Method development for analysis of nanoplastics in drinking water and milk using transmission electron microscopy (TEM)

The characterization of nanoplastics (NPs) in complex matrices remains an analytical challenge. The PlasticTrace project addresses this by developing advanced methodologies for characterizing and measuring NP in food matrices, using transmission electron microscopy (TEM) to assess size and shape — critical parameters for risk assessment.

This TEM-based approach was validated using polystyrene (PS) reference beads in the size range 60-500 nm, encompassing all analysis steps, from sample preparation to image analysis. Typically, the expanded measurement uncertainties for median size and shape measuments of pristine NPs ranged from 2.5 - 7.5 % and 3.0 - 8.9 %, respectively, setting a reliable baseline for further studies.

As a next step, preliminary tests for the validation within food matrices were initiated by spiking drinking water and milk with PS NPs. In drinking water, scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (STEM-EDX) allowed differentiating plastic particles from mineral contaminants on the grid by their elemental composition. The limit of detection, determined by the sample preparation procedure, was significantly improved from ~10¹⁰ to ~10⁸ particles/mL by implementing a two-step centrifugation protocol.

For milk, advanced matrix digestion methods are crucial for recovering nanoplastics. We propose testing alkaline and enzymatic digestion strategies in combination with (ultra)centrifugation techniques to optimize particle recovery and ensure accurate analysis.