Classifying environmental pollutants: Part 3. External validation of the classification system

In order to validate a classification system for the prediction of the toxi c effect concentrations of organic environmental pollutants to fish, all av ailable fish acute toxicity data were retrieved from the ECETOC database, a database of quality-evaluated aquatic toxicity measurements created and ma intained by the European Centre for the Ecotoxicology and Toxicology of Che micals. The individual chemicals for which these data were available were c lassified according to the rulebase under consideration and predictions of effect concentrations or ranges of possible effect concentrations were gene rated. These predictions were compared to the actual toxicity data retrieve d from the database. The results of this comparison show that generally, th e classification system provides adequate predictions of either the aquatic toxicity (class 1) or the possible range of toxicity (other classes) of or ganic compounds. A slight underestimation of effect concentrations occurs f or some highly water soluble, reactive chemicals with low log K-ow values. On the other end of the scale, some compounds that are classified as belong ing to a relatively toxic class appear to belong to the so-called baseline toxicity compounds. For some of these, additional classification rules are proposed. Furthermore, some groups of compounds cannot be classified, altho ugh they should be amenable to predictions. For these compounds additional research as to class membership and associated prediction rules is proposed . (C) 2000 Elsevier Science Ltd. All rights reserved.