FATE AND TRANSPORT OF NANOSCALE PLASTICS IN THE AQUATIC ENVIRONMENT

Mehnaz   Shams

Plastic debris is common in the environment due to its durability and widespread use. Large plastic debris can be eventually broken down to microplastics and nanoscale plastics which are recently getting attention. Moreover, their persistent nature and long residence time enable these microplastics and nanoscale plastics to accumulate in the environment and be susceptible to various transformation processes influencing their aggregation, deposition, and transport behavior. While microplastics have been investigated extensively, fate and transport of nanoscale plastics are still unknown. The overall goal of this research is to identify the fundamental mechanisms involved in the stability of nanoscale plastics in the presence of NaCl, CaCl2, and MgCl2 at different ionic strength, their transport through filtration media and their interactions with different surfaces (silica, natural organic matter (NOM) surfaces) using the quartz crystal microbalance with dissipation monitoring (QCM-D). The research specifically focused on the polyethylene and polystyrene nanoscale plastic, commonly detected in the environment. Stability studies showed that CaCl2 (critical coagulant concentration (CCC 0.1 mM) destabilized polyethylene nanoscale plastics more aggressively than NaCl (CCC 80 mM) and MgCl2 (CCC 3 mM). Transport studies showed that the mobility of both nanoscale plastics was higher than microplastics through porous media. Mobility decreased with increasing ionic strength and increasing particle size and this transport was mainly governed by secondary energy minimum. Furthermore, polystyrene was three-fold more mobile than polyethylene at the same ionic strength due to its size and surface charge. Conversely, the presence of NOM improved the stability and increased the mobility of both nanoscale plastics in water due to steric repulsion. QCMD studies showed higher interactions of both nanoscale plastics with NOM-coated surfaces than silica surfaces, with polystyrene having at least five-fold higher deposition than polyethylene on both surfaces. Combined results indicate that size and surface functionalization of nanoscale plastics will play a major role in their fate in aquatic environment, which will also be governed by NOM-coated surfaces. Overall, findings from this research will be useful in predicting fate, transport and removal of nanoscale plastics from the aquatic environment for the safety of public health and the environment.

FATE AND TRANSPORT OF NANOSCALE PLASTICS IN THE AQUATIC ENVIRONMENT

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