Release of nanoplastic from polypropylene kettles

Plastic products can release particles during everyday use, contaminating food and beverages and ultimately entering the human body through ingestion. However, the concentrations of these particles and the extent of human exposure remain poorly understood. While many studies have focused on characterizing the release of microplastics (MPs, > 1 μm), studies on nanoplastics (NPs, < 1 μm) remain limited due to significant analytical challenges associated with their small size. This study addressed this knowledge gap by investigating the release of both NPs and MPs from Australian-sourced polypropylene plastic kettles under normal use conditions using multiple orthogonal analytical techniques. During the initial boil cycles, the average releases were 0.011 ± 0.005 µg/cm2 for NPs and 0.032 ± 0.016 µg/cm2 for MPs. These releases decreased to around 0.003 ± 0.002 µg/cm2 for NPs and 0.013 ± 0.007 µg/cm2 for MPs by the tenth boil, stabilizing at levels below 0.002 ± 0.001 µg/cm2 and 0.006 ± 0.004 µg/cm2, respectively following 50 boils. After 150 boil cycles, the release declined significantly to 0.0004 ± 0.0002 µg/cm2 for NPs and 0.002 ± 0.001 µg/cm2 for MPs. The release of particles followed first-order kinetics, indicating that the release rate was directly proportional to the concentration of particles on the kettle’s inner surface. Although the number of nanoparticles declined over time, their size remained constant, with modal diameters of approximately 210 nm (measured via nanoparticle tracking analysis) and 580 nm (measured using Microtrac Sync particle analysis). To identify and characterize the polymeric composition of the released nanoparticles, we employed a novel analytical approach combining asymmetrical flow field-flow fractionation with multi-angle light scattering (AF4-MALS) with fraction collection followed by pyrolysis-gas chromatography-mass spectrometry (Pyr-GC-MS/MS). This integrated method enabled precise detection and chemical profiling of polypropylene NPs, representing a significant methodological advancement in NP analysis. Notably, the study also found that water chemistry influences particle release: boiling with hard tap water (125 ppm) significantly reduced NP concentrations compared to ultrapure MilliQ water. These findings provide new evidence on the release of NPs and MPs from plastic kettles, contributing to our understanding of potential exposure sources.