The main objective of this project is to provide parameterised data on the toxicity of oil in water dispersions to fish larvae toxicity, using cod fry as the main target in order to:1. Determine the relative contribution to acute toxicity from the dissol ved and particulate phase of dispersed oil.2. Expand the time frame for toxicity tests with oil-in-water dispersions to quantify the effects of delayed toxic effects from acute exposures to early life stages.3. Provide data that can be used to predict p hoto-enhanced toxicity.The project addresses and challenges the notion that the dissolved oil components are the main contributors to toxicity from an oil spill, as well as the apparent lack of photo-enhanced toxicity and the uncertainty concerning delay ed (long term) in operative impact and risk assessment models. The hypothesis we whish to test are:A. The dominating toxic impact in the water column is caused by the dissolved oil components.C. The delayed effects from acute (short term) sublethal oil exposure are insignificantB. The effects of photo-enhanced toxicity subsequent to an oil spill are insignificant. The approach used to test the hypotheses is to parameterize the exposure characteristics in order to be able to separate the toxic contribu tion from each parameter. Theoretical approaches based on established dissolution theory will be used together with extended toxicity unit approaches for acute toxicity. These approaches will be verified and calibrated by chemical and toxicological measur ements. The project involves personnel with special competency in oil weathering, experimental design, chemical analysis, numerical modelling, risk assessment, aquaculture and ecotoxicology.The project will provide data on the relative toxicity of partic ulate and dissolved factions of oil-in water dispersions on fish larvae (Atlantic cod), as well as provide quantitative data on the additional impact caused by delayed effects and photo-enhanced toxicity.