[Preparation of Nanoplastic Particles as Potential Standards for the Study of Nanoplastics]

Nanoplastics (NPs) are plastic fragments that are small enough to be absorbed by organisms through ingestion or inhalation. Recent studies indicate that nanoplastics can be ubiquitous in the environment, and there are growing concerns regarding the impacts of nanoplastics on the health of humans and other organisms. However, quantitative information on nanoplastics in the environment is still very limited, and most previous toxicity studies have used only polystyrene (PS) particles because of a lack of appropriate model particles of other plastics. We developed a nanoprecipitation-based method for the preparation of nanoplastic particles of five major polymers: low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene. A major advantage of our method is that the nanoplastic particles are prepared without using reagents that can remain in the particles as impurities. Analysis of the prepared particles' molecular weight (M_w) distributions, crystallinities, and thermal properties revealed that their compositions and constitutions were within the general ranges for commercial products. The mechanisms underlying the formation of low-density polyethylene particles via our method were investigated by means of a simple population balance model, and particle diameter was found to be linearly correlated with the suspension density of the nanoplastic dispersion up to 0.4 mg·mL^-1. Future studies should focus on improving our method to allow for precise, scale-independent production of nanoplastic particles. Methods for the preparation of labeled particles are also needed so that such particles can be used in nanoplastic risk assessments.