Abstract:
Information about diffusivity of diverse organic contaminants in water and ethanol
phases provides insight about their chemo dynamics in aquatic and mucosal
phases. The experimental techniques to measure diffusivities are expensive, time-
consuming, and not readily available. On the other hand, the existing
computational methods are parameter intensive, computationally expensive, and
have a limited domain of applicability. Here, I present a simple estimation
approach based on solvation properties of contaminants using widely available
partition coefficients data for the octanol-water (logK ow ) and air-water (logK aw )
systems. For this purpose, the experimental data of diffusion coefficients for 133
polar and non-polar compounds in water and 58 compounds in ethanol — taken
from literature — were used to train and validate the models. Diffusion
coefficients in ethanol showed an excellent correlation with logK aw and other
intermolecular interaction parameters. The model based on linear combination of
logK ow and logK aw was developed with an R 2 of 0.80 and an RMSE of 0.060. In this
model, logK aw exhibited a very influential role in describing the variation in
diffusivity data for ethanol phase. For water phase the variance in the diffusivities
depicted an R 2 of 0.54 and an RMSE of 0.101 based on linear combination of
logK ow and logK aw . The performance of our models was similar to widely used
Abraham Solvation Model (ASM). However, the Abraham models are limited by
the scarcity of experimental ASDs (<8000 chemicals). I evaluated the theoretical
rigor and robustness by applying supervised and unsupervised machine learning
techniques such as principal component analysis, Pearson correlation analysis,
hold-out, leave one out, k-fold, and bootstrap approaches. The results of these
analyses showed that the logK ow and logK aw respectively correspond to non-specific
and specific intermolecular interactions. Furthermore, there was a good agreement
between the train and test datasets for both models. Lastly, I parametrized a mass
transfer model to evaluate the transport resistance of organic contaminants in
water and ethanol using basic principles of Fick’s Law. Taken together this study
sheds light on the kinetics of bioavailability of diverse organic contaminants.
