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

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.

Microplastic analysis in drinking water based on fractionated filtration sampling and Raman microspectroscopy.

Microplastics (MP) as emerging persistent pollutants were found in raw and drinking water worldwide. Since different methods were used, there is an urgent need for harmonized protocols for sampling, sample preparation, and analysis. In this study, a holistic and validated analytical workflow for MP analysis in aqueous matrices down to 5 µm is presented. For sampling of several cubic meters of water, an easily portable filter cascade unit with different pore sizes (100-20-5 µm) was developed and successfully applied for the sampling of three processed drinking waters, two tap waters and one groundwater. The size distribution and polymer types of MP were determined using a two-step semi-automated Raman microspectroscopy analysis. For quality control, comprehensive process blanks were considered at all times and a recovery test yielded an overall recovery of 81%. The average concentration of identified MP was 66 ± 76 MP/m3 ranging from 1 MP/m3 to 197 MP/m3. All found concentrations were below the limit of quantitation (LOQ) of 1880 MP/m3. The majority consisted of PE (86% ± 111%) while comparatively low numbers of PET (10% ± 25%), PP (3% ± 6%), and PA (1% ± 4%) were found. 79% of all particles were smaller than 20 µm. In summary, this study presents the application of a workflow for sampling and analysis of MP down to 5 µm with first results of no significant contamination in drinking water and groundwater.

When Good Intentions Go Bad-False Positive Microplastic Detection Caused by Disposable Gloves.

Apart from being considered a potential threat to ecosystems and human health, the ubiquity of microplastics presents analytical challenges. There is a high risk of sample contamination during sampling, sample preparation, and analysis. In this study, the potential of sample contamination or misinterpretation due to substances associated with disposable laboratory gloves or reagents used during sample preparation was investigated. Leachates of 10 different types of disposable gloves were analyzed using Raman microspectroscopy (µ-Raman), Fourier-transform infrared microspectroscopy (µ-FTIR), and pyrolysis-gas chromatography/mass spectrometry (pyr-GC/MS). There appeared to be polyethylene (PE) in almost all investigated glove leachates and with all applied methods. Closer investigations revealed that the leachates contained long-chain compounds such as stearates or fatty acids, which were falsely identified as PE by the applied analytical methods. Sodium dodecyl sulfate, which is commonly applied in microplastic research during sample preparation, may also be mistaken for PE. Therefore, µ-Raman, µ-FTIR, and pyr-GC/MS were further tested for their capability to distinguish among PE, sodium dodecyl sulfate, and stearates. It became clear that stearates and sodium dodecyl sulfates can cause substantial overestimation of PE.

Microplastic analysis-are we measuring the same? Results on the first global comparative study for microplastic analysis in a water sample.

This paper presents the results of the first international comparative study of commonly applied analytical methods for microplastic analysis. Although it was shown that the comparability between previously published studies is highly limited, there are ambitious efforts regarding the standardization of microplastic analysis. This comparative study serves as a first step to assess the suitability of frequently used methods in microplastic research. Furthermore, it highlights obstacles when conducting a comparative study for microplastics. Results from 17 laboratories from eight different countries are compared. Samples comprised of five different types of microplastic reference particles with diameters ranging from 8 µm to 140 µm suspended in ultrapure water. Microscopy, Fourier-transform infrared microspectroscopy (µ-FTIR), Raman microspectroscopy (µ-Raman), thermo-extraction-and-desorption- or pyrolysis- combined with gas chromatography coupled to mass spectrometry (Σ-GC/MS), scanning electron microscopy and particle counter were compared regarding results on total particle number, polymer type, number of particles and/or particle mass for each polymer type. In the scope of this comparative study, for the identification of polymer type µ-Raman and Σ-GC/MS performed best. The quantification of polymer mass for identified polymer types was questionable for Σ-GC/MS, whereas other methods failed to determine the correct polymer mass. Quantification of particle number per identified polymer type was evaluated successful for µ-FTIR and the quantification of total particle numbers was best for microscopy and to a lesser extent for µ-FTIR. Remarkable was the large variance of results between the methods but also within the methods. The latter is likely due to individual interpretations of methods and preparation protocols, in particular in regard to the handling of blank values. Results strongly emphasize the need for standardization and validation of analytical methods in microplastic research both on a global scale as well as in the context of individual laboratories.