APPLICATION OF CHEMOMETRICS TO THE SCREENING OF HAZARDOUS CHEMICALS - A CASE-STUDY

The key aspects of a priority setting process for risk assessment of chemicals are reviewed. The process is based on the assumption that chemical and biological properties can be modelled within series of closely similar compounds. It rests heavily on multivariate methodologies for the development of predictive models. Statistical design, in particular, is essential for optimizing the selection of the most informative objects and variables to be used in the calibration of the models. A case study is presented where the process is applied to all (EEC-wide) commercially available halo-methanes, -ethanes and -propanes with the objective of modelling their tropospheric reactivity and, hence, estimating their lifetimes. A training set of just nine, property informative haloalkanes was first selected from a series of 142; their reactivity was expressed in terms of the rate constant of their reaction with the OH radical, k(OH); their structure was parametrized by a selected set of variables that, by using a new statistical method, were found to optimize the k(OH) model. The experimentally validated model provided k(OH) estimates, and hence allowed the formulation of a persistency ranking for the non-tested compounds in the series, which also included several hydro-chlorofluorocarbons, H-CFCs, presently considered as possible replacement chemicals for the extremely stable, environmentally incompatible ozone-depleting CFCs.