A molecular topology approach to predicting pesticide pollution of groundwater

Various models have proposed methods for the discrimination of polluting an d nonpolluting compounds on the basis of simple parameters, typically adsor ption and degradation constants. However, such attempts are prone to site v ariability and measurement error to the extent that compounds cannot be rel iably classified nor the chemistry of pollution extrapolated from them. Usi ng observations of pesticide occurrence in U.S. groundwater it is possible to show that polluting from nonpolluting compounds can be distinguished pur ely on the basis of molecular topology. Topological parameters can be deriv ed without measurement error or site-specific variability. A logistic regre ssion model has been developed which explains 97% of the variation in the d ata, with 86% of the variation being explained by the rule that a compound will be found in groundwater if (6)chi (v)(P) < 0.55. Where (6)chi (P) is t he sixth-order molecular path connectivity. One group of compounds cannot b e classified by this rule and prediction requires reference to higher order connectivity parameters. The use of molecular approaches for understanding pollution at the molecular level and their application to agrochemical dev elopment and risk assessment is discussed.