Inter-laboratory comparison (ILC) report on the validity and applicability of the developed characterisation methods and reference materials

The Plastic Trace project addresses the urgent need for harmonised methods to characterise small microplastics (SMPs) and nanoplastics (NPs) in support of new EU regulations. Candidate SMPs reference materials produced in the frame of the project were characterised by the partners of the consortium using thermo-analytical, spectroscopic, and size-distribution techniques. Results showed strong inter-technique comparability and material suitability for method validation. In parallel, the VAMAS TWA 45 Project 3 interlaboratory comparison engaged international laboratories to assess repeatability and reproducibility of targeted methods for NPs characterisation. These efforts provide a foundation for best-practice guidance, harmonisation, and future ISO standards. Interlaboratory comparisons (ILCs) play a central role in standardising methodologies for the characterisation of small microplastics (SMPs) and nanoplastics (NPLs). They strengthen research consistency by identifying best practices and areas for improvement, thereby ensuring reproducibility and reliability of results across laboratories.Within the Plastic Trace project, LNE, BAM, INRIM, LGC, and NIVA jointly defined a strategy for ILCs on selected SMP/NP neat materials. Insights gained from the production and characterisation of these materials — including homogeneity and stability testing using a range of analytical techniques — guided the decision to focus on three key measurands: particle number concentration, mass fraction, and particle size.This report is divided into two parts. Part I presents work on the development and characterisation of candidate reference materials for microplastics. Tablets containing polyethylene terephthalate (PET) particles (10–100 μm, irregular and sharp-edged) were produced at three concentration levels. A broad suite of techniques was applied to assess particle size, morphology, polymer type, homogeneity, and stability, including mass-based methods (TGA, Py-GC/MS, TED-GC/MS), spectroscopic methods (μ-FTIR, μ-Raman), and size distribution approaches (SEM, laser diffraction). Results obtained across different instruments, laboratories, and analytical principles demonstrated strong inter-technique comparability, supporting the suitability of the PET tablets as reference materials for method validation and harmonisation.Part II presents a key achievement of the project: the organisation of the VAMAS TWA 45 Project 3 ILC. This international study focused on validating targeted techniques for measuring nanoplastics in terms of size distribution, number concentration, and mass fraction. By involving multiple laboratories worldwide, the ILC provides critical data for assessing method repeatability and reproducibility, supporting harmonisation and pre-standardisation.Together, these efforts contribute directly to method harmonisation and best-practice guidance, paving the way for the validated techniques to be widely implemented in regulatory and industrial applications. Ultimately, they represent a crucial step towards improving the comparability of SMP/NP measurements and towards the development of new environmental and food safety standards. “The project 21GRD07 PlasticTrace has received funding from the European Partnership on Metrology, co-financed from the European Union’s Horizon Europe Research and Innovation Programme and by the Participating States.”• Funder name: European Partnership on Metrology• Funder ID: 10.13039/100019599• Grant number: 21GRD07 PlasticTrace