The present study has been performed by the Section for Ecotoxicology and Risk Assessment at the Norwegian Insitute for Water Research (NIVA) under the auspices of the Water Column Monitoring survey 2007. The work was funded by Norsk olje og gass (Norsk olje og gass) and key oil production companies operating on the Norwegian sector of the North Sea. The authors are grateful to Tor Fadnes (StatoilHydro) and the personnel at Statfjord C for supplying the produced water.