Towards enhancing tidally-induced water renewal in coastal lagoons

Environmental Fluid Mechanics - In order to address the problem of limited water renewal in restricted lagoons of moderate size having at least two tidal inlets, a method is proposed to enhance...     

Polychlorinated biphenyls in marine sediments from the southern North Sea and Scheldt estuary: a ten-year study of concentrations, patterns and trends

The paper reports the concentrations and patterns of CBs in sediments of the Belgian part of the southern North Sea and the Scheldt estuary for the period 1991-2001. The long-term analytical performance was well within the quality assurance boundaries set at the outset of the study and is consistent with the state of the art for this type of analysis. The CB concentrations (given as the median of the sum of IUPAC Nos 28, 52, 101, 118, 138, 153 and 180) vary between 0.1 microg kg(-1) and 50 microg kg(-1) dry weight in the total sediment and it could be demonstrated that CB patterns in the fine fraction of the sediment were closely similar throughout the investigated area. Isolation of the fine fraction (<63 microm) by sieving can be regarded as a physical normalisation to reduce the differences in sediment granulometric composition. It allows for a better understanding of CB distribution and patterns and improves the trend analysis. A significant downward trend could not be found at any of the stations, which suggests that CB levels have not been changing in the area of interest in the past decade.     

Vegetation as an indicator of environmental changes

Composition of the vegetation and the properties of its environment are related, as was shown by research. In these, mostly statistical-correlative studies, both the vegetation and some growth factors, such as plant nutrients and moisture supply were analyzed and studied on interdependence. At present the environmental conditions can be estimated in the field from the floristic composition with regard to differences both in the combination of plant species and in their relative biomass production. With a vegetation survey the spatial pattern of the different environmental conditions can be indicated. For instance, the places where moisture supply gradients occur can be detected, also a better understanding is obtained of the environmental equalization and the decreasing number of plant species and spatial diversity. Conclusions can be drawn about changes in the vegetation to be expected, from the combined occurrence of, a terrestrial vegetation indicating an eutrofied environment and a water vegetation indicating a relatively oligotrophic environment. By comparing vegetation recordings of the past and present, environmental changes that have occurred in the same place can be indicated. By vegetations situated in different places in relation with soil profile properties the consequences of environmental changes can be predicted. For instance, lowering of the ground water table and intensifying the agricultural use. On the other hand, measures can be suggested to increase the biological value of land and water, for instance, indication of seepage areas and floristically rich areas in the field.     

Rat metabolism of polychlorinated dibenzo-p-dioxins

In rats, dibenzo-p-dioxin, 1-chlorodibenzo-p-dioxin, 2-chlorodibenzo-p-dioxin, 2,3-dichlorodibenzo-p-dioxin, 2,7-dichlorodibenzo-p-dioxin, 1,2,4-trichlorodibenzo-p-dioxin and 1,2,3,4-tetrachlorodibenzo-p-dioxin are metabolized to mono- and dihydroxy derivatives, whilst in case of dibenzo-p-dioxin and both the two monochloro isomers, also sulphur containing metabolites are excreted. Primary hydroxylation exclusively takes place at the 2-, 3-, 7- or 8-position in the molecule. In none of the experiments metabolites resulting from fission of the C-O bonds (ortho, ortho'-dihydroxychlorodiphenyl ethers, chlorocatechols) or hydroxylated derivatives thereof, were detected. No metabolites were found from octachlorodibenzo-p-dioxin.     

Determination of metoxuron and 3-chloro-4-methoxyaniline via direct derivatization with heptafluorobutyric anhydride and GC-ECD

The phenylurea herbicide metoxuron and its main metabolite, 3-chloro-4-methoxyaniline, can be determined rapidly in aqueous samples via extraction, derivatization with heptafluorobutyric anhydride (HFBA), washing with an aqueous bufferof pH 8, and analysis by capillary GC with electron capture detection. Linear calibration curves are obtained over two orders of magnitude, and the detection limit for the HFB derivatives is about 0.5 pg. The method has successfully been applied to several types of water samples.     

Environmental chemistry of PCB-replacement compounds - V - the metabolism of chloro-isopropylbiphenyls in fish,frogs, fungi and bacteria

The metabolism of 2,5-dichloro-4'-isopropylbiphenyl and 4-chloro-4'-isopropylbiphenyl, two model compounds for alkylated chlorobiphenyls (Chloroalkylenes), has been investigated in fish, frogs, fungi and mixed cultures of bacteria. Fish (Carassius auratus) and frogs (Rana aesculenta) show a very limited metabolism of these compounds. A pure strain of fungus (Cunninghamella echinulata Thaxter) metabolized 2,5-dichloro-4'-isopropylbiphenyl both by stepwise oxidation of the isopropyl group to 2,5-dichloro-4'-biphenylcarboxylic acid and by hydroxylation of the chlorine substituted phenyl ring. A mixed culture of aerobic bacteria from activated sludge shows extensive degradation of 4-chloro-4'-isopropylbiphenyl to p-chlorobenzoic acid via stepwise oxidation of the isopropyl group when using the compound as sole carbon source. However, in the presence of D-glucose as additional carbon source, no metabolism is observed.