Molecular Dynamics Simulation Prediction of the Partitioning Constants (K_H, K_iw, K_ia) of 82 Legacy and Emerging Organic Contaminants at the Water–Air Interface

Abstract

The tendency of organic contaminants (OCs) to partition between different phases is a key set of properties that underlie their human and ecological health impacts and the success of remediation efforts. A significant challenge associated with these efforts is the need for accurate partitioning data for an ever-expanding list of OCs and breakdown products. All-atom molecular dynamics (MD) simulations have the potential to help generate these data, but existing studies have applied these techniques only to a limited variety of OCs. Here, we use established MD simulation approaches to examine the partitioning of 82 OCs, including many compounds of critical concern, at the water–air interface. Our predictions of the Henry’s law constant (K H) and interfacial adsorption coefficients (K iw, K ia) correlate strongly with experimental results, indicating that MD simulations can be used to predict K H, K iw, and K ia values with mean absolute deviations of 1.1, 0.3, and 0.3 logarithmic units after correcting for systematic bias, respectively. A library of MD simulation input files for the examined OCs is provided to facilitate future investigations of the partitioning of these compounds in the presence of other phases.

Experimental determination of the partitioning of representative organic pollutants to the air–water interface

“…Other approaches to predicting the partitioning of organics to the air-water interface have used polyparameter free energy relationships, 18 the use of commercial soware packages, 25 and molecular dynamics simulations. 14 The report by Lemay et al 14 gives three compounds which are also determined here (pyrene, uoranthene and bisphenol A); that of Goss 27 has only one (naphthalene). The different choice of standard states in these earlier works makes a direct comparison with our predictions and measurements not straightforward.…”

“…A very recent study using molecular dynamics simulations has reported a systematic approach to the air–water interfacial partitioning. 14 Nevertheless, it is clear that there remains a clear need for experimental measurements of the water surface partitioning thermodynamics over a range of organic compounds, especially when this surface is modified by organic coating.…”

Computational Chemistry as Applied in Environmental Research: Opportunities and Challenges

“…MD simulations have also been used to study photosynthesis and the behavior of pollutants in gas, solid, and liquid interfaces , and model the fate and transport of pollutants and compounds, , among other applications. The behavior of pollutants in gas, solid, and liquid interfaces, such as predicting their Henry’s law constant and interfacial adsorption coefficients, has also been explored using MD. , …”

Phase State, Surface Tension, Water Activity, and Accommodation Coefficient of Water–Organic Clusters Near the Critical Size for Atmospheric New Particle Formation

“…We note that MD simulation predictions are well-known to be sensitive to the choice of interatomic potential models. The SPC/E model was selected as it provides one of the most accurate representations of the properties of liquid water, including surface tension, static and dynamic dielectric properties, hydrogen-bond structure, and self-diffusion coefficient. − The OPLS-AA model has been extensively tested against the structural and energetics properties of organic compounds in liquid water and at the water–air interface. − Our recent results obtained using a variety of organic compounds show that the combination of the SPC/E and OPLS-AA models reasonably predicts the adsorption of organic compounds from liquid water to the water–air interface …”

“…69−71 Our recent results obtained using a variety of organic compounds show that the combination of the SPC/E and OPLS-AA models reasonably predicts the adsorption of organic compounds from liquid water to the water−air interface. 72 Converting Organic Bulk Concentration to Size-Dependent Particle Organic−Water Mass Fraction. A significant challenge in comparing our simulation predictions with published experimental results is that experimental studies generally report the organic concentration in bulk solution (C b ) as a key variable.…”