1,720,972 research outputs found
TOXICITY EVALUATION OF PLASTIC NANOPARTICLES ON AQUATIC ORGANISMS
Full text linkPlastics are an immense family of unique and versatile materials which play an essential role in modern society and are an indispensable part of our daily lives. With a global production of nearly 440 million tons in 2019, plastic waste has been described to accumulate in virtually any environment, from marine to freshwater ecosystems. The irreversibility and global ubiquity of marine plastic pollution has turned plastics into a potential planetary boundary threat. Nanoplastics (NPs) represent the smallest fraction of plastic litter and can result in the environment as the degradation products or larger plastic items. Nevertheless, only recently such particles have been detected in real environments, albeit not yet accurately quantified. Although today there is still a lack of clarity as regards their toxicological effects, the high exposure potential, together with the physical and chemical heterogeneity of NPs, the likely significant diffusive release of plastic additives and adsorbed substances, combined with their small size and enhanced accessibility to biological tissues, potentially make NPs highly hazardous pollutants. Ecological risk assessment of nanoplastics are urgently needed. In the absence of reliable environmental exposure estimates to date, ecotoxicological research has focused on defining a hazard assessment of NPs. This thesis aimed at investigating the mechanism of toxicity of NPs, taking advantage of high-throughput sequencing technologies. In an initial experiment, described in Chapter 2, adult specimens of the freshwater benthic crayfish Procambarus clarkii were exposed to 100 μg of 100 nm carboxylated polystyrene nanoparticles in a 72h dietary exposure experiment. The cosmopolitan red swamp crayfish Procambarus clarkii, is widely used as bioindicator of environmental pollution and was selected here as a representative non-model decapod of the freshwater ecosystem. An integrated approach was conceived to assess the biological effects of polystyrene NPs, by analyzing both transcriptomic and physiological responses. Total hemocyte counts, basal and total phenoloxidase activities, glycemia and total protein concentration were investigated in crayfish hemolymph at 0h, 24h, 48h and 72h to evaluate general stress response over time. Transcriptomes of hemocytes and hepatopancreas were analyzed after 72h. At the physiological level, crayfish were able to compensate for the induced stress by not exceeding the generic stress thresholds. The RNA-Sequencing analysis revealed the altered expression of few genes involved in immune response, oxidative stress, gene transcription and translation, protein degradation, lipid metabolism, oxygen demand, and reproduction in P. clarkii exposed to NPs. Activation of oxidative stress pathways and inflammatory responses has been widely recognized as primary molecular mechanisms of NPs-induced toxicity, in agreement with our findings. In particular, we note an alteration of several genes related to the ubiquitin-proteasome system, one of the major degradation pathways for maintaining cellular protein homeostasis, which has not been described before. Moreover, a rather clear transcriptomic response to NPs emerged as a strong downregulation of vitellogenin expression in the hepatopancreas of female crayfish, which may indicate a shift in energy allocation induced by plastic exposure from reproduction to organism maintenance, as previously advocated. This finding may provide the basis for a deeper exploration of the potential population-level effects of nanosized polystyrene particles. Overall, this study suggests that a low concentration of PS NPs may induce mild stress in crayfish, and sheds light on molecular pathways possibly involved in nanoplastic toxicity. In Chapter 3 we examined the underlying mechanism of NPs toxicity in a sensitive early developmental stage of a key marine invertebrate species, the bivalve Mytilus galloprovincialis
L’importanza dell’elaborazione statistica nella valutazione del pericolo potenziale da organoclorurati nella stenella striata (Stenella coeruleoalba) del Mar Mediterraneo
No full textS.T.R.E.S.S. (Statistical Toxicological Risk Elaboration System in Stenella coeruleoalba) from organochlorine compounds (OCs): white (no hazard) or red (emergency) code?
No full textMERCURY LEVELS IN SEVERAL SPECIES OF CETACEANS IN THE WORLD: A REVIEW
No full textThis review summarizes the significant amount of data which was published on mercury (Hg) in cetacean species all over
the world, since the first manuscript was printed in 1971 regarding the Hg in a Pacific pilot whale stranded in San Clemente
Island (California - USA) (Hall et al., 1971). The aim of this paper is to provide a snapshot on existing peer-reviewed
papers and technical reports on levels and spatial and temporal trends of this contaminant in different species of cetaceans,
and provide an initial evaluation on which species should be considered more at risk for mercury and in what water basins
Monk seals (Monachus monachus) in the Mediterranean Sea: The threat of organochlorine contaminants and polycyclic aromatic hydrocarbons
Full text linkThe Mediterranean monk seal (Monachus monachus) is an emblematic species of conservation concern. Anthropogenic pressures have led to severe population declines and significant fragmentation of the remaining populations. Because of their close relationship with coastal areas, Mediterranean monk seals may be potentially exposed to pollution from agricultural sources, as well as from oil tanker spills. Although monitoring of pollution has long been considered a priority for this species, data on monk seal contamination levels are scarce. In this study, 55 blubber samples of all genders and age classes collected during necropsies (1995-2013) from seals of the Eastern Mediterranean subpopulation were analyzed for organochlorine compounds (OCs), i.e., hexachlorobenzene (HCB), polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDTs), and polycyclic aromatic hydrocarbons (PAHs). Overall, PCBs > DDTs ≫ PAHs > HCB in all samples. Results showed a significant downward trend over the 19-year period for DDTs and HCB. No marked pattern was found for PAHs, even though relative abundance of cancerogenic PAH fraction rose in recent years. PCB levels in subadult specimens increased noticeably over time despite worldwide ban. Our findings did not suggest recent releases of DDT or new pesticides (e.g., Dicofol) in the environment, but may indicate an improper disposal of ancient storages of PCBs or a remobilization from reservoirs. OC levels exceeded thresholds that are commonly associated with immunosuppression and reproductive impairment in other pinnipeds. Hence, OCs could be responsible of potential toxicological effects in this subpopulation. This study represents the first report on PAH and one of the few reports on OC bioaccumulation in Mediterranean monk seals. Based on the levels found in the blubber of monk seals from the Eastern Mediterranean, and given the known harmful effects associated to the prolonged exposure to these substances and the reduced long-term expectations of species recovery, regular monitoring is advocated
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
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