763 research outputs found

    Study of heavy metals and radionuclides in Scottish freshwater loch sediments

    Get PDF

    Storage and hydrolysis of seawater samples for inorganic carbon isotope analysis

    Get PDF
    Preservation of seawater samples was tested for total inorganic carbon (ÎŁCO2), stable carbon isotope (ÎŽ13C), and radiocarbon (14C) applications using foil bags and storage by refrigeration and freezing. The aim was to preserve representative samples with minimal storage effects but without using toxic methods such as mercuric chloride poisoning. Hydrolysis of samples to CO2 was based on existing methods. Results of IAEA-C2 standard used with deionized water stored in the foil bags showed complete reaction yields, 14C results within 2σ of the consensus value, and ÎŽ13C that were internally consistent, indicating that there were no procedural effects associated with the foil bags. 14C results were statistically indistinguishable across the storage times, for frozen and refrigerated seawater samples from a coastal site, Elie Ness, Fife, UK. The scatter of ÎŁCO2 concentrations and ÎŽ13C was within scatter observed in other studies for lake- and seawater samples preserved by acidification or using mercuric chloride. However, both ÎŁCO2 and ÎŽ13C were less variable for frozen samples compared with refrigerated samples. The foil bags are lighter, safer to transport, and similar in cost to glass bottles and allow sample collection in the field and transfer to the hydrolysis vessel without exposure of the sample to atmosphere. Storage of seawater samples in the foil bags was considered a reliable, alternative method to poisoning for ÎŁCO2, ÎŽ13C, and 14C, and freezing the samples is recommended for storage time beyond a week

    Tracing organic matter composition and distribution and its role on arsenic release in shallow Cambodian groundwaters

    Get PDF
    Biogeochemical processes that utilize dissolved organic carbon are widely thought to be responsible for the liberation of arsenic from sediments to shallow groundwater in south and southeast Asia. The accumulation of this known carcinogen to hazardously high concentrations has occurred in the primary source of drinking water in large parts of densely populated countries in this region. Both surface and sedimentary sources of organic matter have been suggested to contribute dissolved organic carbon in these aquifers. However, identification of the source of organic carbon responsible for driving arsenic release remains enigmatic and even controversial. Here, we provide the most extensive interrogation to date of the isotopic signature of ground and surface waters at a known arsenic hotspot in Cambodia. We present tritium and radiocarbon data that demonstrates that recharge through ponds and/or clay windows can transport young, surface derived organic matter in to groundwater to depths of 44 m under natural flow conditions. Young organic matter dominates the dissolved organic carbon pool in groundwater that is in close proximity to these surface water sources and we suggest this is likely a regional relationship. In locations distal to surface water contact, dissolved organic carbon represents a mixture of both young surface and older sedimentary derived organic matter. Ground-surface water interaction therefore strongly influences the average dissolved organic carbon age and how this is distributed spatially across the field site. Arsenic mobilization rates appear to be controlled by the age of dissolved organic matter present in these groundwaters. Arsenic concentrations in shallow groundwaters (< 20 m) increase by 1 ÎŒg/l for every year increase in dissolved organic carbon age compared to only 0.25 ÎŒg/l for every year increase in dissolved organic carbon age in deeper (> 20 m) groundwaters. We suggest that, while the rate of arsenic release is greatest in shallow aquifer sediments, arsenic release also occurs in deeper aquifer sediments and as such remains an important process in controlling the spatial distribution of arsenic in the groundwaters of SE Asia. Our findings suggest that any anthropogenic activities that alter the source of groundwater recharge or the timescales over which recharge takes place may also drive changes in the natural composition of dissolved organic carbon in these groundwaters. Such changes have the potential to influence both the spatial and temporal evolution of the current groundwater arsenic hazard in this region

    Investigation into background levels of small organic samples at the NERC Radiocarbon Laboratory

    Get PDF
    Recent progress in preparation/combustion of submilligram organic samples at our laboratories is presented. Routine methods had to be modified/refined to achieve acceptable and consistent procedural blanks for organic samples smaller than 1000 g C. A description of the process leading to a modified combustion method for smaller organic samples is given in detail. In addition to analyzing different background materials, the influence of different chemical reagents on the overall radiocarbon background level was investigated, such as carbon contamination arising from copper oxide of different purities and from different suppliers. Using the modified combustion method, small amounts of background materials and known-age standard IAEA-C5 were individually combusted to CO2. Below 1000 g C, organic background levels follow an inverse mass dependency when combusted with the modified method, increasing from 0.13 0.05 pMC up to 1.20 0.04 pMC for 80 g C. Results for a given carbon mass were lower for combustion of etched Iceland spar calcite mineral, indicating that part of the observed background of bituminous coal was probably introduced by handling the material in atmosphere prior to combustion. Using the modified combustion method, the background-corrected activity of IAEA-C5 agreed to within 2 s of the consensus value of 23.05 pMC down to a sample mass of 55 g C

    Progress in AMS target production in sub-milligram samples at the NERC Radiocarbon Laboratory

    Get PDF
    . Recent progress in graphite target production for sub-milligram environmental samples in our facility is presented. We describe an optimized hydrolysis procedure now routinely used for the preparation of CO2 from inorganic samples, a new high-vacuum line dedicated to small sample processing (combining sample distillation and graphitization units), as well as a modified graphitization procedure. Although measurements of graphite targets as small as 35 ”g C have been achieved, system background and measurement uncertainties increase significantly below 150 ”g C. As target lifetime can become critically short for targets <150 ”g C, the facility currently only processes inorganic samples down to 150 ”g C. All radiocarbon measurements are made at the Scottish Universities Environmental Research Centre (SUERC) accelerator mass spectrometry (AMS) facility. Sample processing and analysis are labor-intensive, taking approximately 3 times longer than samples ≄500 ”g C. The technical details of the new system, graphitization yield, fractionation introduced during the process, and the system blank are discussed in detail

    Developing a new empathy-specific admissions test for applicants to medical schools: A discourse-pragmatic approach.

    Get PDF
    The ability to empathise with patients is an important professional skill for doctors. Medical students practise this skill as part of their medical education and are tested on their use of empathy within their final examination. Evidence shows that appropriate training makes a difference but natural aptitude also plays a role. Most medical schools do, therefore, probe applicants’ basic understanding of empathy at admissions interviews. The purpose of the project presented in this paper was to apply existing understanding of how empathy may be communicated in a clinical context (building on the first author’s previous literature review, 2011) to develop a new empathy-specific medical admissions interview station, probing applicants’ empathic communicative performance (not just theoretical knowledge) and fitting in the widely used Multiple Mini Interview (MMI) interview format. The paper outlines how this tool was developed, trialled and implemented by: 1) Conceptualising empathic communication in discourse-pragmatic terms, that is, as a set of specific but context-dependant empathic speech acts. 2) Formulating and trialling a written and two oral versions of a situational test, capable of probing the applicants’ ability to communicate empathically in everyday conversation and suitable for use at Norwich Medical School and other similar educational institutions

    Nachhaltige dramapĂ€dagogische Sprachförderung fĂŒr Grundschulkinder mit DaZ

    Get PDF
    Vielerorts finden in den Schulferien Theatercamps statt, die vor allem sprachschwachen Kindern eine Chance bieten, ihre Sprachkenntnisse spielerisch und handlungsgebunden zu erweitern. Anschlussprojekte, die die Nachhaltigkeit der Fördereffekte sichern und auf diesen aufbauen, gibt es hingegen kaum. Es fehlt an bereichsĂŒbergreifenden Konzepten, die im Camp gewonnenen positiven Einstellungen gegenüber Sprache und Schrift in den Schulalltag zu transferieren. Diesem Desiderat begegnend wird in TĂŒbingen derzeit ein durchgĂ€ngiges Förderkonzept fĂŒr Grundschulkinder mit Deutsch als Zweitsprache (DaZ) und Sprachförderbedarf erprobt: Im Rahmen von Theater-AGs werden die Kinder, die zur Zeit des Feriencamps die Klasse 2 besuchten, zwei weitere Jahre gefördert, die Kinder der Klasse 3 mindestens ein Jahr. In einem solchen Förderzeitraum ist es möglich, systematisch die Sprachkompetenz aufzubauen und die GrundschĂŒlerInnen auf die bildungssprachlichen Anforderungen der Sekundarstufe I vorzubereiten. WĂ€hrend sich die thematisch-inhaltlichen Vorgaben für die Sprachförderung im Camp aus dem gemeinsam zu entwickelnden und aufzuführenden Theaterstück ergeben, werden in den Theater-AGs Inhalte aus dem Schulfach MeNuK (Mensch, Natur, Kultur) dramapĂ€dagogisch erarbeitet. Im folgenden Beitrag wird die Entwicklung vom außerschulischen Ferien-Theatercamp hin zum Anschlussprojekt der fachsensiblen Sprachförderung in schulischen Theater-AGs noch einmal im Detail nachvollzogen, wobei exemplarische Fördereinheiten die bereichsĂŒbergreifende methodische KontinuitĂ€t illustrieren
    • 

    corecore