The influence of iron (oxyhdr)oxides on the surface properties of polystyrene in aquatic environments

, Schmidtmann Johanna, Ottermann Katharina, Helfricht Nicolas, Papastavrou Georg, Peiffer Stefan.

Microplastic particles in the environment are expected to undergo numerous processes associated with natural colloids, for example heteroaggregation with iron oxides, which may influence the surface properties and transport behaviour of microplastics. We incubated 1 µm polystyrene (PS) particles with synthesized ferrihydrite, a weakly crystalline Fe(III)-(oxyhydr)oxide that occurs in large quantities in aquatic and soil environments. The surface properties of PS were examined before and after incubation using dynamic light scattering techniques. We observed that heteroaggregation between PS and ferrihydrite strongly depends on the pH value and on the reaction time. The size of aggregates increased with reaction time (between 0 h and 1 week). Strongest heteroaggregation was found at pH values between 6 and 8, close to the point of zero charge. In this pH range, the zeta potential values of incubated PS were nearly the same as those of ferrihydrite. Scanning electron microscopy images showed that the PS surface was covered entirely with ferrihydrite at a neutral pH. Our observations clearly demonstrate that the surface properties of PS particles were modified through interaction with ferrihydrite. Overall, our research suggests that Fe(III)-(oxyhydr)oxides are highly important reactants to control the environmental behaviour of microplastic particles. (Part of the CRC1357 local node event University of Bayreuth)

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