Investigations into the Reactivity of Microplastics in Water

Microplastics, plastic pieces less than 5 mm in size, are a significant part of the plastic pollution in surface waters. Given the massive, global extent of this pollution, it is important to understand the chemical reactivity of microplastics in water. This study used radiation chemistry techniques to explore the transformations of plastics in water. Adsorption experiments were also conducted with microplastics and other model water contaminants. When water mixtures are exposed to gamma radiation, radicals that are prominent in nature, namely the hydroxyl radicals (●OH), are created. The reported irradiation experiments were done to simulate stagnant waters. Water mixtures containing either polyethylene (PE) or polyethylene terephthalate (PET) in closed containers were exposed to different irradiation dose rates and doses. Caffeine, dodecane, and benzophenone, commonly occurring pollutants, were used as model compounds in microplastics adsorption experiments. Infrared and Raman spectroscopies, along with GC-MS and LC-MS, were the main techniques used to assess the changes to the microplastics. A few compounds, such as dodecane and 2-dodecanone, were detected in the water/PE mixtures after exposure to the radicals. The surface chemistry of the microplastics was mostly unchanged, even after high doses of irradiation. Adsorption experiments showed that caffeine does not adsorb to PE or PET, dodecane strongly adsorbs to PE, and benzophenone partly adsorbs. The natural ●OH-mediated breakdown of caffeine was not affected by the presence of PE. Even though benzophenone adsorbs to PE, the degradation rate of benzophenone in solution did not change in the presence of PE microplastics.