An experimental rig has been built to explore the relative contribution of oil droplets and water soluble fraction of oil to acute toxicity. The exposure principle was based on generating dispersion and establishing a dilution series by repeated dilution of this dispersion. For each dilution step the dispersion was diluted by 50 %. In order to separate the water soluble phase of the dispersions it was pumped through a filter consisting of fine glass wool in order to remove oil droplets. At each dilution step the resulting water soluble fraction (WSF) of the dispersion was used as exposure medium for determining LC50 of the WSF. This created a system of parallel series of dispersions in one group and their dissolved fractions in another group. The toxicity of the dispersions was thus directly compared to the water soluble fraction separated from the same dispersion.

This rig has also been tested on cod larvae (Gadus morhua) as well as C. finmarchicus, and the procedure is available for testing of oil dispersions. Verification of the method has been done with respect to droplet size, chemical characterization and exposure biomarkers on C. finmarchicus.