Predicting three narcosis mechanisms of aquatic toxicity.

In this study, the use of solute descriptors (the McGowan's characteristic volume V(X), the excess molar refraction R, the dipolarity/dipolarizability pi(H), the effective or summation hydrogen-bond acidity summation operatoralpha(H) and the effective or summation hydrogen-bond basicity summation operatorbeta(H)) in classifying and predicting the non-polar, polar, and ester narcosis toxicity mechanisms for organic compounds was investigated. Discriminant analysis was performed and the significant discriminating variables were found to be R, pi(H), sigma alpha(H), and (sigma beta (H))(2), the latter of which was created to aid the mechanism classifications. Cross-validation of the non-linear discriminant functions showed a small total error rate of approximately 5% which was reduced to approximately 2% when seven compounds with uncertain a priori mechanism designations were removed. Compared with other methods for toxicity mechanism classification and prediction, the method developed in this study has advantages. It relies on the use of objective numerical values of molecular descriptors that can be calculated and does not require additional experimental work when used for new compounds. The descriptor values can also aid the interpretation of the toxicity mechanism classifications and predictions. Because of the possibility of making incorrect mechanism predictions using a single method, it was recommended that several methods be used together to make the most appropriate mechanism designations and to increase the confidence level associated with the mechanism designations.