Letter to the Editor pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Letter to the Editor Regarding “Are We Speaking the Same Language? Recommendations for a Definition and Categorization Framework for Plastic Debris”
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samples (2nd derivative of FT-IR spectra).4 Any assignment of fibers found in the environment to a natural or to an artificial origin based only on spectroscopic analyses is erroneous.
he publication by Nanna Hartmann and colleagues1 is using a reasonable approach for the definition of microplastics. The proposed distinction of particles in microand nanosized dimensions is meaningful from analytical and toxicological perspectives. Both particle size categories should not be merged, which was done in the recently published report by the European Chemicals Agency (ECHA) for the restriction of intentionally added microplastics.2 But, it needs to be mentioned that the stated dimensions (as 1 up to 1000 μm for “microplastic”) are the same as those that were agreed recently by a working group of ISO/TC 61 SC 5. I missed in this publication also a discussion about the biodegradability as an additional criterion. This should have some relevance as the persistence of microplastics in the terrestrial or aquatic environment is the main concern about their emissions. However, the distinction of artificial and natural polymers in the publication and the presented examples are obviously based on misunderstandings, which represents a wrong perception of artificial material manufactured from natural polymer, often found also in other publications. Whereas “dyed natural fibers” from cotton or wool are assigned as “slightly modified natural polymers” and excluded from the scope of microplastics, regenerated cellulose materials are classified as “heavily modified natural polymers (semi-synthetic)” and included in the definition of microplastics. But, this ignores their composition and the similarity of these cellulose materials. Cellophane and the regenerated man-made cellulosic fibers viscose, modal, or lyocell are artificial/man-made films and fibers from the natural occurring polymer cellulose, which is chemically not modified, and therefore, the term “(semi)synthetic” is inappropriate. Raw material for the manufacturing of regenerated cellulose is mostly wood pulpwith a higher degree of cellulose than the fibers used for paper making. The cellulose is processed either by dissolving the pulp solely in a solvent (manufacturing of lyocell) or via a salt formation through xanthate with regeneration of the original cellulose by hydrolysis (cellophane, viscose, and modal). These regenerated cellulosic fibers have therefore the same chemical composition as cotton and the polymer α-cellulose as constituent. They provide therefore very similar spectra, are dyeable with the same colorants and are similar biodegradable3 (even viscose slightly better than cotton due to higher ratio of amorphous regions). They differ in some physical characteristics, such as fiber cross sections (flat and twisted in case of cotton; multilobal, serrated in case of standard viscose) and the crystalline structures. Regenerated cellulosic fibers have the more stable crystalline modification “cellulose II” (also achieved in mercerized cotton fibers). This different type of crystals is responsible for small variations in IR spectra which could be used for their differentiation in case of clean and pure © XXXX American Chemical Society
Michael Stark*
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Freiburg, Germany
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The author declares no competing financial interest.
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REFERENCES
(1) Hartmann, N. B.; Hüffer, T.; Thompson, R. C.; Hassellöv, M.; Verschoor, A.; Daugaard, A. E.; Rist, S.; Karlsson, T.; Brennholt, N.; Cole, M.; Herrling, M. P.; Hess, M. C.; Ivleva, N. P.; Lusher, A. L.; Wagner, M. Are we speaking the same language? Recommendations for a definition and categorization framework for plastic debris. Environ. Sci. Technol. 2019, 53, 1039−1047. (2) ECHA’s ANNEX XV Restriction ReportProposal for a restriction: Intentionally added microplastics, 20 March 2019. https://echa.europa.eu/documents/10162/12414bc7-6bb2-17e7c9ec-652a20fa43fc. (3) Park, C. H.; Kang, Y. K.; Im, S. S. Biodegradability of cellulose fabrics. J. Appl. Polym. Sci. 2004, 94, 248−253. (4) Comnea-Stancu, I. R.; Wieland, K.; Ramer, G.; Schwaighofer, A.; Lendl, B. On the identification of rayon/viscose as a major fraction of microplastics in the marine environment: discrimination between natural and man-made cellulosic fibers by Fourier transform infrared spectroscopy. Appl. Spectrosc. 2017, 71, 939−950.
Received: March 4, 2019 Accepted: March 14, 2019
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DOI: 10.1021/acs.est.9b01360 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
