The relation of acute to prolonged toxicity of existing and new chemicals and active ingredients of numerous pesticides in the aquatic environment have been compared with their physico-chemical properties. The data had been presented to the authorities in behalf of the pesticide registrations, the notification of new chemicals or research projects. The ecotoxicity ratios are expressed as acute to prolonged ratios (APR). They are determined for fish and crustacea with existing and new chemicals and pesticides. In the case of the pesticides the data are subsummarized into fungicides, herbicides, insecticides. The variability of the APR is evaluated. According to the statistic evaluation of the data it must be summarized, that the toxic effects are often extremely specific and depend not only on the substance, but also on the aquatic species, the duration of the exposure, and the endpoint of the test. In general, a factor of 100 between the EC/LC(50) of acute toxicity and NOEC of prolonged toxicity is scientifically justified. The data indicate that there is no significant correlation between lipophilic properties (logP(OW)) or water solubility and toxicity in aquatic organisms. For that reason structure-activity relationships based on lipophilic properties of the substance cannot lead to reasonable results. It must be stated, that the prolonged ecotoxicity can not be exactly extrapolated from acute toxicity data on the basis of physico-chemical properties.
