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1I - Physicochemical properties (MOP/55) A new model to estimate the octanol/air partition coefficient. Schüürmann, Gerrit1, Ebert, Ralf-Uwe1, Kühne, Ralph1, 1 Department of Chemical Ecotoxicology, Department of Chemical Ecotoxicology, Leipzig, Germany ABSTRACT- In the recent years, the octanol/air partition coefficient Koa became an important parameter in environmental fate modeling. Apart from its use to estimate the accumulation of airborne chemicals in plants, Koa is used to model the compound partitioning between air and aerosols and also between air and soil. Whilst in recent years there have been published some direct measurements of Koa, this parameter is often not directly available. As a consequence, Koa is often calculated from Kow and Henry's law constant that in turn need to be known or estimated from other methods. In the present study, experimental data (both directly measured and from experimental Kow and Henry's law constant) were collected from literature for about 1500 organic chemicals that cover a broad range of compound classes. 90% of these data were used as training set to develop an estimation method for log Koa at 25°C from structural fragments and correction factors. The final model consists of about 125 descriptors, and the standard error is below 0.7, with an error below 0.5 for most of the important compound classes. The prediction capability is demonstrated by applying the model on the test set of 10% of the compounds that were not used for the model derivation. Moreover, the opportunity to improve the estimation quality by means of a similarity-based error correction is investigated. Key words: Estimation method, Partition coefficient octanol/air, Organic compounds |
