Effects of size and origin of natural dissolved organic matter compounds on the redox cycling of iron in sunlit surface waters

Abstract.: The effects of size and origin of natural dissolved organic matter compounds (DOM) on the redox cycling of iron were investigated in water samples from a marine system (Strait of Gibraltar), from a freshwater system (Lake of Murten, i.e., Murtensee, Switzerland), and from a "river-to-ocean” system (Rivers Scheldt and Rhine and corresponding estuaries). In the irradiated seawater samples, Fe(II) steady-state concentrations ([Fe(II)]ss), both as percentage of total dissolved iron and normalized to 1mg C L−1, were higher in the low-molecular-weight (LMW) than in the high-molecular-weight (HMW) DOM fractions, despite higher net rates of H2O2 formation in the HMW DOM fractions. Also in the samples from Murtensee, [Fe(II)]ss, both as percentage of total dissolved iron and normalized to the decadic absorption coefficient at 350nm (α350, unit m−1), were higher in the LMW than in the HMW DOM fractions. Unlike in the seawater samples, however, net rates of H2O2 production, normalized to α350, were higher in the LMW DOM fractions, as compared to the HMW DOM fractions, indicating a higher efficiency of O2• − formation with these LMW compounds from Murtensee. Based on the simulation of experimental data with mathematical kinetic modeling, we hypothesize that Fe(II) is formed through photolysis of Fe(III) complexes in the LMW DOM fractions from the Strait of Gibraltar and from Murtensee and that Fe(II) is stabilized by a ligand in the water samples from Murtensee. In the irradiated HMW DOM fractions from the "river-to-ocean” system, [Fe(II)]ss, normalized to α350, were generally higher in the water samples from the Rivers Scheldt and Rhine than in the water samples from their estuaries, suggesting that terrestrially derived DOM has a higher photochemical reactivity towards Fe(II) formation than autochthonous DO

Reductive Transformations of Anthropogenic Chemicals in Natural and Technical Systems

Reductive transformation reactions of chemical pollutants (e.g., polyhalogenated hydrocarbons, aromatic azo and nitro compounds, chromium(VI) species) in the environment are important both from an ecotoxicological and from an environmental technology point of view. Using well-defined model reactors as well as more complex 'real world' systems, several groups at EAWAG are trying to unravel compound- and system-specific factors that control the reduction of a variety of anthropogenic chemicals under different conditions in the environment. The examples presented in this article include the reduction of nitroaromatic compounds under iron- and sulfate-reducing conditions, the reductive dehalogenation of chlorinated ethenes by cob(I)alamin and by a bacterium that uses such compounds as terminal electron acceptors, and the reduction of chromium(VI) by various reduced iron species. The link between microbial and abiotic (chemical) processes involved in reductive transformations of pollutants is emphasized. The major goal of this article is to illustrate the approaches taken to elucidate the mechanisms and kinetics of environmentally relevant reduction reactions of pollutants, and to discuss how the results of such studies can be used 1) to gain insight into what is actually happening in the environment, and 2) to develop methods for the treatment of chemical wastes or contaminated sites

Characterization of Environmental Solids and Surfaces

The characterization of the solid phase is one of the first steps in the study of any of the myriad of environmental reactions that involve solids and solid-liquid interfaces. Environmental solids range from relatively pure and crystalline phases to heterogeneous and multiphasic particle aggregates whose characterization requires a combination of a number of analytical methods and methodologies. The first section of this paper gives a cross section of general strategies used in different departments at EAWAG for the characterization of field samples of both natural and anthropogenic origin. The morphological characterization and the determination of the chemical composition is described in respect to the properties of anthropogenic solids. As an example, the long-term behavior of incinerator bottom ash is discussed in a case study. A second section gives two examples of molecular level studies on environmental solids: application of Extended X-Ray Absorption Fine Structure (EXAFS) spectroscopy for the characterization of poorly crystallized manganese lake particles in the context of the genesis of lake sediments, and in situ Atomic Force Microscopy (AFM) and Fourier Transform Infrared (FTIR) studies on synthetic goethite particles during the oxidation of FeII and the reduction of CrVI

Sorption Phenomena at Environmental Solid Surfaces

Sorption phenomena from the aqueous and from the gaseous phase to solid surfaces play an important role for the fate of inorganic and organic compounds and of bacteria in the environment. Case studies illustrating the role of different sorption mechanisms for various classes of compounds and for bacteria are presented. They show that sorption at solid surfaces ranges from weak unspecific interactions to very specific and strong complexation. Strong surface complexation in particular affects the surface reactivity. Studies of model systems provide a conceptual framework to understand and predict the behavior of substances and of bacteria in complex environmental systems, such as aquifers and sediments

Enhancing arsenic mitigation in Bangladesh: Findings from institutional, psychological, and technical investigations

As part of a trans-disciplinary research project, a series of surveys and interventions were conducted in different arsenic-affected regions of rural Bangladesh. Surveys of institutional stakeholders identified deep tubewells and piped water systems as the most preferred options, and the same preferences were found in household surveys of populations at risk. Psychological surveys revealed that these two technologies were well-supported by potential users, with self-efficacy and social norms being the principal factors driving behavior change. The principal drawbacks of deep tubewells are that installation costs are too high for most families to own private wells, and that for various socio-cultural-religious reasons, people are not willing to walk long distances to access communal tubewells. In addition, water sector planners have reservations about greater exploitation of the deep aquifer, out of concern for current or future geogenic contamination. Groundwater models and field studies have shown that in the great majority of the affected areas, the risk of arsenic contamination of deep groundwater is small; salinity, iron, and manganese are more likely to pose problems. These constituents can in some cases be avoided by exploiting an intermediate depth aquifer of good chemical quality, which is hydraulically and geochemically separate from the arsenic-contaminated shallow aquifer. Deep tubewells represent a technically sound option throughout much of the arsenic-affected regions, and future mitigation programs should build on and accelerate construction of deep tubewells. Utilization of deep tubewells, however, could be improved by increasing the tubewell density (which requires stronger financial support) to reduce travel times, by considering water quality in a holistic way, and by accompanying tubewell installation with motivational interventions based on psychological factors. By combining findings from technical and social sciences, the efficiency and success of arsenic mitigation in general - and installation of deep tubewells in particular - can be significantly enhanced

A functional triazine framework based on N-heterocyclic building blocks

Covalent organic frameworks constitute a subclass of polymeric materials offering enhanced porosity, functionality and stability. In this work a covalent triazine framework based on bipyridine building blocks is presented, along with a comprehensive elucidation of its local structure, porosity, and capacity for metal uptake. A typical synthesis was carried out under ionothermal conditions at 400-700 degrees C using ZnCl2 as a Lewis acidic trimerization catalyst. A high degree of local order and the presence of triazine and bipyridine moieties are ascertained at a synthesis temperature of 400 degrees C, along with micropores and specific surface areas of up to 1100 m(2) g(-1). Mesopores are increasingly formed at synthesis temperatures above 450 degrees C, yielding highly porous frameworks with hierarchical porosity and exceptionally large surface areas in excess of 3200 m(2) g(-1) at 700 degrees C. We demonstrate the capability of the bipyridine unit to provide specific and strong binding sites for a large variety of transition metal ions, including Co, Ni, Pt and Pd. The degree of metal loading (up to 38 wt%) can be tuned by the metal concentration in solution and is dependent on both the type of metal as well as the temperature at which the CTF was synthesized. Evidence for site-specific metal coordination bodes well for the use of metal-loaded CTFs as heterogeneous catalysts carrying homogeneous-type active sites

Treatment of Refractory Cardiac Arrest by Controlled Reperfusion of the Whole Body:A Multicenter, Prospective Observational Study

Background: Survival following cardiac arrest (CA) remains poor after conventional cardiopulmonary resuscitation (CCPR) (6–26%), and the outcomes after extracorporeal cardiopulmonary resuscitation (ECPR) are often inconsistent. Poor survival is a consequence of CA, low-flow states during CCPR, multi-organ injury, insufficient monitoring, and delayed treatment of the causative condition. We developed a new strategy to address these issues. Methods: This all-comers, multicenter, prospective observational study (69 patients with in- and out-of-hospital CA (IHCA and OHCA) after prolonged refractory CCPR) focused on extracorporeal cardiopulmonary support, comprehensive monitoring, multi-organ repair, and the potential for out-of-hospital cannulation and treatment. Result: The overall survival rate at hospital discharge was 42.0%, and a favorable neurological outcome (CPC 1+2) at 90 days was achieved for 79.3% of survivors (CPC 1+2 survival 33%). IHCA survival was very favorable (51.7%), as was CPC 1+2 survival at 90 days (41%). Survival of OHCA patients was 35% and CPC 1+2 survival at 90 days was 28%. The subgroup of OHCA patients with pre-hospital cannulation showed a superior survival rate of 57.1%. Conclusions: This new strategy focusing on repairing damage to multiple organs appears to improve outcomes after CA, and these findings should provide a sound basis for further research in this area.</p

Treatment of Refractory Cardiac Arrest by Controlled Reperfusion of the Whole Body:A Multicenter, Prospective Observational Study

Background: Survival following cardiac arrest (CA) remains poor after conventional cardiopulmonary resuscitation (CCPR) (6–26%), and the outcomes after extracorporeal cardiopulmonary resuscitation (ECPR) are often inconsistent. Poor survival is a consequence of CA, low-flow states during CCPR, multi-organ injury, insufficient monitoring, and delayed treatment of the causative condition. We developed a new strategy to address these issues. Methods: This all-comers, multicenter, prospective observational study (69 patients with in- and out-of-hospital CA (IHCA and OHCA) after prolonged refractory CCPR) focused on extracorporeal cardiopulmonary support, comprehensive monitoring, multi-organ repair, and the potential for out-of-hospital cannulation and treatment. Result: The overall survival rate at hospital discharge was 42.0%, and a favorable neurological outcome (CPC 1+2) at 90 days was achieved for 79.3% of survivors (CPC 1+2 survival 33%). IHCA survival was very favorable (51.7%), as was CPC 1+2 survival at 90 days (41%). Survival of OHCA patients was 35% and CPC 1+2 survival at 90 days was 28%. The subgroup of OHCA patients with pre-hospital cannulation showed a superior survival rate of 57.1%. Conclusions: This new strategy focusing on repairing damage to multiple organs appears to improve outcomes after CA, and these findings should provide a sound basis for further research in this area.</p