Elucidating the formation of nanoplastics from plastic nurdles in hydrocarbon-contaminated water

Abstract

Plastics and hydrocarbons are two major pollutants affecting oceans and freshwater systems. In this study, we investigate the transformation and behavior of three types of microplastic (MP) nurdles in water co-contaminated with various liquid hydrocarbons under ultrasonic agitation and rotary-orbital shaking conditions. Our findings reveal that the high-energy ultrasonic agitation produces a combination of secondary microplastics (sMPs) and nanoplastics (NPs), whereas the low energy rotary orbital shaking predominantly generates NPs. The formation of sMPs is attributed to the top-down mechanical fragmentation of nurdles, resulting in irregularly shaped particles with fibrous fractures. In contrast, NPs are primarily formed via a bottom-up process, wherein oligomeric species present in the nurdles dissolve into the hydrocarbon contaminants. These oligomers in hydrocarbons subsequently undergo emulsification under both high- and low-energy mixing conditions and precipitate as NPs in water. Characterization of the plastic particles was performed using scanning electron microscopy (SEM), dynamic light scattering (DLS), Fourier-transform infrared (FTIR) microscopy, and quartz crystal microbalance (QCM) analysis. The presence of oligomeric species was confirmed by nuclear magnetic resonance (NMR) spectroscopy and gas chromatography-mass spectrometry (GC-MS). This study provides critical insights into a potential new mechanism of NP formation in hydrocarbon-contaminated aquatic environments, highlighting the complex interactions between plastic waste and hydrocarbon co-contaminants.