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(440) Consistency in the bioassay-based evaluation of contaminated marine and fresh water dredged sediments. Brils, Jos1, Foekema, Edwin1, Jak, Robbert1, 1 ABSTRACT- Different bioassays have been developed to evaluate the risks of contaminated dredged sediments (marine and fresh water). Since the contamination of both types of aquatic sediments is derived from land based (point and diffusive) sources, and because most sedimentation in the Netherlands occurs at tidal areas where a fresh to saline gradient is present, it makes sense to evaluate the actual risk with similar tools, i.e. bioassays using similar organisms. A study was performed to test the suitability of the fresh water species Chironomus riparius (midge larvae), and the marine species Corophium volutator (mudshrimp) for use at different salinities. Experiments were set up with pure marine and pure fresh water sediment, and different mixtures of both sediments. As overlying water, either natural fresh water, marine water, or a mixture of both was used, resulting in a wide range of salinities in the water column. The salinity tolerance of the bioassay species was tested, applying standardised tests; 28 day larval development and survival for C. riparius, and 10 day survival for C. volutator. The results show that both species give a good survival at salinities around 5 ‰. Moreover, it was shown that the fresh water species could be used to assess the effects of contaminated marine sediments, and the marine species for fresh water sediments, provided that overlying water has a salinity of approx. 5 ‰. Tests with contaminated harbour sediments show consistent responses for both bioassays, although differences in sensitivity were found. It is foreseen that these bioassays at a fixed salinity could be used to assess the actual risks of polluted marine and fresh water sediments. Furthermore, these bioassays were used in whole sediment TIE (Toxicity Identification Evaluation) studies. Key words: bioassays, dredged sediment, salinity, whole-sediment TIE |
