Predicting the behaviour of pesticides in soil from their physical and chemical properties.

Increasingly stringent environmental requirements for pesticides mean that both biological activity and favourable environmental behaviour must be assessed at an early stage in pesticide discovery. Soil behaviour is governed by the physical properties of the molecule: partition coefficient, dissociation constant, vapour pressure and melting point, which control potential movement under particular soil and environmental conditions and the soil persistence. Established chemical structure-physical property correlations generally allow physical properties to be estimated for the large number of compounds in a synthesis programme with adequate precision. Stability to chemical or biological transformations in soil is more difficult to estimate but a combination of measurement for a few compounds and analogy with known chemical and biological transformation rates for various functional groups can give useful structure-stability correlations.