Estimation of Organic Carbon Normalized Sorption Coefficient (K_OC) for Soils Using the Fragment Constant Method

Abstract

A fragment constant model for prediction of K OC was developed and evaluated with a diverse database of 592 chemicals belonging to 17 classes. The range of experimental K OC covered 7.65 log-units. The 592 chemicals were randomly divided into a training set and a testing set for model development and validation. A general model was then established using the entire database having 74 fragment constants and 24 structural factors. Statistically, the regression model accounted for as much as 96.96% of the variation in the measured log K OC . The mean residual between the experimental and predicted K OC values was 0.366 log-units. In more than 74% of the chemicals studied the residual values were less than 0.5 log-units. The robustness of the regression model, with respect to either specific individual chemicals or particular compound classes, was evaluated through use of jackknife tests. The experimental results confirmed the ability of the fragment model to predict K OC for a wide variety of untested chemicals.

Statistical external validation and consensus modeling: A QSPR case study for Koc prediction

“…Indeed, in the various models, the same structural aspects, mainly those related to molecular size, are represented by alternative descriptors with a similar meaning for K oc modeling: for instance log K ow , fragments parameters, topological descriptors and MW. Some useful electronic parameters are captured in the different alternative descriptors such as E-state indices [9,30], quantum chemical descriptors (PNSA-1, h[AM1], [AM1], P max ) [32], correction factors [8,27], the number of phenyls, oxygen, nitrogen and sulfur atoms [31] and the number of hydrogen acceptor atoms (nHA, that is the same as using nF plus nO plus nN), the number of nitro groups (nNO), or the maximum positive intrinsic state difference related to the electrophilicity of the molecule (MAXDP) [28].…”

“…The experimental data of the soil sorption partition coefficient, normalized on organic carbon (K oc ), of 643 heterogeneous organic compounds were collected from the literature [1,8,9] and compiled into a single database (see Table 1 in supporting information). Some of the chemicals in the literature databases have more than one K oc value, the result of being derived from different sources; in these cases the median was adopted.…”

“…The object of this study is the proposal of different MLR-QSAR models of K oc for a wide and highly heterogeneous data set of 643 non-ionic organic chemicals collected from three main sources [1,8,9]. The peculiarity of these models, that are based on different theoretical molecular descriptors selected by genetic algorithm as a variable subset selection procedure, is their development on a training set very much smaller than the prediction set (in a 1:6 ratio) and their applicability to a very heterogeneous set of chemicals.…”

Estimation of Soil Organic Carbon Normalized Sorption Coefficient (Koc) Using Least Squares‐Support Vector Machine

“…It was demonstrated that the K oc magnitude for different organic compounds was primarily due to their partition into soil organics [1]. Many linear models have been established, to relate K oc with molecular structures through the methodology of quantitative structureactivity relationships (QSARs), including the models employing molecular connectivity indices (MCI) [2,3], fragment constants [4], characteristic root index (CRI) [5], quantum chemical descriptors [6], etc. To promote the predictivity of log K oc , a general-purpose multilinear regression model (MLR) was developed by Schüürmann et al [7], which is a combination of 24 fragments covering the atoms C, H, N, O, P, S, F, Cl, and Br in various chemical functionalities and 4 molecular descriptors including molecular weight, bond connectivity, molecular E-state, and an indicator for non-polar and weakly polar compounds.…”

Effects of carbonate and organic matter on sorption and desorption behavior of polycyclic aromatic hydrocarbons in the sediments from Yangtze River

“…In natural water, sorption and desorption processes affect the fate of hydrophobic organic matters (HOCs) [11][12][13]. Once the PAHs, previously bound to sediments, are released into the aquatic environment, they will act as a natural repository for these HOCs.…”