(419e) Degradation of Microplastics in Wastewater Treatment Facilities: The Role of Particle-Particle Collisions

Microplastics are everywhere around us: from the tea we drink to the Arctic ice. Microplastics originate from the release of micron-sized particles (primary microplastics) in consumer products or by the degradation of larger pieces littered into the environment (secondary microplastics). The physicochemical properties of microplastics, such as size and surface characteristics, change upon weathering via sunlight exposure and exposure to incidental or natural oxidants. The role of particle-particle collisions in microplastic degradation has been scarcely investigated. Since the concentrations of microplastics in most ecosystems are low, particle-particle collisions are rare events. However, microplastic concentrations in wastewater treatment plants could be much higher, such as in efflux from industrial polymer manufacturing and recycling or waste streams from the textile industry. In those situations, particle-particle collisions could become a relevant mechanism of weathering that has to be considered when evaluating the transport and fate of microplastics. Additionally, some laboratory studies on microplastic weathering are performed at high concentrations, but the role of particle-particle collisions is typically not taken into account when evaluating the results. In this work, we evaluate the role of particle-particle collisions in microplastic physicochemical properties. Namely, we assessed the particle size distribution and composition for commercial primary microplastics (glitter) of different sizes in simulated wastewater for a month. We used optical and X-ray microscopy to quantify the size distribution of the microplastics and Raman and Fourier transform infrared spectroscopy to evaluate changes in polymer and additive composition over time. We observed that the glitter particles delaminate, changing the surface roughness of the primary particles and forming smaller secondary particles. The chemical changes in polymer and additive compositions observed through molecular spectroscopy were minimal within the studied period. Longer-term studies may reveal more significant chemical changes. Overall, this study reveals that particle-particle collision must be considered an additional mechanism for microplastic degradation when studying microplastic transport in settings where high concentrations of microplastics might be present.