1,720,958 research outputs found
Impact of materials used in lab and field experiments on the recovery of organic micropollutants
No full textOrganic micropollutants are frequently detected in the aquatic environment. Therefore, a large number of field and laboratory studies have been conducted in order to study their fate in the environment. Due to the diversity of chemical properties among these compounds some of them may interact with materials commonly used in field and laboratory studies like tubes, filters, or sample bottles. The aim of our experiment was to study the interaction between those materials and an aqueous solution of 43 widely detected basic, neutral, and acidic organic micropollutants hereby covering a broad range of polarities. Experiments with materials were conducted as a batch study using spiked tap water and for different syringe filters by filtration with subsequent fraction collection. The best recoveries over a wide range of organic compounds were observed for batches in contact with the following materials (in descending order) acryl glass, PTFE, HDPE, and PP. The use of Pharmed0, silicone, NBR70, Tygon0, and LDPE should be avoided. Flexible tubing materials especially influence many of the investigated compounds here. Filtration with most of the tested filter types leads to no significant loss of almost all of the investigated micropollutants. Nonetheless, significant mass losses of some compounds (loratadine, fluoxetine, sertraline, and diuron) were observed during the first mL of the filtration process. No systematic correlation between compound properties, tested materials, and observed mass losses could be identified in this study. The behavior of each compound is specific and thus, not predictable. It is therefore suggested to study the interaction of compounds with filters and material prior to the actual experiment or include blank studies. (C) 2013 Elsevier B.V. All rights reserved
Preliminary results on the dynamics of particles and their size distribution at a karst spring during a snowmelt event
No full textRecharge events in karst catchments are often accompanied by rapid changes of electrical conductivity, temperature or turbidity in associated karst springs. Turbidity is usually used as a proxy for suspended matter. However, it is not capable to characterize suspended matter in detail as it lumps signals of particles of a wide range of sizes. Changes in particle size distribution (PSD) of suspended matter have rarely been measured although they may contain information on particles' origin, transport, or mobilization. In few cases PSD could even be used to predict bacterial contamination of karst springs. This study is one among few, measuring concentrations of suspended particles in the size range of 0.5-150 mu m on-site and in real-time. The study was performed during a single snow-melt event at one individual karst spring (Gallusquelle, Germany), the findings are therefore of preliminary character. Generally, the PSDs follow a power law (Pareto distribution). In some cases, however, a two parted Pareto distribution provides a better fit. The combination of chemograph analysis and turbidigraph separation demonstrates remobilized (autochthonous) and freshly infiltrated suspended (allochthonous) matter. Visually, there is no relation between PSD and the origin of the suspended matter. This may be caused by the superposition of signals from both origins. Therefore, utilizing the PSD as an indicator for the origin of suspended matter may be restricted to local applications. Furthermore, PSD does not seem to be a clear indicator for a bacterial contamination at the investigated spring, at least for this particular event. The study indicates, that the karst system itself and the type of discharge event may play a crucial role in the successful application of PSD as an adequate source indicator for suspended matter. (C) 2015 Elsevier B.V. All rights reserved.Federal Ministry of Education and Research (BMBF) [02WRS1277A/B
Relationship between organic micropollutants and hydro-sedimentary processes at a karst spring in south-west Germany
No full textKarst aquifers are known to be highly vulnerable to contamination due to their particular hydraulic characteristics. A number of parameters (such as turbidity, dissolved organic matter concentration, particle size distribution) have been proposed as proxies that can be used to detect changes in water quality or contamination of karst springs. However, most of these are not very specific concerning the source of any contamination. Organic micropollutants (OMPs) such as artificial sweeteners or herbicides are possible source-specific indicators that can be used in karst catchment areas, but real time monitoring is not as yet possible for these compounds. We have investigated the possibility of combining the source-specific features of OMPs with real-time measurements of electrical conductivity (EC) and turbidity by means of ECturbidity hysteresis plots. These plots allow for identifying different hydro-sedimentary processes. Our investigations were carried out at the Gallusquelle karst spring in south-west Germany, during high flow conditions that occurred in 2013 after heavy precipitation. The herbicide atrazine, which derives from the aquifer matrix, was detectable in the spring water until resuspended particles appeared at the spring. The herbicide metazachlor, which is present in recharge from cropland, was found to be associated with periods of direct transfer of particles originating from the land surface. The artificial sweetener cyclamate was used as a wastewater indicator, but neither hysteresis plots of EC and turbidity nor any other real-time parameters were able to detect the presence of cyclamate following a wastewater spill. Since EC and turbidity are easily measurable parameters, the systematic relationships of ECturbidity hysteresis behavior to OMPs might assist in the sustainable management of raw water within karst catchments. (C) 2015 Elsevier B.V. All rights reserved.Federal Ministry of Education and Research (BMBF) [02WRS1277A/B
Use of two artificial sweeteners, cyclamate and acesulfame, to identify and quantify wastewater contributions in a karst spring
No full textThe identification and differentiation of different sources of contamination are crucial aspects of risk assessment in water resource protection. This is especially challenging in karst environments due to their highly heterogeneous flow fields. We have investigated the use of two artificial sweeteners, cyclamate and acesulfame, as an indicator set for contamination by wastewater within the rural catchment of a karst spring. The catchment was investigated in detail to identify the sources of artificial sweeteners and quantify their impact. Spring water was analysed following two different but typical recharge events: (1) a rain-on-snow event in winter, when no wastewater overflow from the sewer system was observed, and (2) an intense rainfall event in summer triggering an overflow from a stormwater detention basin. Acesulfame, which is known to be persistent, was quantified in all spring water samples. Its concentrations decreased after the winter event with no associated wastewater spillage but increased during the summer event following a recent input of untreated wastewater. Cyclamate, which is known to be degradable, was only detected following the wastewater inflow incident. The cyclamate signal matched very well the breakthrough of faecal indicator bacteria, indicating a common origin. Knowing the input function, cyclamate was used quantitatively as a tracer in transport modelling and the impact of 'combined sewer overflow' on spring water quality was quantified. Signals from artificial sweeteners were compared to those from bulk parameters (discharge, electrical conductivity and turbidity) and also to those from the herbicides atrazine and isoproturon, which indicate 'old' and 'fresh' flow components, respectively, both originating from croplands. High concentration levels of the artificial sweeteners in untreated wastewater (cyclamate and acesulfame) and in treated wastewater (acesulfame only) make them powerful indicators, especially in rural settings where wastewater input is relatively low, and in karst systems where dilution is often high. (C) 2015 Elsevier B.V. All rights reserved
Redox-sensitivity and mobility of selected pharmaceutical compounds in a low flow column experiment
No full textIn this study a laboratory column experiment under water saturated conditions was conducted to investigate the transport behaviour of the pharmaceutical compounds sulfamethoxazole, carbamazepine, diclofenac, and ibuprofen under varying nitrate concentrations. Organic rich sediment (f(OC)=0.01) and surface water from a formerly investigated field site were used. The water was spiked with the four compounds and the specific redox conditions in the column (0.351 m height) were varied throughout the experiment by adding nitrate in the influent water. Stepwise controlled decreasing influent nitrate concentrations between 131 and 20 mg L-1. were applied in the course of the experiment which lasted 71 days. This established temporarily denitrifying conditions in the column during the reduction of nitrate. Sulfamethoxazole was severely influenced by this process. During denitrification sulfamethoxazole concentrations in the effluent water decreased rapidly and significantly. This experiment demonstrates the strong dependency of sulfamethoxazole transformation specifically on nitrate reducing redox conditions and therefore may help to explain the wide ranges of reported degradability for this compound. Ibuprofen was more stable under denitrifying redox conditions. Both for carbamazepine and diclofenac apparent retardation was observed. For carbamazepine this was attributed to sorption and also to degradation. For diclofenac nitrate controlled degradation seems the dominating process for the apparent retardation of this compound. (C) 2012 Elsevier B.V. All rights reserved
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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