Classifying environmental pollutants. 1: Structure-activity relationships for prediction of aquatic toxicity

In this paper a scheme is presented that makes it possible to classify a large number of organic pollutants into one of four classes, viz: [l] inert chemicals, [2] less inert chemicals, [3] reactive chemicals and [4] specifically acting chemicals. For chemicals that are thus classified as belonging to one of these four classes it is possible to calculate either an expected effect concentration (inert chemicals), such as the LC50or an expected range of possible effect concentrations, from a compound's octanol/water partition coefficient (Log K(ow)). For chemicals that cannot be classified as belonging to one of these four classes no prediction can be made. This approach can be implemented to estimate aquatic effect concentrations, which can be used to derive preliminary environmental quality objectives, or for the prioritisation of chemicals for subsequent testing. Moreover, these estimates could be of great value in risk and hazard assessment. To our opinion, this approach represents the current state-of-the-art in estimation methods for aquatic toxicology. This paper is especially focused on identifying the limits of applicability of Quantitative Structure-Activity Relationships for predicting aquatic toxicity, as, according to Hart (1991) it '...is important not to exaggerate the accuracy of prediction for models...' [and] '...to make clear to the user the limitations of the relationship.'