Abstract
A biotest system for continuous exposure of aquatic organisms to the water soluble fraction of oil hydrocarbons is described. A stock solution was prepared in a separate tank, diluted with clean sea water to appropriate test concentrations, and continuously transferred to the exposure aquaria. The system was cleaned every week to avoid bacterial contamination. The hydrocarbon levels of aquaria and stock solution correlated with a coefficient of 0.96. Due evaporation, however, on the way from the stock solution tank to the aquaria, the oil concentration of the aquaria were 40–60 % lower than expected from the dilution ratios. The test solutions also contained traceable amounts of polar components which probably were oxidized compounds of oil hydrocarbon origin. These compounds could be of importance for the evaluation of eventual effects on test organisms.