CLASSIFICATION OF ENVIRONMENTALLY OCCURRING CHEMICALS USING STRUCTURAL FRAGMENTS AND PLS DISCRIMINANT-ANALYSIS

Chemicals were classified according to one of the four classes as desc ribed by Verhaar et al. (Chemosphere 1992, 25,471-491) based on the st ructural information present in fragments of these chemicals. A PLS di scriminant analysis method with the classes as the response variables and the screens as the predictor variables was used. The data were mod eled in two different ways. The response variables were either modeled individually (PLS1), resulting in one model for each class, or togeth er in a unified PLS2 model. This method resulted in some good models a nd a few moderate ones. The inert and less inert chemicals are concent rated in a relatively small region, whereas the reactive and specifica lly acting chemicals were more spread out. The reactive chemicals show ed some diffuse border with the inert chemicals. Distinction between r eactive and specifically acting chemicals is not straightforward. Pred iction of class membership for a set of high production volume chemica ls (HPVCs), not formerly classified, was reasonably good. The results of the study are promising. The easily generated characterization of t he compounds, by means of presence OF absence of specific fragments, c ontained useful information for clustering and classification. The mos t obvious advantage of the strategy is the speed. The characterization of several thousands of compounds can be made in less than 1 h.