Quantitative structure-transformation relationships of phenylurea herbicides

Quantitative relationships between the structure of phenylurea herbicides a nd their transformation in different matrices have been developed. Experime ntal data on microbial transformation by pure and mixed cultures of soil mi cro-organisms in inoculated and native soil, as well as on chemical transfo rmation by hydrolysis in sterile soil and water, were available from previo us studies. Around 60 experimental or calculated descriptors were used. Qua ntum chemical calculations were performed with three different semi-empiric al methods. Models developed with multiple linear regression were generally easier to interpret than those derived with partial least-squares projecti on to latent structures. Quite simple and interpretable models could be fou nd to predict transformation rates by pure cultures from lipophilicity, by mixed cultures from adsorption distribution coefficients, and by chemical o r enzymatic hydrolysis from electronic properties. Transformation in inocul ated soil could not be predicted, but for native soil the use of a quantum chemical descriptor for reactivity (energy of LUMO) together with molar ref raction resulted in a general model. (C) 2001 Society of Chemical Industry.