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Biomedical subjects

P Warwick

Publications and source records attributed to P Warwick.

At least 19 recordsLinked to original sources
PubMed2006

Competitive effect of iron(III) on metal complexation by humic substances: characterisation of ageing processes.

Aiming at an assessment of counteractive effects on colloid-borne migration of actinides in the event of release from an underground repository, competition by Fe(III) in respect of metal complexation by dissolved organic matter was investigated for the example of Eu(III) as an analogue of trivalent actinides. Complexation with different humic materials was examined in cation exchange experiments, using (59)Fe and (152)Eu as radioactive tracers for measurements in dilute systems as encountered in nature. Competitive effects proved to be significant when Fe is present at micromolar concentrations. Flocculation as a limiting process was attributed to charge compensation of humic colloids. Fe fractions bound to humic acids (HA) were higher than 90%, exceeding the capacity of binding sites at high Fe concentrations. It is thus concluded that the polynuclear structure of hydrolysed Fe(III) is maintained when bound to HA, which is also inferred from UV-Vis spectrometry. The competitive effect was found to be enhanced if Fe and HA were in contact before Eu was added. Depending on the time of Fe/HA pre-equilibration, Eu complexation decreased asymptotically over a time period of several weeks, the amount of bound Fe being unchanged. Time-dependent observations of UV-Vis spectra and pH values revealed that the ageing effect was due to a decline in Fe hydrolysis rather than structural changes within HA molecules. Fe polycations are slowly degraded in contact with humic colloids, and more binding sites are occupied as a consequence of dispersion. The extent of degradation as derived from pH shifts depended on the Fe/HA ratio.

Benzopyrans↗
PubMed2006

Degradation of tetraphenylphosphonium bromide at high pH and its effect on radionuclide solubility.

Recently, tetraphenylphosphonium bromide (TPPB) has been used to remove technetium from some radioactive waste streams. However, before TPPB could be approved for use it was necessary to show that TPPB and its degradation products would not have a significant detrimental effect on post-closure performance of a radioactive waste repository. TPPB is known to be stable at neutral pH, however, under alkaline conditions it degrades by an alkaline hydrolysis mechanism to triphenylphosphonium oxide (TPPO). Degradation can also occur by radiolysis to produce triphenylphosphine (TPP). The kinetics of the alkaline hydrolysis degradation of TPPB is described and the solubility of europium, iodine, nickel, technetium(VII) and uranium(VI) in aqueous solutions of TPPB and its degradation products is reported. These results were used to support the use of TPPB in removing technetium from some waste streams.

Hydrolysis↗
PubMed2006

Trends in energy and macronutrient intakes in non-under-reporters vary with the method used to identify under-reporters.

OBJECTIVE: To investigate effects of using different methods to identify under-reporters on trends in dietary intake and physical activity level (PAL) in non-under-reporters. DESIGN: Dietary intake and activity pattern were recorded by 887 female university students from 1988 to 2003. Energy expenditure (EE) and PAL were measured using a factorial method. Nine methods were used to identify under-reporters. Trends between 1988 and 2003 were determined from linear regression of median data for each year. RESULTS: Prevalence of under-reporting varied with the method used, ranging from 22.2% to 66.7%. Trends that were consistent using all methods were a decrease in per cent of energy from fat and no change in alcohol intake or PAL (P<0.05). Trends in energy and macronutrient intakes varied with the method used. Using the four methods that excluded the most under-reporters there were increases in energy and gram carbohydrate (CHO) intakes (P<0.05), but no change in gram fat intake. Using the four methods that excluded the fewest under-reporters there was no change in energy or gram CHO intake, but a decrease in gram fat intake (P<0.05). CONCLUSION: Trends in energy, fat and CHO intakes in non-under-reporters varied with the method used to identify under-reporters.

Adult↗
PubMed2005

Combination of chemical separation and data treatment for 55 Fe, 63 Ni, 99 Tc, 137 Cs and 90 Sr/90Y activity determination in radioactive waste by liquid scintillation.

Routine operations involving nuclear reactors and decommissioning activities require numerous chemical analyses. Most of the procedures developed for these chemical characterisations involve several separation steps to prepare the sample for measurement. Chemical treatments are time- and manpower-consuming, labour intensive and produce significant quantities of waste. In order to address this problem, we evaluate a data treatment procedure (multivariate calibration--PLS), which we propose as a substitute to some of these separation steps. Mixtures of beta emitter radionuclides of increasing complexity ((90)Sr/(90)Y--(99)Tc, (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs and (90)Sr/(90)Y--(99)Tc--(63)Ni--(137)Cs--(55)Fe) have been measured by liquid scintillation (LS) counting. The influences of quenching and level of activity was evaluated and the activity of unknown samples determined. Despite the spectra overlapping and low resolution of LS, relative errors in the activities quantification of unknown samples inside the range covered by the calibration matrix are lower than 15% whatever the number of radionuclides included in the solution was.

Algorithms↗
PubMed2003

Uranium(VL) interactions with OPC/PFA grout.

The sorption of uranium on to Ordinary Portland Cement (OPC)/Pulverized Fuel Ash (PFA, fly ash) grout material has been investigated with respect to time, pH, grout:uranium ratio and the chemical composition of the supporting solution. The information obtained is of relevance to the disposal of low-level nuclear waste. The grout material has been chemically characterised and is negatively charged above pH 2.3. At the uranium concentrations studied (2 microM) all uranyl hydroxide aqueous species are expected to be monomeric, rather than polymeric. Uranium(VI) sorption on to the grout material has been explained in terms of inner sphere complexation binding by means of hydroxide bridge formation between the uranium and grout surface. It is also proposed that oligomeric uranyl species are formed across the grout surface, perhaps stabilising the repulsive effects of the negatively charged grout surface and anionic uranyl hydroxide species. Thermodynamic modelling has been used to explain the sorption variation versus solution pH and identifies potential binding mechanisms.

Adsorption↗
PubMed2002

Sampling and analyses of colloids at the Drigg low level radioactive waste disposal site.

Water samples have been extracted from inside (from standpipes) and from outside (from boreholes) of the trenches at the low level radioactive waste disposal site at Drigg in Cumbria, UK. The samples were taken anaerobically from between 8.5 and 10.0 m below the surface using a submersible pump at low flow rates to ensure that the waters in the standpipes and boreholes were maintained at constant levels. To ensure representative samples, the Eh, pH. conductivity, temperature, iron and dissolved oxygen concentrations of the waters were taken during initial purging and during sampling. The gross tritium, gross non-tritium beta, gross alpha and gamma activities of each sample were determined using suitable sample preparation and counting techniques. Samples were then anaerobically, sequentially filtered through 12 microm, 1 microm, 30 kDa and 500 Da filter membranes. The filtrates were analysed for gross alpha, gross non-tritium beta and gamma activities. SEM and STEM analyses were used to determine the colloid population. An energy dispersive analyser on the SEM was used to determine the major elements present in the colloids. UV-visible spectrophotometry, fluorescence spectrophotometry and high performance size exclusion liquid chromatography were used to analyse the waters before and after treatment with ion exchange materials to determine whether natural organic matter was present in the waters. Results showed that two major types of colloids (iron containing colloids and silicon containing colloids) were present in the waters. There were also a small number of other colloids that contain, as major elements, aluminium, calcium and chromium. Organic colloids were also present. The majority of the radioactivity in the waters was due to tritium. Waters taken from outside the trenches contained low levels of non-tritium beta activities and alpha activities which were lower than the minimum detectable amount. Waters taken from the trenches contained non-tritium beta activities and low levels of alpha emitters. Filtration of the trench waters showed that some of the alpha activity was retained by the 30 kDa and 500 Da membranes suggesting that this activity was associated with small colloids. Radioactivity was not found to be associated with colloids present in the waters taken from outside the trenches. Possible reasons for this observation could be that radionuclide bearing colloids have not yet reached the far-field or that the radionuclide concentration is diluted to below the minimum detectable amount. After concentrating two of the samples by factors of x20 and x 16 respectively, 2.4+/-0.1 and 0.6+/-0.1 Bq dm(-3) of 137Cs were measured.

Colloids↗
PubMed2001

Investigation of the permeability of humic molecules using zeta potential measurements.

Zeta potential measurements have been performed on colloidal humate in the presence of differing concentrations of sodium ions at pH = 6.0. A series of calculations has been performed in which the radius of the humic colloid was varied until the predicted surface potential was equal to the experimentally determined zeta potential. The results of the calculations showed that as the ionic strength increases, the apparent radius of the colloid decreases. Similar calculations in which a model colloid was treated as a rigid sphere, i.e., the radius of the colloid was kept constant, failed to simulate the observed zeta potential measurements.

Colloids↗
PubMed2001

Patient-controlled analgesia and intra-operative suggestion.

In a double-blind randomised study, we investigated the influence of positive intra-operative suggestions, presented to anaesthetised patients undergoing total abdominal hysterectomy, on postoperative pain, nausea and vomiting. One hundred and forty patients were randomly allocated to listen to one of four tapes containing either white noise or positive suggestions. The positive suggestions related to pain, postoperative nausea and vomiting, or both. We found that the positive intra-operative suggestions had no beneficial effects in reducing postoperative pain or nausea scores, nor was the consumption of morphine or anti-emetics reduced.

Adult↗
PubMed1999

Carbonate induced dissolution of uranium containing precipitates under cement leachate conditions.

The effects of carbonate on uranium (VI) solubility under aerobic and cementitious conditions have been investigated. The information is of relevance to low level nuclear waste disposal. Aqueous NaOH, KOH, Ca(OH)2 and a cement leachate solution were added to uranyl nitrate solution. Afterwards, increasing amounts of ammonium carbonate were added to re-dissolve the precipitates. The precipitates were characterised by means of X-ray powder diffraction (XRPD) measurements and modelling studies. The model calculations were performed using the MINTEQA2 speciation code, with an expanded database incorporating uranium stability constants taken from the HATCHES database. The measured and predicted amounts of CO3(2-) needed to dissolve the precipitates were compared. The knowledge gained from the 'pure' systems was used to rationalise the precipitation and re-dissolution behaviour observed in the leachate system. The lack of uranium solubility at low carbonate levels brought into question literature formation constants for UO2(OH)3- and UO2(OH)4(2-). An approximate log K value of 26.8 for K2U2O7 formation was estimated from the KOH results at pH 12. Generally, uranium solubilities are expected to be insignificant at low level nuclear waste sites because anaerobic conditions should persist. However, this study has demonstrated that solubility in leachate could rise at high pH and high carbonate levels, if aerobic conditions were to develop. Soluble U(VI) species would be formed. The novel part of the study has been to reproduce the effects and to correlate enhanced solubilities with model predictions. Consequently, the study has re-emphasised the need for appropriate environmental monitoring of such sites.

Carbonates↗
PubMed1996

A comparison of retrospective versus contemporaneous nausea scores with patient-controlled analgesia.

In the search for an effective method of reducing the incidence of postoperative nausea, a standardised system of patient assessment is required. We examined 76 patients who had undergone elective total abdominal hysterectomy and were receiving patient-controlled analgesia with morphine. Nausea scores were obtained using an 11-point rating score. Repeated contemporaneous assessments were compared with a single retrospective score made 5 days after surgery. Retrospective nausea scores were higher than those recorded contemporaneously. Maximum contemporaneous score showed greater agreement with the retrospective score than did the median, mean, or minimum contemporaneous score. Collectively, these results suggest that patients tend to remember their episodes of nausea vividly, even if these episodes were punctuated by relatively nausea-free periods. The variability between the two sets of results suggests that contemporaneous and retrospective nausea scores should not be used interchangeably.

Adult↗
PubMed1996

Antiemetic efficacy of ondansetron with patient-controlled analgesia.

A double-blind, randomised, placebo-controlled study was performed to assess the antiemetic efficacy of ondansetron in women receiving morphine from a patient-controlled analgesia system after total abdominal hysterectomy. Sixty-six ASA grade 1 or 2 patients scheduled for total abdominal hysterectomy were randomly allocated into one of two groups. All patients received a standardised anaesthetic and postoperative patient-controlled analgesia regimen. Group 1 received ondansetron 4 mg at induction of anaesthesia, repeated 8 h later. Group 2 received saline as a placebo at the same times. Pain scores, nausea scores, episodes of vomiting, use of rescue antiemetics and recollection of nausea and vomiting were not different between the groups. Only 15% of patients who received ondansetron and 30% of patients who received the placebo recorded no nausea or vomiting in the first 24 h. We conclude that ondansetron, in the dose studied, does not reduce nausea and vomiting in women receiving morphine from a patient-controlled analgesia system after total abdominal hysterectomy.

Adult↗
PubMed1995

Determination of strontium-90 in milk samples using a controlled precipitation clean-up step prior to ion-chromatography.

Strontium-90 may be determined by beta-counting its yttrium-90 daughter following separation by ion-chromatography, using a three column system comprising a chelating concentrator column, a cation-exchange column and an anion-exchange separator column. The column system has previously been applied to the determination of strontium-90 in water and urine samples. The applicability of the system to the analysis of milk is hampered by the large concentrations of calcium present, which significantly reduces the extraction of yttrium-90 by the concentrator column. A maximum of approximately 200 mg of calcium can be present for the successful extraction of yttrium-90, which greatly limits the quantity of milk that can be analysed. The quantity of milk analysed can be increased by the inclusion of a controlled precipitation step prior to the ion-chromatographic separation. The precipitation is carried out on acid digested milk samples by the addition of ammonia solution until the addition of one drop causes a reduction in pH resulting in the precipitation of calcium hydrogenphosphate. Under these conditions, approximately 20% of the calcium present in the original milk sample is precipitated, yttrium-90 is precipitated whereas strontium-90 is not precipitated. Dissolution of the precipitate, followed by separation of yttrium-90 using the ion-chromatography system facilitates the analysis of a litre of milk with recoveries of greater than 80%.

Animals↗
PubMed1994

Determination of strontium-90 in water and urine samples using ion chromatography.

A semi-automated method was developed for the determination of 90Sr in water and urine samples using ion chromatography. Yttrium-90 in secular equilibrium with 90Sr was initially extracted from the sample solution buffered to pH 5 using a high-capacity iminodiacetate chelating resin. At this pH, transition metals, lanthanides and actinides were extracted by the resin. The extracted metals were then transferred on to a separator column where they were separated and eluted as weak acid anionic complexes. The transition metals were eluted first by using a pyridine-2,6-dicarboxylate eluent, then the lanthanides, actinides and 90Y were eluted from the column by using an oxalate-diglycolate eluent. The fraction containing 90Y was then collected and beta-counted. For water samples, a minimum of sample preparation was required prior to chromatography, whereas an oxalate coprecipitation was included as a preconcentration step for urine samples. The derived recoveries for 90Sr for surface water, rain water and urine samples were 91.7 +/- 1.8, 91.9 +/- 1.6 and 90.0 +/- 2.7%, respectively, and the minimum detectable activity using gas flow proportional counting was 8 mBq.

Chromatography↗
PubMed1979

Resting metabolic rate, weight, surface area and body composition in obese women.

Resting metabolic rate was measured in 22 women with varying degrees of obesity. Body composition was estimated from total body potassium and from total body water, and creatinine excretion in urine was measured over a period of three weeks while the patients were on a creatinine and creatine-free reducing diet. Resting metabolic rate was highly significantly correlated with body weight, surface area, creatinine excretion and lean body mass calculated either from potassium or water measurements (P less than 0.001). Correlation with adipose tissue was less strong, and when multiple regression of both fat and lean on metabolic rate was performed, the relationship was seen to depend mostly on the mass of lean rather than adipose tissue. In obese people the water content of fat-free tissue is greater than that in normal subjects, so it is not valid to assume that fat content can be calculated accurately from a measurement of total body water.

Adipose Tissue↗