The estimation of the toxic effects of plant protection products on non-target aquatic organisms is essential for risk assessment evaluation. In this study the acute toxicity of two fungicide and two herbicide formulations was determined in four marine species in comparison with the toxicity assessed for the freshwater crustacean Daphnia magna. From the study it is indicated that the marine crustacean species are effectively protected when acute toxicity data on Daphnia magna are used as surrogate for risk assessment while the comparative sensitivity of the unicellular green algae may vary considerably, depending on the mode of action of the specific formulation.