1,720,962 research outputs found
Improvements in the analysis of decabromodiphenyl ether using on-column injection and electron-capture detection
No full textDuring the development of a method to determine polybrominated diphenyl ethers (PBDEs) using GC/MS-MS equipped with a programmed temperature vaporizer (PTV) injector, a dramatic decrease in sensitivity to decabromodiphenyl ether (BDE-209) occurred and lack of sensitivity and repeatability was observed. An alternative method using GC/ECD equipped with an on-column injector was evaluated for this congener optimizing pre-column and column length. A coated retention gap (50 cm of length, 0.53 mm I.D., 0.15 mu m d(f)) connected to a short capillary column (7 m of length, 0.32 mm I.D., 0.25 mu m d(f)) showed the better sensitivity and repeatability. Finally, a double system based on the programmed temperature vaporizer injector/MS detector (for tri- to hepta-BDEs) and on-column injector/electron-capture detector (for BDE-209) was evaluated using two candidate certified materials (fish muscle tissue and river sediment)
Contamination by polybrominated diphenyl ethers of sediments from the Lake Maggiore basin (Italy and Switzerland)
No full textPolybrominated diphenyl ethers (PBDEs) are characterized by chemical properties and toxicological profiles similar to other POPs (persistent organic pollutants) included in the EU Priority Pollutant List (2455/01/CE). However, limited data have been available for these compounds thus far for Italian freshwater abiotic matrices. Lake Maggiore basin, a heavily industrialized and densely populated area, was selected for studying PBDE contamination in Italy. PBDEs and OCs (organochlorine compounds) in the basin were quantified by analysing both sediment cores collected in 2005 from the lake and grab samples from the main tributaries and the emissary. Fourteen PBDEs, from tri-BDE to hepta-BDE congeners and BDE209, were compared with some organochlorine POPs (PCBs and DDTs) characterizing Lake Maggiore basin contamination. Analyses of tri-to hepta-BDEs, PCBs and DDTs were undertaken by GC-MS/MS, while BDE-209 was analysed by GC/ECD. Results showed a dominant presence of BDE-209 (>95% of ΣBDE) and limited amounts of BDE-47, BDE-99, BDE-100, BDE-153 and BDE-154. Lake core profiles highlighted a decreasing trend in PCB concentrations starting from the year 2000, while PBDEs showed greater concentrations after the beginning of the 1990s (up to 30 ng g-1 d.w.). Among the tributaries, the Bardello and Boesio rivers were the most PBDE-contaminated (up to 290 ng g-1 d.w.)
Seasonal changes and temperature-dependent accumulation of polycyclic aromatic hydrocarbons in high-altitude soils
No full textPolycyclic Aromatic Hydrocarbons (PAHs) are a group of priority pollutants whose occurrence in the environment is mainly of anthropogenic origin. In this paper, the effect of the slope exposure on the PAH contamination and the seasonal change of the PAH concentrations in soils were discussed on the base of several soil samples taken on three dates in 2007 (early May, end of July and beginning of November) from the south and north aspect at 1900 m a.s.l. on the central Italian Alps. The first characteristic was the higher PAH contamination in soils from the north in comparison to those from the south in all seasons. The North-South Enrichment Factors were calculated as the ratio between the north and the south concentration, giving a range from 1.4 to 1.9 for lighter PAHs (from 2 to 4 rings). These values were in agreement with theoretical calculations based on temperature-specific octanol-air partition coefficients (predicted North-South Enrichment Factors from 1.6 and 2.0). For heavier PAHs (from 5 to 6 rings), lower differences were observed according to the gas/particle distribution of these compounds. A second finding was the consistent differences in normalised concentrations during the three periods of the year. The majority of compounds showed a significant decreasing trend from the beginning of May to the end of July, according to the year cycle of the physical processes (deposition vs. volatilisation) and the biological processes (uptake and/or biotransformation). Only few compounds showed different trends presumably due to seasonal-specific local emission sources
Biomarker responses and contamination levels in crabs (Carcinus aestuarii) from the Lagoon of Venice: an integrated approach in biomonitoring estuarine environments.
No full textAn integrated biological–chemical approach is necessary to evaluate correctly the
environmental status of bodies of water, as suggested by the EU Water Framework
Directive. The shore crab Carcinus aestuarii, sampled in the Lagoon of Venice (NE Italy), was
used as a biomonitor species, and the chemical concentrations of 42 organic pollutants
(HCHs, PAHs, PCBs, DDTs, PBDEs), biological responses related to neurotoxicity (AChE
inhibition), detoxification mechanisms (CYP450 induction) and endocrine alterations
(vitellogenin-like protein induction) were measured at the same time. The responsiveness
of biomarkers as predictors (or descriptors) of chemical contamination was evaluated by
multivariate regression analysis, revealing good predictor potential for the selected
biomarkers. Biomonitoring in the Lagoon of Venice revealed a predominance of DDT and
PCB compounds, especially near industrial sites or large cities. Endocrine alterations, not
always correlated with the presence of measured compounds, were also detected in many
areas, suggesting exposure to compounds able to interfere with the crab endocrine system
Organochlorine pesticide residues in sediment cores of Sunderban wetland, Northeastern part of Bay of Bengal, India, and their ecotoxicological significance
No full textThis paper presents the first comprehensive report of the organochlorine pesticide residues (OCs) such as hexachlorocyclohexane isomers (HCHs), dichlorodiphenyltrichloroethane and its six metabolites (DDTs), and hexachlorobenzene (HCB) in core sediments (<63-μm particle size) from the Indian Sunderban wetland. The pooled mean values of the mass fraction of ΣHCHs, HCB, and ΣDDTs in the sediments were 0.05–12, 0.05–1.4, and 0.05–11.5 ng g−1 dry weight, respectively. The vertical distribution of pesticides reveals an erratic pattern. The concentration of four isomers of HCHs reveals a heterogenic distribution where γ-HCH (lindane) and β-HCH shared the dominant part. The mass fraction of HCB did not show any sharp spatial variation. The prevailing sequence of DDT metabolites indicates an active degradation of the parent compound in the sediments and/or inputs of already degraded pp’DDT to the region. Peak concentrations of HCH isomers and DDT metabolites have the potential to induce ecotoxicological impact as per the sediment quality guidelines
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
- …
