The potential for atmospheric transport of contaminants to remote lakes: An assessment using COSMO-RS solvation theory.

Pharmaceuticals and personal-care products (PPCPs), pesticides, and per-and polyfluoroalkyl substances (PFAS) have been detected in lakes far from known point sources. These compounds may be transported into the atmosphere in the gas phase or associated with aerosols or particulates. Here, the CONductor-like Screening MOdel for Realistic Solvation (COSMO-RS) theory is used to estimate key partition ratios for selected chemicals from these classes and used to map their tendency to partition within the atmosphere under typical conditions. In cloud-free conditions, the target chemicals partition to one or more of the organic or aqueous phases of aerosols and the gaseous phase in air. Changing the pH of aerosols in the range 0-7 results in most chemicals shifting from one phase to another. Most acids and bases shift strongly to the water phase under ionizing conditions (i.e., pH 0 for bases and pH 7 for acids. Adjustments to the modelling for an increased volume in the water phase and changes in the pH of aerosols under cloudy conditions results in the prediction that most of these chemicals will partition into water droplets (i.e. rain) at some pH value between 0 and 7. It is proposed that wastewater treatment plants are point sources for PPCPs and possibly PFAS, while agricultural applications are the source of pesticides. Partitioning into the atmosphere and medium- or long-range transport, followed by wet deposition or direct diffusion could explain the presence of many of these chemicals in remote lakes.