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Karakterisering af havnesediment ved hjælp af biotest Summary and conclusionUsually harbour sediments are contaminated with chemical substances to a larger or smaller extent dependent on the types of ships frequenting the harbours, the types of cargo transported via the harbours and the related land-based activities. The contaminants may directly affect the sediment fauna as harbour sediment has proven often to be acutely toxic to sediment-living organisms. Moreover, contaminants may to some extent leach to the pelagial water both by resuspension of the sediment as the result of the water current conditions and navigation activities and by dredging and subsequent dumping in the sea. This may result in also pelagic organisms being at risk of exposure and toxic effects. In this project, an assessment of ecotoxicological test methods for the examination of the toxicity of contaminated harbour sediments was made. It was evaluated whether the methods were suitable for characterising the content of environmental pollutants in the sediments and for assessment of potential effects in connection with the handling and dredging and dumping of sediments. Three different methods were selected and tried out for test of sediments (tests with amphipods, mussels and brittle stars, respectively) and three methods for test of sediment extracts (copepods, planktonic algae and bacteria (the Microtox test system)). The methods were tested in tests of sediments from four stations (Copenhagen, Odense and Horsens harbours and one reference station from the open waters). Tests were performed of both sediments and sediment extracts so that dredging and dumping of sediment were simulated. The applied tests for survival are relatively insensitive to the partly heavily polluted sediments while effects on behaviour are registered to a greater extent. On the basis of the short-term tests and assessments made, a test strategy can be proposed including potential methods for characterisation of contaminated harbour sediments. At the drawing-up of the test strategy, it was taken into account that the test results do not necessarily have to directly reflect the analytically determined concentrations of chemical substances as ecotoxicological test of sediments or their extracts should be regarded as a supplement to chemical analyses. By such a supplement, a more graduated picture may be achieved of the level of contamination of the sediments than can be achieved by performing only chemical analyses or ecotoxicological tests. On the face of it, the costs of biological testing of a sediment sample will be in approximately the same order as the costs of carrying out an exhaustive chemical analysis programme. In this study, no attempts have been made to prioritise the different test methods as the actual application should reflect the purpose of the testing and as some of the methods require further development and standardisation. The following methods are recommended:
The results of the ecotoxicological tests were compared with the content of chemical substances (in both sediments and sediment extracts), which had been determined by chemical analysis. As a measure of the environmental impact, the total risk quotient (RQ) was calculated for each sample. The risk quotient is defined as the ratio of the measured concentration to the sediment quality standard for each individual substance and is summed up for all the measured substances. If a total risk quotient exceeds 1, theoretical risks of ecotoxic effects will exist. By comparing the calculated risk quotients with the measured effects, it is obvious that there is a large gap between the level of contamination, at which risks of ecotoxic effects may be assumed (i.e., RQ > 1), and the level of contamination, at which effects are measured in biological short-term tests. Acute mortality can only be measured at RQ ³ 7-10,000 while behavioural effects are measurable at RQ = 3,000 with the test methods applied in this study. This difference can be explained by various facts, i.e., on the one hand that the chemical substances sorb to the sediment content of organic matter and particles thereby limiting the bioavailability and that the total effect of the chemical substances in combination is less than the sum of the effects of the individual substances, and on the other that the applied short-term tests are not sufficiently sensitive to measure ecotoxic effects. It is estimated that the real effect limit measured by RQ will be somewhere in the interval <100-1,000 but it has not been possible on the basis of the tests performed in this study to make a closer estimate. It thus appears that on the basis of only chemical analyses, it is not possible to lay down a limit for the level at which ecotoxic effects can be expected. Nor is it, however, possible to lay down such a limit on the basis of the biotest methods tested in this study. It would be conservative to choose the results from chemical analyses combined with sediment quality standards as a starting point but such a basis for a regulation would probably not be realistic as practically all harbour sediments would then be considered as environmentally hazardous. Therefore, there will be a need for further method development within both bioavailability and sublethal or chronic biotesting with sediment-living species before limits for the environmental hazard of contaminated sediments can be established.
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