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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.

The effect of controlled pH and dissolved oxygen (DO) tension on the production of total glucosyltransferase activity (GTF), extracellular GTF and alternansucrase was studied in controlled batch fermentations of Leuconostoc mesenteroides NRRL B‐1355. Controlled aeration had a positive effect on the production of extracellular GTF in pH‐uncontrolled fermentations. An aerated batch fermentation controlled at 90% DO at controlled pH 6·7 resulted in complete utilisation of the carbon source. At controlled pH 5·5, maximal extracellular GTF (0·6 U cm−3), total GTF (3·4 U cm−3) and alternansucrase activities (1·2 U cm−3) were higher in a controlled aerated (75% DO) batch fermentation than in a non‐aerated batch fermentation. Acetic acid production was lowest in the non‐aerated fermentation process. Controlled DO batch fermentations carried out at pH 5·5, 6·0 and 6·5 resulted in an increasing energy efficiency. While highest alternansucrase activity (1·5 U cm−3) occurred in pH 6·5 controlled batch cultures, the highest total GTF activity (3·4 U cm−3) was found in the pH 5·5 controlled fermentation. © 1997 SCI.

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