Methodologies to characterize, identify and quantify nano- and sub-micron sized plastics in relevant media for human exposure: a critical review

Abstract

Micro- and nanoplastics (MNPs) in the environment are an emerging issue of global concern. They accumulate in natural ecosystems, and are ingested by organisms and transferred to humans potentially causing adverse toxicological effects. Knowledge on the magnitude of these effects is limited due to the lack of knowledge on realistic exposures especially for nano- and sub-micron size plastics. Their size and shape have a significant influence on the encountered health effects as well as the presence of additives. Currently, there are no standardized protocols for their reliable characterization (size, shape), identification and quantitation. There is a growing number of reported studies on occurrence of microplastics above 10 μm in size and of limited polymer types (mainly polystyrene, polyethylene terephthalate, polycarbonate and polyethylene). New analytical approaches are needed for a complete and reliable risk assessment of MNPs, especially of sizes below 1 μm, on human health. This review evaluates the progress made concerning the sub-micron (100 nm to 1 μm) and nanometer (<100 nm) size range of MNPs on: (i) human exposure to evaluate the intrinsic hazards, (ii) sampling and sample preparation methods and (iii) methods for characterization (size, shape), identification and quantitation, with a focus on relevant media for human exposure. Methods that could be used for the extraction of submicron and nanoplastics from relevant matrices are recommended. Novel methods (e.g. Raman imaging and single-particle inductively coupled plasma-mass spectrometry) and new combinations of analytical methods (e.g. atomic force microscopy coupled to infrared/raman spectroscopy, field-flow fractionation-multiangle light scattering offline coupled to pyrolysis-gas chromatography-mass spectrometry) are proposed and discussed.