On the Identification of Rayon/Viscose as a Major Fraction of Microplastics in the Marine Environment: Discrimination between Natural and Manmade Cellulosic Fibers Using Fourier Transform Infrared Spectroscopy

Abstract

This work was sparked by the reported identification of man-made cellulosic fibers (rayon/viscose) in the marine environment as a major fraction of plastic litter by Fourier transform infrared (FT-IR) transmission spectroscopy and library search. To assess the plausibility of such findings, both natural and man-made fibers were examined using FT-IR spectroscopy. Spectra acquired by transmission microscopy, attenuated total reflection (ATR) microscopy, and ATR spectroscopy were compared. Library search was employed and results show significant differences in the identification rate depending on the acquisition method of the spectra. Careful selection of search parameters and the choice of spectra acquisition method were found to be essential for optimization of the library search results. When using transmission spectra of fibers and ATR libraries it was not possible to differentiate between man-made and natural fibers. Successful differentiation of natural and man-made cellulosic fibers has been achieved for FT-IR spectra acquired by ATR microscopy and ATR spectroscopy, and application of ATR libraries. As an alternative, chemometric methods such as unsupervised hierarchical cluster analysis, principal component analysis, and partial least squares-discriminant analysis were employed to facilitate identification based on intrinsic relationships of sample spectra and successful discrimination of the fiber type could be achieved. Differences in the ATR spectra depending on the internal reflection element (Ge versus diamond) were observed as expected; however, these did not impair correct classification by chemometric analysis. Moreover, the effects of different levels of humidity on the IR spectra of natural and man-made fibers were investigated, too. It has been found that drying and re-humidification leads to intensity changes of absorption bands of the carbohydrate backbone, but does not impair the identification of the fiber type by library search or cluster analysis.

Toward an Improved Understanding of the Ingestion and Trophic Transfer of Microplastic Particles: Critical Review and Implications for Future Research

“…With the increase in the number of studies reporting fibrous particles also comes a need to accurately characterize their polymeric composition, particularly if natural cellulosic fibers and/or semisynthetic fibers such as rayon are to be differentiated from synthetic plastic fibers (Remy et al 2015; Comnea‐Stancu et al 2017). In some instances in which fibers have been reported as the dominant shape, verification has been included and polymer composition reported (e.g., Lusher et al 2013; Bessa et al 2018).…”

Microplastic concentrations, size distribution, and polymer types in the surface waters of a northern European lake

“…Cellulose fibers can originate from manufactured materials, such as textiles and paper, and natural materials such as plants. Resolving the cellulose origin with FTIR would have required more insightful approach than exploited in this study, because samples contained much biological material from the lake (Comnea‐Stancu, Wieland, Ramer, Schwaighofer, & Lendl, ). Moreover, as the contamination control indicated (see below), that risk for contamination was present especially regarding cellulose fibers.…”

Microplastic ingestion ubiquitous in marine turtles

“…However, from further inspection of other digital photographs, individual spectra and high match qualities (over 80%–90%), we propose that these are SRCF such as viscose or rayon. Although originally derived from natural sources they undergo several chemical processes in regeneration to become reconstructed (Comnea‐Stancu et al, ; Gago et al, ). There are distinct differences between native and regenerated cellulose regarding their crystalline structure.…”

“…There are numerous challenges in studying microplastics in the environment including the analytical chemistry to identify particles (Comnea-Stancu, Wieland, Ramer, Schwaighofer, & Lendl, 2017;Silva et al, 2018). Visual examination is the most common method used to identify microplastics.…”

“…Although originally derived from natural sources they undergo several chemical processes in regeneration to become reconstructed (Comnea-Stancu et al, 2017;Gago et al, 2018). There are distinct differences between native and regenerated cellulose regarding their crystalline structure.…”