FA II in the ATR-FTIR measurements. The reproducibility of the changing heterogeneous coating as a function of AgNP sulfidation provided a transferable method to determine the extent of Ag sulfidation without further need for the high resolution, high cost measurement tools that underpinned validation of the method. The relationship was not observed for HA, where a lower affinity to the AgNP surface was observed, suggesting distinct binding to the NP.