Ice Nucleation of Pharmaceutical and Synthetic Organic Emerging Contaminants: The Impact of Selected Environmental Conditions

Organic and inorganic emerging contaminants are omnipresent in the Earth’s ecosystem. Biological emerging contaminants, such as pharmaceutical materials, are of environmental and health concern. In this study, the ice nucleation efficiency (INE) for immersion freezing under mixed-phase cloud conditions of eight emerging contaminants, synthetic antibiotics and hormones, progesterone, testosterone, gentamicin sulfate, l-thyroxine, daidzein, dichloro-diphenyl-trichloroethane (DDT), bisphenol A, and estradiol, were evaluated. The effect of adding hematite, a component of dust and soil, was also examined. Furthermore, the impacts of selective environmentally relevant physicochemical conditions on INE, notably various pH, temperatures, and UV exposure, were explored. Gentamicin sulfate and daidzein were the most efficient tested ice nucleating materials (mean freezing temperature −13.7 ± 0.4 and −15.1 ± 0.6 °C, respectively). The addition of hematite decreased the INE of gentamicin sulfate, while daidzein’s INE increased to ∼ −11 °C. Progesterone was the poorest ice-nucleating contaminant (mean freezing temperature −19.9 °C ± 0.2 °C) and showed a minor increase in the presence of hematite. Several techniques, including high-resolution scanning/transmission electron microscopy (S/TEM), nanoparticle tracking, and X-ray diffraction were used in a suite of experiments to explore physicochemical processes at different environmentally relevant conditions, namely, the effect of change in concentrations on INE. Small angle X-ray scattering (SAXS) spectroscopy provided surface characteristics such as crystallinity and polydispersity. High daidzein and gentamicin INE is attributed to the distinct combination of high polydispersity and high crystallinity. This study suggests that this new class of ice-nucleating emerging contaminants may affect biogeochemical processes.