A COMPARISON OF NORTH-AMERICAN AND WEST-EUROPEAN OYSTER EMBRYO-LARVAL TOXICITY TESTS ON NORTH-SEA SEDIMENTS

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 carried 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 toxicity at the most contaminated sites on the German Bight transect, but data were not consistent on the drilling 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.