Optimisation and Validation of a Quantitative Method for the Analysis of Polymers of Nanoplastics in Human Faeces

Concerns about human exposure to micro- and nanoplastics (MNPLs), particularly nanoplastics (NPLs), have intensified in recent years. Consequently, there is a growing need for validated quantitative analytical methods capable of assessing NPLs in complex human biological matrices. Current approaches for NPL analysis are still limited by the absence of standardised protocols, difficulties in avoiding background contamination, and challenges associated with the selective identification and quantification of polymer-specific nanoparticles. Moreover, most common approaches for quantification by particle counting cannot be applied for NPLs < 500 nm. In this study, we developed and validated an analytical method for the detection and quantification of NPLs in human faeces. As an initial step, polyethylene (PE) and polypropylene (PP) nanoparticles (NPs) were synthesised using bottom-up methods and characterised by dynamic light scattering (DLS) and electron microscopy (SEM and TEM). To optimise and assess the extraction, synthetic faeces were prepared and used in spiking experiments to avoid background contamination from plastics. Two digestion strategies were evaluated: (i) Fenton's reagent followed by strong acid digestion, and (ii) alkaline digestion. Quantitative determination of polymer-specific NPLs was performed by size-exclusion liquid chromatography coupled with high-resolution mass spectrometry and atmospheric-pressure photoionization (SEC-APPI-HRMS). Polymer identification was based on characteristic monomer-loss patterns and Kendrick Mass Defect analysis. Fenton-based digestion showed superior performance, yielding recoveries about 55-66% for PE and 59-61% for PP. The validated method achieved limits of detection and quantification of 0.015 and 0.058 μg/kg for PE, and 0.025 and 0.083 μg/kg for PP, respectively. Precision, expressed as %RSD, was 10.1% for PE and 20.1% for PP. These results demonstrate that SEC-APPI-HRMS combined with Fenton-based digestion provides a sensitive and reliable approach for the quantification of polymer-specific NPLs in human faeces. The method represents an important advance for human biomonitoring studies and supports future research aimed at assessing human exposure and the potential health risks associated with nanoplastics.