Marc Elskens

Bio: Marc Elskens is an academic researcher from Vrije Universiteit Brussel. The author has contributed to research in topics: CALUX & Phytoplankton. The author has an hindex of 32, co-authored 147 publications receiving 3926 citations.

Accumulation of trace metals in the muscle and liver tissues of five fish species from the Persian Gulf.

Abstract: In this study, concentrations of 16 elements were quantified in muscles and livers of 141 fishes belonging to five commercially species. It was also our intention to evaluate potential risks to human health associated with seafood consumption. The grunt, flathead, greasy grouper, tiger-tooth croaker and silver pomfret fish species were obtained from Abadan, Deylam, Bushehr-Nirogah, Dayyer port, Lengeh port and Abbas port in Hormozgan, Bushehr and Khozesran provinces at the Iranian waters of the Persian Gulf. The contents of Al, As, Be, Cd, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, Sb, Tl, V and Zn in fish muscles and livers were determined by Inductively Coupled Plasma Mass Spectrometry (ICP MS), after digestion in a CEM (Mars 5) microwave oven using nitric acid and hydrogen peroxide. Our results indicated that almost all metals were more accumulated in younger flathead, greasy grouper and tiger-tooth fishes. Contrary to the other fish species, grunt seems to stronger accumulating elements in the older fishes. Strong and positive correlations were observed in three or more of the fish species between V, Al, Fe, Tl, Co and Pb. The results confirmed that fish muscle and liver tissues appeared to be good bio-indicators for identification of coastal areas exposed to metallic contaminants. The results also showed that the element levels in the muscles of all fishes in our study were lower than the maximum allowable concentrations and pose no threat to public health, except for arsenic.

Linearity of calibration curves: use and misuse of the correlation coefficient

Abstract: The correlation coefficient is commonly used to evaluate the de- gree of linear association between two variables. However, it can be shown that a correlation coefficient very close to one might also be ob- tained for a clear curved relation- ship. Other statistical tests, like the Lack-of-fit and Mandel's fitting test thus appear more suitable for the validation of the linear calibration model. A number of cadmium cali- bration curves from atomic absorp- tion spectroscopy were assessed for their linearity. All the investigated calibration curves were characterized by a high correlation coefficient (r >0.997) and low quality coeffi- cient (QC <5%), but the straight-line model was systematically rejected at the 95% confidence level on the ba- sis of the Lack-of-fit and Mandel's fitting test. Furthermore, significant- ly different results were achieved be- tween a linear regression model (LRM) and a quadratic regression (QRM) model in forecasting values for mid-scale calibration standards. The results obtained with the QRM did not differ significantly from the theoretically expected value, while those obtained with the LRM were systematically biased. It was con- cluded that a straight-line model with a high correlation coefficient, but with a lack-of-fit, yields signifi- cantly less accurate results than its curvilinear alternative.

Metabolism and functions of glutathione in micro-organisms.

Abstract: Publisher Summary The chapter discusses the biologically relevant chemistry of glutathione (GSH) and its occurrence in microbial cells The GSH-related biochemical reactions and the physiological roles of GSH are summarized The biosynthesis of GSH is remarkable in two ways: it is mRNA independent, and the glutamic residue is joined in an unusual peptide linkage of the γ -carbon atom to the cysteine residue Due to this structural peculiarity, GSH is protected against proteolytic cleavage The GSH status of cells is defined by the total concentration of GSH and the nature and distribution of the possible forms of occurrence of the tripeptide in the cell GSH and related compounds are widespread in the microbial world, especially amongst organisms with an aerobic lifestyle This observation emphasizes the role of GSH in cellular protection against by-products generated by oxidative metabolism, but it does not limit its functions to this role Glutathione acts as an enzyme cofactor, transport component, nucleophilic substrate, and sulphur reservoir; and participates in key cellular processes such as protein synthesis and degradation, regulation of enzyme activity, synthesis of DNA, and maintenance of the integrity of cell membranes and organelles Having a functional diversity, GSH is interrelated with a number of metabolic pathways and its intracellular modulation could have an impact on the entire cell, making it extremely difficult to associate directly a given cellular end-point with one molecule or system Both in Escherichia coli and Saccharomyces cerevisiae, GSH plays an important role in cellular protection during chemical stresses in spite of the fact that key enzymes of detoxification, such as GSH peroxidase and GSH S-transferase, remain at a low level

Bioconcentration and Biomagnification of Mercury and Methylmercury in North Sea and Scheldt Estuary Fish

Abstract: Total Hg and MMHg concentrations were assessed in more than 350 fish and shellfish samples. Hg concentrations in Greater North Sea fish of prey range from 0.039 mg kg 1 wet weight (ww; for ray) to 0.61 mg kg 1 ww (for dogfish) and for all other fish species, from 0.045 mg kg 1 ww (for plaice) to 0.33 mg kg 1 ww (for sand sole), with 95 2% of the Hg content in the MMHg form. In Belgian coastal zone, fish concentrations range from 0.063 mg kg 1 ww for plaice to 0.13 mg kg 1 ww for flounder, with 82- 87% of the Hg content in the MMHg form. In fish of the Scheldt, which is a very polluted estuary, Hg levels, as well as the percent MMHg of the total Hg, were lower than in the two zones previously mentioned. The intraspecies variability is of the order of 50% in each of the three zones. In liver tissue, a much larger variability was observed than in muscle tissue, except for fish species of the Scheldt. In most cases, the MMHg fraction in a particular fish species is inversely related to the intraspecies variability. Bioconcentration and biomagnification factors (BCF and BMF, respectively) were assessed. MMHg-BMFs were a few orders of magnitude higher than Hg(inorganic)-BMFs, and for the same species were always highest in the Greater North Sea and lowest in the Scheldt. For each of the Belgian coastal zone four species, a weak positive correlation between Hg content and fish length was found; however, the larger the size-range, the better the correlation. Taking fish length into account, a statistically significant difference in contamination level was observed for species sampled from the different geographical zones.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Input Output Analysis Foundations And Extensions

Abstract: Thank you very much for reading input output analysis foundations and extensions. As you may know, people have search hundreds times for their chosen readings like this input output analysis foundations and extensions, but end up in infectious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they are facing with some malicious virus inside their desktop computer.