Evidence of estrogenic mixture effects on the reproductive performance of fish

The official published version can be obtained from the link below - Copyright @ 2007 American Chemical SocietyRecent research into the effects of mixtures of estrogenic chemicals has revealed the capacity for similarly acting chemicals to act in combination, according to the principles of concentration addition. This means that, collectively, they may pose a significant environmental risk, even when each component is present at a low and individually ineffective concentration. The aim of this study was to investigate the ecological significance of mixture effects at low-effect concentrations by assessing the combined effect of estrogenic chemicals on the reproductive performance of fish. Pairs of fathead minnows were exposed to five estrogenic chemicals. Endpoints analyzed included fecundity, the expression of male secondary sexual characteristics, somatic indices, and vitellogenin induction. In the first phase of the study, a concentration-response analysis was performed to investigate the relative sensitivity of these endpoints. In the second phase, mixture effects at low-effect concentrations were explored by exposing fish to each of the mixture components, individually and in combination. Data from these experiments provide evidence of mixture effects on fitness and fecundity, demonstrating the capacity for chemicals to act together to affect reproductive performance, even when each component is present belowthe threshold of detectable effects. This has important implications for hazard assessment and contributes to our understanding of mixture effects at increasing levels of biological complexity.This work was funded by the European Commission, under contract EVK1-2001-00091

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Asymmetric polyelectrolyte multilayer membranes:Influence of bottom section polycation on layer growth and retention mechanisms

It has been previously demonstrated that asymmetric polyelectrolyte multilayer (PEM) membranes are highly promising for use in water treatment due to their ability to combine a high selectivity with a high permeability. This is achieved by first coating a more open (highly permeable) bottom PEM to fill the pores of the support membrane, and subsequently a more dense (highly selective) top PEM. However, fundamental understanding on the interaction between top and bottom PEM section and the effect of the bottom section on the resulting membrane properties is still lacking. In this study, symmetric membranes with different polycations are prepared and compared with asymmetric membranes which contain an additional poly (allylamine hydrochloride)/poly (acryl amide) (PAH/PAA) top section. PEM layer growth was first studied with optical reflectometry, demonstrating that the growth of the top PEM section is dependent on the previously deposited bottom PEM section. Membrane performance was assessed with cross-flow measurements, where permeability and molecular weight cutoff (MWCO) measurements showed distinct differences for the symmetric membranes. Although these properties converge upon coating of the top section, differences remain. This can be explained by a contribution of the bottom section to hydraulic resistance and by intermixing of the top and bottom section. The degree of intermixing is attributed to differences in mobility of the used polycations. Single salt retention measurements even show that changing the bottom section polycation allows for tuning of the salt retention mechanism of the resulting asymmetric membranes. Whereas membranes with PAH in the bottom section are dominated by dielectric exclusion, membranes with Poly (vinylbenzyltrimethylammonium chloride) (PVBTMAC) in the bottom section show a dominant Donnan exclusion. These observations were confirmed by varying both the salt concentration and the operational flux. Overall, our work demonstrates that asymmetric coating on different bottom PEM chemistries can be used as a promising tuning parameter in layer-by-layer coating. This allows for a more rational design of asymmetric PEM membranes, opening opportunities for tuning membranes towards specific applications.</p

Magnetoresistance of a semiconducting magnetic wire with domain wall

We investigate theoretically the influence of the spin-orbit interaction of Rashba type on the magnetoresistance of a semiconducting ferromagnetic nanostructure with a laterally constrained domain wall. The domain wall is assumed sharp (on the scale of the Fermi wave length of the charge carriers). It is shown that the magnetoresistance in such a case can be considerably large, which is in a qualitative agreement with recent experimental observations. It is also shown that spin-orbit interaction may result in an increase of the magnetoresistance. The role of localization corrections is also briefly discussed.Comment: 5 pages, 2 figure

Fate and occurrence of alkylphenolic compounds in sewage sludges determined by liquid chromatography tandem mass spectrometry

This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ 2009 Taylor & Francis.An analytical method has been developed and applied to determine the concentrations of the nonionic alkylphenol polyethoxylate surfactants and their metabolites, alkylphenoxy carboxylates and alkyphenols, in sewage sludges. The compounds were extracted with methanol/acetone (1:1 v/v) from sludge, and concentrated extracts were cleaned by silica solid‐phase extraction prior to determination by liquid chromatography tandem mass spectrometry. The recoveries, determined by spiking sewage sludge at two concentrations, ranged from 51% to 89% with method detection limits from 6 µg kg−1 to 60 µg kg−1. The methodology was subsequently applied to sludge samples obtained from a carbonaceous activated sludge plant, a nitrifying/denitrifying activated sludge plant and a nitrifying/denitrifying activated sludge plant with phosphorus removal. Concentrations of nonylphenolic compounds were two to three times higher than their octyl analogues. Long‐chain nonylphenol polyethoxylates (NP3–12EO) ranged from 16 µg kg−1 to 11754 µg kg−1. The estrogenic metabolite nonylphenol was present at concentrations ranging from 33 µg kg−1 to 6696 µg kg−1.Public Utilities Board of Singapore, Thames Water and Yorkshire Water