Biomedical subjects

B L Parker

Publications and source records attributed to B L Parker.

11 recordsLinked to original sources

PubMed2004

Effect of source variability and transport processes on carbon isotope ratios of TCE and PCE in two sandy aquifers.

Chlorinated ethenes often migrate over extended distances in aquifers and may originate from different sources. The aim of this study was to determine whether stable carbon isotope ratios remain constant during dissolution and transport of chlorinated ethenes and whether the ratios can be used to link plumes to their sources. Detailed depth-discrete delineation of the carbon isotope ratio in a tetrachloroethene (PCE) plume and in a trichloroethene (TCE) plume was done along cross-sections orthogonal to groundwater flow in two sandy aquifers in the Province of Ontario, Canada. At the TCE site, TCE concentrations up to solubility were measured in one high concentration zone close to the bottom of the aquifer from where dense non-aqueous phase liquid (DNAPL) was collected. A laboratory experiment using the DNAPL indicated that only very small carbon isotope fractionation occurs during dissolution of TCE (0.26 per thousand), which is consistent with field observations. At most sampling points, the delta(13)C of dissolved TCE was similar to that of the DNAPL except for a few sampling points at the bottom of the aquifer close to the underlying aquitard. At these points, a (13)C enrichment of up to 2.4 per thousand was observed, which was likely due to biodegradation and possibly preferential diffusion of TCE with (12)C into the aquitard. In contrast to the TCE site, several distinct zones of high concentration were observed at the PCE site and from zones to zone, the delta(13)C values varied substantially from -24.3 per thousand to -33.6 per thousand. Comparison of the delta(13)C values in the high concentration zones made it possible to divide the plume in the three different domains, each probably representing a different episode and location of DNAPL release. The three different zones could still be distinguished 220 m from the DNAPL sources. This demonstrates that carbon isotope ratios can be used to differentiate between different zones in chlorinated ethene plumes and to link plume zones to their sources. In addition, subtle variations in delta(13)C at plume fringes provided insight into mechanisms of plume spreading in transverse vertical direction. These variations were identified because of the high-resolution provided by the monitoring network.

Biodegradation, Environmental↗

PubMed2003

Monitoring oxidation of chlorinated ethenes by permanganate in groundwater using stable isotopes: laboratory and field studies.

Permanganate injection is increasingly applied for in situ destruction of chlorinated ethenes in groundwater. This laboratory and field study demonstrates the roles that carbon isotope analysis can play in the assessment of oxidation of trichloroethene (TCE) by permanganate. In laboratory experiments a strong carbon isotope fractionation was observed during oxidation of TCE with similar isotopic enrichment factors (-25.1 to -26.8 per thousand) for initial KMnO4 concentrations between 67 and 1,250 mg/L. At the field site, a single permanganate injection episode was conducted in a sandy aquifer contaminated with TCE as dense nonaqueous liquid (DNAPL). After injection, enriched delta13C values of up to +204% and elevated Cl- concentrations were observed at distances of up to 4 m from the injection point. Farther away, the Cl- increased without any change in delta13C of TCE suggesting that Cl- was not produced locally but migrated to the sampling point Except for the closest sampling location to the injection point, the delta13C rebounded to the initial 613C again, likely due to dissolution of DNAPL Isotope mass balance calculations made it possible to identify zones where TCE oxidation continued to occur during the rebound phase. The study indicates that delta13C values can be used to assess the dynamics between TCE oxidation and dissolution and to locate zones of oxidation of chlorinated ethenes that cannot be identified from the Cl- distribution alone.

Chlorine Compounds↗

PubMed2001

Geochemical reactions resulting from in situ oxidation of PCE-DNAPL by KMnO4 in a sandy aquifer.

Although the potential for KMnO4 to destroy chlorinated ethenes in situ was first recognized more than a decade ago, the geochemical processes that accompany the oxidation have not previously been examined. In this study, aqueous KMnO4 solutions (10-30 g/L) were injected into an unconfined sand aquifer contaminated by the dense non-aqueous-phase liquid (DNAPL) tetrachloroethylene (PCE). The effects of the injections were monitored using depth-specific, multilevel groundwater samplers, and continuous cores. Two distinct geochemical zones evolved within several days after injection. In one zone where DNAPL is present, reactions between KMnO4 and dissolved PCE resulted in the release of abundant chloride and hydrogen ions to the water. Calcite and dolomite dissolved, buffering the pH in the range of 5.8-6.5, releasing Ca, Mg, and CO2 to the pore water. In this zone, the aqueous Ca/Cl concentration ratio is close to 5:12, consistent with the following reaction for the oxidation of PCE in a carbonate-rich aquifer: 3C2Cl4 + 5CaCO3(s) + 4KMnO4 + 2H+ --> 11CO2 + 4MnO2(s) + H2O + 12Cl- + 5Ca2+ + 4K+. In addition to Mg from dolomite dissolution, increases in the concentration of Mg as well as Na may result from exchange with K at cation-exchange sites. In the second zone, where lesser amounts of PCE were present, KMnO4 persisted in the aquifer for more than 14 months, and the porewater pH increased graduallyto between 9 and 10 as a resultof reaction between KMnO4 and H2O. A small increase in SO4 concentrations in the zones invaded by KMnO4 suggests that KMnO4 injections caused oxidation of sulfide minerals. There are important benefits of carbonate mineral buffering during DNAPL remediation by in situ oxidation. In a carbonate-buffered system, Mn(VII) is reduced to Mn(IV) and is immobilized in the groundwater by precipitating as insoluble manganese oxide. Energy-dispersive X-ray spectroscopy analyses of the manganese oxide coatings on aquifer mineral grains have detected the impurities Al, Ca, Cl, Cu, Pb, P, K, Si, S, Ti, U, and Zn indicating that, similar to natural systems, precipitation of manganese oxide is accompanied by coprecipitation of other elements. In addition, the consumption of excess KMnO4 by reaction with reduced minerals such as magnetite will be minimized because the rates of these reactions increase with decreasing pH. Aquifer cores collected after the KMnO4 injections exhibit dark brown to black bands of manganese oxide reaction products in sand layers where DNAPL was originally present. Mineralogical investigations indicate that the manganese oxide coatings are uniformly distributed over the mineral grains. Observations of the coatings using transmission electron microscopy indicate that they are on the order of 1 microm thick, and consequently, the decrease in porosity through the formation of the coatings is negligible.

Environmental Pollutants↗

PubMed2000

Teen-friendly services. Advocates for successful teen contraception.

Teenagers seeking contraceptive advice need teen-friendly services that are accessible, free or low-cost, confidential, and convenient. From the teen's perspective, the picture is quite simple: "I need help now, I don't want my parents to know about it, I have no money, and I'm not sure what to do." It is the responsibility of the clinical staff to walk new patients through the steps of becoming a successful health care consumer, keeping in mind that they have never acted independently in this area before.

Adolescent↗

PubMed1999

The influences of behavior valence and actor race on black and white children's moral and liking judgments.

Preschoolers, 1st graders, and 4th graders were shown line drawings that depicted 2 prosocial and 2 aggressive behaviors. Black actors or White actors were depicted in the scenarios, and a brief description of each behavior was read to the child. For each scenario, children rated their liking for the actor and the morality of the actor's behavior. Findings indicated that children at each age level significantly differentiated the actors by behavior valence for moral and liking judgements. However, the moral judgements of White preschoolers were more differentiated by behavior valence than the judgments of Black preschoolers. Also, there was more differentiation of actors by behavior valence for liking judgments as the age levels of the children increased. Black actors received more negative moral judgments than did White actors only at the preschool level.

Black or African American↗

PubMed1996

The influences of goal-related actions and reward information on children's and adults' perceptions of effort expenditure and goal desire.

An action perception approach (i.e., Heider, 1958) was used to investigate the influences of qualitatively different goal-related actions on 2nd- and 5th-grade children's and college students' perceptions of actors' effort expenditure (i.e., trying) and goal desire (i.e., wanting). Actors performed three repetitive actions or three equifinal actions within 2 reward conditions (offer of reward or no reward, for attempting to attain a prosocial goal). At each age level, perceptions of effort and want varied significantly by goal-related actions, whereas reward information did not emerge as an influential factor in differentiating perceptions of effort and want. Age-related findings suggested that, compared with the college students, the children overattributed trying and wanting to the actors. In the repetitive-actions condition, both 2nd and 5th graders gave significantly higher effort and want ratings than college students did. In the equifinal-actions condition, 2nd and 5th graders gave significantly higher effort ratings than college students did.

Adult↗

PubMed1995

Declaring pediatric brain death: current practice in a Canadian pediatric critical care unit.

OBJECTIVE: To document the criteria used to declare brain death in a pediatric critical care unit (PCCU). DESIGN: Retrospective chart review. SETTING: Regional PCCU in southwestern Ontario. PATIENTS: Sixty patients 16 years of age or less declared brain dead from January 1987 through December 1992. OUTCOME MEASURES: Presence or absence of documentation of irreversible deep coma, nonresponsive cranial nerves, absent brain-stem reflexes, persistent apnea after removal from ventilator, presence or absence of blood flow detected by radioisotope scanning, presence or absence of electroencephalographic evidence of electrocerebral activity. RESULTS: The 60 patients accounted for 1.5% of all PCCU admissions; 17 were under 1 year of age. In 39 cases brain death was diagnosed using clinical criteria ("certified brain death"), which could not be fully applied in the remaining 21 cases ("uncertifiable but suspected brain death"). Electroencephalography and cerebral blood-flow studies with technetium-99m hexamethyl-propyleneamine oxime were used as ancillary tests in 16 patients with certified brain death and in 17 with uncertifiable but suspected brain death who survived long enough to be tested. Electrocerebral silence was demonstrated in all nine patients who underwent electroencephalography. Cerebral blood flow was undetectable in 26 of the 30 patients tested, and an abnormal pattern of blood flow was seen in the remaining 4, all of whom received a diagnosis of certified brain death. CONCLUSIONS: Pediatricians in this large tertiary care referral centre are using clinical criteria based on the 1987 guidelines of the CMA to diagnose brain death in pediatric patients, including neonates. When clinical criteria cannot be fully applied, ancillary methods of investigation are consistently used. Although the soundness of this pattern of practice is established for adults and older children, its applicability to neonates and infants still needs to be validated.

Adolescent↗

PubMed1994

Photosynthesis and water-use efficiency of sugar maple (Acer saccharum) in relation to pear thrips defoliation.

An experimental introduction of pear thrips (Taeniothrips inconsequens Uzel), a major defoliator in sugar maple (Acer saccharum Marsh.) forests in northeastern North America, was conducted in a field plantation to determine if compensatory gas exchange occurs in response to feeding damage by this piercing-sucking insect. Sugar maple trees were enclosed in netting (167 micro m mesh) and pear thrips adults were introduced before leaf expansion in the spring. Pear thrips reduced whole-tree leaf area by approximately 23% and reduced leaf size (both mass and area) by 20% in the upper crown. Measurements of net CO(2) assimilation rate (A(net)) and stomatal conductance (g(s)) were made on tagged foliage that was later analyzed for stable carbon isotope composition (delta(13)C) to provide estimates of short- and long-term leaf water use efficiency (WUE). Pear thrips feeding reduced A(net) for fully expanded leaves by approximately 20%, although leaf chlorophyll content and leaf mass per unit area were apparently not affected. Comparison of A(net), g(s), instantaneous WUE and leaf delta(13)C between damaged and control trees as well as visibly undamaged versus moderately damaged foliage on pear thrips-infested trees indicated that there were no effects of pear thrips feeding damage on WUE or leaf delta(13)C. Long-term WUE among sugar maple trees in the field plantation, indicated by leaf delta(13)C analysis, was related to shorter-term estimates of leaf gas exchange behavior such as g(s) and calculated leaf intercellular CO(2) concentration (C(i)). We conclude that pear thrips feeding has no effect on leaf WUE, but at the defoliation levels in our experiment, it may reduce leaf A(net), as a result of direct tissue damage or through reduced g(s). Therefore, even small reductions in leaf A(net) by pear thrips feeding damage may have an important effect on the seasonal carbon balance of sugar maple when integrated over the entire growing season.

Journal Article↗

PubMed1994

Usefulness of (Tc 99m) HM-PAO scan in supporting clinical brain death in children: uncoupling flow and function.

OBJECTIVE: To determine the usefulness of (Tc 99m) HM-PAO scan in supporting the clinical diagnosis of brain death. DESIGN: Retrospective review. SETTING: Paediatric Intensive Care Unit. SUBJECTS: A total of 39 paediatric patients had HM-PAO scans conducted to confirm the presence of brain death or to assess the degree of brain injury. INTERVENTIONS: All patients had (Tc 99m) HM-PAO injected before the scan was conducted. MEASUREMENTS AND MAIN RESULTS: Fifty-four scans were done in 39 patients. The majority of cerebral injury was as a result of closed head injury or asphyxia/anoxia. There were 20 scans which demonstrated no cerebral blood flow (CBF); however, in 26 situations patients were clinically brain dead. All of the patients who continued to have CBF in the presence of clinical brain death sustained asphyxial/anoxic injuries. CONCLUSIONS: The HM-PAO scan is a useful non-invasive portable tool for supporting the diagnosis of brain death when there is absent CBF. However, continued flow may be present in asphyxial/anoxic injuries in the presence of clinical brain death.

Adolescent↗

PubMed1991

A state-university collaboration program: residents' perspectives.

Little information is currently available about how residents perceive the recently developed state-university collaboration programs in psychiatry. To determine the opinions of residents participating in the collaboration program in Kentucky, the authors administered a questionnaire to 18 residents who had completed at least one rotation at Eastern State Hospital in Lexington. The questionnaire asked the residents to respond to statements about the clinical, organizational, and educational aspects of the experience. Most respondents rated the experience as favorable, and 78 percent indicated interest in state employment. In addition, the state hospital was noted as one of residents' three future career choices.

Academic Medical Centers↗

PubMedDate not supplied

Vertical cross contamination of trichloroethylene in a borehole in fractured sandstone.

Boreholes drilled through contaminated zones in fractured rock create the potential for vertical movement of contaminated ground water between fractures. The usual assumption is that purging eliminates cross contamination; however, the results of a field study conducted in a trichloroethylene (TCE) plume in fractured sandstone with a mean matrix porosity of 13% demonstrates that matrix-diffusion effects can be strong and persistent. A deep borehole was drilled to 110 m below ground surface (mbgs) near a shallow bedrock well containing high TCE concentrations. The borehole was cored continuously to collect closely spaced samples of rock for analysis of TCE concentrations. Geophysical logging and flowmetering were conducted in the open borehole, and a removable multilevel monitoring system was installed to provide hydraulic-head and ground water samples from discrete fracture zones. The borehole was later reamed to complete a well screened from 89 to 100 mbgs; persistent TCE concentrations at this depth ranged from 2100 to 33,000 microg/L. Rock-core analyses, combined with the other types of borehole information, show that nearly all of this deep contamination was due to the lingering effects of the downward flow of dissolved TCE from shallower depths during the few days of open-hole conditions that existed prior to installation of the multilevel system. This study demonstrates that transfer of contaminant mass to the matrix by diffusion can cause severe cross contamination effects in sedimentary rocks, but these effects generally are not identified from information normally obtained in fractured-rock investigations, resulting in potential misinterpretation of site conditions.

California↗