Surfactive stabilization of multi-walled carbon nanotube dispersions with dissolved humic substances

Soil humic substances (HS) stabilize carbon nanotube (CNT) dispersions, a mechanism we hypothesized arose from the surfactive nature of HS. Experiments dispersing multi-walled CNT in solutions of dissolved Aldrich humic acid (HA) or water-extractable Catlin soil HS demonstrated enhanced stability at 150 and 300 mg L⁻¹ added Aldrich HA and Catlin HS, respectively, corresponding with decreased CNT mean particle diameter (MPD) and polydispersivity (PD) of 250 nm and 0.3 for Aldrich HA and 450 nm and 0.35 for Catlin HS. Analogous trends in MPD and PD were observed with addition of the surfactants Brij 35, Triton X-405, and SDS, corresponding to surfactant sorption maximum. NEXAFS characterization showed that Aldrich HA contained highly surfactive domains while Catlin soil possessed a mostly carbohydrate-based structure. This work demonstrates that the chemical structure of humic materials in natural waters is directly linked to their surfactive ability to disperse CNT released into the environment.     

Effect of humic matter on metal adsorption onto clay materials: Testing the linear additive model

Migration of contaminants with low affinity for the aqueous phase is essentially governed by interaction with mobile carriers such as humic colloids. Their impact is, however, not sufficiently described by interaction constants alone since the humic carriers themselves are subject to a solid–liquid distribution that depends on geochemical parameters.In our study, co-adsorption of the REE terbium (as an analogue of trivalent actinides) and humic acid onto three clay materials (illite, montmorillonite, Opalinus clay) was investigated as a function of pH. ¹⁶⁰Tb(III) and ¹³¹I-labelled humic acid were employed as radiotracers, allowing experiments at very low concentrations to mimic probable conditions in the far-field of a nuclear waste repository. Humate complexation of Tb was examined by anion and cation exchange techniques, also considering competitive effects of metals leached from the clay materials.The results revealed that desorption of metals from clay barriers, occurring in consequence of acidification processes, is generally counteracted in the presence of humic matter. For all clay materials under study, adsorption of Tb was found to be enhanced in neutral and acidic systems with humic acid, which is explained by additional adsorption of humic-bound Tb.A commonly used composite approach (linear additive model) was tested for suitability in reconstructing the solid–liquid distribution of Tb in ternary systems (Tb/humic acid/clay) on the basis of data determined for binary subsystems. The model can qualitatively explain the influence of humic acid as a function of pH, but it failed to reproduce our experimental data quantitatively. It appears that the elementary processes (metal adsorption, metal–humate complexation, humic acid adsorption) cannot be considered to be independent of each other. Possible reasons are discussed.     

Degradation of carbofuran and carbofuran-derivatives in presence of humic substances under basic conditions

The influence of humic aggregates in water solution upon the chemical stability of carbofuran (CF) and the carbofuran-derivatives, 3-hydroxy-carbofuran (HCF) and 3-keto-carbofuran (KCF), has been investigated in basic media. An inhibition upon the basic hydrolysis of 3-hydroxy-carbofuran and 3-keto-carbofuran (∼1.7 and ∼1.5-fold, respectively) was observed and it was rationalized in terms of the micellar pseudophase model. Nevertheless, non-significant effect upon the carbofuran stability was found in the presence of humic substances. These behaviors have been compared with the corresponding ones in other synthetic colloidal aggregates.     

Investigation of metal ions binding of humic substances using fluorescence emission and synchronous‐scan spectroscopy

Abstract

The binding site interactions of IHSS humic substances, Suwannee River Humic Acid, Suwannee River Fulvic Acid, Nordic Fulvic Acid, and Aldrich Humic Acid with various metals ions and a herbicide, methyl viologen were investigated using fluorescence emission and synchronous‐scan spectroscopy. The metal ions used were, Fe(III), Cr(III), Cr(VI), Pb(II), Cu(II) and Ni(II). Stern‐Volmer constants, K_SV for these quenchers were determined at pH 4 and 8 using an ionic strength of 0.1M. For all four humic substances, and at both pH studied, Fe(III) was found to be the most efficient quencher. Quenching efficiency was found to be 3–10 times higher at pH 8. The bimolecular quenching rate constants were found to exceed the maximum considered for diffusion controlled interactions, and indicate that the fluorophore and quencher are in close physical association. Synchronous‐scan spectra were found to change with pH and provided useful information on binding site interactions between humic substances and these quenchers.     

Development of Tools for Integrated Monitoring and Assessment of Hazardous Substances and Their Biological Effects in the Baltic Sea

The need to develop biological effects monitoring to facilitate a reliable assessment of hazardous substances has been emphasized in the Baltic Sea Action Plan of the Helsinki Commission. An integrated chemical–biological approach is vitally important for the understanding and proper assessment of anthropogenic pressures and their effects on the Baltic Sea. Such an approach is also necessary for prudent management aiming at safeguarding the sustainable use of ecosystem goods and Services. The BEAST project (Biological Effects of Anthropogenic Chemical Stress: Tools for the Assessment of Ecosystem Health) set out to address this topic within the BONUS Programme. BEAST generated a large amount of quality-assured data on several biological effects parameters (biomarkers) in various marine species in different sub-regions of the Baltic Sea. New indicators (biological response measurement methods) and management tools (integrated indices) with regard to the integrated monitoring approach were suggested.     

Differential Sensitivity of a Coccal Green Algal and a Cyanobacterial Species to Dissolved Natural Organic Matter (NOM) (8 pp)

Background

and Aim. In non-eutrophicated freshwaters, humic substances (HS) pose chemical stresses on aquatic organisms and, hence, separating sensitive from less sensitive or even tolerant species. One of the stresses, identified so far, is the reduction of photosynthetic oxygen production and reduction in growth in freshwater macrophytes and algae. In a previous paper, it has been shown that even closely related coccal green algae responded differently upon identical stress by HS, which is consistent with the hypothesis above. Due to their much simpler cellular ultrastructure, cyanobacteria are supposed to be more sensitive to HS exposure than eukaryote should be. One coccal green algal species (Desmodesmus communis) and one cyanobacterium (Chroococcus minutus) were exposed to four natural organic matter (NOM) isolates. One NOM has been isolated from a brown water lake (Schwarzer See) in Brandenburg State; three were obtained from a comprehensive Scandinavian NOM research project and originated from Norway (Birkenes), Finland (Hietajärvi), and Sweden (Svartberget).

Methods

Cultures of D. communis and C. minutus were obtained from the Culture Collection of Algae, Göttingen, and maintained in a common medium. The cultures were non-axenic. The algae and cyanobacteria were exposed under identical conditions to environmentally realistic NOM concentrations. Cell numbers were counted microscopically in Neugebauer cuvettes in triplicates. To avoid limitation by nutrient depletion, the experiments were terminated after 14 to 15 days. Until culture day 12, no growth limitation has been observed in the controls.

Results

All NOM isolates modulated the growth of the algae and cyanobacteria. During the early culture days, there was a slight growth promotion with the coccal green alga and to a much lesser degree with the cyanobacterium. Yet, the major effect were significant reductions in cell yield in both primary producer cultures. C. minutus was much more affected than D. communis. This applies particularly to the three tested Scandinavian NOM isolates, which were effective at concentrations even below 1 mg L-1 DOC.

Discussion

The growth promoting effect may be due to an increase in bioavailability of some trace nutrients in the presence of NOM, the release of some growth promoting substances by microbial or photochemical processing of the NOM, and/or a hormetic effect. The growth reducing effect can be explained as a herbicide-like mode of action that affects the photosystem II most prevalent by blocking the electron transport chain, absorption of electrons, or production of an internal oxidative stress after processing the bioconcentrated HS. Furthermore, it may be postulated that also photo-toxicity of these HS in the algal cells contributes to the overall toxicity; however, experimental evidence is lacking so far.

Conclusions

Upon exposure to HS, cyanobacteria appear to be much more sensitive than coccal green algae and respond in growth reduction. This high sensitivity of cyanobacteria to HS may explain phytoplankton patterns in the field. Eutrophic, humic-rich lakes do not support the cyanobacterial blooms characteristic of eutrophic, but humic-poor lakes. In the humic-rich systems, raphidophytes or, less frequent, specific coccal greens are more common. Obviously, cyanobacteria appear to be unable to make advantage of their accessory pigments (phycocyanin) to exploit the reddish light prevailing in humic-rich lakes.

Recommendation

. At present, no effective structure can be figured out which may be responsible for the adverse effect on the cyanobacterial species. It is reserved to future research whether or not HS may be applied more specifically (for instance, with elevated moieties of the effective structures) as a natural geochemical to combat cyanobacterial blooms.

     

Susceptibility to acidic precipitation contributes to the decline of the terricolous lichens Cetraria aculeata and Cetraria islandica in central Europe

The effective quantum yield of photochemical energy conversion in photosystem II (Phi2) was shown to be reduced in the terricolous lichens Cetraria aculeata and Cetraria islandica by short-term exposure to aqueous SO2 at pH values occurring in the precipitation of areas with high SO2 pollution. Significant reduction of Phi2 was found at pH相似文献   

Persistence of perfluoroalkylated substances in closed bottle tests with municipal sewage sludge

BACKGROUND, AIM, AND SCOPE: Perfluoroalkylated substances (PFAS) are chemicals with completely fluorinated alkyl chains. The specific properties of the F-C bond give PFAS a high stability and make them very useful in a wide range of applications. PFAS also pose a potential risk to the environment and humans because they have been recently characterized as persistent, bioaccumulative, and toxic. The objective of this work is to study the bacterial degradation of PFAS under aerobic and anaerobic conditions in municipal sewage sludge as a contribution toward understanding their environmental fate and behavior. MATERIALS AND METHODS: Bacterial communities from sewage sludge were exposed to a mixture of PFAS under aerobic or anaerobic conditions. Individual PFAS concentrations were determined in the experiment media at different exposure times using liquid chromatography-mass spectrometry analysis after extraction with solid-phase extraction. RESULTS: The PFAS analyses of samples of sludge showed repeatable replicate results, allowing a reliable quantification of the different groups of PFAS analyzed. No conclusive evidence for PFAS degradation was observed under the experimental conditions tested in this work. Reduction in concentrations, however, was observed for some PFAS in sludge under aerobic conditions. DISCUSSION: The largest concentration decrease occurred for the fluorotelomer alcohols (FTOHs), especially for the 8:2 FTOH, which have been described as biodegradable in the literature. However, this concentration decrease could be due to different causes: sorption to glass, septa, or matrix components, as well as bacterial activity. Therefore, it is not certain that biodegradation occurred. CONCLUSIONS: PFAS are very recalcitrant chemicals, especially when fully fluorinated. Although some decreases in concentration have been observed for some PFAS, such as the FTOHs, there is no conclusive evidence for biodegradation. It can be concluded that the PFAS tested in these experiments are non-biodegradable under these experimental conditions. RECOMMENDATIONS AND PERSPECTIVES: Since the presence of PFAS is ubiquitous in the environment and they can be toxic, more research is needed in this field to elucidate which PFAS are susceptible to biodegradation, the conditions required for biodegradation, and the possible routes followed. A possible inhibitory effect of PFAS on bacteria, the threshold concentrations, and conditions of inhibition should also be investigated.     

Modelling accidental releases of dangerous gases into the lower troposphere from mobile sources

The article reports the results of different methods of modelling releases and dispersion of dangerous gases or vapours in cases of major accidents from road and rail transportation in urban zones. Transport accidents of dangerous substances are increasingly frequent and can cause serious injuries in densely inhabited areas or pollution of the environment. For quantitative risk assessment and mitigation planning, consequence modelling is necessary.

The modelling of dangerous substance dispersion by standard methods does not fully represent the behaviour of toxic or flammable clouds in obstructed areas such as street canyons. Therefore the predictions from common software packages as ALOHA, EFFECTS, TerEx should be augmented with computational fluid dynamics (CFD) models or physical modelling in aerodynamic tunnels, and further studies are planned to do this.

The goal of this article is to present the results of the first approach of modelling using these standard methods and to demonstrate the importance of the next development stage in the area of transport accident modelling of releases and dispersions of dangerous substances in urban zones in cases of major accident or terrorist attacks.     

Monitoring the Trihalomethanes Present in Water After Treatment with Chlorine Under Laboratory Condition

In this work assays involving chlorinated water samples, which were previous spiked with humic substances or algae blue green and following the production of the THMs for 30 days is described. To implement the assays, five portions of 1,000 ml of water were stored in glass bottles. The water samples were treated with solutions containing 2, 3, 4 and 5 mg l⁻¹ chlorine. The samples aliquots (60 ml) were transferred into the glass vials, 10 ml were removed to have a headspace and 100 μl of the 10 mg l⁻¹ pentafluortoluene bromide solution was added to each vial. The extraction step was performed by adding 10 g of Na₂SO₄ followed by 5 ml of n-pentane. The vials were stopped with a TFE-faced septum and sealed with aluminum caps. The generated THMs were determined by gas chromatography with electron capture detector using reference solutions with concentration ranging from 8 to 120 μg l⁻¹ THMs. Three assays were monitored during 30 days and chloroform was the predominant compound found in the water samples, while other species of THMs were not detected. The results showed that when the chlorine concentration was increased in water samples containing algae the concentration of THM varied randomly. Nevertheless, in water samples containing humic substances the increase of the THM concentration presented a relationship with the chlorine concentration. It was also observed that chloroform concentration increased with the elapsed time up to one and six days to water samples spiked with humic substances and algae blue green, respectively and decreased along 30 days. By other hand, assays performed using water samples containing decanted algae material showed that THM was not generated by the chlorine addition.