The assessment of a no-effect concentration of oil in thermally treated OBM drill cuttings for marine benthos : ecotoxicity

This report describes the results of research on the possible effects of discharges of thermally treated cuttings on a North Sea macrobenthic community. Experiments were performed in boxcosms with intact sediment sections collected in the "Frisian Front" area. The boxcosms were stocked with a test species (Echinocardium cordatum) and discharges were simulated by artificially dosing various amounts of SCS cuttings. Because the effect of the resulting oil concentrations in the sediment was questioned, a complementary amount of uncontaminated material was added to the lower doses to standardize the total amount of material dosed. To this end SCS cuttings were used that were cleaned from any organic material by combustion at 550 oC. The standard amount was in correspondence with the maximum amount to be expected at 100 m from an imaginary discharge point, as calculated by a simulation model. Two types of controls were used, viz. one without any addition and one with addition of the standard amount of combusted cuttings, to test possible effects due to the composition of the oil-free material dosed. Biological effects are described in terms of observed lethal and sublethal effects in test animals and estimated mortality rates among natural infauna species.