Sammendrag
The aim of the project has been to establish methodology and theoretical framework for separating the acute toxic effect of oil droplets and dissolved fraction of oil dispersions. The project is based on environmental modeling tools and their ability to predict the concentrations of dissolved and dispersed oil as well as the oil droplet size distribution in the water column during different oil spill situations. At present there is virtually no information on the toxicity of oil droplets per se, or on the toxicity related to droplet size distribution in dispersions. Based on theoretical models for droplet formation, a system for controlled generation of dispersions with defined droplet size distributions were constructed and tested. The system is based on repeated turbulence in a system with multiple nozzles. In this system the mean droplet size and the droplet size distribution is determined by a combination of energy input (flow rate) and the number of nozzles used. The system was tested at different temperatures with different oil types. In order to perform controlled experiments with oil droplets for long periods of time it is essential the keep the droplets in suspension without contaminating the exposure system. The principle is based on short and relatively short tubing and no pumping upstream the exposure chambers. The dilution is achieved by dislocation of exposure solution by pumping clean sea water into the system at each dilution step. Flow through in each individual exposure chamber is controlled by pumping exposure solution out near the surface, causing fresh solution to flow passively into the chamber at a corresponding rate. Removal of droplets in order to produce pure water soluble fractions (WSF´s) was achieved by an in-line glass-filter that is changed once a day.Preliminary tests with cod larvae were performed at Institute of Marine Research in early December 2006. Chemical measurements have been used to verify concentrations and quality of the di