Quantitative structure-transformation relationships of phenylurea herbicides

Quantitative relationships between structure of phenylurea herbicides and their transformation in different matrices were developed. Experimental data on microbial transformation by pure and mixed cultures of soil microorganisms, in inoculated and native soil, as well as on chemical transformation by hydrolysis in sterile soil and water were available from previous studies. Around 60 experimental or calculated descriptors were used. Quantum chemical calculations were performed with three different semi-empirical methods. Models developed with multiple linear regression were generally easier to interpret that those derived with partial least-squares projection to latent structures. Quite simple and interpretable models could be found to predict transformation rates with lipophilicity (by pure cultures), with adsorption-distribution coefficients (mixed cultures), and electronic properties (chemical transformation). Biotranformation in inoculated soil could not be predicted, but in native soil a quantum chemical descriptors (energy of LUMO) and molrefraction yielded a satisfying, general model.