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Étude du comportement de sorption des congénères du toxaphène sur la matière particulaire du milieu marin = Sorptive behaviour study of the toxaphene congeners on marin particulate matter
Full text linkRÉSUMÉ : Le toxaphène a été un des chloropesticides les plus utilisés dans le monde avec une
utilisation globale de 1,33 x 106 tonnes. Cette quantité est équivalente à celle des BPCs utilisée
pour la même période (1950-1990). Le toxaphène technique est constitué d'un mélange complexe
de centaines de chlorobomanes (CHBs) et de chloroterpènes. Bien que le toxaphène ait été banni
depuis 1990, des concentrations relativement importantes des congénères persistants du
toxaphène sont observés dans les compartiments des milieux aquatiques (eaux, les sédiments et
les matrices biologiques). Les CHBs sont repartis différemment dans ces compartiments. Trois
groupes de CHBs sont particulièrement intéressants pour leurs distributions dans l'environnement
aquatique. Les heptachlorobomanes, contenant sept atomes de chlore, sont majoritaires dans les
sédiments (25-55%) alors qu'ils ne constituent qu'une faible proportion du toxaphène observé (~
15%) dans les matrices biologiques. À l'inverse, les octachlorobomanes et les
nanochlorobomanes, contenant respectivement huit et neuf atomes de chlore, peuvent représenter
jusqu'à 80% du toxaphène mesuré dans les matrices biologiques tandis qu'ils ne constituent
qu'une faible proportion (3,5-20%) du toxaphène rapporté dans les sédiments.
La matière particulaire en suspension (MPS) constitue un élément clé dans le transfert et
la distribution des contaminants organiques hydrophobes (COHs), comme le toxaphène, dans les
compartiments des milieux aquatiques. En effet, les interactions des COHs avec la MPS sont
déterminants pour la réactivité, la mobilité et la disponibilité de ces composés dans
l'environnement aquatique.
La sorption et la désorption des congénères du toxaphène sur la MPS sont deux processus
importants pouvant affecter leur distribution dans l'environnement. Cependant, aucune étude n'a
été entreprise jusqu'à présent pour étudier les interactions de sorptionldésorption des congénères
du toxaphène sur la MPS . Cette étude vise à combler cette lacune en aidant à mieux comprendre
les comportements de sorptionldésorption de trois congénères du toxaphène (B7 -1450, B8-1413
et B9-1679) sur du sédiment marin utilisé comme MPS.
La sorption du B7-1450, utilisé comme congénère modèle des heptachlorobomanes, a été
réalisée pour la première fois sur du sédiment marin à l'aide d'un réacteur de sorption. Les pertes
du B7-1450 sur les parois du réacteur et les pertes dues à l'évaporation du B7-1450 durant le
protocole d'analyse de ce congénère ont été évaluées. Les coefficients de sorption (KI et Kac) du
B7 -1450 peuvent être surévalués jusqu'à 30 % si ces pertes ne sont pas prises en compte. De ce
fait, des équations ont été établies, validées et utilisées pour déterminer correctement les
coefficients de sorption du B7-1450. Les valeurs de Kac varient entre 3,5 x 104 à 6,5 x 104 mLig
pour l'intervalle de concentrations utilisées. Ces valeurs indiquent une forte affinité du B7 -1450
pour la matière particulaire (MP) de l'environnement comme les sédiments ou les sols.
Les comportements de sorptionldésorption du B7 -1450 ont été étudiés en fonction du
temps afin de comprendre les interactions des heptachlorobomanes avec le sédiment. De plus, les
processus de sorptionldésorption du B7-1450 sur du sédiment ont été étudiés dans des conditions
de salinité et température différentes afin d'évaluer la sorption et la séquestration (désorption
faible ou sorption irréversible) du B7 -1450 en fonction des conditions du milieu. Les données
obtenues ont été caractérisées avec des modèles de sorption. Les processus de sorption et de
désorption ont atteint l'équilibre au bout d'une courte période (16.4 h.). Ces résultats indiquent
que le transfert du B7-1450 vers l'intérieur du sédiment serait retardé. De plus, la désorption du
B7 -1450 à partir du sédiment est moins importante au début du temps de contact
comparativement à la période d'équilibre. Ces comportements suggèrent que les molécules de
B7 -1450 pourraient accéder à différents sites de sorption disponibles sur le sédiment. Les valeurs
de Koc et KI varient respectivement de 3,2 x 104 à 6,0 X 104 mL!g et de 560 à 1100 mL!g à
l'intérieur de la gamme de salinités et de températures testées pour l'intervalle de concentrations
utilisées. Les coefficients de sorption, Koc et KI, augmentent avec la salinité et diminuent avec la
température. De plus, la séquestration du B7 -1450 est moins importante à faible salinité
comparativement aux conditions de hautes salinités. Par ailleurs, les coefficients de sorption sont
plus importants à faibles concentrations quelque soit les conditions du milieu. Ces résultats
suggèrent que les heptachlorobomanes pourraient être plus séquestrés sur la MPS en milieu de
forte salinité et de faible température de type marin froid.
Enfin, une étude de la sorptionldésorption du B8-1413 et du B9-1679, utilisés comme
congénères modèles des octachlorobomanes et des nonachlorobomanes, a été réalisée sur un
sédiment marin. Comme pour le B7 -1450, des équations correctives des pertes ont été établies,
validées et utilisées pour déterminer les paramètres de sorption des congénères B8-1413 et B9-
1679. Les données obtenues montrent des comportements similaires de sorptionldésorption du
B8-1413 et B9-1679 sur le sédiment. Les valeurs du coefficient de sorption Koc, varie de 1,5 x
105 à 2,1 x 105 mL! g pour le gradient de concentrations étudiées. Ces valeurs montrent une
sorption importante de ces deux congénères sur le sédiment. Cependant, nous avons observé une
séquestration du B8-1413 et du B9-1679 par le sédiment deux fois moins importantes que celle
du B7 -1450 qui est connu pour être présent dans la matrice sédimentaire. Les résultats suggèrent
que les octachlorobomanes et nonachlorobomanes peuvent être plus disponibles dans la phase
aqueuse comparativement aux heptachlorobomanes. -- ABSTRACT : The toxaphene has been one of the most widely used pesticides in the world, with a
cumulative worldwide use estimated at 1.33 x 106 tons corresponding to the PCBs amount used
during the same period of time (1950-1990). Technical toxaphene is a complex mixture of
several hundred chlorobornanes (CHBs) and other chloroterpene congeners. Despite its ban in
most parts of the world since the 1990s, toxaphene residues were reported in compartments of
several aquatic ecosystems (water column, sediments and biological matrices) at significant
levels. CHBs were distributed differentely in these compartments. Three homologue CHB groups
have distinctive distributions in the aquatic environment. The heptachlorobornanes, having seven
chlorine atoms, are observed in relatively high content (25-55%) in sediments whereas they
account for a sm aIl fraction (15%) of aIl toxaphene detected in biological matrices. In contrast,
octachlorobornanes and nanochlorobornanes, having eight and nine chlorine atoms, respectively,
could contribute to up to 80% of the toxaphene congeners isolated from biological matrices.
Octachlorobornanes and nanochlorobornanes account only for 3.5-20% of toxaphène reported in
the sedimentary matrices.
The suspended particulate matter (SPM) plays a key role in the distribution and transfer of
hydrophobic organic compounds (HOCs), such as toxaphene, in the aquatic system. The
interactions of HOCs with the SPM are important in the reactivity, availability and mobility of
these compounds in the aquatic environment.
Sorption and desorption of toxaphene congeners on MPS are both important processes in
the distribution of these compounds in the environment. To the best of our knowledge, there is no
study characterising the sorptionldesorption of toxaphene congeners on particulate matter, such
as SPM or sediments. Our work aims to study the sorption and desorption behaviours of three
toxaphene congeners (B7-1450, B8-1413 and B9-1679) on sediment used as SPM.
The sorption of the B7-1450, used as model compound of the toxaphene
heptachlorobornane congeners found in sediments, has been investigated for the first time on
sediment using batch sorption reactor. We firstly evaluated B7-1450 losses due to adsorption
onto glass waIls and to evaporation occurring during analytical treatment. Sorption coefficients,
KI and K,c, of B7-1450 could be overestimated by > 30% if the losses were not corrected.
Therefore, loss correction equations were established, validated and applied to determine sorption
coefficients for the B7-1450 congener. The Koc values for B7-1450 determined over a gradient of
concentrations ranged from 3.5 x 104 to 6.5 x 104 mL/go These values suggest a strong affinity of
B7 -1450 for particulate matter (PM) of the environement such as sediments or soils.
Then, sorptionldesorption behaviours of the B7-1450 on sediment were studied as a
function of time to understand heptachlorbornes interactions with sediment. Moreover,
sorptionldesorption processes of the B7 -1450 on sediment were studied in different sali nit y and
temperature conditions. The sorption and sequestration of B7 -1450 were assessed in these
conditions using sorption models. Kinetic behaviours showed that sorption and desorption
processes reached the equilibrium over short periods of time (16.4 h.). These results suggest that
the diffusion process of the B7-1450 in sediment are retarded. The results indicate a less
important desorption of B7-1450 by sediment at the initial sorption time comparatively to the
equilibrium. This behaviour suggests that the B7 -1450 may access to different sorption sites
available on sediment. Koc and Ki values ranged from 3.2 x 104 to 6.0 x 104 mL/g and from 560
to 1100 mL/g in the range of salinities and temperatures tested. Sorption coefficients, Koc and Ki,
increase with the salinity and decrease when the temperature increases. Otherwise, the B7-1450
entrapment on the sediment is more important in the low salinity medium than in the high salinity
medium. The results showed also higher sorption coefficients at low B7-1450 concentrations
under all tested experimental conditions. Thus, heptachlorobomanes could be more entrapped by
the SPM in low salinity medium or in cold marine medium.
Finally, the sorption/desorption of the B8-1413 and the B9-1679, used as model
compounds of the octachlorobomanes and nonachlorobomanes, were studied on marine
sediment. Equations were established, validated and applied to determine correctly sorption
parameters of B8-1413 and B9-1679 congeners like for B7 -1450 congener. The study showed a
similar sorption/desorption behaviours of the B8-1413 and the B9-1679 on the sediment. The Koc
values determined over a gradient of concentration ranged from 1.5 x 105 to 2.1 x 105 mL/go
These values indicate an important sorption of B8-1413 and the B9-1679 on sediment. However,
results showed that the B8-1413 and the B9-1679 were entrapped on the sediment twice less than
the B7-1450 which is a toxaphene congener known to be present in sediment matrix. Results
suggest that octachlorobomanes and nonachlorobomanes could be more available in the aqueous
phase than the heptachlorobomanes
Origin of nitrate and sulfate sources in volcano-sedimentary aquifers of the East Africa Rift System: An example of the Ali-Sabieh groundwater (Republic of Djibouti)
Full text linkWithin the East African Rift System (EARS), the complex Ali-Sabieh aquifers system, located in the south of the Republic of Djibouti, was overexploited and subjected to anthropogenic and/or geogenic pollution with high concentrations of dissolved nitrate (up to 181 mg/l) and sulfates (up to 1540 mg/l). This study is the first undertaken on the hydrochemistry of this aquifer system, combining geochemical tools and multi-isotope - δ2H(H2O), δ18O(H2O), δ18O(SO4), δ34S(SO4), δ15N(NO3), δ18O(NO3), δ13C(DIC), and 14C- was used to decipher the origin and fate of different nitrate and sulfate sources to groundwater. The groundwater samples of the region show a chemical evolution from fresh Ca(Na)-bicarbonate to brackish Na-Cl , mainly due to water-rock interaction. The combined chloride and water isotope data show that evaporation and transpiration are present, with the latter occurring primarily in the shallow alluvial aquifer waters. Inspection of δ15N(NO3) vs. δ18O(NO3) and NO3/Cl vs. Cl diagrams show that dissolved nitrates are primarily of anthropogenic origin. In particular, higher nitrate concentrations may be related to animal manure used as organic fertilizers during agricultural activities. Sulfates are from a natural origin related to the interaction of water with gypsum of hydrothermal or sedimentary origin. SO4/Cl ratio and isotopic composition show that dissolved sulfates in saline and ancient groundwater of the Cretaceous sandstone aquifer (between 7.4 ± 2.2 and 5.8 ± 1.4 k-years before the present) are generated by interaction with gypsum from oxidation of pre-existing (Jurassic?) sulfides. This work highlight that isotopic ratios of the two molecules -δ18O(SO4), δ34S(SO4), δ15N(NO3), δ18O(NO3)- are not sufficient for tracing the origin of nitrate and sulfates in groundwater, but that a complete hydrogeochemical study is needed. In the absence of this, the relatively high concentration of chloride and sulfates could be wrongly linked to the anthropogenic source of nitrate (manure or sewage)
Formation of highly quaternized N,N,N-trimethylchitosan: a chemoselective methodology in aqueous media
Full text linkN,N,N-Trimethylchitosan (TMC) represents a rare example of cationic polysaccharides and numerous studies have shown its potential in biological and biomedical applications. TMC with high degrees of quaternization (DQ) were synthesized from N-methylation of N,N-dimethylchitosan (DMC), which was obtained by reductive alkylation of high molecular weight chitosan in a simple step process and in good yields. The effects of base and solvents were evaluated on the quaternization reaction. The N-methylation of DMC was performed selectively by CH3I and carbonate in water where quaternization was achieved quantitatively with a low degree of O-methylation (17 %). Moreover, the greener procedure allows easy recovery and purification by conventional filtration as a carbonate salt, in which the anion can be exchanged by an acid-base reaction. Quantification of DQ involving 1H NMR integration of methyl peaks must be performed on protonated TMC. High field NMR spectra of TMC showed two specific chemical shifts for anomeric peaks (5.0 and 5.4 ppm) that can also be used for the determination of DQ. This latter method avoids the superimposition problems with other pyranosyl peaks. -- Keywords : cationic polymer ; degree of quaternization ; N-alkylation ; N,N,N-trimethylchitosan ; POC-17 ; quantification
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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