In the last few years, microplastics have been detected in fresh- and seawater, atmosphere, sediments, soils, sewage sludge, biota and food. However, these microplastics can degrade to even smaller plastic particles in the sub-micron range, the nanoplastics. Only a few studies so far confirmed the presence of NP in environmental samples and their release during the use of personal care products, the boiling of plastic teabags and the use of plastic infant bottles. Due to their smaller dimensions and colloidal properties, nanoplastics could pose an increased hazard to the environment, biota and humans. While there are methods for detecting microplastics, the reliable detection and quantification of size and particle number concentrations of plastic particles less than a micrometre in size are still difficult. In this study, the performance characteristics of nanoparticle tracking analysis (NTA) for detecting nanoplastics using an NS300 instrument were determined after optimisation. The NS300 proved to be accurate and precise for a 102 nm Nanospheres suspension, showing favourable results for accuracy, repeatability and reproducibility at high and low particle number concentrations. While the concentration range was linear from 5.0x106 to 2.0x109 particles/mL, the particle size range of the NS300 instrument was linear from 46 to >350 nm. From the measurements of mixtures of particles, it is clear that NTA has difficulties with polydisperse mixtures resulting in an underestimation of the smaller particle sizes. Finally, eight brands of bottled mineral water were analysed. The particle number concentrations ranged from 1.0x106 to 2.2x107 particles/mL, with mean particle sizes in the range of 110 to 170 nm and mode particle sizes <100 nm for all samples. Particle size distributions showed a particle size range of 50 to 500 nm.
ACEnano is an EU-funded project which aims at developing, optimising and validating methods for the detection and characterisation of nanomaterials (NMs) in increasingly complex matrices to improve confidence in the results and support their use in regulation. Within this project, several interlaboratory comparisons (ILCs) for the determination of particle size and concentration have been organised to benchmark existing analytical methods. In this paper the results of a number of these ILCs for the characterisation of NMs are presented and discussed. The results of the analyses of pristine well-defined particles such as 60 nm Au NMs in a simple aqueous suspension showed that laboratories are well capable of determining the sizes of these particles. The analysis of particles in complex matrices or formulations such as consumer products resulted in larger variations in particle sizes within technologies and clear differences in capability between techniques. Sunscreen lotion sample analysis by laboratories using spICP-MS and TEM/SEM identified and confirmed the TiO2 particles as being nanoscale and compliant with the EU definition of an NM for regulatory purposes. In a toothpaste sample orthogonal results by PTA, spICP-MS and TEM/SEM agreed and stated the TiO2 particles as not fitting the EU definition of an NM. In general, from the results of these ILCs we conclude that laboratories are well capable of determining particle sizes of NM, even in fairly complex formulations.
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