Chemical topology and ecotoxicology.

The experimental determination of environmental parameters (e.g. soil sorption, bioconcentration, biodegradation and biotransformation, toxic effects, etc.) of commercial chemicals is a costly and time-consuming process. Since there is a large number of chemicals currently in common use (approximately 100,000) and new chemicals are registered at a very high rate (1000/year) it is obvious that our human and material resources are insufficient to obtain experimentally even basic information on environmental fate and effects for all those chemicals. Thus, it is necessary to develop quantitative models that will accurately and rapidly predict environmental behaviour for large sets of chemicals. Thus far, molecular connectivity indices have been shown to be the most successful structural property for describing and predicting soil sorption coefficients, association with dissolved humic substances, Henry's law constants, bioconcentration factors in aquatic organisms and vegetation, biodegradation, and acute toxicity. We describe and discuss the most recent results on modelling environmental fate of organic pollutants by the application of molecular connectivity indices. Two sections describe the usefulness of environmental QSAR models based on n-octanol/water coefficients and the systematics and possible physical interpretation of molecular connectivity indices. Some practical and theoretical weaknesses and pitfalls are discussed concerning the use of n-octanol/water partition coefficients in environmental QSAR research.