Abstract
HypothesisThe implementation of the proposal from the European Chemical Agency (ECHA) to restrict the use of nanoplastics (NP) and microplastics (MP) in consumer products will require reliable methods to perform size and mass-based concentration measurements. Analytical challenges arise at the nanometre to micrometre interface, e.g., 800 nm–10 µm, where techniques applicable at the nanometre scale reach their upper limit of applicability and approaches applicable at the micrometre scale must be pushed to their lower limits of detection. ExperimentsHerein, we compared the performances of nine analytical techniques by measuring the particle size distribution and mass-based concentration of polystyrene mixtures containing both nano and microparticles, with the educational aim to underline applicability and limitations of each technique. FindingsLight scattering-based measurements do not have the resolution to distinguish multiple populations in polydisperse samples. Nanoparticle tracking analysis (NTA), nano-flowcytometry (nFCM) and asymmetric flow field flow fractionation hyphenated with multiangle light scattering (AF4-MALS) cannot measure particles in the micrometre range. Static light scattering (SLS) is not able to accurately detect particles below 200 nm, and similarly to transmission electron microscopy (TEM) and flow cytometry (FCM), is not suitable for accurate mass-based concentration measurements. Alternatives for high-resolution sizing and concentration measurements in the size range between 60 nm and 5 µm are tunable resistive pulse sensing (TRPS) and centrifugal liquid sedimentation (CLS), that can bridge the gap between the nanometre and micrometre range.
Highlights
With regards to sizing measurements, the mode diameters of the monomodal distributions measured by Nanoparticle tracking analysis (NTA), tunable resistive pulse sensing (TRPS), multi-angle dynamic light scattering (MADLS), nano flowcytometry (nFCM) and AF4MALS are in close agreement with nominal diameters for all samples
If the expected values are compared with the measured particle size distribution widths, TRPS, NTA, centrifugal liquid sedimentation (CLS), nFCM and Asymmetric flow field flow fractionation (AF4)-multiangle laser light scattering (MALS) are in close agreement with the nominal widths, whereas MADLS PSD are far broader than the others
Particle concentration measurements are generally prone to a larger error. nFCM, TRPS and CLS are the most accurate techniques in estimating the total mass-based particle concentration
Summary
It is important to highlight that results published by many studies should be treated with caution They are often limited by the use of unrealistically high exposure doses, and by lack of standardized analytical methods for measuring and reporting the particle physico-chemical properties in relevant environmental media, including size, shape, agglomeration state and concentrations [2,6,13,14,15]. There is strong evidence, showing that MP particles can act as concentrator of different pollutants adsorbed on the particle surface, including polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCB), organochlorine pesticides, polybrominated diphenyl ethers (PBDEs), and heavy metals [7,17,18,19,20,21,22] They can be a source of plasticizers [23], that are released in the organisms after particle ingestion and uptake [10,11,12]. Shape and surface area influence the toxicity profile, with smaller particles and non-spherical shapes being a potential major source of risk [10,12,13,16]
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