SEDIMENT POREWATER TOXICITY ASSESSMENT STUDIES IN THE VICINITY OF OFFSHORE OIL AND GAS-PRODUCTION PLATFORMS IN THE GULF-OF-MEXICO

As part of a multidisciplinary program to assess the potential long-te rm impacts of offshore oil and gas exploration and production activiti es in the Gulf of Mexico, sediment chemical analyses and porewater tox icity tests were conducted in the vicinity of five offshore platforms. Based on data from sea urchin fertilization and embryological develop ment assays, toxicity was observed near four of the five platforms sam pled; the majority of the toxic samples were collected within 150 m of a platform. There was excellent agreement among the results of porewa ter tests with three different species (sea urchin embryological devel opment, polychaete reproduction, and copepod nauplii survival). The se diment concentrations of several metals were well in excess of sedimen t quality assessment guidelines at a number of stations, and good agre ement was observed between predicted and observed toxicity. Porewater metal concentrations compared with EC(50), LOEC, and NOEC values gener ated for water-only exposures indicated that the porewater concentrati ons for several metals were high enough to account for the observed to xicity. Results of these studies utilizing highly sensitive toxicity t ests suggest that the contaminant-induced impacts from offshore platfo rms are limited to a localized area in the immediate vicinity of the p latforms.