1,720,964 research outputs found
LOCAL AND REGIONAL DISTRIBUTION OF POPS IN MOUNTAIN ENVIRONMENTSEVALUATION OF BURDEN AND FLUXES IN BIOTIC AND ABIOTIC MATRICES
Full text linkIn this work some of the main factors that influence the partition and distribution of POPs in mountain environments and the behaviour of pollutants inside a pasture environment are evidenced. The variability of contamination at a local scale has been deeply analyzed in the main study area of the Andossi plateau, giving some useful information about the dependence of contamination from seasonality, soil and meteorological features.
With the findings of chapter II (which gave a good definition of the horizontal, vertical and seasonal variability of contamination at local scale) and the modeling of chapter III it is possible to integrate a set of simple data (about OM content and soil temperatures) with concentration data from few samples to obtain detailed maps of potential contamination and release in a mountain environment. By knowing the local variability with a high definition it is possible to draw realistic pictures of concentration into complex alpine environments and evaluate exposure risk for the local fauna or for the domestic animals grazing on alpine pastures.
In chapter IV it is reported the first field work about the different retention potential of humic substances. OM is generally considered in POPs distribution papers as a whole indistinct component of soil and its effect is only viewed as quantitative (general direct relationship between OM content and POPs concentration), but the different retention potential of humin, humic acids and fulvic acids may change this view. Moreover the three humic substances have different behaviour in terms of mobility and general ability to distribute vertically and horizontally within the soil affecting the transport of the pollutants adsorbed.
In chapters V and VI the distribution into biotic matrices has been evaluated, evidencing a strict relation between soil and vegetation contamination (taking also into account local variability due to different solar exposition) and also a good relation between POPs concentration in vegetation and milk. Seasonality of contamination and grazing location could lead to different intake of contaminants by cows and so higher or lower milk contamination.
The first POPs contamination data in the Mt.Meru area (Tanzania) have been reported in chapter VII and some of the findings about regional scale distribution factors have been confirmed in an equatorial area
Highly spatially- and seasonally-resolved predictive contamination maps for persistent organic pollutants : development and validation
No full textA reliable spatial assessment of the POPs contamination in soils is essential for burden studies and flux evaluations. Soil characteristics and properties vary enormously even within small spatial scale and over time; therefore soil capacity of accumulating POPs varies greatly. In order to include this very high spatial and temporal variability, models can be used for assessing soil accumulation capacity in a specific time and space and, from it, the spatial distribution and temporal trends of POPs concentrations. In this work, predictive contamination maps of the accumulation capacity of soils were developed at a space resolution of 1 × 1 m with a time frame of one day, in a study area located in the central Alps. Physical algorithms for temperature and organic carbon estimation along the soil profile and across the year were fitted to estimate the horizontal, vertical and seasonal distribution of the contamination potential for PCBs in soil (Ksa maps). The resulting maps were cross-validated with an independent set of PCB contamination data, showing very good agreement (e.g. for CB-153, R2 = 0.80, p-value ≤ 2.2 . 10−06). Slopes of the regression between predicted Ksa and experimental concentrations were used to map the soil contamination for the whole area, taking into account soil characteristics and temperature conditions. These maps offer the opportunity to evaluate burden (concentration maps) and fluxes (emission maps) with highly resolved temporal and spatial detail. In addition, in order to explain the observed low autumn PCB concentrations in soil related to the high Ksa values of this period, a dynamic model of seasonal variation of soil concentrations was developed basing on rate parameters fitted on measured concentrations. The model was able to describe, at least partially, the observed different behavior between the quite rapid discharge phase in summer and the slow recharge phase in autumn
The effect of the organic matter composition on POPaccumulation in soil
No full textThe effect of different humic fractions on polychlorinated biphenyl (PCB) contamination in soils was tested in the field by means of 53 soil samples from a high altitude grassland plateau in the Italian Alps. The three humic fractions (humin, humic acids and fulvic acids) were characterised in parallel by quantifying 12 PCB congeners to establish a direct relationship between PCB levels and humic fraction concentrations. Humin (the most hydrophobic fraction) appears to be the most closely correlated with the amount of PCBs in soil (R2 = 0.83), while fulvic acid shows the lowest correlation (R2 = 0.49). The idea of preferential sorption of hydrophobic compounds in the humin fraction is discussed, and the humin carbon content (fhuminC) is proposed as an improved parameter for evaluating the potential for POP accumulation in soils, replacing total organic carbon (foc). Congener studies revealed that penta- and hexa-substituted-CBs show the optimal combination of physicochemical properties for equilibrating with the humin content in soil. Moreover, fhuminC/foc is conceptually equivalent to the empirical coefficients used in predictive Ksa equations. In our samples, the fhuminC/foc was 0.55, a value in between the empirical coefficients proposed in the literature. In predictive equations, the use of fhuminC instead foc avoids the necessity of using an empirical parameter for a ‘generic’ condition by introducing an experimental parameter (fhuminC) that takes into account a local conditions (organic matter composition)
Background levels of polybrominated diphenyl ethers (PBDEs) in soils from Mount Meru area, Arusha district (Tanzania)
No full textThis study investigates the contamination by 13 polybrominated diphenyl ether (PBDE) congeners in an altitudinal soil transect on Mt. Meru area, Northern Tanzania. A ∑13PBDEs mean concentration of 386±200pg/g d.w. (4900±3500pg ∑13PBDEs/g soil organic matter - SOM) was measured, pointing out that, in a prevalently agricultural area from the southern hemisphere, PBDE contamination can be even higher than in similar semi-remote environment of industrialized country of the northern one. The Mt. Meru PBDE pattern of contamination was characterized by the prevalence of intermediate brominated congeners (tetra- and penta-BDEs). Among the detected compounds, BDE-47 was the main congener, followed by BDE-99, BDE-190 and BDE-100. The distribution of PBDEs confirmed that organic carbon had a substantial impact on their accumulation in Tanzanian soils. The altitudinal profile of PBDEs (log TOC-normalized concentrations) fitted a second order polynomial model with altitude, with an initial concentration decrease, interpreted as a dilution effect from local/regional sources, and a following consistent increase with altitude according to the cold condensation theory. Evidences of distillation effect among PBDE congeners were also observed
Environmental variables affecting the distribution of POPs on Mt. Meru, Tanzania
No full textTanzania is an equatorial country characterized by warm temperatures, which should increase the volatilization of persistent organic pollutants (POPs), but this scenario could be different in mountainous areas like Mount Meru, a volcano situated in the East African Rift (Tz). We collected soil samples along an altitudinal transect upto 4577 m a.s.l., reporting the first data about POP contamination in this area (DDX, HCHs, HCB and PCBs). The DDX contamination pattern in Mt. Meru shows levels slightly higher than those of other remote places with a strong increase in the metabolites/DDT historical trend, which is different from DDX, PCBs, HCHs and particularly HCB as this shows very low contamination levels. Back trajectory analysis allowed a discussion about putative contamination sources, while analysis of the environmental features (climatic and pedological) allowed us to discriminate their relative importance. The distribution of POPs shows a strong correlation with soil organic matter and vegetation. SOM-normalization evidenced altitudinal dependence according to cold condensation for PCBs and HCHs, while DDX are present in larger amounts in the agricultural area at the volcano foot. OM-normalized concentrations suggested also a possible role of the OM composition on the POPs' distribution
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
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