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(M/MF194) Evaluation of PAH laboratory ecotoxicity studies with marine plankton enclosures. Jak, Robbert1, Johnsen, Hanne2, Smit, Mathijs1, Buffagni, Melania3, 1 2 3 ABSTRACT- Several PAHs are among the substances that are expected to contribute most to the chronic toxicity of produced water discharged from offshore oil production platforms. In order to assess the ecotoxicity of a number of PAHs, and also alkylated phenols, laboratory experiments were set-up with the marine copepod Acartia tonsa (see abstract Johnsen et al.). These experiments included acute, and chronic tests in which the exposure concentration was controlled. In the receiving environment of produced water, however, plankton organisms experience decreasing concentrations of contaminants, due to o.a. dilution and degradation. In order to evaluate the laboratory derived toxicity data, and to mimic exposure in a natural environment, enclosure studies were performed with marine water, including natural plankton communities. Two PAHs were selected as model compounds, viz. naphthalene and phenanthrene. A regression design experiment was set up with single treatments of 6 concentrations of each substance, next to 4 control systems. Results show that although phenanthrene disappeared more rapidly from the water column (DT50 approx. 2 days), it was more toxic than naphthalene, as was also predicted from the laboratory tests. Toxic concentrations from the enclosure experiments were high in comparison to the chronic toxicity experiments, due to the decreasing exposure concentrations. Reduced copepod grazing resulted in enhanced phytoplankton development in the high dosed phenanthrene systems. The results from the enclosure test provides data to evaluate the outcome of the risk assessment tool DREAM (Dose related Risk and Effect Assessment Model) for environmentally realistic conditions. Key words: semi-field effects, pah, plankton communities |
