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C M Davidson

Publications and source records attributed to C M Davidson.

At least 19 recordsLinked to original sources
PubMed2006

Estimating the extractability of potentially toxic metals in urban soils: a comparison of several extracting solutions.

Metals released by the extraction with aqua regia, EDTA, dilute HCl and sequential extraction (SE) by the BCR protocol were studied in urban soils of Sevilla, Torino, and Glasgow. By multivariate analysis, the amounts of Cu, Pb and Zn liberated by any method were statistically associated with one another, whereas other metals were not. The mean amounts of all metals extracted by HCl and by SE were well correlated, but SE was clearly underestimated by HCl. Individual data for Cu, Pb and Zn by both methods were correlated only if each city was considered separately. Other metals gave poorer relationships. Similar conclusions were reached comparing EDTA and HCl, with much lower values for EDTA. Dilute HCl extraction cannot thus be recommended for general use as alternative to BCR SE in urban soils.

Chemical Phenomena↗
PubMed2006

Variability in concentrations of potentially toxic elements in urban parks from six European cities.

Use of a harmonised sampling regime has allowed comparison of concentrations of copper, chromium, nickel, lead and zinc in six urban parks located in different European cities differing markedly in their climate and industrial history. Wide concentrations ranges were found for copper, lead and zinc at most sites, but for chromium and nickel a wide range was only seen in the Italian park, where levels were also considerably greater than in other soils. As might be expected, the soils from older cities with a legacy of heavy manufacturing industry (Glasgow, Torino) were richest in potentially toxic elements (PTEs); soils from Ljubljana, Sevilla and Uppsala had intermediate metal contents, and soils from the most recently established park, in the least industrialised city (Aveiro), displayed lowest concentrations. When principal component analysis was applied to the data, associations were revealed between pH and organic carbon content; and between all five PTEs. When pH and organic carbon content were excluded from the PCA, a distinction became clear between copper, lead and zinc (the "urban" metals) on the one hand, and chromium and nickel on the other. Similar results were obtained for the surface (0-10 cm depth) and sub-surface (10-20 cm depth) samples. Comparisons with target or limit concentrations were limited by the existence of different legislation in different countries and the fact that few guidelines deal specifically with public-access urban soils intended for recreational use.

Cities↗
PubMed2006

Mercury in urban soils: a comparison of local spatial variability in six European cities.

The objective of this study was to quantify and assess for the first time the variability of total mercury in urban soils at a European level, using a systematic sampling strategy and a common methodology. We report results from a comparison between soil samples from Aveiro (Portugal), Glasgow (Scotland), Ljubljana (Slovenia), Sevilla (Spain), Torino (Italy) and Uppsala (Sweden). At least 25 sampling points (in about 4-5 ha) from a park in each city were sampled at two depths (0-10 and 10-20 cm). Total mercury was determined by pyrolysis atomic absorption spectrometry with gold amalgamation. The quality of results was monitored using certified reference materials (BCR 142R and BCR 141R). Measured total mercury contents varied from 0.015 to 6.3 mg kg(-1). The lowest median values were found in Aveiro, for both surface (0-10 cm) and sub-surface (10-20 cm) samples (0.055 and 0.054 mg kg(-1), respectively). The highest median mercury contents in soil samples were found in samples from Glasgow (1.2 and 1.3 mg kg(-1), for surface and sub-surface samples, respectively). High variability of mercury concentrations was observed, both within each park and between cities. This variability reflecting contributions from natural background, previous anthropogenic activities and differences in the ages of cities and land use, local environmental conditions as well as the influence of their location within the urban area. Short-range variability of mercury concentrations was found to be up to an order of magnitude over the distance of only a few 10 m.

Cities↗
PubMed2004

Surface analysis and depth profiling of corrosion products formed in lead pipes used to supply low alkalinity drinking water.

Modern analytical techniques have been applied to investigate the nature of lead pipe corrosion products formed in pH adjusted, orthophosphate-treated, low alkalinity water, under supply conditions. Depth profiling and surface analysis have been carried out on pipe samples obtained from the water distribution system in Glasgow, Scotland, UK. X-ray diffraction spectrometry identified basic lead carbonate, lead oxide and lead phosphate as the principal components. Scanning electron microscopy/energy-dispersive x-ray spectrometry revealed the crystalline structure within the corrosion product and also showed spatial correlations existed between calcium, iron, lead, oxygen and phosphorus. Elemental profiling, conducted by means of secondary ion mass spectrometry (SIMS) and secondary neutrals mass spectrometry (SNMS) indicated that the corrosion product was not uniform with depth. However, no clear stratification was apparent. Indeed, counts obtained for carbonate, phosphate and oxide were well correlated within the depth range probed by SIMS. SNMS showed relationships existed between carbon, calcium, iron, and phosphorus within the bulk of the scale, as well as at the surface. SIMS imaging confirmed the relationship between calcium and lead and suggested there might also be an association between chloride and phosphorus.

Corrosion↗
PubMed2003

Clinical manifestations of VX poisoning following percutaneous exposure in the domestic white pig.

Nerve agents are a class of organophosphorus chemicals that inhibit certain cholinesterase enzymes (ChE). If untreated, percutaneous exposure to nerve agents, such as VX (O-ethyl-S-[2(diisopropylamino)ethyl] methylphosphonothioate) can cause paralysis, apnoea and death. Much of the information concerning the percutaneous absorption and subsequent toxicity of nerve agents has been obtained using various rodent models. However, the most relevant 'skin model' is arguably the pig. Therefore, the purpose of this study was to examine the clinical manifestations of VX intoxication in the domestic white pig following a 2 LD50 (120 microg/kg) percutaneous challenge. There was a consistent onset of signs (where present) in each animal: mastication was followed by miosis, salivation, fasciculations and apnoea. Whilst ChE activity did not correlate with the onset of signs, there was a qualitative relationship in that mastication preceded substantial ChE inhibition, miosis lagged behind the linear decrease in acetylcholinesterase (AChE) activity and fasciculations and apnoea occurred after maximum ChE inhibition had been attained (5-10% of normal). These observations may be of use for the triage of patients exposed to VX. In comparison with similar studies with GD, VX did not affect glucose utilization. However, VX was similar to GD in that it caused a mild hyperkalaemia and hyperphosphataemia, although the significance of this observation was not clear. There was substantial lateral diffusion of the initial droplet of VX over the application site, indicating that, when decontaminating exposed skin, attention should also be directed to areas peripheral to the original site of exposure.

Acetylcholinesterase↗
PubMed2001

Effect of ultrasonic agitation on the release of copper, iron, manganese and zinc from soil and sediment using the BCR three-stage sequential extraction.

An ultrasonic bath and an ultrasonic probe have been used to develop rapid versions of the three-stage Community Bureau of Reference (BCR, now the Standards, Measurement and Testing Programme) sequential extraction procedure. The effect of the ultrasonic treatments on the extraction of copper, iron, manganese and zinc from a sewage sludge-amended soil has been assessed. Recoveries similar to those of conventional shaking (i.e., conventional value, +/- 30%) could generally be obtained for copper, manganese and zinc, but not for the important matrix element iron. With the use of compromise sonication conditions, steps 1, 2 and 3 of the sequential extraction (excluding the hydrogen peroxide digestion in step 3, which was not performed with sonication) could be completed in 3, 5 and 1 min, respectively, using the ultrasonic probe, and in 3, 1 and 1 h, respectively, using the bath. The extraction procedures developed using the soil performed well when applied to lake sediment BCR CRM 601. Analyte partitioning was generally similar to that obtained with mechanical shaking, and overall metal recoveries were 84-98% of those obtained with the conventional BCR protocol, except for copper extracted with the probe (74%). Poorer performance (analyte recoveries, 58-104%) was obtained when the methods were applied to an intertidal sediment. This highlights the difficulty of developing a version of the BCR extraction, with ultrasonic assistance, which gives a performance equivalent to conventional shaking when applied to different substrates.

Copper↗
PubMed2000

Chronic cerebral hypoperfusion: loss of pupillary reflex, visual impairment and retinal neurodegeneration.

Adult rats underwent permanent bilateral occlusion of the common carotid arteries (2VO) to determine the effect of chronic cerebral ischemia on vision and retina. They were monitored post-surgically for the presence of the pupillary reflex to light. Some rats were tested for 6 months post-surgically on a radial arm maze task and then tested in another water-escape task which explicitly tested visual function. Another group of rats were tested post-surgically for 3 months on a task which simultaneously assessed visual and tactile discrimination ability. The thicknesses of the retinal sub-layers were then measured for some rats. Fourteen of the 25 rats that underwent 2VO lost the pupillary reflex. This seemed to occur within 5 days. Rats that lost the pupillary reflex but not rats whose reflex was intact, were impaired on all visually guided mazes. Tactile discrimination ability was unaffected. Only rats that lost the pupillary reflex showed reduced thickness of the retinal outer nuclear and plexiform layers, reduced cell density in the retinal ganglion cell layer and astrocytosis and degeneration of the optic tract. We conclude that 2VO can eliminate the pupillary reflex. Photoreceptors and retinal ganglion cells degenerate, but it is unclear if these are the cause(s) or result(s) of the loss of the pupillary reflex. These effects are accompanied by impairment of visually guided behavior. The possibility that visual system damage may also occur in acute ischemia merits further investigation.

Animals↗
PubMed2000

Rotation and asymmetry of the mitotic spindle direct asymmetric cell division in the developing central nervous system.

The asymmetric segregation of cell-fate determinants and the generation of daughter cells of different sizes rely on the correct orientation and position of the mitotic spindle. In the Drosophila embryo, the determinant Prospero is localized basally and is segregated equally to daughters of similar cell size during epidermal cell division. In contrast, during neuroblast division Prospero is segregated asymmetrically to the smaller daughter cell. This simple switch between symmetric and asymmetric segregation is achieved by changing the orientation of cell division: neural cells divide in a plane perpendicular to that of epidermoblast division. Here, by labelling mitotic spindles in living Drosophila embryos, we show that neuroblast spindles are initially formed in the same axis as epidermal cells, but rotate before cell division. We find that daughter cells of different sizes arise because the spindle itself becomes asymmetric at anaphase: apical microtubules elongate, basal microtubules shorten, and the midbody moves basally until it is positioned asymmetrically between the two spindle poles. This observation contradicts the widely held hypothesis that the cleavage furrow is always placed midway between the two centrosomes.

Anaphase↗
PubMed2000

Column leaching and sorption experiments to assess the mobility of potentially toxic elements in industrially contaminated land.

Made-up ground collected from layers of a trial pit excavated on a former industrial site was treated with artificial rainwater in a series of column leaching and sorption experiments. Metal mobility and the ability of various layers of material obtained from the pit to act as sources or sinks of potentially toxic elements were assessed. Samples from different layers varied in their abilities to raise the pH of rainwater applied at pH 3.5 and 4.3, and this was reflected in the amounts of metals mobilised by the rainwater as it percolated through the soil column. Material from the top two layers of the pit released cadmium, copper, manganese, lead, nickel and zinc to the aqueous phase, but the lower layers, with higher buffering capacity, were able to resist acidification even when the equivalent of 12 months' rainfall (western UK) was applied. Column sorption experiments confirmed the ability of material from layer 4 (48-50 cm) to take up copper, manganese and zinc. Metals were determined in the leachates by flame and electrothermal atomic absorption spectrometry and principle anions by ion chromatography.

Adsorption↗
PubMed2000

Application of a modified BCR sequential extraction (three-step) procedure for the determination of extractable trace metal contents in a sewage sludge amended soil reference material (CRM 483), complemented by a three-year stability study of acetic acid and EDTA extractable metal content.

This paper provides additional data on a sewage sludge amended soil certified reference material, CRM 483, which was certified in 1997 for its EDTA and acetic acid extractable contents of some trace metals, following standardised extraction procedures. The additional work aimed to test the long-term stability of the material and the applicability of an improved version of the BCR three-step sequential extraction procedure on the sewage sludge amended soil (CRM 483). The paper demonstrates the CRM 483 long-term stability for EDTA and acetic acid extractable contents of Cd, Cr, Cu, Ni, Pb and Zn and gives the results (obtained in the framework of an interlaboratory study) for the extractable contents of the same elements in the CRM 483, following the BCR three-step sequential extraction scheme. The aqua regia extractable contents following the ISO 11466 Standard are also given. The data are given as indicative (not certified) values.

Acetic Acid↗
PubMed1998

Miranda mediates asymmetric protein and RNA localization in the developing nervous system.

Neuroblasts undergo asymmetric stem cell divisions to generate a series of ganglion mother cells (GMCs). During these divisions, the cell fate determinant Prospero is asymmetrically partitioned to the GMC by Miranda protein, which tethers it to the basal cortex of the dividing neuroblast. Interestingly, prospero mRNA is similarly segregated by the dsRNA binding protein, Staufen. Here we show that Staufen interacts in vivo with a segment of the prospero 3' UTR. Staufen protein and prospero RNA colocalize to the apical side of the neuroblast at interphase, but move to the basal side during prophase. Both the apical and basal localization of Staufen are abolished by the removal of a conserved domain from the carboxyl terminus of the protein, which interacts in a yeast two-hybrid screen with Miranda protein. Furthermore, Miranda colocalizes with Staufen protein and prospero mRNA during neuroblast divisions, and neither Staufen nor prospero RNA are localized in miranda mutants. Thus Miranda, which localizes Prospero protein, also localizes prospero RNA through its interaction with Staufen protein.

Animals↗
PubMed1998

Chronic cerebral hypoperfusion elicits neuronal apoptosis and behavioral impairment.

Chronic reductions in cerebral blood flow associated with aging and progressive neurodegenerative disorders can precipitate cognitive failure. To assess whether chronic cerebrovascular insufficiency elicits neuronal apoptosis, apoptotic cell death in the hippocampus was quantitated in a rat model of permanent carotid occlusion. Bilateral carotid artery occlusion (2VO) was shown to induce apoptotic morphology and DNA strand breaks in hippocampal neurons 2 and 27 weeks after ligation. The rate of pyramidal cell apoptosis was higher at chronic (27 weeks) compared to sub-chronic (2 weeks) time points. 2VO-induced apoptosis resulted in a decrease in total pyramidal cell number at 27 weeks but not at earlier time points, indicating progressive neuronal loss. Working and reference memory errors in the radial arm maze were strongly correlated with the number of apoptotic neurons in CA1 but not CA3 pyramidal cell fields. These data provide the first indication that apoptotic loss of pyramidal neurons may play a role in memory impairment associated with clinical conditions of chronic cerebrovascular insufficiency.

Animals↗
PubMed1996

192 IgG-saporin lesion of basal forebrain cholinergic neurons in neonatal rats.

Seven day old rats received bilateral intraventricular injections (200 ng) of the immunotoxin 192 IgG-saporin. When assayed in adulthood, these rats showed an 84% loss of hippocampal and a 52% loss of cortical choline acetyltransferase (ChAT) activity. ChAT was unaffected in the caudate. Cholinergic neurons immunoreactive (IR) for the low affinity neurotrophin receptor (P75NTR) were severely reduced throughout the basal forebrain nuclei. Cortical and hippocampal norepinephrine were increased and these areas showed ingrowth of ectopic, P75NTR and dopamine beta-hydroxylase IR varicosities. These were probably sympathetic axons. No obvious forebrain dysmorphogenesis was observed and cortical thickness was unaffected. These rats showed no evidence of impaired spatial learning/memory as assessed by the Morris water maze and delayed spatial alternation. However, they were less active on the elevated plus apparatus and spent less time on the open arms, suggestive of increased timidity. 192 IgG-saporin appears to be a powerful tool to selectively lesion basal forebrain cholinergic neurons in the neonatal rat. Surprisingly, the neuromorphological and behavioral sequelae seem minimal. It may be necessary to achieve near-total neonatal destruction of forebrain cholinergic neurons before severe, lasting mnemonic effects are evident.

Acetylcholine↗
PubMed1996

Chronic reduction of cerebral blood flow in the adult rat: late-emerging CA1 cell loss and memory dysfunction.

Ten-month-old rats were subjected to permanent bilateral occlusion of both common carotid arteries (2-VO) to chronically but moderately reduce brain blood flow. 2-VO impaired Morris water maze acquisition as soon as 7 days post-surgery. 2-VO also caused a later-appearing impairment on the radial arm maze which did not reach significance until 63 days post-surgery. At 14 dats post-surgery there were no effects of 2-VO on hippocampal CA1 pyramidal cell number or density of glial fibrillary acidic protein (GFAP). Hippocampal choline acetyltransferase activity at 70 days was also unaffected by 2-VO. At 190 days post-surgery, however, the 2-VO rats showed loss of cells and increased GFAP density in CA1. The increased density of hippocampal GFAP correlated with radial arm maze but not Morris water maze impairment. It is suggested that 2-VO causes neuronal dysfunction which can be exacerbated by stress and thereby manifested on aversively motivated tasks such as the water maze. As well, CA1 neurons begin to degenerate after several weeks of the reduced energy availability caused by 2-VO and this impairs memory. Since reduced neuronal energy metabolism is associated with the progressive neurodegeneration that underlies disorders such as Alzheimer's, research should further explore the possibility that the effects of 2-VO may model age-related dementia.

Animals↗
PubMed1996

Age-related changes in the content of the C-terminal region of aggrecan in human articular cartilage.

The content of the C-terminal region of aggrecan was investigated in samples of articular cartilage from individuals ranging in age from newborn to 65 years. This region contains the globular G3 domain which is known to be removed from aggrecan in mature cartilage, probably by proteolytic cleavage, but the age-related changes in its abundance in human cartilage have not been described previously. The analysis was performed by immunosorbant assay using an antiserum (JD5) against recombinant amino acid residues of human aggrecan, on crude extracts of cartilage without further purification of aggrecan. The results showed that the content of the C-terminal region decreased with age relative to the G1 domain content (correlation coefficient = 0.463). This represented a 92% fall in the content of this region of the molecule from newborn to 65 years of age. furthermore, when the G1 content of the cartilage extracts was corrected to only include the G1 attached to aggrecan and to exclude the G1 fragments which accumulate as a by-product of normal aggrecan turnover (free G1), the age-related decrease in the C-terminal region remained very pronounced. Analysis by composite agarose/PAGE showed that the number of subpopulations of aggrecan resolved increased from one in newborn to three in adult cartilage. All of these reacted with an antiserum to the human G1 domain, but only the slowest migrating species reacted with the C-terminal region antiserum (JD5). Similar analysis by SDS/PAGE confirmed the presence of high-molecular-mass (200 kDa) proteins reactive with JD5, but no reactive fragments of lower electrophoretic mobility were detected. In contrast, when probed with the antiserum to the human G1 domain, the immunoblots showed protein species corresponding to the free G1 and G1-G2 fragments, which were present at high concentrations in adult cartilage. The results suggest that the loss of the C-terminal region is not directly part of the process of aggrecan turnover, but it is a slow independent matrix process that occurs more extensively with aging as turnover rates become slower. Young cartilage with the fastest turnover contains least molecules lacking the C-terminal region, whereas in old tissue with slow turnover few molecules retain this region. An increase in the cleavage of this region with age may also contribute to this change. The content of the C-terminal region may thus give a measure of the abundance of newly synthesized aggrecan.

Adolescent↗
PubMed1992

Intussusception in the adult: clinical, radiological and histological features.

Intussusception in the adult is an unusual cause of bowel obstruction. Unlike in childhood the clinical presentation is not clear cut and there are no distinct pathognomonic features. The radiological features are variable. Five patients presented to Frenchay Hospital over a five month period. The patients' clinical courses demonstrate the differing presenting features. Ultrasound investigation and CT scanning may show characteristic signs. Surgical treatment is mandatory as there is nearly always an underlying pathological abnormality which may be malignant.

Aged↗