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Environmental Chemistry
Volume 12 Number 2 2015
RESEARCH FRONT: Tribute to Bill Davison
EN14105Use of diffusive gradients in thin-films for studies of chemical speciation and bioavailability
Environmental context. The health of aquatic organisms depends on the distribution of the dissolved forms of chemical components (speciation) and their rates of interaction (dynamics). This review documents and explains progress made using the dynamic technique of diffusive gradients in thin-films (DGT) to meet these challenges of measuring directly chemical speciation and associated dynamics in natural waters. The relevance of these measurements to uptake by biota of chemical forms in soils, sediments and water is discussed with reference to this expanding literature.
EN14047Measurement of labile arsenic speciation in water and soil using diffusive gradients in thin films (DGT) and X-ray absorption near edge spectroscopy (XANES)
Environmental context. Both inorganic and organic arsenic species are toxic to the environment when labile. The Diffusive Gradients in Thin Films technique, equipped with ferrihydrite binding gel enables measurement of labile arsenic species from water and soil solutions. This study indicated that labile arsenic species are quantitatively adsorbed to the gel, and that they are stable for up to 2 weeks following deployment.
EN14068Interpretation of diffusion gradients in thin films (DGT) measurements: a systematic approach
Environmental context. Dynamic speciation of an element in a natural medium is essential for understanding its availability. The technique of diffusion gradients in thin films (DGT) has become a widely used tool for in situ environmental studies, being applied to determine fluxes of metal cations, anions, organics and nanoparticles. The interpretation of the measurements with suitable physicochemical models gives valuable insights into the behaviour of the system.
EN14016Voltammetric study of an FeS layer on a Hg electrode in supersaturated FeS chloride solution
Environmental context. During the electrochemical analysis of natural waters, the Hg electrode could become the site for surface metal sulfide formation, such as FeS, which can have significant influence on the voltammetric determination of FeII. Reduction of FeII in such conditions can occur both on the bare Hg surface and on the FeS-modified Hg surface. Until recently, measurements of FeII have considered only the signal obtained from reduction on the bare Hg surface, and hence may have underdetermined the true FeII content of natural samples.
EN14086Metal ion complexation by soft nanoparticles: the effect of Ca2+ on electrostatic and chemical contributions to the Eigen-type reaction rate
Environmental context. The speciation of trace metals in the environment is often dominated by complexation with natural organic matter such as humic acid. Humic acid is a negatively charged soft nanoparticle and its electrostatic properties play an important role in its reactivity with metal ions. The presence of major cations, such as Ca2+, can decrease the effective negative charge in the humic acid particle body and thus modify the chemodynamics of its interactions with trace metal ions.
EN14049Dissolution of metal and metal oxide nanoparticles under natural freshwater conditions
Environmental context. Engineered nanomaterials (e.g. silver, zinc oxide and copper oxide) are being widely used in many consumer products such are cosmetics, food packaging and textiles. During their usage and treatment, they will be released to natural waters and partly dissolve, depending on the water type and nanomaterial characteristics. These nanomaterials may thus have some toxic effects to aquatic organisms and indirectly to humans because of higher concentrations of dissolved silver, zinc and copper in natural waters.
EN14124The formation and fate of organoarsenic species in marine ecosystems: do existing experimental approaches appropriately simulate ecosystem complexity?
Environmental context. In marine environments, inorganic arsenic present in seawater is transformed to organoarsenic species, mainly arsenoribosides in algae and arsenobetaine in animals. These transformations decrease the toxicity of arsenic, yet the fate of arsenoribosides and arsenobetaine when marine organisms decompose is unknown. We review the current literature on the degradation of these organoarsenic species in marine systems detailing the drivers behind their degradation, and also discuss the environmental relevance of laboratory-based experiments.
EN13216Interpretation of heavy metal speciation in sequential extraction using geochemical modelling
Environmental context. Heavy metal pollution is a worldwide environmental concern, and the risk depends not only on their total concentration, but also on their chemical speciation. Based on state-of-the-art geochemical modelling, we pinpoint the heavy metal pools approached by the widely used sequential extraction method. The finding of this paper can help users of sequential extraction methods to better interpret their results.
EN14116Degradation of oxytetracycline in the aquatic environment: a proposed steady state kinetic model that takes into account hydrolysis, photolysis, microbial degradation and adsorption by colloidal and sediment particles
Environmental context. Pollution of the aquatic environment by oxytetracycline can lead to microbial resistance thereby compromising the efficacy of current medication regimes. Adsorption by colloidal and sediment particles reduces the rate at which oxytetracycline degrades, whereas the longer the antimicrobial remains in the aquatic environment, the greater the danger of microbial resistance. There is need therefore for a fuller understanding of the kinetics of degradation of oxytetracycline in aquatic ecosystems before measures for mitigating pollution by the antimicrobial can be designed.
EN14135Comparative characterisation of two fulvic acids from East Lake and Liangzi Lake in central China
Environmental context. Fulvic acids account for a large proportion of dissolved organic matter in aquatic environments and affect the transportation and bioavailability of organic and inorganic pollutants. The structural and spectroscopic characteristics of fulvic acids mainly depend on the sources, seasons and anthropogenic activity. We present an advanced approach using fluorescence spectroscopy as a rapid and cost-effective method to investigate the composition, properties and origins of fulvic acids.
EN14093Reversible exchange of stable nitroxyl radicals on nanosilver particles
Environmental context. Nanometre-sized silver particles promote unique chemical reactions on their surface. This work examines the ability of silver nanoparticles to collect and store unpaired electrons, called radicals, on their surface. This capability by silver nanoparticles could potentially serve to drive degradation reactions in the environment.
EN14126Characterising sediments of a tropical sediment-starved shelf using cluster analysis of physical and geochemical variables
Environmental context. Australia's tropical marine estate is a biodiversity hotspot that is threatened by human activities. Analysis and interpretation of large physical and geochemistry data sets provide important information on processes occurring at the seafloor in this poorly known area. These processes help us to understand how the seafloor functions to support biodiversity in the region.
EN14129Characterisation of oil contaminated soils by comprehensive multiphase NMR spectroscopy
Environmental context. Novel technology is used to examine oil contaminated soil to better understand this longstanding problem. The data indicate that oil forms a non-discriminant layer over all the soil components, which in their natural state would be exposed to water, and that it retains certain polar compounds while contributing other oil contaminants to the surrounding porewater and groundwater. Such molecular level information helps to better understand the reoccurrence of hydrophobicity in remediated soil, and could lead to novel clean-up methods.
EN14138Hydroxyl radical initiated oxidation of formic acid on mineral aerosols surface: a mechanistic, kinetic and spectroscopic study
Environmental context. The presence of air-borne mineral dust containing silicates in atmospheric aerosols should be considered in any exploration of volatile organic compound chemistry. This work reports the mechanisms, relative energies and kinetics of free-radical reactions with formic acid adsorbed on silicate surface models. We find that silicate surfaces are more likely to act as a trap for organic radicals than to have a catalytic effect on their reactions.
EN14185Source identification of atmospheric particle-bound metals at Terra Nova Bay, Antarctica
Environmental context. The atmosphere above Antarctica, the cleanest part of the Earth’s troposphere, serves as a valuable laboratory for studying natural atmospheric processes and for monitoring the impact of human activities on the global environment. Central to these studies is an understanding of long-range transport of pollutants to Antarctica, and distinguishing the relative contribution of natural and anthropogenic sources. We use chemical tracers and isotopic analysis to assess the origin of metals associated with atmospheric particulates in Antarctica.
EN14182Determination of diffusion coefficients of dissolved organic matter in the Churchill River estuary system, Hudson Bay (Canada)
Environmental context. Reliable interpretation of metal levels measured by diffusive gradients in thin film (DGT) requires a sound understanding of the diffusion properties of dissolved organic matter (DOM), the main ligand of metals in natural waters. The present study determined that the molecular weight of DOM and conductivity are the main factors controlling the diffusion of freshly collected estuarine DOM across the DGT diffusive gel.