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Nanoplastics entering riverine and marine environments, either directly as components of waste streams or resulting from the breakdown of larger plastic particles, represent a growing area of water quality concern.  As nanoplastics become an increasingly prevalent type of plastic pollution in aquatic systems, understanding their physicochemical behavior is essential to understand their fate and transport in the environment and their impact on organisms. Agglomeration is one factor that influences nanoparticle transport specifically, as it can affect particle suspension and organism uptake. Herein, agglomeration behavior in salinity gradients that model transport from headwaters to the ocean of four 50 nm plastic nanospheres was investigated: carboxylated poly(methyl methacrylate) (PMMA), plain PMMA, red color dyed polystyrene (PS), and blue color dyed PS. Plastics were tested at 10 ppm in solutions at each salinity (0, 1, 5, 10, 15, 20, 25, 30, and 35 g/L) prepared from filtered Pacific Ocean water (POW) and Milli-Q water. Dynamic light scattering was used to detect agglomerate size (or primary particle size if well dispersed) at each salinity. For the red and the blue PS, there was no significant difference in the primary peak size distributions and significant agglomeration was detected at 25 g/L. No agglomeration point was detected for carboxylated PMMA, as size does not significantly differ across the tested salinities. In contrast, the plain PMMA showed significant agglomeration at salinities of only 1 g/L. Thus, our data suggest that plastic nanoparticle composition can impact how environmental salinity affects plastic nanoparticle agglomeration. This salinity-based agglomeration, in turn, may impact the fate of these plastics in the environment as well as the organisms potentially impacted. This project examined only a few properties of nanoplastics in pristine saline solutions. Additional work will be required to characterize and model agglomeration of other nanoplastic types, shapes, and sizes in complex systems where heteroagglomeration might occur.

This project presenter is available for live video chat on Sept. 1, 2020 from 10:15 a.m. - 12:00 p.m. PDT.