2,029 research outputs found
Bioaccumulation surveillance in Milford Haven Waterway
Biomonitoring of contaminants (metals, organotins, PAHs, PCBs) was
carried out along the Milford Haven Waterway (MHW) and at a reference site in the
Tywi Estuary during 2007-2008. The species used as bioindicators encompass a
variety of uptake routes - Fucus vesiculosus (dissolved contaminants); Littorina
littorea (grazer); Mytilus edulis and Cerastoderma edule (suspension feeders); and
Nereis diversicolor (omnivore which often reflects contaminants in sediment).
Differences in feeding strategy and habitat preference have subtle implications for
bioaccumulation trends though, with few exceptions, contaminant body burdens in
Milford Haven (MH) were higher than those at the Tywi reference site, reflecting
inputs.
Elevated concentrations of metals were occasionally observed at individual MH sites,
whilst As and Se (molluscs and seaweed) were, for much of MHW, consistently at the
higher end of the UK range. However, for the majority of metals, distributions in MH
biota were not exceptional by UK standards. Several metal-species combinations
indicated increases in bioavailability at upstream sites, which may reflect the
influence of geogenic or other land-based sources – perhaps enhanced by lower
salinity (greater proportions of more bioavailable forms).
TBT levels in MH mussels were below OSPAR toxicity thresholds and in the Tywi
were close to zero. Phenyltins were not accumulated appreciably in Mytilus, whereas
some Nereis populations may have been subjected to localized (historical) sources.
PAHs in Nereis tended to be evenly distributed across most sites, but with somewhat
higher values at Dale for acenaphthene, fluoranthene, pyrene, benzo(a)anthracene and
chrysene; naphthalenes tended to be enriched further upstream in the mid-upper
Haven (a pattern seen in mussels for most PAHs). Whilst concentrations in MH
mussels were mostly above reference site and OSPAR backgrounds, it is unlikely that
ecotoxicological guidelines would be exceeded.
PCBs in mussels were between upper and lower OSPAR guidelines and were unusual
in their distribution in that highest levels occurred at the mouth of MH.
Condition indices (CI) of bivalves (mussels and cockles) were highest at the Tywi
reference site and at the seaward end of MH, decreasing upstream along the
Waterway. There were a number of significant (negative) relationships between CI
and body burdens and multivariate analysis indicated that a combination of
contaminants could influence the pattern in condition (and sub-lethal responses such
as MT and TOSC) across sites. Cause and effect needs to be tested more rigorously in
future assessments
Theoretical Analysis of Concentration Polarization Effect on VOC Removal by Pervaporation
Pervaporation is an innovative membrane-based separation technology for volatile organic compound (VOC) removal from contaminated groundwater. Concentration polarization is a process phenomenon occurring in pervaporation and several other membrane-based separation technologies. Concentration polarization, defined as concentration gradient of permeating solute between the bulk and the region near the membrane surface, becomes a limiting factor in pervaporation separations using high-performance membrane materials in VOC removal operations. Thus, the ability to predict the impact of concentration polarization upon process performance is highly desirable in process design and optimization. A mathematical model was developed to illustrate the interplay between concentration polarization and process performance in pervaporation operation of VOC removal in a membrane channel with rectangular cross section. By incorporating pervaporative mass transfer, laminar hydrodynamics, and boundary-layer theory, the model was built to allow theoretical analysis of the sensitivity of flow velocity, feed concentration, and concentration polarization index (CPI) upon the transmembrane flux and longitudinal mass flow
The Mersey Estuary : sediment geochemistry
This report describes a study of the geochemistry of
the Mersey estuary carried out between April 2000 and
December 2002. The study was the first in a new programme
of surveys of the geochemistry of major British estuaries
aimed at enhancing our knowledge and understanding of the
distribution of contaminants in estuarine sediments.
The report first summarises the physical setting, historical
development, geology, hydrography and bathymetry of the
Mersey estuary and its catchment. Details of the sampling
and analytical programmes are then given followed by a
discussion of the sedimentology and geochemistry. The
chemistry of the water column and suspended particulate
matter have not been studied, the chief concern being with
the geochemistry of the surface and near-surface sediments
of the Mersey estuary and an examination of their likely
sources and present state of contamination
A light-fronts approach to electron-positron pair production in ultrarelativistic heavy-ion collisions
We perform a gauge-transformation on the time-dependent Dirac equation
describing the evolution of an electron in a heavy-ion collision to remove the
explicit dependence on the long-range part of the interaction. We solve, in an
ultra-relativistic limit, the gauged-transformed Dirac equation using
light-front variables and a light-fronts representation, obtaining
non-perturbative results for the free pair-creation amplitudes in the collider
frame. Our result reproduces the result of second-order perturbation theory in
the small charge limit while non-perturbative effects arise for realistic
charges of the ions.Comment: 39 pages, Revtex, 7 figures, submitted to PR
Coulomb Effects on Electromagnetic Pair Production in Ultrarelativistic Heavy-Ion Collisions
We discuss the implications of the eikonal amplitude on the pair production
probability in ultrarelativistic heavy-ion transits. In this context the
Weizs\"acker-Williams method is shown to be exact in the ultrarelativistic
limit, irrespective of the produced particles' mass. A new equivalent
single-photon distribution is derived which correctly accounts for the Coulomb
distortions. As an immediate application, consequences for unitarity violation
in photo-dissociation processes in peripheral heavy-ion encounters are
discussed.Comment: 13 pages, 4 .eps figure
Distribution and speciation of phosphorus in foreshore sediments of the Thames estuary, UK
Estuarine sediments can be a source of Phosphorus (P) to coastal waters, contributing to nutrient budgets and geochemical cycles. In this work, the concentration and speciation of P in 47 cores were examined from the inter-tidal mud flats of the tidal river Thames (~ 120 km). Results of P concentration and speciation were combined with published data relating to known sediment dynamics and water chemistry (salinity) within the estuary to produce a conceptual model of sediment-P behaviour. Results demonstrated significant P desorption occurring after sediment passed through the Estuarine Turbidity Maximum and when the salinity of the river water exceeded ~ 6 ppt. It was found that organic P was desorbed to a greater extent than inorganic P in the lower estuary. Models were used to identify those geochemical parameters that contributed to the Total P (R2 = 0.80), oxalate extractable P (R2 = 0.80) and inorganic P (R2 = 0.76) concentrations within the Thames estuary
Strong suppression of Coulomb corrections to the cross section of e+e- pair production in ultrarelativistic nuclear collisions
The Coulomb corrections to the cross section of pair production in
ultrarelativistic nuclear collisions are calculated in the next-to-leading
approximation with respect to the parameter
( are the Lorentz factors of colliding nuclei). We found
considerable reduction of the Coulomb corrections even for large
due to the suppression of the production of pair
with the total energy of the order of a few electron masses in the rest frame
of one of the nuclei. Our result explains why the deviation from the Born
result were not observed in the experiment at SPS.Comment: 4 pages, RevTe
- …