UV-weathering affects heteroaggregation and subsequent sedimentation of polystyrene microplastic particles with ferrihydrite

• Published in: Environmental science--processes & impacts Vol. 27; no. 4; pp. 992 - 12
• Main Authors: Schmidtmann, Johanna, Weishäupl, Hannah-Kristin, Hopp, Luisa, Meides, Nora, Peiffer, Stefan
• Format: Journal Article
• Language: English
• Published: England Royal Society of Chemistry 16.04.2025
• Subjects: Aggregation behavior; Aquatic environment; Colloiding; Colloids; Degradation; Degradation products; Environmental behavior; Ferric Compounds - chemistry; Functional groups; Hydrogen-Ion Concentration; Irradiation; Microplastics; Microplastics - analysis; Microplastics - chemistry; Particle Size; pH effects; Plastic pollution; Polystyrene; Polystyrene resins; Polystyrenes - analysis; Polystyrenes - chemistry; Sedimentation; Sedimentation & deposition; Sediments; Surface charge; Surface properties; Ultraviolet radiation; Ultraviolet Rays; Water circulation; Water column; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Weathering
• ISSN: 2050-7887; 2050-7895; 2050-7895
• DOI: 10.1039/d4em00666f

Microplastic (MP) particles are ubiquitous in aquatic environments where they become exposed to UV-irradiation with subsequent alteration of surface properties. Such particles will interact with naturally occurring colloids being subject to processes like heteroaggregation that affect both MP surface properties and their removal rates from the water column. In this study, we investigated heteroaggregation and subsequent sedimentation of 1 μm polystyrene (PS, pristine and UV-weathered) with ferrihydrite (Fh), an iron (oxy)hydroxide commonly found in nature. Heteroaggregation of pristine PS with Fh was controlled by electrostatic attraction. At neutral pH values, strong heteroaggregation was observed which led to the sedimentation of almost all PS particles. UV-weathering of PS led to lower negative surface charge, decrease of particle size, and formation of degradation products. Changes in surface properties of PS resulted in a different aggregation behavior with Fh. With increasing weathering time, the isoelectric point (pH IEP ) of suspensions with PS and Fh shifted to lower pH values. Furthermore, we observed aggregation and subsequent sedimentation of weathered PS and Fh for a wider pH range (pH 3-7) compared to pristine PS (pH 6.5-7.5). We attribute this observation to increased surface reactivity of PS due to the formation of functional groups on the surface through UV-weathering. In addition, degradation products ( e.g. oligomers) formed during weathering might have also interacted with PS and Fh and therefore further affected the surface properties of the particles. Overall, UV-weathering but also interactions of MP particles with environmental particles cause changes of MP surface properties, which influence its environmental behavior in water and might lead to a removal from the water column and accumulation in sediments. Microplastic (MP) particles are ubiquitous in aquatic environments where they become exposed to UV-irradiation and environmental particles with subsequent alteration of surface properties.