Surface interactions of model microplastic particles in seawater

Microplastic is classified as fragmented polymeric particles up to 500 microns in diameter. In an aqueous system, microplastic does not always present as a single particle, and these microparticles tend to aggregate and subsequently causing severe ecological risks. The exploration of the underlying mechanisms on how microplastics aggregate in seawater and freshwater enables the prediction of their diffusivity, distribution, and bioavailability in the water environment. In this study microplastic model systems of polypropylene (PP) and poly(vinyl chloride) (PVC) were used to investigate the interactions and aggregation size between microplastics in seawater and with the response anionic sodium dioctyl sulfosuccinate (AOT) surfactant dosages via electrophoretic mobility and Dynamic Light Scattering (DLS) measurements, supported by the UV-Vis spectrum analysis. This investigation revealed that mobile ions present in water ecosystems played a vital role in the surface interactions between microplastics and their aggregation behaviour. The surface charge of both PP and PVC microplastics were switched to a positive value at 5 wt.% of AOT and continued in the negative regime with increasing AOT concentration. Upon the addition of surfactant, surface charge neutralization and aggregation of PP and PVC microplastics were detected; however, the restabilization of microplastic was observed with increasing concentration of surfactant.