Report on the harmonised Standard Operating Procedures (SOPs) of the developed SMPs (10 μm - 100 μm) characterisation methods in terms of: (i) chemical identity of the SMPs polymer type; (ii) physical particle characterisation and quantification, size distribution and particle morphologies; and (iii) quantification of the mass fraction in complex matrices.

This document outlines the development and harmonization of procedures for the characterization of Small Microplastic Particles (SMP) in complex food and environmental matrices. Initially, existing documentation, including publications and proprietary protocols from the partners, was collected and distributed.Two matrices were investigated in detail: one food-related matrices and one environmental matrix. These included infant milk powder and suspended particulate matter (SPM). Infant milk powder was purchased from each partner, while the suspended particulate matter (SPM) was collected and characterized. The characterization of these matrices involved analysing elemental composition, organic carbon content, and the background level of SMP.Specifically, the SMP containing tablets produced in WP1 were selected as a reference material and spiked into the matrices. Tablets with different amount of SMP of PET and PP from were used, as well as tablets with different particle numbers. Different spiking levels were considered, using different SMP batches and different content of matrices. The analyses were performed using various techniques, including thermo-analytical methods such as Thermal Extraction Desorption Gas Chromatography Mass Spectrometry (TED-GC/MS) and Pyrolysis Gas Chromatography Mass Spectrometry (Py-GC/MS), as well as spectroscopic methods like Micro Fourier Transform Infrared Spectroscopy (μ-FTIR), μ-Raman, and Quantum Cascade Laser Laser Direct Infrared (QCL-LDIR).A series of standard operating procedures (SOPs) were compiled, employing different technical approaches to identify and characterize SMP in these complex matrices. These include sample preparation protocols for oxidative and enzymatic treatment to reduce the organic matrix, as well as density separations steps, using different salt solutions to reduce inorganic components. The changes of spiked SMP mass fraction and particle numbers in size distribution and recovery rates including error derivations were determined.In sum two finalized SOPs for the spiking of milk with PET were provided. This matrix only needs a reduction of organic matrix. Acceptable recovery rates of more than 80 % with error derivations of around 10 - 20 % were determined for mass determination and particle number-based methods.For SPM with PET or PP only indicative information could by implemented in the SOP. This matrix needs a reduction of organic and inorganic matrix and is therefore more complex. However, recovery rates of more around 120 % with error derivations of around 10 - 20 % were determined for mass determination. For detection methods of particle number-based methods only good recovery rates were determined for very high spiking levels. For moderate and realistic spiking levels only recovery rates of less than 50 % could be developed. Here the number of repetitions is still very low.During the development of all SOPs, it became very clear that protocols developed with thermo-analytical SMP detection are faster to realise than with spectroscopic methods. However, with thermo-analytical methods only relatively high levels can be reliably analysed here compared to the matrix. The application of spectroscopic methods is therefore than preferred, when low SMP contamination are expected in a matrix.The different SOPs developed for the various techniques and matrices will be soon available on Zenodo at the PlasticTrace Community page (https://zenodo.org/communities/plastictrace/). “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