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Toxicity testing of whole sediments was conducted as part of the Bremerhaven Workshop designed to test various methods (chemical and biological) for assessing the status of North Sea waters, sediments and biota. Six investigators from 4 countries were involved; laboratory testing was conducted after transporting field-collected sediments distances varying from tens of miles to thousands of miles. Sediments were tested from 2 contamination gradients, one from an abandoned drilling site, and the other from the mouth of the Elbe northwest across the German Bight. Methods included 11 different tests (20 end-points), 3 species of amphipod, a polychaete, a clam, an oyster and a bacterium. Amphipod 10 d acute lethality tests and a 48 h oyster larvae abnormal development test most clearly determined gradients in toxicity that corresponded with chemical and in situ con~munity data. Lack of response was observed in Microtox and clam reburial tests. A polychaete growth test conducted in North America provided useful but not convincing information. A 24 h oyster larvae survival test conducted separately in England and The Netherlands gave results that were counter to the other tests and difficult to interpret. Survival and metamorphosis tests with older oyster larvae did not show consistent, interpretable gradients for the drilling site but did for the German Bight. The responsiveness of some tests may have been affected by a maximum 3 wk sediment holding time prior to testing; other tests did not provide usable information relative to either the burden of evidence of all tests, or corresponding chemical contamination data and benthic infaunal community structure. Based on the results of this workshop, currently the most useful sediment toxicity tests for general assessment and regulatory use in Europe are infaunal amphipod survival and 48 h oyster larval development tests.

During the Bremerhaven Workshop, sediment samples from 2 pollution gradients in the North Sea were tested in a 10 d static bioassay with infaunal amphipods. One gradient was downstream from a former drilling site, the second was offshore of the Elbe-Weser plume in the German Bight. Four participating laboratories used basically the same technique to test sediment toxicity with 1 of 3 different amphipod specles: Rhepoxynius abronius, Corophium volutator or Bathyporeia sarsi. The measured endpoints were mortality and sublethal effects, including the inability to reburrow after exposure, avoidance and immobilisation. Results show that sediment samples from the stations on each gradient closest to contaminant sources were toxic to nearly all test species. Samples from other stations only caused mortality in the tests with C. volutator.

ABSTRACT. During the Bremerhaven Workshop, Pacific oyster embryos Crassostrea gigas were exposed both directly to sediment and to elutriates of sediment from 2 transects through contamination gradients in the North Sea. One transect consisted of 7 stations down-current from an abandoned drilling site off the Dutch coast. The other transect comprised 9 stations in the German Bight positioned in a northwesterly direction from the Elbe-Weser plume out to the Dogger Bank. The toxicity tests, conducted by 4 research laboratories, were carned out either immediately following sediment sampling on board a research vessel, or after periods of up to 4 wk after sediment collection at mainland laboratories in the UK, Canada and The Netherlands. Oyster embryo-larval sediment elutriate tests showed highest levels of tox~city at the most contaminated sites on the German Bight transect, but data were not consistent on the drill~ng site transect. The optimal method of sediment elutriation should be determined by further studies. Oyster embryos exposed directly to sediment over a 48 h period identified the most toxic and contaminated sites from both transects and gave comparable results to infaunal amphipod acute toxicity tests. This study has demonstrated that oyster embryo-larval tests can easily be carried out on board a sea-going research vessel, although there is no absolute requirement to do so when sediment samples can be returned to mainland laboratories within a few days after collection.