Extraction and concentration of nanoplastic particles from aqueous suspensions using functionalized magnetic nanoparticles and a magnetic flow cell

Although a considerable knowledge base exists for environmental contamination from nanoscale and colloidal particles, significant knowledge gaps exist regarding the sources, transport, distribution, and effects of microplastic pollution (plastic particles < 5 mm) in the environment. Even less is known regarding nanoplastic pollution (generally considered to be plastic particles < 1 μm). Due to their small size, nanoplastics pose unique challenges and potential risks. We herein report a technique focused on the concentration and measurement of nanoplastics in aqueous systems. Hydrophobically functionalized magnetic nanoparticles (HDTMS-FeNPs) were used as part of a method to separate and concentrate nanoplastics from environmentally relevant matrices, here using metal-doped polystyrene nanoplastics (PAN-Pd@NPs) to enable low-level detection and validation of the separation technique. Using a magnetic separation flow cell, PAN-Pd@NPs were removed from suspensions and captured on regenerated cellulose membranes. Depending on the complexity of solution chemistry, variable extraction rates were possible. PAN-Pd@ NPs were recovered from ultrapure water, synthetic freshwater, synthetic freshwater with a model natural organic matter isolate (NOM; Suwannee River Humic Acid), and from synthetic marine water, with recoveries for PAN-Pd@NPs of 84.9%, 78.9%, 70.4%, and 56.1%, respectively. During the initial method testing, it was found that the addition of NaCl was needed in the ultrapure water, synthetic freshwater and synthetic fresh water with NOM to induce particle aggregation and attachment. These results indicate that magnetic nanoparticles in combination with a flow-through system is a promising technique to extract nanoplastics from aqueous suspensions with various compositions.