Systematic study of effects of pH and ionic strength on attachment of phage PRD1

Objectives of this work are to investigate effects of pH and ionic strength (IS) on virus transport in saturated soil and to develop a quantitative relationship for these effects. A series of 50-cm column experiments with clean quartz sand under saturated conditions and with pH values of 5, 6, 7, 8, and IS values of 1, 10, and 20 mM were conducted. Bacteriophage PRD1 was used as a model virus. Applying a one-site kinetic model, attachment, detachment, and inactivation rate coefficients were determined from fitting breakthrough curves using the software package Hydrus-1D. Attachment rate coefficients increased with decreasing pH and increasing IS, in agreement with DLVO theory. Sticking efficiencies were calculated from the attachment rate coefficients and used to develop an empirical formula for sticking efficiency as a function of pH and IS. This relationship is applicable under unfavorable conditions for virus attachment. We compared sticking efficiencies predicted by the empirical formula with those from field and column experiments. Within the calibrated range of pH and IS, the predicted and observed sticking efficiencies are in reasonable agreement for bacteriophages PRD1 and MS2. However, the formula significantly overestimates sticking efficiencies for IS higher than 100 mM. In addition, it performs less well for viruses with different surface reactivity than PRD1 and MS2. Effects of pH and IS on detachment and inactivation rate coefficients were also investigated but the experimental results do not allow constraining these parameters with sufficient certainty.     

Metal speciation and toxicity of Tamar Estuary water to larvae of the Pacific oyster, Crassostrea gigas

As part of the PREDICT Tamar Workshop, the toxicity of estuarine waters in the Tamar Estuary (southwest England) was assessed by integration of metal speciation determination with bioassays. High temporal resolution metal speciation analysis was undertaken in situ by deployment of a Voltammetric In situ Profiling (VIP) system. The VIP detects Cd (cadmium), Pb (lead) and Cu (copper) species smaller than 4?nm in size and this fraction is termed 'dynamic' and considered biologically available. Cadmium was mainly present in the dynamic form and constituted between 56% and 100% of the total dissolved concentration, which was determined subsequently in the laboratory in filtered discrete samples. In contrast, the dynamic Pb and Cu fractions were less important, with a much larger proportion of these metals associated with organic ligands and/or colloids (45-90% Pb and 46-85% Cu), which probably reduced the toxicological impact of these elements in this system. Static toxicity tests, based on the response of Crassostrea gigas larva exposed to discrete water samples showed a high level of toxicity (up to 100% abnormal development) at two stations in the Tamar, particularly during periods of the tidal cycle when the influence of more pristine coastal water was at its lowest. Competitive ligand-exchange Cu titrations showed that natural organic ligands reduced the free cupric ion concentration to levels that were unlikely to have been the sole cause of the observed toxicity. Nonetheless, it is probable that the combined effect of the metals determined in this work contributed significantly to the bioassay response.     

Biomarker responses as indication of contaminant effects in blue mussel (Mytilus edulis) and female eelpout (Zoarces viviparus) from the southwestern Baltic Sea

During a field study performed in spring and autumn 2001 and 2002, blue mussels (Mytilus edulis) and female eelpout (Zoarces viviparus) were collected at three locations in the Wismar Bay (Baltic Sea), and several biomarkers of contaminant effects were analysed. Besides seasonal and inter-annual variations, biomarker signals were most pronounced at the location closest to Wismar Harbour (Wendorf) in both species. Lysosomal membrane stability (LMS) was lowest and acetylcholinesterase activity (AChE) was significantly reduced. Frequency of micronuclei (MN) was significantly higher (in blue mussels), indicating mutagenic effects. In eelpout elevated levels of DNA adducts, EROD induction and PAH-metabolites were measured. Metallothionein (MT), biomarker for trace metal exposure, showed a gradient only in spring. Organochlorine contaminant analyses (PCBs, DDTs) corresponded to the observed biomarker levels. The results obtained clearly demonstrate pollution effects in the southwestern Baltic Sea. Moreover, they show that a multibiomarker approach is also applicable in a brackish water environment.     

Legal aspects of conserving native oysters in Scotland

Native oysters (Ostrea edulis) historically supported valuable fisheries in Scotland, but are now absent from areas of former abundance on the east coast and occur mainly in isolated populations in west coast sea lochs. The main contemporary threat is from unauthorized gathering. In most places, the exclusive right to gather is retained by the Crown, as a remnant of the feudal system, but in some areas the right has been acquired by individuals or institutions. A temporary right to gather oysters may be obtained by permit from the proprietor, or through a Several or Regulating Order made under shellfish fisheries legislation. The right to gather oysters is separate from ownership of the foreshore or sea bed on which they are located. To receive the maximum legal protection, oyster beds must be marked out, or the rights to them otherwise adequately made known. Wild or formerly-cultivated oyster beds may not meet this criterion and, in any case, enforcement is difficult in remote locations. It has been proposed that there should be a statutory public right to gather oysters. Were this to be created, then strong conservation measures would need to be implemented to protect native oysters from eradication by uncontrolled gathering.     

Porosity and permeability in sediment mixtures

Porosity in sediments that contain a mix of coarser- and finer-grained components varies as a function of the porosity and volume fraction of each component. We considered sediment mixtures representing poorly sorted sands and gravely sands. We expanded an existing fractional-packing model for porosity to represent mixtures in which finer grains approach the size of the pores that would exist among the coarser grains alone. The model well represents the porosity measured in laboratory experiments in which grain sizes and volume fractions were systematically changed within sediment mixtures. Permeability values were determined for these sediment mixtures using a model based on grain-size statistics and the expanded fractional-packing porosity model. The permeability model well represents permeability measured in laboratory experiments using air- and water-based permeametry on the model sediment mixtures.     

Thomson Thick X-Ray Absorption in a Broad Absorption Line Quasar, PG 0946+301

We present results of new ASCA observations of the low-luminosity active galactic nucleus (LLAGN) NGC 4579 obtained on 1998 December 18 and 28, and we report on the detection of variability of an iron K emission line. The X-ray luminosities in the 2-10 keV band for the two observations are nearly identical (LX approximately 2x1041 ergs s(-1)), but they are approximately 35% larger than that measured in 1995 July by Terashima et al. An Fe K emission line is detected at 6.39+/-0.09 keV (source rest frame), which is lower than the line energy 6.73+0.13-0.12 keV in the 1995 observation. If we fit the Fe lines with a blend of two Gaussians centered at 6.39 and 6.73 keV, the intensity of the 6.7 keV line decreases, while the intensity of the 6.4 keV line increases, within an interval of 3.5 yr. This variability rules out thermal plasmas in the host galaxy as the origin of the ionized Fe line in this LLAGN. The detection and variability of the 6.4 keV line indicates that cold matter subtends a large solid angle viewed from the nucleus and that it is located within approximately 1 pc from the nucleus. It could be identified with an optically thick standard accretion disk. If this is the case, a standard accretion disk is present at the Eddington ratio of Lbol/LEdd approximately 2x10-3. A broad disk-line profile is not clearly seen, and the structure of the innermost part of accretion disk remains unclear.