Analysis of microplastics in drinking water and other clean water samples with micro-Raman and micro-infrared spectroscopy: minimum requirements and best practice guidelines

Authors:  Schymanski, D., Oßmann, B. E., Benismail, N., Boukerma, K., Dallmann, G., Esch, E. von der, Fischer, D., Fischer, F., Gilliland, D., Glas, K., Hofmann, T., Käppler, A., Lacorte, S., Marco, J., Rakwe, M. EL, Weisser, J., Witzig, C., Zumbülte, N., & Ivleva, N. P. (2021). Analysis of microplastics in drinking water and other clean water samples with micro-Raman and micro-infrared spectroscopy: minimum requirements and best practice guidelines. Analytical and Bioanalytical Chemistry 2021, 1–26. https://doi.org/10.1007/S00216-021-03498-Y

Abstract

Microplastics are a widespread contaminant found not only in various natural habitats but also in drinking waters. With spectroscopic methods, the polymer type, number, size, and size distribution as well as the shape of microplastic particles in waters can be determined, which is of great relevance to toxicological studies. Methods used in studies so far show a huge diversity regarding experimental setups and often a lack of certain quality assurance aspects. To overcome these problems, this critical review and consensus paper of 12 European analytical laboratories and institutions, dealing with microplastic particle identification and quantification with spectroscopic methods, gives guidance toward harmonized microplastic particle analysis in clean waters. The aims of this paper are to (i) improve the reliability of microplastic analysis, (ii) facilitate and improve the planning of sample preparation and microplastic detection, and (iii) provide a better understanding regarding the evaluation of already existing studies. With these aims, we hope to make an important step toward harmonization of microplastic particle analysis in clean water samples and, thus, allow the comparability of results obtained in different studies by using similar or harmonized methods. Clean water samples, for the purpose of this paper, are considered to comprise all water samples with low matrix content, in particular drinking, tap, and bottled water, but also other water types such as clean freshwater.

 

Discussion and conclusions

The lack of harmonized methods and analytical standard substances and the difficulty to validate methods for the variable and even sometimes contradictory data [15]. The proposed quality criteria by Koelmans and colleagues include the sampling method, sample size, sample processing and storage, laboratory preparation, clean air conditions, positive and negative controls, sample treatment, and polymer identification. The present consensus paper discusses and sums up details regarding the most important spectroscopic methods that can be used for MP analysis in clean water. All of the above-mentioned quality criteria were integrated in this guideline (see Table 1). It allows the reader to compare and evaluate existing studies. Furthermore, the guidelines can be used to better understand and thus make a more advantageous choice when setting up MP research studies. Given best practice approaches will contribute to a better harmonization of analytical methods for MP analysis in clean water samples down to 1 μm. A schematic overview of important precautions for MP analysis and sampling advices are given in Figure 1.

All these elements are intended to support the standardization processes throughout the different normalization committees. While this consensus paper from twelve European analytical laboratories and institutions has concentrated on (FT)IR/RM methods, for the purpose of monitoring as well as gaining a more comprehensive knowledge on MP contamination in food, water, air, and environmental samples, both spectroscopic and thermo-analytical methods are required. Therefore, it will also be important that a similar consideration be given to harmonizing thermo-analytical methods for MP detection. Above all, an ongoing exchange of scientists and laboratories, ILC studies with certified polymer standards and coordinating structures are required. These will pave the way to enable progress in the harmonization and standardization of MP detection and to allow for representative and reliable MP analysis in different environmental and food samples.

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