Investigating the ice nucleation activity of microplastics colonized with microorganisms

Microplastics (MPs) are an emerging contaminant with many unknown health and environmental consequences. Once MPs enter the environment, they are exposed to natural weathering, which can alter their wettability and increase their exposed surface area. This increase in surface area provides a substrate for microorganisms, which in turn, modify the surface characteristics of the MPs. Additionally, MPs can be easily aerosolized and transported long distances before being deposited. While MPs are in the atmosphere, not only are they interacting with other pollutants, but they may also function as ice nucleating particles (INPs) providing a foundation for cloud formation and influencing precipitation. In fact, a recent study has found MPs present in clouds. To evaluate the hypothesis that MPs may act as INPs, polystyrene microplastics varying in size (1µm to 100µm) and surface roughness were subjected to a freezing droplet assay from 0°C to approximately -14°C. A subset of these MPs were then added to the culture of a known bacterial ice nucleator, Pseudomonas syringae, which has been shown to play a role in the water cycle. These MPs cultured with P. syringae were also exposed to the same freezing droplet assay and results were compared to MPs alone. Our results suggest that the size, roughness, and presence of biofilm on MPs affect their ability to serve as INPs. These results have implications for modeling the transport of MPs throughout the environment and their impacts on the clouds and climate. Also see: https://micro2024.sciencesconf.org/559193/document