Micro and Nanoplastics Identification: Classic Methods and Innovative Detection Techniques

Abstract

Micro and nanoplastics are fragments with dimensions less than a millimeter invading all terrestrial and marine environments. They have become a major global environmental issue in recent decades and, indeed, recent scientific studies have highlighted the presence of these fragments all over the world even in environments that were thought to be unspoiled. Analysis of micro/nanoplastics in isolated samples from abiotic and biotic environmental matrices has become increasingly common. Hence, the need to find valid techniques to identify these micro and nano-sized particles. In this review, we discuss the current and potential identification methods used in microplastic analyses along with their advantages and limitations. We discuss the most suitable techniques currently available, from physical to chemical ones, as well as the challenges to enhance the existing methods and develop new ones. Microscopical techniques (i.e., dissect, polarized, fluorescence, scanning electron, and atomic force microscopy) are one of the most used identification methods for micro/nanoplastics, but they have the limitation to produce incomplete results in analyses of small particles. At present, the combination with chemical analysis (i.e., spectroscopy) overcome this limit together with recently introduced alternative approaches. For example, holographic imaging in microscope configuration images microplastics directly in unfiltered water, thus discriminating microplastics from diatoms and differentiates different sizes, shapes, and plastic types. The development of new analytical instruments coupled with each other or with conventional and innovative microscopy could solve the current problems in the identification of micro/nanoplastics.

Keywords: analytical methods; characterization; environmental matrices; microplastics; microscopy; nanoplastics; spectroscopy.

Figure 1

Images of different shapes of MPs in biological samples. The arrows indicate fibers (A–D), fragments (E,F), the film (G) and granules (H,I). Scale bar = 100 μm. This figure is reproduced from Ding et al. (2019) with permission of Royal Society of Chemistry (RSC).

Figure 2

Microplastic particles extracted from laboratory medaka GI tracts. For all FTIR spectra, extracted MPs (red) are compared to the original reference MPs (blue). (A) 150 μm PVC and (B) 300 μm PET particles prepared in 10% KOH, showing strong FTIR peaks for proteins and fats (red arrows) and potassium salts (green arrows). (C) SEM/EDS of KOH-treated microplastic showing redeposited particulate material and strong potassium peak. (D) 150 μm PS, 250 μm PE, 250 μm PET, and 150 μm PVC extracted with ultrapure H₂O and PUE, exhibiting reduced FTIR protein and fat peaks and no salt peaks. This figure is reproduced from Wagner et al. (2017) with permission of Royal Society of Chemistry (RSC).

Figure 3

Representative confocal fluorescence microscopy images of MPs dispersed in water and stained with Nile Red. From left to right: low-density polyethylene (LDPE), polystyrene (PS), polyethylene terephthalate (PET), and polyamide (nylon). Fluorescence emission signals are acquired in the range of 520–720 nm at λex = 500 nm. The scale bar is 200 μm. This figure is reproduced from Sancataldo et al. (2020) with permission of Royal Society of Chemistry (RSC).